Occupational Safety Training Document for Electrical Work

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The material for the occupational safety training course in the electrical industry helps workers equip themselves with safety knowledge and prevent hazards when working with power sources and electrical equipment.

PART 1: ELECTRICAL SAFETY ENGINEERING

A: PRINCIPLES OF ELECTRIC CURRENT

I. General Concepts in Electrical Safety Documents

1. Introduction

Electricity plays a very important role in production and daily life. However, it can also cause very serious accidents and incidents if electrical safety standards and regulations are not followed.

Electrical accidents often occur when: touching a live conductor; touching metal parts of electrical equipment when insulation is damaged; due to an electric arc; due to step voltage; due to static electricity…

2. Factors Related to Electrical Accidents

Factors related to electrical accidents include: The resistance of the human body; the type and magnitude of the current passing through the body; the path of the current through the body; and the frequency of the current passing through the body.

• 2.1. Resistance of the human body (R_hb)
  • The resistance of the human body is an unstable quantity. The lower the R_hb, the higher the level of danger.
• 2.2. Type and magnitude of current passing through the body
  • The greater the magnitude of the current passing through the body, the higher the level of danger.
  • Alternating current (AC) is more dangerous than direct current (DC). With a frequency of 50 to 60 Hz, the safe current value is considered to be 10 mA, whereas for direct current, the safe current value is 50 mA.

CURRENT MAGNITUDE (MA)	EFFECTS OF ALTERNATING CURRENT (AC)	EFFECTS OF DIRECT CURRENT (DC)
0.6 – 1.5	Fingers begin to feel numb	No sensation
2 – 3	Fingers are very numb	No sensation
3 – 7	Muscles contract and tremble	Pain like a needle prick, sensation of heat
8 – 10	Hand has difficulty letting go of the live object but can still be released. Fingers, joints, and palm feel pain	Heat increases
20 – 25	Hand cannot let go of the live object, pain, difficulty breathing	Heat increases further, muscles contract but not yet strongly
50 – 80	Respiratory system becomes paralyzed. Heart begins to beat strongly	Strong sensation of heat. Arm muscles contract, difficulty breathing.
90 – 100	Respiratory system becomes paralyzed. If it lasts for 3 seconds or more, the heart becomes paralyzed and stops beating.	Respiratory system becomes paralyzed

 

• 2.3. Duration of current passing through the body in electrical safety documents
  • The longer the current passes through the body, the higher the level of danger.
• 2.4. Path of the current through the human body
  • Regarding the path of current through the body, there can be many different scenarios, but the common basic paths are: hand-to-foot, hand-to-hand, foot-to-foot. A debatable issue is which path is the most dangerous.
  • Most researchers believe that the most dangerous path depends on the percentage of the total current that passes through the heart and lungs. According to this view, the paths from the right hand to the foot, head to the foot, and head to the hand are the most dangerous:
    • Current from hand to hand: 3.3% of total current passes through the heart
    • Current from left hand to foot: 3.7% of total current passes through the heart
    • Current from right hand to foot: 6.7% of total current passes through the heart
    • Current from foot to foot: 0.4% of total current passes through the heart
    • Current from head to hand: 7% of total current passes through the heart
    • Current from head to foot: 6.8% of total current passes through the heart.
• 2.5. Frequency of current passing through the body in electrical safety documents
  • At a frequency of 50 to 60 Hz, the danger is at its greatest. At lower frequencies, the danger decreases. At significantly higher frequencies, the danger is greatly reduced.

3. Basic Concepts of Electrical Safety

• 3.1. The phenomenon of current flowing in the ground and the distribution of charge on the ground surface
  • In the case of a broken wire falling to the ground or when the insulation of electrical equipment is punctured, a ground fault current will flow, creating a leakage current zone at and around the point of contact.
  • The voltage is highest at the point of ground contact. At a distance of ≥ 20 m from the contact point, the voltage is zero.
  • As it flows into the ground, the leakage current is impeded by the earth’s resistance. This resistance is called dissipation resistance or the resistance of the grounding object.
  • R_g = U_g / R_g

• • Ground fault current entering the ground through a hemispherical electrode

• 3.2. Touch Voltage (U_tv) in electrical safety documents
  • Touch voltage is the potential difference between two points on the current path that a person can touch.
  • The farther from the grounding object, the greater the U_tv, and vice versa.

• 3.3. Step Voltage (U_sv) in electrical safety documents
  • Step voltage is the voltage between a person’s two feet caused by a ground fault current. The closer to the grounding object, the greater the U_sv, and vice versa. At a distance of ≥ 20 m from the grounding object, U_sv = 0.
• 3.4. Permissible Voltage (U_per)
  • Permissible voltage is used to determine the safety limit for people.
  • The standard for permissible voltage differs in each country. In Vietnam, depending on the hazardous nature of the environment, U_per is valued from 12 to 36 V.

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II. SAFETY ANALYSIS IN ELECTRICAL NETWORKS

1. Safety analysis in simple electrical networks in electrical safety documents

• 1.1. Simple electrical network
  • A simple electrical network is a direct current (DC) and single-phase alternating current (AC) network.
• 1.2. Electrical network isolated from ground
  • In this type of network, when a person comes into contact with electricity, the following situations can occur:
  • When touching one pole:

• • Through calculation and experiment, it has been determined that:
    • I_hb = U / (2*R_hb + R_is)
    • Where:
    • I_hb: current through the person
    • U: voltage of the grid
    • R_hb: resistance of the human body
    • R_is: insulation resistance of the network to ground
  • From this, we can conclude: the better the network’s insulation, the lower the danger.
  • When touching two poles:
    • I_hb = U / R_hb
    • This is the most dangerous case. Accidents often occur when repairing live electrical equipment, touching one pole with one hand, and another part of the body touching the other pole.
  • Touching one pole while the other is grounded:
    • At that time:
    • I_hb = U / R_hb
    • This case is also very dangerous.
• 1.3. Network with one pole or one phase grounded
  • 1-wire network:
    • With this network, when touching a live part, the value of the current through the person is:
    • I_hb = U / R_hb
    • This case is very dangerous because the network’s insulation does not help limit the current through the person.
  • 2-wire network:
    • When touching the grounded pole:
      • Normally, touching the grounded pole is not dangerous because, under normal grid operation, the voltage applied to the person is always < 5% of U. However, during a short circuit, the voltage is distributed along the line according to the wire's resistance. The level of danger will vary depending on where the person makes contact.
    • When touching the ungrounded pole:
      • I_hb = U / R_hb
    • When touching both wires:
      • I_hb = U / R_hb
    • Both cases above (2 and 3) are dangerous to people.
• 1.4. Remarks
  • In the above cases, for a network isolated from ground, the network’s insulation always helps limit the current through the person (I_hb).
  • In a grounded network, the network’s insulation does not help limit the current through the person.

2. Safety analysis in 3-phase electrical networks in electrical safety documents

• 2.1. Network with an isolated neutral
  • A network with an isolated neutral is a network where the neutral is not connected to grounding devices or is connected through devices to compensate for current in the network, through transformers, or through electrical apparatuses with high resistance.
  • Case of touching 1 phase:
    • When a person touches 1 phase, through calculation and experiment, it has been determined that:
    • I_hb = 3*U_ph / (3*R_hb + R_is)
    • Where:
    • U_ph: phase voltage of the network
    • R_is: insulation resistance of the network to ground
    • R_hb: resistance of the human body
    • Thus, the better the network’s insulation, the lower the danger.
  • Case of touching 2 phases or touching 1 phase while another phase is grounded:
    • I_hb = U_l / R_hb
    • Where: U_l is the line voltage of the electrical network.

• 2.2. Network with a directly grounded neutral in electrical safety documents
  • A network with a grounded neutral is one where the neutral is directly connected to a grounding device or connected to the ground through a small resistance.
  • When touching 1 phase:

 

• • • I_hb = U_ph / R_hb
  • When touching 2 phases or touching 1 phase while another phase is grounded:

 

• • • I_hb = U_l / R_hb

• 2.3. Remarks
  • In a network with an isolated neutral, when a person touches 1 phase, the insulation resistance of the network helps to limit the current through the person;
  • In a network with a grounded neutral, the network’s insulation does not help limit the current through the person;
  • The danger level is the same in the case of a person touching 2 phases or touching 1 phase while another phase is grounded.

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III. PREVENTIVE MEASURES AGAINST ELECTRICAL ACCIDENTS

1. Insulation of electrical equipment in electrical safety documents

• Insulation is the primary and most important measure to prevent electricity from leaking to the machine casing, which is dangerous for users, and to avoid electrical transmission between phases causing short circuits.
• Insulation is essentially the electrical separation between live parts, and between live parts and other components of the equipment, structure, etc.
• For insulation, insulating materials such as porcelain insulators, insulating paint, enamel, fabric, rubber, plastic, and insulating oil are used.
• Insulation is characterized by its insulation resistance (R_is). The permissible value of R_is depends on the voltage of the electrical network. For electrical equipment with a voltage up to 500 V, R_is = 0.5 MΩ.
• To ensure safety, it is necessary to strictly comply with the regulations for use, inspection, and testing of the electrical equipment’s insulation during its operation.
• Insulation inspection and testing can be carried out in many ways. A Megohmmeter is typically used. When conditions permit, a high-potential (hi-pot) test is conducted.
• To increase safety for users, double insulation is sometimes used. Double insulation consists of two independent layers of insulation, each capable of withstanding the rated voltage of the electrical equipment.

2. Protective Earthing (Grounding)

• 2.1. Purpose and significance in electrical safety documents
  • When insulation fails, the metal parts of electrical equipment or other machines that were previously not energized can become fully live at the working voltage. Touching them can cause injury. For safety, grounding is used to reduce the voltage to ground on these parts (during a fault) to a safe value.
  • Thus, grounding is the intentional connection of the equipment casing to the grounding system. The grounding system consists of a ground electrode (rod or bar) and a grounding conductor. Its purpose is to create a low-resistance path between the equipment casing and the earth, so that the current flowing through a person (I_hb) who touches the casing during an insulation failure becomes non-hazardous.
  • There are two types of grounding: concentrated grounding and grid (ring) grounding.
  • Due to the high resistivity of soil, concentrated grounding often fails to meet safety requirements, so grid grounding systems are commonly used.

• 2.2. Application of protective earthing in electrical safety documents
  • For electrical equipment with voltage < 1000 V: protective earthing is used in cases where the neutral is isolated from the ground.
  • Protective earthing is difficult to implement because ensuring insulation for the entire network is very challenging. Furthermore, creating a reliable grounding system is very costly, so it is currently only used in locations with high safety requirements (such as coal mines, tunnels, etc.).
  • For electrical equipment with voltage > 1000 V: protective earthing is used in all cases, regardless of the neutral’s operating mode and the type of building.

• 2.3. Grounding Resistance in electrical safety documents
  • Grounding resistance includes dissipation resistance and the combined resistance of the conductors and grounding bars.
  • Current regulations specify:
    • For electrical equipment with voltage ≤ 1000 V, R_g ≤ 4 Ω. In cases where the generator or transformer capacity is ≤ 100 kVA, the grounding system resistance is allowed to be ≤ 10 Ω.
    • For electrical equipment with voltage > 1000 V: R_g ≤ 0.5 Ω at any time of the year, taking into account natural grounding resistance. The artificial grounding resistance must not exceed 1 Ω.

3. Neutral Wire Protection (Protective Neutral) in electrical safety documents

• 3.1. Significance of neutral wire protection
  • Neutral wire protection involves connecting the equipment casing to the neutral wire, which is grounded at multiple points. This protection is used for low-voltage 4-wire networks (380/220 V; 220/110 V) with a directly grounded neutral.
  • The significance of this is that in a < 1000 V network with a directly grounded neutral, using only protective earthing does not ensure safety when a phase-to-casing fault occurs. Moreover, the voltage of the other two phases with respect to the ground will increase. A method is needed to increase this ground fault current to a value that allows a protection device to quickly clear the fault, thus ensuring safety.
  • The simplest measure is to use a conductor to connect the equipment casing to the neutral wire. Its purpose is to turn a casing fault into a single-phase short circuit so that the protection device can act quickly to disconnect the faulty section.

• 3.2. Scope of application in electrical safety documents
  • Neutral wire protection is used for 4-wire electrical networks with a voltage < 1000 V and a grounded neutral.
  • In these networks, neutral wire protection is used in all production facilities regardless of the surrounding environment. This method is simple, inexpensive, and easy to implement, which is why it is used in most production facilities today.

• 3.3. Requirements for neutral wire protection
  • The neutral point of generators and transformers on the side with voltage up to 1000 V must be connected to the ground electrode by a grounding conductor. The ground electrodes must be placed directly near the machine.
  • The resistance of the grounding equipment connected to the neutral point of a generator, transformer, or the output of a single-phase source must, at any time of the year, be ≤ 2, 4, and 8 Ω corresponding to line voltages of 660, 380, and 220 V for three-phase sources, or 380, 220, and 127 V for single-phase sources.
  • The neutral wire must be re-grounded at intervals. To ensure automatic disconnection of the faulty section and to ensure thermal stability, the total conductance of the protective neutral (‘zero’) wire must, in all cases, be no less than 50% of the total conductance of the phase wire. The re-grounding resistance of the ‘zero’ wire must be ≤ 15, 30, and 60 Ω corresponding to the voltage levels above.
  • When implementing neutral wire protection, a separate protective neutral (‘zero’) wire must be used, distinct from the working neutral wire (as in a 5-wire 3-phase network), or a part of the protective neutral wire, separated from the working neutral, must be used to connect the neutral for the equipment.
  • In the neutral wire circuit, switches or fuses must not be used. To disconnect the neutral wire, a circuit breaker must be used, and it must simultaneously disconnect the neutral wire and the other phase wires.
  • When the ‘zero’ wire runs parallel to the phase wires, its insulation must be equivalent to that of the phase wires.
  • In small mechanical installations where running a ‘zero’ wire is difficult, grounding or protective disconnection measures may be used as an alternative to ‘zero’ protection.

• 3.4. Inspection of grounding and “zeroing” works in electrical safety documents
  • Grounding and ‘zeroing’ equipment for electrical devices must be inspected upon commissioning, periodically, and in extraordinary circumstances.
  • Commissioning inspection is performed after the grounding and ‘zeroing’ equipment has been installed.
  • Periodic inspection is performed at specified intervals from 6 months to 2 years, depending on the hazard level of the location.
  • Extraordinary inspection is performed when: an accident or incident occurs, or there is a risk of an accident; after repairs to the grounding or ‘zeroing’ equipment; when new construction or repairs to other structures might damage parts of the grounding or ‘zeroing’ equipment.
  • The specific inspection steps vary depending on the type of inspection.
    • The content of a commissioning inspection includes:
      • Checking the actual installation against the design;
      • Checking the use of materials as per design requirements;
      • Checking all welds and connections for mechanical strength and contact resistance;
      • Checking anti-corrosion and anti-rust measures;
      • Checking the protection of conductors passing through expansion joints and other obstacles;
      • Checking measures against touch and step voltages in necessary areas;
      • Checking the backfill and measuring the ground resistance;
      • Checking the phase-to-‘zero’ wire circuit resistance and the tripping capability of the protective device (fuse size, circuit breaker current setting);
  • The inspection is performed through visual examination, using measuring tapes, ground resistance meters, and phase-to-‘zero’ circuit resistance meters.
    • The content of periodic and unscheduled inspections includes:
      • Measuring ground resistance and phase-to-‘zero’ circuit resistance;
      • Inspecting the entire grounding and ‘zeroing’ system;
      • Checking all welds and connections;
      • Checking the condition of plating or anti-corrosion paint;
      • Checking electrical contact surfaces;
      • Inspecting underground parts and suspicious areas (by excavating and measuring);
      • Inspecting conductors passing through obstacles;
      • Checking the condition of the soil.

4. Protective Disconnection in electrical safety documents

• Protective disconnection is a measure that automatically isolates the faulty electrical equipment or section from the grid in a very short time after a hazardous fault occurs.
• This measure has the advantage that when the voltage on the equipment casing reaches a certain value, the protection will activate to disconnect the faulty equipment, ensuring safety for anyone who might touch the casing.
• This measure can be used to supplement or replace protective earthing and ‘zeroing’.
• Protective disconnection can be controlled based on voltage or current principles. Currently, leakage relays, controlled by the voltage principle, are mainly used.

5. Lowering Voltage in electrical safety documents

• The working environment affects R_hb (human body resistance) and U_tv (touch voltage) applied to a person. Improving the environment is necessary but not always feasible. Therefore, to ensure safety, the operating voltage is lowered.
• However, due to technological and economic requirements, lowering the voltage is only done to a certain extent.
• The permissible voltage for electrical equipment is chosen according to the type of environment and the hazardous nature of the working conditions.
• To supply low voltage, isolation transformers with separate primary and secondary windings are used.

6. Equipotential Bonding in Electrical Safety Documents

• Although de-energizing the circuit during repairs is very important, in some necessary cases, repairing live power lines is still permitted, especially for lines supplying important consumers.
• The requirement of this method is to isolate the person from all other objects with different electrical potentials while in contact with the live conductor. This is done to eliminate and limit the current closing the circuit through the person to the ground to a safe level.
• When using the equipotential bonding method, very strict safety measures are required, workers must be well-trained and fully equipped with safety means and tools.
• To implement the equipotential bonding method, there are many different specific forms of execution. In Vietnam, some of the following forms are currently being applied:
  • The worker stands on a metal platform that has been insulated from the ground, uses an insulating pole to connect a conductor (one end already connected to the metal platform) to the phase to be repaired, and only then touches it directly by hand. After the repair is finished, this wire must be removed afterwards using an insulating pole;
  • Using links made of insulating material to create insulating chairs and then bringing them to the position needing repair. The worker sits on the insulating chair, wearing specialized clothing made of metal-blended fibers with nodes and conductors for equipotential bonding connection, uses an insulating pole to connect the conductors from the clothing to the phase to be repaired, and only then makes direct contact by hand.

7. Equipping with Protective Means in Electrical Safety Documents

• Barriers, signs
  • To avoid unexpected contact with live conductors, they are hung high, well shielded, or fenced off. In addition to fixed shielding, temporary mobile barriers, rubber covers, etc., are also used.
  • Warning signs are often used to warn of danger to people approaching live objects, to prohibit operations on equipment that could cause accidents, or as reminders…

• Equipping with protective means
  • During the repair and operation of the power grid, depending on the nature of the danger, protective means are equipped such as: insulating poles, insulating pliers, insulating gloves, insulating shoes and boots, voltage testers, clamp meters, portable grounding protection…
  • Protective means must be well-maintained and regularly tested periodically.

8. Organizing Safe Operation in Electrical Safety Documents

• Practice shows that most electrical accidents occur due to violations of electrical safety standards, regulations, and technical procedures, poor operating skills…
• For safety, it is necessary to strictly adhere to electrical safety standards and technical regulations right from the design, manufacturing, and installation of electrical equipment.
• During operation, it is necessary to regularly inspect, repair, and maintain to overcome and eliminate risks that cause accidents.
• People who do electrical work must have good health, good professional qualifications, and a firm grasp of the relevant electrical procedures and regulations.
• Lax management of power switching often leads to extremely serious accidents and incidents. Therefore, the assignment of people on duty and for power switching must be extremely strict.
• There must be a power supply diagram at the duty station.
• When repairing electrical equipment or parts of the electrical network, there must be a work permit and an operating procedure sheet. Depending on the nature of the work, the work permit and operating procedure sheet require different levels of rigor.

9. Static Electricity – Prevention in Electrical Safety Documents

• Causes of static electricity and its harmful effects
  • The main cause of static electricity is friction between insulating materials, or between insulating materials and conductive materials, the impact of insulating liquids when pouring, or the impact of insulating liquids with metal.
  • Static electricity also exists on small, solid insulating particles during the crushing process.
  • In production, static electricity can be the cause of explosions, fires, serious accidents, and is a factor affecting human health.
  • Static electricity often appears on large power transmission belts, in the wool, textile, paper, rubber, printing, grinding, and screening industries, and during fuel transportation processes…

• Measures to prevent the danger of static electricity
  • There are 3 types of preventive measures:
    • Reduce the potential of static electricity to a safe level to prevent discharge;
    • Dissipate the accumulation of static electricity charge;
    • Prevent the appearance of static electricity charge.
  • These preventive measures have different forms depending on the characteristics and conditions of generation./.

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B: SAFETY REQUIREMENTS FOR SOME ELECTRICAL EQUIPMENT

I. ELECTRIC MOTORS

• In terms of safety, electric motors can be divided into: open-type motors, enclosed-type motors, explosion-proof motors, moisture-proof motors… Depending on the working conditions, the appropriate type of motor should be chosen. Open-type motors: Used in rooms with little electrical hazard. When installing these motors, they must be shielded to prevent people from coming into contact with the electrical parts.
• Enclosed-type motors: In addition to preventing people from coming into contact with live parts, they also prevent dust, chips, and other objects from entering the motor.
• Explosion-proof motors: Avoid the possibility of causing explosions in places with explosive dust, vapors, or gases.
• Moisture-proof motors: used for working in environments with water, underwater. This type of electric motor is not explosion-proof; conversely, explosion-proof motors cannot work underwater. Motors must be regularly maintained. If stopped for more than a month, before restarting, the insulation must be checked, the grounding wire must be rechecked, and the mechanical parts must be checked.
• If there is anything unusual or damaged, it must be repaired before the power is turned on. Motors with a power of ≥ 40kW must have V and A meters installed. The rated U and I of the motor should be marked on them.

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II. ELECTRICAL SWITCHGEAR

1. Switches in Electrical Safety Documents

• A switch is a simple electrical switching device used to open and close an electrical circuit during operation. If switched under load, an arc can occur. Therefore, the switch must have an arc chute. If the switch box casing is metal, it must be grounded. If the switch is placed on distribution and control panels, it must be placed at the back, and the switch control handle must be made of insulating material and placed at the front. Insulating gloves must be worn when operating the main switch. When cutting power for repairs, a “Do Not Operate” sign must be hung on the switch. If there is no one on duty, an insulating liner must be used so that it cannot be closed by mistake. Manual switching should only be performed at voltages < 500V.

2. Isolators in Electrical Safety Documents

• Used in electrical equipment >1000V. The operation of opening and closing an isolator is performed when the network has voltage but no load current. This is because the isolator does not have an arc-quenching device. If it cuts a load, it will burn the contacts of the isolator, and the arc can cause a short circuit or an accident. Opening and closing an isolator requires an operation ticket and must be done by two people. When operating, one must wear boots, insulating gloves, stand on an insulating platform, and use an insulating pole.
• When opening an isolator, the circuit breaker must be opened first, and when closing an isolator, the circuit breaker must be closed afterwards.
• When opening or closing an isolator, if an arc is seen, it must be quickly returned to the closed position. During thunderstorms and lightning, do not operate isolators connected to outdoor lines.

3. Automatic Circuit Breakers in Electrical Safety Documents

Automatic circuit breakers are manufactured with an automatic arc-quenching device, so they can switch large load currents.

• Oil Circuit Breakers
  • Used to interrupt load currents and short-circuit currents at voltages >1000V. The oil serves to extinguish the arc and also to insulate from the casing. The following types exist:
    • Manual operation type.
    • Manual closing, automatic tripping type.
    • Automatic operation type.
  • When using, be aware of the oil losing its insulating properties, which can lead to voltage on the casing. Spilled oil can cause a fire. If the oil loses its arc-quenching properties, the breaker can explode and cause a large fire. To avoid these hazards, the following requirements must be met:
    • If the machine has an oil capacity of more than 60 kg, each phase must be separated.
    • All other live parts must be far from where the circuit breaker is installed.
    • There must be a barrier wall completely separating it from the workers’ area.
    • Unauthorized personnel are not allowed to enter the circuit breaker room.
    • The circuit breaker must have an indicator showing its open/closed status.
    • The control buttons of the machine must be clearly labeled with their function.
    • The quality of the oil must be checked annually and after each trip.
    • The oil must be replaced after the breaker has tripped three times.

• Minimum Oil Circuit Breakers in Electrical Safety Documents
  • Minimum oil circuit breakers are also used in electrical equipment >1000V. Due to their design, when tripping, the arc is dispersed and elongated, so the oil extinguishes the arc more easily, and thus less oil is contained in the machine. Because there is less oil, the casing of the machine is live.
  • When using, the following requirements must be ensured:
    • The mounting frame of the circuit breaker must have good insulation.
    • Metal mesh guards must be grounded.
    • There is a warning on the machine casing that the casing is live.
    • After each trip of the circuit breaker, the oil must be rechecked, and the oil level in the machine must be checked regularly. When checking and controlling the circuit breakers, there must also be 2 people and according to an operation ticket.
    • Wear insulating gloves and boots.

4. Magnetic Starter

• A magnetic starter is used to start and stop a machine more safely and conveniently than a switch (operated by a control button). Magnetic starters are now widely used. When using, pay attention to:
  • Properly protect the contact surfaces, coil, magnet, and thermal overload relay.
  • Depending on the conditions, use the appropriate type of magnetic starter such as: open type, enclosed type, protected type, dust-proof type, explosion-proof type…

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III. FUSES

Fuses are used to protect power lines and electrical equipment systems. This is the simplest automatic mechanism. For a fuse to be effective, it must be used with the correct rating; otherwise, it will lose its protective function (overload or short circuit). There are various types of fuses such as: plug fuses, blade fuses, cartridge fuses, and fuse wire.

1. Plug Fuses in Electrical Safety Documents

• Has a plug made of insulating material, with the fuse wire inside. The empty space around the wire is filled with asbestos to quench the arc when the fuse blows. It is designed so that power is only transmitted when it is almost tightened to prevent electric shock to the installer. Plug fuses are used in lighting networks and small power motors.

2. Blade Fuses in Electrical Safety Documents

• Consists of one or more fuse blades mounted on an insulating base. The blade fuse is placed in a box with an insulating cover to prevent electric shock and arcing when the fuse blows. Blade fuses are used in networks ≤ 220V.

3. Cartridge Fuses in Electrical Safety Documents

• Consists of a hollow porcelain tube with two metal caps at the ends.
• A fuse wire runs through the tube connecting the two ends. Some types have quartz sand inside the tube to quench the arc.
• Any fuse must be placed after the switch so that the power can be cut off during replacement. Fuses should only be replaced under voltage while wearing safety glasses and insulating gloves.

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IV. TRANSFORMERS

Regarding safety with transformers, pay attention to the following:

• Transformers contain a large amount of oil for arc quenching and insulation. To prevent a fire from spreading if the transformer explodes and oil is sprayed out, when the machine is placed indoors, there must be a pit underneath the machine to contain all the oil from the machine.
• Transformers installed indoors must have a separate room, with a locked door that opens outwards. A sign “High Voltage, No Entry” should be hung on the door. If installed outdoors, there must be a sturdy fence with a locked gate. In the area where the machine is located, gravel should be laid to prevent slipping. The transformer casing must be protectively grounded.
• The oil must be tested and the machine repaired annually. The insulation of the transformer must be measured regularly. The room where the machine is located must be cool and well-ventilated for good heat dissipation. All work on the transformer can only be carried out when the machine has been de-energized on both the high and low voltage sides. The wire ends must be temporarily grounded.

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V. PORTABLE ELECTRIC TOOLS

• Portable electric tools must meet safety requirements such as being able to be quickly disconnected from the power grid and preventing the user from touching live parts.
• In places with low electrical hazard, a voltage of 220V can be used. In hazardous and especially hazardous electrical environments, only tools with a voltage of up to 36V should be used. If it is not possible to lower the voltage of the tool to 36V, the equipment casing must be grounded and protective equipment must be provided.

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VI. SAFETY REQUIREMENTS FOR FACTORY POWER GRIDS

1. Network within the workshop in electrical safety documents

• The network within the workshop includes a system of conductors and electrical cables. They come in many types with different features. When using them, a type with features suitable for the characteristics and nature of production must be chosen to ensure insulation and mechanical strength.
• Conductors in workshops must be insulated wires. If buried underground, the correct type of cable must be chosen. Wires passing through walls, floors, or on the roof must not touch metal parts to prevent current leakage if the insulation fails. Wires passing through walls must be run in insulated porcelain tubes. Wires run overhead must be mounted on insulators.
• In production facilities, it is common to use cables laid underground in cable trenches with reinforced concrete covers. Cables can also be run along the walls in the workshop, along the ceiling, and the metal structures of the building. Special hooks or nails are used to secure them.

2. Outdoor electrical network in electrical safety documents

• If bare conductors are used, they must be placed on insulators and must ensure a minimum height of 6m for voltages up to 1000V and 7m for voltages from 1000V to 10kV.
• Conductors passing over roofs must be placed in steel pipes and must ensure a distance of at least 2m between the conductor and any point of the building.
• Conductors on the factory premises must be calculated with a 3-fold reserve for mechanical strength and reinforced insulation when mounted on insulators.
• For voltages >1000V, multi-stranded conductors must be used. When high-voltage and low-voltage wires cross, the high-voltage wire must be placed above the low-voltage wire, and if buried, the low-voltage wire must be placed above the high-voltage wire, with a layer of bricks between them and a minimum separation of 0.35m.

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VII. LIGHTNING PROTECTION

1. Concept

• Lightning is an electrical discharge phenomenon in the atmosphere between a charged thundercloud and the ground or between oppositely charged thunderclouds.
• The formation of charged clouds is very complex. There are many theories explaining this process, but the most widely accepted one is the Simpson theory.
• According to this theory: water droplets have an uneven distribution of charge. The negative charge is on the outside, while the positive charge is on the inside. When there is a very strong whirlwind, the water droplets break up into many small particles. The outer part, carrying a negative charge, is carried away by the wind, forming a negatively charged cloud. The remaining part carries a positive charge.

2. Harmful effects of lightning

• For people, lightning is primarily dangerous as a source of high voltage and large current. If struck by lightning, a person will die instantly.
• Often, even an indirect lightning strike is dangerous because when the lightning current passes through a grounded object, it creates a very dangerous step voltage.
• The harmful effects of lightning can also cause large fires. If it directly strikes buildings or equipment, it will cause great destruction.
• The harmful effects of lightning come in many forms, but can be divided into two main types: harm from direct lightning strikes and harm from the indirect effects of lightning.

3. Lightning Protection

• Protection against direct lightning strikes:
  • To protect against direct lightning strikes, lightning rods are used. The working principle of a lightning rod is to attract the lightning to itself, preventing it from striking the protected objects.
  • The protective ability of a lightning rod is due to the easy discharge characteristic of a sharp point at a higher position to conduct the lightning current to the ground.
  • In addition to lightning rods, depending on the characteristics of each structure, lightning conductors, lightning nets, etc., are also used.
  • For the lightning current to dissipate into the ground quickly, the smaller the grounding resistance, the better. Depending on the hazardous nature of the structure, different values of lightning protection grounding resistance are specified.
  • For normal structures, the lightning protection grounding resistance is less than or equal to 10 Ohms.

• Protection against indirect lightning (electrostatic induction and electromagnetic induction lightning):
  • Protection against electrostatic induction lightning: To prevent electrostatic induction from lightning, equipment and metal structures of the building are grounded.
  • Protection against electromagnetic induction lightning: To prevent electromagnetic induction, all metal structures isolated from the ground and smaller than 10 cm; places with poor flange contact must have measures to connect them into a closed loop and must be well-grounded so that there is no potential difference. The connecting wires must be tightened with bolts or welded.

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PART 2: ELECTRICAL SAFETY TECHNICAL PROCEDURE

(Decision No: 1559 EVN/KTAT dated October 21, 1999, of Vietnam Electricity Corporation on the issuance of the electrical safety technical procedure for the management, operation, repair, and construction of power lines and substations)

I. SCOPE OF APPLICATION OF THE PROCEDURE

Article 1: This procedure applies to all officials and employees directly involved in managing, operating, repairing, testing, and constructing power lines and substations of Vietnam Electricity Corporation. This procedure also applies to employees of other organizations working on electrical works and equipment managed by Vietnam Electricity Corporation.

For power plants of the Corporation, in addition to this procedure, technical staff and employees must master and use Volume 1 of the “Technical Safety Code for the Operation of Electrical Installations in Power Plants and Grids”. The regulations in this procedure are primarily aimed at ensuring the prevention of accidents caused by electricity to humans.

When drafting safety technical procedures for each specific type of work, measures must be included to prevent not only electrical accidents but also other hazardous factors that may occur during the work. All provisions in previously issued electrical safety technical procedures that contradict this procedure are no longer valid for implementation.

Article 2: In this procedure, electrical equipment is divided into two types:

High voltage is conventionally defined as 1000 V and above, and low voltage is conventionally defined as below 1000 V. Under normal conditions, direct contact with equipment having an alternating voltage of 50 V or more can be life-threatening.

Article 3: It is strictly forbidden to give instructions or orders to those who have not been trained, have not passed the procedure examination, and do not clearly understand the tasks they will have to perform.

Article 4: If an order contradicts this procedure, the person receiving the order has the right not to comply and must provide the reasons for non-compliance to the person who issued the order. If the person who issued the order does not agree, the recipient has the right to report to a higher authority.

Article 5: When discovering that officials or workers are violating the procedure or there is a situation threatening human life and equipment, it must be immediately stopped, and at the same time, reported to the competent authority.

Article 6: The unit head, team leader, and technical staff are responsible for inspecting and proposing occupational safety measures within their unit. The unit’s safety officer has the responsibility and authority to inspect, make a record, or issue a safety notice as a reminder. In cases of violations of safety measures that could lead to an accident, the work must be suspended until all safety measures are fully implemented before work can continue.

Article 7: The safety equipment used must comply with the technical standards issued by the State.

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II. CONDITIONS FOR WORKING IN THE ELECTRICAL INDUSTRY

Article 8: Those who are directly involved in the work of managing, operating, testing, repairing, and constructing electrical systems must be in good health and have a physical fitness certificate from a medical authority.

Article 9: Annually, units must organize health check-ups for officials and workers:

• Once for workers in management, operation, and repair.
• Twice for officials and workers conducting tests, and specialized workers on power lines.
• For those working on high lines above 50 m, a health check-up must be done again before starting work.

Article 10: When a worker is found to have a neurological, cardiovascular, rheumatic, or pulmonary tuberculosis disease, the organization must reassign them to suitable work.

Article 11: New employees must undergo a period of mentorship by an experienced employee to acquire the necessary technical skills, after which they must pass a direct oral examination. Only if they meet the requirements will they be assigned duties.

Article 12: Workers, technicians, and engineers directly involved in production must have their knowledge of the safety technical procedure tested once a year. The Director authorizes the unit head to organize the training and examination within their unit.

The results of the examinations must be fully documented to decide on the recognition of permission to work with the equipment and to assign a safety level.

Article 13: Heads and deputy heads of production teams, electrical branches (or equivalent levels), and technicians shall have their knowledge of the safety technical procedure tested once every two years by the enterprise’s knowledge examination board and be assigned a safety level (the criteria for safety level classification are in Appendix 4).

Article 14: While working with colleagues or when not on duty, if anyone sees a person suffering an electric shock, anyone must find a way to rescue the victim from the electrical circuit and continue to provide first aid according to the methods presented in Appendix 1 of this procedure.

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III. HANDLING OF PROCEDURE VIOLATIONS

Article 15: For individuals who violate the procedure, depending on the severity of the fault, the following measures shall be taken:

1. Cutting or reducing the monthly safe operation bonus.
2. Criticism, reprimand (in writing).
3. Demotion in work status, reduction in salary grade.
4. Prohibition from working in electrical-related jobs, transfer to other work.
5. Those who are criticized, reprimanded (in writing), or demoted must undergo retraining and re-examination and meet the requirements before being allowed to continue working.

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IV. OPERATING PERMIT SYSTEM AND IMPLEMENTATION

Article 16: All operations on equipment with a voltage of 1000 V or higher must comply with an operating permit according to the unified form in the procedure. The permit must be written by a system operator, shift leader, technical staff, team leader, or chief on duty. It must be checked and signed by the approver to be valid for implementation.

Article 17: The person ordering the power on/off must recheck the sequence of operations and the power grid diagram for the last time and sign the operating permit before giving the order and handing the permit to the operator, giving necessary instructions. The task is only considered complete when the operator reports that the operation is finished.

Article 18: All switching operations on the high-voltage electrical distribution system must be performed by two people. These two people must clearly understand the grid diagram; one person directly performs the operation and one supervises. The operator must have a safety level of at least III, and the supervisor must have a safety level of at least IV. In all cases, both are equally responsible for their actions.

Article 19: Under normal operating conditions, the operator and supervisor must adhere to the following regulations:

1. Upon receiving the operating permit, read it carefully and re-check the content of the operation against the diagram. If anything is unclear, ask the person who gave the order again. If the order is received by telephone, the full order must be recorded in the operating log. The person receiving the order must repeat each action over the phone and then write down the name of the person giving the order, the person receiving it, and the date and time of the order in the logbook.
2. After the operator and supervisor have reviewed and have no further questions, they both sign the permit and take it to the operating location.
3. Upon arriving at the operating location, they must check again against the diagram (if available) and verify that the actual position of the equipment matches the content recorded in the permit. They must also check for any obstacles around or on the equipment before being allowed to operate.
4. The supervisor reads each action aloud in the order written on the permit. The operator must repeat it. The supervisor gives the command “close” or “open”… only then is the operator allowed to perform the action. After each action is completed, the supervisor must mark the corresponding item on the permit.
5. During the operation, if there is any doubt about the action just performed, the work must be stopped immediately to recheck everything before continuing. If an incorrect operation is performed or an incident occurs, the operating permit must be stopped immediately and the person who gave the order must be informed. The continuation of the operation must be carried out with a new permit.

Article 20: In the event of an accident or incident that is deemed to have the potential to damage equipment, the operating worker is permitted to trip circuit breakers or disconnectors without an order or permit, but must subsequently report the actions taken to a higher-level operating staff and the unit head, and must record it in the operating log.

Article 21: In cases where the operating location is far from residential areas and there are no means of communication, it is temporarily permitted to switch power on/off at a pre-arranged time, but the time must be synchronized and adjusted to be uniform, using the order issuer’s clock as the standard. There must be a convention to test the lights before the operation (test all 3 phases). If the appointment is missed for any reason, the operation is prohibited.

Article 22: It is forbidden to switch power on/off or change fuses for outdoor equipment during heavy rain when water is flowing in streams over the equipment and safety tools, or during a thunderstorm. It is only permitted to open the disconnector on branch lines where the power has already been cut. It is permitted to replace fuses in humid, wet weather after the disconnector has been opened on both the low and high voltage sides.

Article 23: To prevent accidental energization of equipment where people are working, the operating mechanisms of disconnectors in the station must be locked and a safety sign hung. The key is kept by the person who cut the power or the on-duty operator.

Article 24: When opening and closing manually operated circuit breakers and disconnectors, insulating gloves must be worn, and one must wear boots or stand on an insulating stool. It is permitted to perform switching on a pole provided that the distance from the lowest live part to the operator is not less than 3 m.

Article 25: All completed operating permits must be returned to the grid management unit (dispatch center or branch) to be kept for at least 3 months, after which they may be destroyed. Operating permits related to incidents or occupational accidents must be kept in the incident/accident file of the unit.

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V. MEASURES TO ENSURE SAFETY WHEN CARRYING OUT WORK

1. TECHNICAL MEASURES TO ENSURE SAFETY AT WORK

Article 26: To prepare the workplace when partially or completely de-energizing, the following technical measures must be carried out in sequence:

1. Cut the power and implement measures to prevent accidental re-energization of the workplace, such as: using locks to lock the disconnector operating mechanism, removing the operating circuit fuse, locking the compressed air valve, etc.
2. Hang a “Do Not Close! People at Work” sign on the disconnector operating mechanism. A “Do Not Open Valve! People at Work” sign on the compressed air valve, and if necessary, set up barriers.
3. Connect the portable grounding wire to the ground. Check that there is no voltage on the part of the equipment where work will be carried out and proceed with grounding.
4. Set up barriers to separate the work area and hang electrical safety signs according to current Vietnamese standards. If the power is completely cut off, it is not necessary to set up barriers.

a. De-energizing

Article 27: At the workplace, the following parts must be de-energized:

• Live parts on which work will be carried out.
• Live parts which, during work, cannot be avoided from being touched or approached within the following distances:
  • 0.7 m for voltages up to 15 kV.
  • 1.0 m for voltages up to 35 kV.
  • 1.5 m for voltages up to 110 kV.
  • 2.5 m for voltages up to 220 kV.
  • 4.5 m for voltages up to 500 kV.
• When it is not possible to de-energize and the worker is likely to violate the above specified distances, a barrier must be erected. The distance from the barrier to the live part is:
  • 0.35 m for voltages up to 15 kV.
  • 0.60 m for voltages up to 35 kV.
  • 1.50 m for voltages up to 110 kV.
  • 2.50 m for voltages up to 220 kV.
  • 4.50 m for voltages up to 500 kV.
• The requirement for setting up barriers and the method of setting them up are determined depending on the specific conditions and the nature of the work, for which the person preparing the workplace and the direct supervisor of the work are responsible.

Article 28: De-energizing for work must be done in such a way that it is clearly visible that the part of the equipment intended for work has been isolated from all live parts from all sides by opening disconnectors, removing fuses, disconnecting cable ends, disconnecting busbars (except for GIS stations). It is forbidden to de-energize only by means of a circuit breaker, automatic disconnector, or load break switch with an automatic operating mechanism.

Article 29: When de-energizing for work, it is necessary to prevent low-voltage power sources from unexpectedly energizing through equipment such as power transformers, instrument transformers, and diesel generators, which could be dangerous to workers.

Article 30: After de-energizing a circuit breaker or disconnector, the control circuit must be locked, such as: tripping the circuit breaker, removing the fuse, locking the compressed air valve to the circuit breaker, etc. For directly operated disconnectors, after de-energizing, the operating handle must be locked and checked to be in the open position.

Article 31: De-energizing is the responsibility of the operating personnel. It is forbidden to delegate the operation to repair workers, unless the repair workers have been trained in operations.

Article 32: Partial de-energizing for work must be assigned to experienced operating personnel who have a firm grasp of the grid diagram to prevent the possibility of confusion that could endanger repair workers.

Article 33: In case of de-energizing ordered by the National, Regional, or Power Company dispatch by telephone, the operating management unit must be responsible for handing over the power line to the repair unit at the site (including placing grounds).

b. Hanging Signs and Placing Barriers

Article 34: The person carrying out the de-energization must hang a warning sign: “Do Not Close! People at Work” on the operating mechanisms of the circuit breakers and disconnectors from which power can be supplied to the workplace. For single-phase disconnectors, a sign must be hung on each phase. This is done by the operating personnel. Only the person who hung the sign or a designated replacement is allowed to remove these signs. When working on a power line, a sign “Do Not Close! People Working on the Line” must be hung on the line disconnector.

Article 35: Temporary barriers can be made of wood, insulating material sheets, etc. The barrier must be dry and sturdy. The distance from the temporary barrier to the live parts must not be less than the distance mentioned in Article 27. On the temporary barrier, a sign must be hung: “Stop! Live Voltage, Danger of Death”.

Article 36: On electrical equipment with a voltage up to 15 kV, in special cases, depending on the working conditions, the barrier may touch the live part. This barrier (shield, cover) must meet the requirements of the code for the use and testing of safety technical equipment used in electrical installations. When placing the barrier, extreme caution must be exercised, insulating gloves must be worn, insulating boots must be worn or one must stand on an insulating mat, and there must be two people. If necessary, pliers or an insulating pole must be used. Before placing it, the barrier must be wiped clean of dust with a dry cloth.

Article 37: In an indoor electrical distribution facility, on the mesh fence or iron gate of the adjacent and opposite compartments to the work area, a sign must be hung: “Stop! Live Voltage, Danger of Death”. If there is no mesh fence or gate in the adjacent and opposite compartments, as well as in the passages that workers do not need to pass through, a temporary barrier must be used to block it off and the aforementioned sign must be hung. At the workplace, after placing the portable ground, a sign “Work Here!” must be hung.

Article 38: Temporary barriers must be placed in such a way that in case of danger, workers can easily escape from the danger zone.

Article 39: During work, it is forbidden to move or remove temporary barriers and signs.

c. Checking for Absence of Voltage

Article 40: After de-energizing, the operating personnel must verify that there is no voltage on the equipment that has been de-energized.

Article 41: To check for voltage, a voltage tester appropriate for the voltage to be tested must be used. All 3 incoming and outgoing phases of the equipment must be tested.

Article 42: One must not rely on indicator lights, relays, or meters to verify whether the equipment is live or not, but if a meter, relay, etc., indicates that there is voltage, the equipment is considered to be live.

Article 43: Before testing, the voltage tester must be checked at a known live location before testing at the location to be handed over. If there is no power at the work site, it is permissible to test it at another location before testing at the work site, and the voltage tester must be well-maintained during transport.

Article 44: It is forbidden to use the method of lightly tapping the power line with an operating rod to see if it is still live as a basis for handing over the line to the work crew.

d. Placing Grounds

• Location for placing grounds

Article 45: After checking for no voltage, grounding must be placed and all phases must be short-circuited immediately. Wherever grounding is placed, the absence of voltage must be tested at that location.

Article 46: Grounding must be placed on the side from which power can be supplied. The grounding wire must be a specialized wire, made of bare copper (or covered with a transparent plastic sheath), flexible, multi-stranded, with a minimum cross-section of 25 mm².

The grounding location must be chosen to ensure a safe distance to live parts. The number and location of grounds must be chosen so that the workers are completely within the area protected by those grounds.

Article 47: When performing work with a complete power outage at a distribution substation or distribution cabinet, to reduce the number of portable grounding wires, it is permissible to place grounding on the busbar and only on the circuit on which work will be performed. When moving to work on another circuit, the grounding wire must be moved simultaneously. In that case, work is only allowed on the circuit where grounding is placed. When repairing a busbar with sections, one grounding wire must be placed on each section.

Article 48: On a high-voltage trunk line with no branches, grounding must be placed at both ends.

If the repair area is longer than 2 km, an additional ground must be placed in the middle. For a trunk line with branches where the branch cannot be disconnected by a disconnector, each branch (located within the repair area) must have an additional set of grounds at the beginning of the branch.

For two trunk lines sharing the same pole, if one line is being repaired (the other is still in operation), the two sets of grounds must not be placed more than 500 m apart. For river crossings, in addition to the two sets of grounds placed at the two strain towers, additional auxiliary grounds must be placed at the crossing towers themselves.

For branch lines into a substation that are no longer than 200 m, it is permissible to place one ground to block the power source, and the other end must have the transformer’s disconnector opened.

For underground cables, grounding must be placed at both ends of the cable section. For low-voltage lines, when de-energized for repair, grounding must also be placed by shorting the 3 phases with the neutral wire and connecting to the ground. Attention must be paid to checking for customer generators on branches to disconnect them and prevent them from feeding back into the grid.

• Principles of Placing and Removing Grounds

Article 49: Placing and removing grounds must both be carried out by two people, one of whom must have a safety level of at least IV, and the other must have a safety level of at least III.

Article 50: When placing a ground, one end must be connected to the ground first, then the other end is attached to the conductor. When doing this, insulating gloves must be worn and an insulating pole must be used to attach it to the power line. When removing the ground, the reverse procedure must be followed.

Article 51: The end connected to the ground must not be twisted on; it must be fastened with a bolt. If connecting to the pole’s ground or the common grounding system, the connection point must be cleaned of rust before connecting. If the pole’s ground is damaged or it is difficult to attach a bolt, an iron stake must be driven 1m deep to serve as a ground.

2. ORGANIZATIONAL MEASURES TO ENSURE SAFETY AT WORK

Article 52: Repair work and non-operational work on electrical equipment, as a rule, should only be carried out under a work permit or work order.

Article 53: Jobs that require a work permit are:

1. Repairing and reinforcing high-voltage underground cables, overhead lines, or switching connections from newly constructed branch lines to the main grid lines.
2. Repairing, moving, reinforcing, adjusting, and testing electrical equipment on the grid such as: generators, motors, transformers, circuit breakers, switches, surge arresters, capacitors, rectifiers, busbars, protective relays, etc., unless otherwise specified.
3. Working directly with live low-voltage equipment or working near live high-voltage equipment within the permissible distance.

Article 54: The following tasks are permitted to be carried out under a work order:

1. Switching operations and incident handling ordered by the head of the National, Regional, or Power Company dispatch center, or the power plant shift leader.
2. Work done far from live electrical equipment.
3. Simple tasks with small volume and short duration performed directly by operating personnel or by other personnel under the supervision of operating personnel.

Article 55: The work permit must have 2 copies; 1 copy is given to the direct supervisor of the work unit or the supervisor, and 1 copy is kept by the person authorizing the work unit to enter the worksite. The permit must be written clearly and legibly, without erasures, not written in pencil, and must follow the standard form. The validity period is not more than 15 days from the date of issue.

Article 56: Each direct supervisor or supervisor is issued only one work permit. The direct supervisor or supervisor must keep the permit throughout the working period at the work location. The permit must be kept from being torn or smudged. Upon completion of the task, procedures are carried out to close the permit. The work permit issued to the direct supervisor or supervisor, after completion, must be returned to the issuer for checking and signing, and kept for at least 1 month. Permits related to incidents or occupational accidents during the work must be filed in the unit’s incident and accident records.

Article 57: When multiple teams or units are working on the same power line system, substation, or construction site with separate supervisors, each unit will be issued a separate permit and will have separate safety measures so that when they leave the work site, it does not affect other units.

Article 58: Changes in the personnel of the work unit may be decided by the person who issued the work permit or the work leader. In their absence, the decision is made by the person authorized to issue work permits. If the scope of work is expanded, a new work permit must be issued.

a. Persons Responsible for Safety

Article 59: The persons responsible for the safety of a work permit include:

• The permit issuer (or the person who issues the work order):
  • A technical officer (head or deputy of a branch, workshop, station, laboratory, management team, etc.).
  • A grid dispatcher (in necessary cases), a power plant shift leader. These individuals must have a safety level of V. The permit issuer must be fully aware of the work content, scope, and volume to establish the necessary safety measures and to assign a work leader, a direct supervisor, as well as personnel of the work unit who are capable of performing the task safely.

• The work leader:
  • Those assigned the responsibility of leading the work according to the permit are: technical officers, technicians, skilled workers. They must be competent to undertake the task and have a safety level of V. The work leader is responsible for the number and qualifications of the personnel in the work unit, ensuring that the direct supervisor is able to safely supervise them while they are working.
  • When accepting the worksite or when directly carrying out the procedure to allow the work unit to enter the worksite, the work leader is equally responsible with the person authorizing entry for the preparation of the worksite, for the safety measures, as well as for the special conditions recorded in the permit.

• The direct supervisor (or supervisor):
  • The direct supervisor must have a safety level of IV or higher. When accepting the worksite, they are responsible for re-checking and fully implementing the necessary safety measures. They must arrange, assign, and supervise so that everyone in the unit carries out the work safely.
  • The direct supervisor is responsible for the quality of the tools and safety equipment used during work. They must be continuously present at the worksite. If it is necessary to be absent and there is a duly authorized person to take over, they must hand over the worksite and the work permit to that person. If there is no one to take over, the entire work unit must be withdrawn from the worksite.
  • In case the work unit is sent from another place, and the officer in charge does not have the qualifications to supervise electrical safety, or the work unit consists of people doing work such as masonry, carpentry, mechanics, etc., the equipment management side must appoint a person with sufficient qualifications to act as a supervisor. The supervisor accepts the worksite from the authorizer, must be continuously present at the worksite to supervise, and must not do any other work. They must ensure that signs and barriers are not removed or moved. They are responsible for preventing electrical accidents, while the responsibility for the safety of the personnel in their work is borne by the direct supervisor of the work unit.
  • The safety level of the supervisor is IV or higher when the work unit is working with partial de-energization or near live parts. It is III or higher if working with complete de-energization or far from live parts.

• The person authorizing the work unit to enter the worksite (operating personnel):
  • The person authorizing entry must have a safety level of IV or higher, is responsible for the full implementation of necessary safety measures appropriate to the nature of the work and the worksite, as well as for the full implementation of procedures for authorizing entry, accepting the worksite upon completion, and recording the required items in the work permit and the operating log. After handing over the worksite, they keep the permit in the “Permits in Progress” file for monitoring.

• Work unit personnel:
  • These are workers who have been trained and coached to work for the enterprise. When working with partial de-energization or near live parts, each work unit may have one person with a safety level of I, provided that in addition to the direct supervisor, there is at least one other person in the work unit with a safety level of III. When working with complete de-energization or far from live parts, the number of personnel with a safety level of I is determined by the person who issues the permit or the work order.

Article 60: The list of persons assigned the tasks of issuing permits, leading the work, and being direct supervisors is approved by the deputy technical director of the enterprise.

Article 61: For work permits for work on equipment with a voltage up to 1000 V, the work permit may only require the following titles:

• Permit issuer: must have a safety level of at least IV, have worked on electrical equipment for over 3 years, and have a decision from the enterprise granting the right to issue work permits.
• Authorizer for entry: the on-duty operating personnel. The authorizer may assign the direct supervisor to switch power on/off according to the work permit when necessary. The work permit number, the time of power outage, the time of work completion, and the time of re-energizing the equipment must be recorded in the operating log.
• Direct supervisor: along with the authorizer, prepares the worksite, and positions the unit’s personnel to carry out the work. The direct supervisor’s safety level must be at least III. In case of operations on equipment with a voltage level of 1000 V or higher, the operator must have a safety level of IV or higher.
• Work unit personnel: decided by the permit issuer and recorded in the permit.

Article 62: One person is allowed to hold multiple (2-3) titles in the work permit, provided that the person holding multiple titles has the safety level required for the title they are undertaking.

b. Procedure for Executing a Work Permit

Article 63: The person issuing the work permit is responsible for filling in the following sections:

• Work leader.
• Direct supervisor.
• Work location.
• Work content.
• Planned start and end time.
• Necessary safety measures to be implemented (left-hand columns of section 4).
• Special conditions to be noted.
• List of work unit personnel (this section may be assigned to the work unit leader to fill in. If the permit issuer fills it in, they are responsible for the number and qualifications of the work unit personnel as mentioned in Point 59-2).
• Sign, write full name, and time of issue before handing the permit to the executor. Receive the permit back upon completion, re-check the entire implementation process and sign at the end of the permit, and file the permit according to regulations.
• If during the inspection of the permit implementation, errors are found, a review must be organized to draw lessons. In case of serious violations, appropriate disciplinary action must be taken to prevent accidents before they can occur.

Article 64: The work leader, after receiving the permit, records the number of workers in the unit in section 1 (if assigned by the permit issuer). They give one copy of the permit to the direct supervisor (or supervisor), one copy to the authorizer, and complete the procedures for handing over and receiving the worksite. They inspect the work progress when necessary.

c. Procedure for Authorizing a Work Unit to Enter the Worksite

Article 65: After all safety measures have been implemented and before authorizing the work unit to enter the worksite, the authorizer must perform the following tasks:

1. Show the entire unit the worksite, use a voltage tester of the corresponding voltage level to prove that there is no voltage on the de-energized and grounded parts.
2. Check if the number and safety levels of the work unit personnel are as recorded in the permit.
3. Inform the entire unit of the live parts around the worksite.
4. The work leader and direct supervisor sign the work permit, then hand it to the authorizer to sign (with full name written).

Article 66: After signing the permit to allow entry, the direct supervisor keeps one copy, and the authorizer places the other copy in the “Permits in Progress” folder and records the permit number, start time, and end time of the work in the operating log.

d. Supervision During Work

Article 67: From the time the work unit is authorized to enter the worksite, the direct supervisor (or supervisor) is responsible for supervising everyone’s work according to safety regulations.

Article 68: To perform the task of supervision, the direct supervisor (or supervisor) must always be present at the worksite. When the direct supervisor (or supervisor) needs to be absent and there is no replacement, the entire unit must be withdrawn from the worksite.

Article 69: The work leader must periodically inspect the compliance with the safety technical procedure by everyone in the work unit. When a violation of the safety technical procedure or another dangerous phenomenon is detected, the work permit must be withdrawn and the work unit must be removed from the worksite. Only after the shortcomings have been rectified can the procedures be carried out to allow the work unit to return to work, and this must be recorded in the work permit.

e. Procedure for Breaks

Article 70: When work is temporarily suspended during the workday (e.g., for lunch), for work with partial de-energization or without de-energization, the unit must be withdrawn from the worksite. The safety measures remain in place. After the break, no one is allowed to enter the worksite without the presence of the direct supervisor (or supervisor) to authorize the unit to return to the worksite. The direct supervisor (or supervisor) is only allowed to let personnel enter the worksite after checking that all safety measures are still in place.

Article 71: As long as the direct supervisor has not returned the permit and clearly stated that the work is finished, the operating personnel are not allowed to switch on/off the equipment or change the diagram in a way that affects the working conditions. In case of an incident, the operating personnel may switch on the power if they are certain that no one is working on the equipment, without waiting for the permit to be closed, but must take the following measures:

• Remove the signs, grounds, and temporary barriers. Replace the fixed barriers and hang a sign: “Stop! Live Voltage, Danger of Death” instead of the sign: “Work Here!”.
• Before the direct supervisor returns and hands over the permit, a person must be posted on site to inform the direct supervisor and the personnel in the work unit that the equipment has been energized and they are no longer allowed to work on it.

f. Procedure for Ending the Workday and Starting the Next Day

Article 72: If the work lasts for several days, after each workday, the worksite and walkways must be cleaned up, but the signs, barriers, and grounds must remain in place. The work permit and keys are returned to the operating personnel, and both parties must sign the permit.

Article 73: To begin work the next day, the authorizer and the direct supervisor must re-check the safety measures and sign the permit to allow the work unit to enter the worksite. The presence of the work leader is not necessary at this time.

g. Moving the Worksite

Article 74: It is permitted to work at multiple locations on the same circuit under one work permit with the following conditions:

• All worksites must be prepared by the operating personnel and handed over to the work leader and direct supervisor at the beginning of the work.
• The direct supervisor and the entire unit are only allowed to work at one specific location among the locations on the circuit.
• On equipment with a permanent operator, the movement of the worksite is authorized by the operating personnel.
• On unattended distribution equipment, it is authorized by the work leader.
• When moving the worksite, it must be recorded in the work permit, and the direct supervisor and the authorizer must both sign the permit.

Article 75: When working without de-energizing, it is only necessary to complete the procedure for moving the worksite if the work unit moves from an outdoor equipment of one voltage level to an outdoor equipment of another voltage level, or from one distribution room to another.

h. Finishing Work, Closing the Permit, Handing Over the Worksite, and Re-energizing

Article 76: Upon completion of all work, the worksite must be cleaned up and inspected by the work leader. After all personnel have been withdrawn from the worksite, and all grounds and additional safety measures implemented by the work unit have been removed, only then can the work permit be closed.

Article 77: If during the quality inspection, a defect is found that needs to be corrected immediately, the work leader must follow the “Procedure for Authorizing Entry” as for a new job. This additional work does not require a new work permit but the start and end time of the additional work must be recorded in the work permit.

Article 78: When the order to remove the portable ground has been given, everyone must understand that the work is finished. It is forbidden to enter and touch the equipment for any reason.

Article 79: The handover must be conducted directly between the work unit and the equipment management unit. The work leader, the direct supervisor (or supervisor), and the authorizer sign the work completion section and close the permit. Handover by telephone is only permitted if there is an agreement between both parties at the time the permit is issued, and there must be a pre-arranged password.

Article 80: The operation of energizing the equipment is carried out after the permit has been closed, signs and temporary barriers have been removed, and fixed barriers have been re-installed. If there are multiple work units on the equipment to be energized, the power can only be switched on after all work permits have been closed.

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VI. SAFETY MEASURES WHEN WORKING AT HEIGHTS

1. ORGANIZATIONAL MEASURES

Article 81: All officials, contract workers, temporary employees, and students working at heights must strictly adhere to the regulations in this section.

Article 82: Those working at a height of 3 meters or more must be in full health, not suffering from conditions such as heart weakness, neurological disorders, epilepsy, etc., have a health certificate from a medical authority, and have been trained and tested on the procedure with satisfactory results.

Article 83: The group leader, team leader, squad leader, and branch manager are responsible for fully checking safety measures before allowing workers to work, and for reminding them of accident prevention measures and other dangers that may occur around the workplace.

Article 84: If one or more persons act in violation of the safety technical procedure, the person responsible for safety has the right to stop the work to give a reminder or to completely suspend the ongoing work if the issue is considered serious and threatens an accident, but must immediately report to their superior.

Article 85: When there are two or more people working, a group leader must be appointed. When working in places with many people and traffic (vehicles, boats) passing by, measures must be taken such as erecting barriers or placing “Caution! Worksite” signs, setting up barricades, etc., to prevent people, vehicles, and boats from entering the work area.

Article 86: All workers from professional level I and above are allowed to work at heights near or in the presence of electricity but must have been trained and tested to meet the requirements of this procedure. For temporary workers, seasonal contract workers, and students, they are only allowed to work at heights in the absence of electricity and must also be trained and tested to meet the safety technical procedure requirements.

Article 87: Those working at heights must follow the orders and safety measures instructed by the person in charge or the technical officer.

Article 88: It is strictly forbidden for people who have consumed alcohol, are sick, or do not meet health standards to work at heights.

Article 89: If safety measures have not been specifically defined or are not in accordance with the safety technical procedure, the person performing the work has the right to express their opinion to the person who gave the order. If it is not resolved satisfactorily, they can report it to a higher level and have the right not to perform the work.

Article 90: If the person in charge orders a worker to do something that violates the safety technical procedure, the person receiving the order must inform the person who gave the order. In that case, the worker has the right not to comply and to report to a higher authority.

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2. TECHNICAL MEASURES

Article 91: When working at heights, clothing must be neat, sleeves must be down and buttoned, and a helmet, safety shoes, and safety harness must be worn. It is not permitted to wear sandals without a back strap, studded shoes, clogs, etc. In cold weather, one must wear enough warm clothing.

Article 92: When working at a height of 3 meters or more, it is mandatory to wear a safety harness, even for a very short period of work (unless working on a work platform with a sturdy protective railing). The safety harness must not be attached to moving parts such as a mobile ladder or to objects that are not sturdy, are easily broken, or can easily slip. It must be attached to a fixed, sturdy object.

Article 93: When the wind reaches level 6 (60-70 km/hour), or during heavy rain or thunderstorms, working at heights is prohibited.

Article 94: Do not climb on poles that are partially erected or have been erected for less than 24 hours to install cross-arms or insulators. Guy wires may only be removed after the foundation has been poured for 24 hours, and a safety harness must be worn. When climbing a pole or ladder, do so slowly, securely, and with concentration. It is forbidden to talk or look away while climbing. Talking and joking are forbidden while working at heights.

Article 95: Do not carry heavy tools or materials up to a height along with a person. Only light tools such as pliers, screwdrivers, wrenches, adjustable wrenches, small hammers, etc., are allowed to be carried, but they must be kept in a dedicated tool bag. It is forbidden to put these tools in pants or shirt pockets to prevent them from falling on someone else’s head.

Article 96: Tools for working at heights must be placed in secure locations or have hooks to be hung on the pole so that they do not fall to the ground upon strong impact.

Article 97: It is forbidden to bring tools and materials up or down from a height by throwing them. A rope must be used to pull them up or lower them slowly through a pulley. The person below must stand far from the base of the pole and hold one end of the rope.

Article 98: Smoking is prohibited when working at heights.

Article 99: When working on slippery, steep roofs, specific safety measures must be in place for those locations. The person in charge and the technical officer must pay close attention, monitor, and remind.

Article 100: Climbing a centrifugal pole without climbing steps requires the use of a single-rail ladder, double-rail ladder, or specialized climbing spikes. It is absolutely forbidden to climb a pole using the “guy wire”. When using a single-rail ladder or specialized climbing spikes, there must be a separate usage procedure for this type of ladder or spikes.

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3. SAFETY MEASURES WHEN USING PORTABLE LADDERS

Article 101: A portable ladder is a type of ladder made of wood, bamboo, iron, etc., that can be moved from one place to another. In places where it is not possible to erect scaffolding, working on a portable ladder is permitted.

Article 102: When working on a ladder, one person must hold the base of the ladder. On marble, cement, brick floors, etc., the feet of the ladder must be padded with rubber or a wet sack to prevent slipping. On a dirt ground, a recess must be dug for the ladder feet.

Article 103: The ladder must meet the following conditions:

• The material used to make the ladder must be sturdy and dry.
• The width of the ladder base must be at least 0.5 m.
• The ladder must not be termite-infested, bent, or warped when in use.
• The distance between the rungs must be equal.
• The rungs must not be fastened with nails; the first and last rungs must have pins.

– If it is a bamboo ladder, it must also be securely bound with twisted steel wire at both ends and in the middle.

• The ladder must be within its permitted service life.

Article 104: When leaning a ladder against long beams or round pipes, a rope must be used to tie the top of the ladder to that object. The length of the ladder must be appropriate for the required working height.

Article 105: When working on a ladder, one must be at least 1 m from the top of the ladder and must lock their feet onto the ladder or stand with one foot on a higher rung and the other on a lower one. The ladder must be leaned against the wall at a 30-degree angle. Note: Do not attach a safety belt to a portable ladder.

Article 106: Do not carry excessively heavy objects up a ladder or have two people climb the ladder at the same time. Do not stand on a ladder to move it from one position to another.

Article 107: If it is necessary to extend a ladder, an iron strap and bolts must be used, or a splint made of hard wood or bamboo of at least 1 m long must be used to join the two ends, and then steel wire must be used to tightly twist and secure it, ensuring it is not loose or wobbly. The ladder must be regularly inspected; if it is found to be unsafe, it must be repaired immediately or decisively not used.

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4. SAFETY MEASURES WHEN USING A SAFETY HARNESS

Article 108: A safety harness must be tested once every 6 months by hanging a weight or using a specialized safety harness testing device. For an old harness, 225 kg; for a new harness, 300 kg, the test duration is 5 minutes. Before use, the buckle, stitching, etc., must be checked for rust or breakage. If there is any doubt, a weight test must be performed immediately.

Article 109: After testing the safety harness, the team leader must record the test date, test weight, and comments (good or bad) in the team’s safety harness test logbook. A mark must also be made on the tested harness; only marked harnesses are allowed to be used.

Article 110: Every day, before working at heights, workers must personally check their safety harness by wearing it and attaching the rope to a sturdy object on the ground, then bringing their feet together and leaning back to see if there are any issues with the harness.

Article 111: The safety harness must be well-maintained. It should not be left in a damp place but should be hung up or placed in a high, dry, and clean place. After work, it must be rolled up neatly.

Article 112: Production teams are responsible for the strict management of safety harnesses.

If an accident occurs due to the harness breaking, a hook breaking, or failure to test it on schedule, the team leader, squad leader, branch manager, and the unit’s safety technical officer will be held fully responsible.

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VII. SAFETY MEASURES WHEN WORKING

AT SUBSTATIONS

1. MINIMUM REGULATIONS TO REMEMBER

Article 113: It is strictly forbidden to bring unauthorized persons into the substation. Visitors for observation or research must be guided by the head or deputy head of the unit (or a technician).

Article 114: Workers entering the substation for work must have a safety level of at least II; the group leader must have a safety level of III or higher. A person entering the substation alone must have a safety level of V and must be on a list approved by the unit head.

Article 115: When entering the substation for work or a visit, everyone must respect the substation’s rules. First-time visitors must be thoroughly guided. When entering the substation to repair equipment or adjust relays and meters, there must be two people, and they are only allowed to work within the permitted area.

Article 116: The safe distance when working without a barrier must be ensured:

• Low voltage not less than 0.30 m
• Voltage up to 15 kV not less than 0.70 m
• Voltage up to 35 kV not less than 1.00 m
• Voltage up to 110 kV not less than 1.50 m
• Voltage up to 220 kV not less than 2.50 m
• Voltage up to 500 kV not less than 4.50 m
• This only applies to minor repairs and operational observations. For long-term repairs or the transport of bulky equipment, a specific technical plan and safety measures must be established before starting the work.

Article 117: Each time entering the substation for work, anyone, regardless of position, must record the work done in the substation logbook.

Article 118: The substation key must be clearly labeled and managed according to separate regulations.

Each time leaving the substation, the door must be locked and pulled to check if it is securely locked.

Article 119: If equipment in the substation fails, one must stand at least 5 m away from the equipment if it is indoors, and 10 m if it is outdoors. One is only allowed to approach when it is certain that the equipment is completely de-energized. When a thunderstorm is approaching, all work in an outdoor substation and on the incoming disconnectors of overhead lines connected to a built substation must be stopped.

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2. INSPECTING EQUIPMENT OPERATION

Article 120: The person responsible for inspecting live low-voltage equipment must have a safety level of III or higher.

Article 121: A person assigned to inspect or read electricity meters alone is not allowed to cross barriers or repair equipment on their own.

Article 122: If it is necessary to open a gate to inspect operating equipment, the person supervising from the outside must have a safety level of IV or higher, and the person entering for inspection must have a qualification of not less than safety level III and must carefully observe the live parts to ensure a safe distance.

Article 123: Personnel working in the substation must remember that for operating equipment that has lost power or has been de-energized but not grounded, or for standby equipment in the substation, the current can be restored unexpectedly. Working on such equipment is forbidden. Do not inspect outdoor substations during thunderstorms.

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3. OPERATING DISCONNECT SWITCHES

Article 124: Closing and opening high-voltage disconnect switches must be performed by 2 people according to an operating permit, which must be signed and approved by a person authorized by the director.

The operating permit must clearly state the sequence of operations to be performed and the safety precautions to be taken. Before proceeding, the operating team must carefully read the permit to immediately report anything unclear to the person who gave the order. Upon arriving at the operating location, two things must be checked:

• Whether the actual name on the disconnect switch matches the name in the permit.
• Whether the safety conditions, such as the operating rod and insulating stool, are in good condition.

If any discrepancy is found, the operation must not be carried out, but the person who gave the order must be informed immediately.

Article 125: A substation operator is also not permitted to perform operations alone based on a telephone order from the grid operation shift leader, even if they are well-trained professionally.

Article 126: For power grids with a voltage level of 1 kV and above, the safety equipment for operations must include:

• An insulating rod (except where there is a combined switch-disconnector and circuit breaker).
• Insulating gloves.
• Insulating boots.

All of the above equipment must have an insulation voltage appropriate for the voltage to be operated.

Article 127: When it is raining heavily and water is flowing in streams over the safety equipment, outdoor operations are not permitted. On de-energized lines, it is permitted to operate disconnect switches during rain or thunderstorms if necessary.

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4. USING A CLAMP METER

Article 128: Measuring the current intensity in a high-voltage grid with a clamp-on meter requires a work permit. The measurement must be carried out by two people who have been specially trained in how to measure, read the values, and supervise for safety, and they must have a safety level of IV or higher.

Article 129: For high voltage, only a clamp meter with the ammeter built directly into the clamp is permitted. For low voltage, measuring with a separate ammeter is also allowed.

Article 130: When measuring, the safety equipment must include: gloves, boots, and an insulating stool corresponding to the grid voltage. The measurement location must be convenient and the distance between phases must not be less than 0.25 m.

Article 131: The insulated handle of the clamp meter for high-voltage grids must be tested. A clamp meter with a cracked or broken insulated part at the jaw must not be used.

Article 132: When measuring on a low-voltage grid, the person measuring does not need to wear safety equipment. If measuring on a pole, the regulations for working at heights in this procedure must be followed. When measuring, one must stand on a solid floor or support; do not stand on a portable ladder.

Article 133: After measuring, the clamp meter must be kept in its case and stored in a dry place.

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VIII. SAFETY MEASURES WHEN IN CONTACT WITH ELECTRICAL EQUIPMENT

1. CLASSIFICATION OF WORK ON ELECTRICAL EQUIPMENT

Article 134: Work on high-voltage and low-voltage electrical equipment (substations and power lines) is divided into 3 types:

1. Complete power disconnection.
2. Partial power disconnection.
3. Without power disconnection.

Workers must understand and clearly distinguish between the 3 types mentioned above to prepare the necessary safety conditions for the work to be carried out.

Article 135: When the work requires a complete power disconnection in a substation, the work unit must have all 4 of the following conditions:

• Switching procedure sheet;
• Work permit;
• Prepare a sufficient number of grounding cables to be placed on the outer terminals of the incoming and outgoing high-voltage disconnect switches;
• Prepare a sufficient number of necessary safety signs.

Article 136: In cases where only a partial high-voltage power disconnection is required for work, the work unit must pay attention to the following issues:

• Must thoroughly understand the content of the work already recorded in the work permit and switching procedure sheet.
• Must have specific measures to avoid confusion at the work site.
• Must not arbitrarily change the content of the work permit.
• Must ensure a safe distance from adjacent energized equipment or have necessary barriers.
• Must have sufficient warning signs and necessary grounding.

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2. WORKING WITH ENERGIZED HIGH-VOLTAGE ELECTRICAL EQUIPMENT

Article 137: Work performed without power disconnection is divided into two main types, depending on the level of danger:

1. Work performed outside the barriers of energized equipment or outside the safe distance from energized equipment.
2. Work performed near or on energized parts and equipment that cannot be shielded, which may pose a danger to the worker.

Article 138: For work conducted outside the fixed barriers of the substation or in the low-voltage section of the substation, the work team does not need a work permit but must record the work done in the substation logbook. Construction workers entering the substation for work must be supervised by operating personnel.

Article 139: Work that allows opening safety gates while the equipment is still energized includes:

Taking transformer oil samples (note: check the grounding of the machine casing first).

• Performing oil filtration on large operating transformers.
• Checking the temperature at connection points, bushings, and switch jaws using a candle mounted on an insulating pole (safety tool similar to those used for switching operations).
• Cleaning insulators of 35 kV and below with a feather duster (the duster must be tested to meet insulation standards and well-maintained before use. It is forbidden to tie the duster to any conductive object).
• Checking the vibration of busbars with an operating rod.
• Checking for voltage with a neon tester, measuring current with a clamp meter. A work permit is required for these tasks, and prescribed distances must be maintained.

Article 140: The work permitted in Article 139 may only be carried out when the live parts are in front of or above the worker. The worker must stand on a solid floor or scaffolding; working in a stooped position is prohibited.

Article 141: It is strictly forbidden to work on temporary scaffolding or mobile ladders when there is live high-voltage equipment underneath (even if a safe distance is maintained).

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3. WORK ALLOWED WITHOUT GROUNDING

Article 142: Work done with power disconnected but without grounding is divided into two main types:

1. Work that temporarily requires removing the grounding wire.
2. Work that is permitted without installing a portable grounding wire but requires hanging a “Do Not Close Switch!” sign on the disconnect switches that must be opened for work.

When performing this work, the direct supervisor must have a safety qualification of level IV or higher.

Article 143: Work that involves disconnecting power but requires removing the grounding wire includes:

• Checking the resistance of the substation’s system.
• Reinforcing the grounding of equipment or the entire substation system.

A work permit is required for these tasks, and the permit must clearly state which grounding is to be removed and by which operating personnel.

Article 144: The equipment operator may delegate the work in Article 143 to the direct supervisor of the testing unit (by specifying it in the work permit) after completing the power disconnection and hanging safety signs. Cleaning the equipment casing is permitted along with other authorized tasks.

Article 145: Equipment that is de-energized for work may be worked on without grounding if it meets the following 3 requirements:

1. The equipment has a compact block structure that is easy to observe in its entirety.
2. It can be completely isolated from the electrical system by a disconnect switch (1-phase and 3-phase) that is clearly visible from the standing position.
3. It is certain that no induced voltage will appear on the equipment. This is only permitted for voltages of 35 kV and below. Note: This type of equipment includes: circuit breakers, transformers, VTs (with the secondary side fuse removed)…, arc suppression coils, motors, surge arresters, capacitors (after being discharged).

Article 146: It is strictly forbidden to work on sections of underground cables or overhead conductors without grounding them first.

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4. WORK ON ISOLATORS AND CIRCUIT BREAKERS WITH REMOTE CONTROL

Article 147: When working on an isolator with a remote control drive mechanism, the following measures must be taken to prevent accidental closing:

1. A work permit is required.
2. A sufficient number of grounding conductors must be connected, and all necessary prohibition signs must be hung. Only after completing these steps can the work unit be authorized to begin work.

Article 148: When working on a circuit breaker, the safety measures are:

• There must be an order to take the circuit breaker out of service.
• A work permit is required.
• The control fuse of the circuit breaker must be removed.
• The isolating switches before and after the circuit breaker must be opened.
• If it is an air-blast circuit breaker, the valves supplying compressed air to the breaker must be locked, the compressed air in the breaker must be discharged, and a sign must be hung: “Do not open valve! People at work.”
• Hang a sign: “Do not close! People at work” on the circuit breaker’s control switch.

Article 149: To test and adjust the closing and opening of the circuit breaker, the direct supervisor is allowed to install the control circuit fuse and restore compressed air to the tank, but this must be with the consent of the operating personnel.

Article 150: When someone is working inside the air tank, the valves leading air into the tank must be locked and a sign “Do not open valve! People at work” must be hung.

Article 151: It is forbidden to work on operating circuit breakers (including cleaning porcelain insulators with a feather duster attached to an insulating pole).

Article 152: Do not clean the air compressor or perform minor repairs while it is running. Oiling and greasing are only permitted while the machine is running, provided that there are adequate tools and means to ensure safety.

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5. WORKING WITH BATTERIES AND CHARGING EQUIPMENT

Article 153: When no one is working, the battery room must be locked. The key must be given to the person in charge or the specialized inspection personnel.

Article 154: The battery room must have adequate ventilation and fan systems. Portable battery banks with a voltage of 24 V to 36 V can be placed in a cabinet with a ventilation system. For batteries manufactured with new technology, a separate procedure should be developed according to the manufacturer’s regulations.

Article 155: Smoking, using lighters, and heaters are prohibited in the battery room. The door of the battery room must be clearly marked: “Battery Room – No Fire”.

Article 156: Do not leave items that obstruct ventilation openings or walkways between the racks in the battery room.

Article 157: Before and after charging the batteries, the ventilation fan must be turned on for at least 90 minutes. If toxic fumes are detected, the fan must not be turned off. For battery rooms operating on a continuous charge and discharge cycle, the ventilation fan must be turned on periodically at least twice per shift, for 30 minutes each time.

Article 158: Distilled water and a small amount of neutralizing solution are allowed to be kept at the entrance of the battery room.

Article 159: The sides of all containers for solutions and distilled water must be clearly labeled with acid-resistant paint.

Article 160: Concentrated acid must be stored in a separate room. In this room, besides acid, only neutralizing solution is permitted. The acid must be kept in glass or ceramic containers, tightly sealed, and placed on racks with carrying handles.

Article 161: Working with acid must be done by trained professionals. Transporting an acid container requires two people. Pay attention to check the path beforehand to avoid slipping, falling, or spilling the container.

Article 162: When pouring acid from a container, there must be a means to secure the container to prevent it from tipping over and breaking. The container for the acid must be completely dry and clean. When preparing an acid solution, pour the acid in a thin stream along a glass rod into distilled water, stirring constantly to dissipate heat. It is forbidden to pour distilled water into acid to make a solution.

Article 163: When using a selenium rectifier, do not remove the casing to work on any conductive parts until the rectifier circuit has been disconnected.

Article 164: Work in the battery room must be carried out by battery technicians. If repair or testing personnel need to work in the battery room, they must be supervised by a battery operator for safety.

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6. WORKING WITH CAPACITORS AND CAPACITOR PROTECTION

Article 165: Switching high-voltage capacitors on and off must be performed by two personnel with a safety qualification of level III or higher. It is strictly forbidden to use a standard disconnect switch to switch high-voltage capacitors on and off. Taking oil samples while the capacitor is in operation is prohibited.

Article 166: If the protective circuit breaker for the capacitor bank trips or a protective fuse blows, it is only permissible to re-close after the cause has been found and repaired.

Article 167: In case of disconnecting a capacitor for repair, it is essential to discharge the capacitor using a metal conductor with a minimum cross-section of 25 mm² and a maximum of 250 mm². This rod must be firmly attached to the hook of an insulating pole. This pole must meet the standards for operation at the capacitor’s working voltage. If the capacitor has individual or group protection, each unit or group must be discharged separately.

Note: When discharging the residual charge of a capacitor, a limiting resistor should be used first, then discharge directly to the ground to avoid damaging the capacitor.

Article 168: If the capacitor system is located in the same substation as the transformer, the capacitor banks must be placed in a separate room with a dividing wall to prevent fire.

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IX. SAFETY MEASURES

Article 401: Testing high-voltage electrical equipment requires a work permit, in which the direct supervisor must have a safety qualification of level IV or higher. Workers in the work unit must be trained and tested on:

1. Knowledge of testing methods and the rules presented in this chapter.
2. Experience in conducting tests.

This test will be combined with the annual safety technical procedure review of the unit.

Article 402: Operating personnel or persons under the supervision of operating personnel have the right to conduct tests without a work permit but must have a work order and record it in the operating log. In this case, the operating personnel must have a minimum safety qualification of level IV.

Article 403: Using a Kenotron cable tester for testing can be operated by a single person with a safety qualification of level IV or higher. Testing of de-energized electric motors can also be performed by personnel with a safety qualification of level IV or higher without a work permit.

Article 404: Carry out the procedures: writing a work permit, disconnecting power, hanging signs, setting up barriers, checking for no voltage, and placing grounds according to the conditions specified in Part One – Section V of this procedure.

Article 405: Test plans for complex equipment are prepared by the testing personnel but must be approved by the workshop (team) leader.

Article 406: Workers who perform switching operations for equipment testing must be checked on the operating procedure, wiring diagram, permit handover procedures, and personal safety measures, etc., before starting work.

Article 407: The high-voltage testing area must be barricaded. Unauthorized persons are not allowed to enter and there must always be a person on watch. This person can be the one who connects the test equipment and checks the circuit. The person conducting the test is responsible for setting up the barriers. If a rope is used instead of a barrier, a sign “Stop! High Voltage” must be hung on the rope. If the electrical wires pass through corridors, stairs, floors, etc., a guard must be posted at the necessary locations.

Article 408: Before applying power for testing, all workers in the work unit must retreat to a safe place under the guidance of the direct supervisor. Applying power for testing is handled by the direct test supervisor or by ordering a member of the unit to do so.

Article 409: Before closing the switch, the direct supervisor must personally check the test wiring circuit and safety measures, then warn the workers by saying: “I am turning on the power!” before closing the switch or ordering it to be closed. Nothing should be added after the low-voltage side has been energized.

Article 410: When the test is completed, the direct supervisor must disconnect the power, apply grounding, and inform the workers that “the power is off,” then order the rewiring for further testing or the removal of barriers and the conclusion of the work.

Article 411: Grounding should only be removed after the equipment to be tested has been connected. If the equipment to be tested has been completely disconnected by an isolating switch, grounding must be placed at the open circuit points on the sections where other work is still in progress.

Article 412: The switch supplying power for the test must be a 2-pole switch. The circuit breaking part must be clearly visible. From the time the equipment is connected to the test circuit, someone must watch the switch. To prevent accidental closing of the switch, an insulating pad should be placed between the blade and the jaw of the switch.

Article 413: The casing of high-voltage test equipment must be grounded.

Article
414: When using portable testing equipment, the following conditions must be strictly followed:

1. High-voltage parts must be covered and not easily accessible.
2. If the testing equipment is exposed, it must be arranged separately: one side for low-voltage equipment, the other for high-voltage equipment, and there must be a partition between them.
3. Switches, fuses, and other low-voltage electrical equipment should be placed in a convenient location, easy to inspect and control.

Article 415: When testing a cable, a sign must be hung at both ends of the cable: “Do not close switch! People at work”. If the other end of the cable is in a building where other people are working, a guard must be posted during the test, and the area must be roped off with a sign “Stop! High voltage”.

Article 416: When testing cables, wear insulating gloves, insulating boots, or stand on an insulating rubber mat. At the kenotron machine, measures must be taken to protect the operator from the harmful effects of “X-rays” by using a steel plate 0.5 to 1 mm thick or by using special lamps that are designed not to produce “X-rays”.

Article 417: Using a megohmmeter for measurement is done by the following persons:

1. Operating personnel or persons supervised by them do not need a work permit.
2. Testing personnel or other personnel must follow the regulations of the work permit.
3. Workers with a safety level of III or higher are allowed to use a megohmmeter alone to measure on a circuit that has been de-energized without a work permit.

Article 418: A megohmmeter may only be used to measure equipment that is completely isolated on all sides. Before turning the crank, it must be certain that no one is working on the part of the equipment being measured. No one is allowed to touch any conductive parts related to the equipment being measured.

Article 419: After testing with high voltage, the charge must be neutralized, and only after confirming that there is no charge left can it be reported as “de-energized!”.

Note: The period for testing electrical equipment is according to the EVN Regulation – Periodic Testing of Electrical Equipment (2003); Official Letter No. 3075 dated July 14, 2003 of Vietnam Electricity Corporation.

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PART 3: TRANSFORMER OPERATION PROCEDURE

(Issued under Decision No. 623/ĐVN/KTNĐ dated May 23, 1997 of Vietnam Electricity Corporation)

Article 44:

The energization of a transformer must be carried out in the following sequence:

1. Before energizing the transformer, carefully inspect it, remove all grounding wires, and check warning signs and temporary barriers. All work permits must be collected.
2. If more than 3 months have passed since the last test, insulation resistance must be measured, dielectric loss angle increased (for voltage levels higher than 35kV), and a simple oil analysis performed for items 1, 6, 10 (see appendix 1). For transformers filled with nitrogen or with a plastic oil protection membrane, also test item 11. If the transformer is connected to an underground cable without an isolating switch, the insulation resistance of the transformer can be measured together with the cable, but the measuring transformer (if any) must be disconnected during the measurement.
3. Check the readings of thermometers and pressure gauges, and check the oil level.
4. Check for gas in the relay, check if the rapid pressure relief valve, oil pipe valves, cooling system valves, and gas relay valves are open. Check the position of the voltage regulator tap to ensure it matches the setting sheet. Check for foreign objects on the transformer.
5. Check the grounding of the transformer casing and for any oil leaks on the transformer.
6. Check if the transformer’s terminals and neutral are connected to the surge arresters in the protection scheme.
7. Energize the transformer according to the regulations in Article 46.

Article 45: The impulse energization of transformers after installation or repair shall be carried out in the following sequence:

1. Carry out all items as in Article 44, items 1-6.
2. Check the operation of the entire relay protection system of the transformer. A confirmation report must be made after the check. The gas relay contact is switched to the trip position, and the overcurrent relay is set to a time of 0 seconds.
3. Check the operation of all circuit breakers for all protections.
4. The transformer is energized when all protections are in service.
5. The energization of the transformer shall be carried out at least 12 hours after the last oil top-up.
6. The transformer can be energized from any of the high, medium, or low voltage sides. If possible, raise the voltage gradually to the rated level. If not possible, apply the rated voltage for at least 30 minutes to listen and observe the state of the transformer. During this time, the forced air fans of QG and KD type transformers may be turned off, but the temperature of the top oil layer must not exceed 60°C.
7. Perform impulse energization of the transformer at the rated voltage to check if the protection settings are correct (no tripping on magnetizing inrush current).
8. If the impulse test result is good, the transformer is allowed to be loaded and put into operation.

Article 46: When switching transformers on and off, the following regulations should be followed:

• Energizing a transformer must be done from the power supply side that is equipped with protection ready to trip in case of a transformer fault.
• If a circuit breaker is available, it must be used for switching on or off.
• Currently, most substations energize transformers using circuit breakers. If no circuit breaker is available, a 3-phase disconnector with a mechanical or electrical drive can be used to switch the no-load current of transformers according to table 7. Standard 3-phase disconnectors of indoor or outdoor type with a voltage rating of 10kV or less are allowed to switch no-load transformers up to 1000 kVA. The maximum allowable magnetizing current for switching is determined based on the condition that the overvoltage allowed for operation is up to 105% of the voltage corresponding to the respective tap, and at that point, the transformer magnetizing current increases by 1.5 times the rated value.

PARAMETER	RATED VOLTAGE OF DISCONNECTOR
	35 KV				110 KV
	Vertical Break Disconnector		Horizontal Rotating Disconnector		Vertical Break Disconnector			Horizontal Rotating Disconnector
Minimum distance between phases (m)	1 – 1.2	1.6	1 – 1.2	2	2	2.5	3	2.5	3	3.5
Maximum magnetizing current of transformer at 105% rated voltage (A)	2.3	11	2.3	11	2	10	14.5	2	10	14.5
Maximum power of transformer (KVA)	1800	20000	1800	20000	5600	31500	40000	5600	31500	40000

 

• Switching off the no-load current of a transformer with an arc-suppression coil in the neutral can only be done after disconnecting these arc-suppression coils.
• For transformers connected in a “generator-transformer” block scheme, when putting into operation, it is advisable to use the generator to gradually increase the voltage to the rated voltage.
• For transformers with an on-load tap changer (OLTC), after disconnecting the loads on the consumer side, the transformation ratio should be increased before using a disconnector to switch off the supply side.

Article 47: All standby transformers must be ready to be energized at any time. For standby transformers that are out of service for a long time, a schedule for energizing them for drying must be established. The relay of the standby transformer must be left in the signal position to promptly detect a low oil level.

Article 48: For transformers without an on-load tap changer (OLTC), the power must be disconnected before changing the tap, and this must be done according to a work permit. For transformers of 1000 kVA and above, the DC resistance of the windings should be checked again after changing the tap. For transformers below 1000 kVA, continuity should be checked after changing the tap.

Article 49: For transformers with an on-load tap changer (OLTC), the correspondence between the grid voltage and the tap voltage must be constantly maintained. Transformers with a non-functioning OLTC should not be operated for a long time.

Article 50: The on-load tap changer (OLTC) of a transformer must be operated in accordance with the manufacturer’s regulations. The changes in voltage taps must be recorded in the operating log. It is not permitted to change the tap setting when the transformer is overloaded if the load current exceeds the rated current of the OLTC.

Article 51: At each location, the number of transformers operating simultaneously must be determined according to the load curve, taking into account the reliability of power supply to consumers. In distribution grids with a voltage of 15kV or less, load and voltage measurements of transformers must be taken at least once every quarter during the highest and lowest load periods.

Article 52: Transformers are allowed to operate in parallel under the following conditions:

1. The connection group is the same.
2. The transformation ratios are equal or differ by no more than 0.5%.
3. The short-circuit voltage differs by no more than ±10%.
4. Complete phase coincidence.

Article 53: For a transformer after installation or after work that may have changed the phase position, before putting it back into operation, a phase coincidence test must be performed with the grid or with another transformer that will operate in parallel.

Article 54: When the oil level in a transformer rises above the specified level, the cause must be investigated. Before disconnecting the trip circuit of the gas relay, do not open the oil drain valves and air release valves, and do not perform other operations to avoid false tripping of the gas relay.

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PART 4: FIRST AID FOR ELECTRIC SHOCK VICTIMS

While working or in daily life, if you see someone suffering from an electric shock, it is everyone’s duty to rescue the victim. According to statistics, if an electric shock victim receives timely and proper first aid, the survival rate is very high.

The table below shows that if the victim is rescued within the first minute, the chance of survival is up to 98%. By the fifth minute, the chance of survival drops to only 25%.

TIME (MINUTES)	1	2	3	4	5
Survival rate of victims (%)	98	90	70	50	25

 

There are 2 basic steps to saving a person from an electric shock accident:

1. Separating the victim from the electrical circuit.
2. Providing first aid to the victim on the spot.

I. HOW TO SEPARATE AN ELECTRIC SHOCK VICTIM FROM THE ELECTRICAL CIRCUIT

When someone has an electrical accident, every effort must be made to separate the victim from the electrical circuit. When rescuing, pay attention to the following to both save the victim and avoid being electrocuted yourself:

1. If the electrical circuit can be cut off
   • The best way is to cut the power using the nearest switching devices such as: an electric switch, fuse, or by unplugging the plug, circuit breaker, etc. When cutting the power, note:
     • If the circuit that was cut supplies lighting at night, prepare another light source immediately.
     • If the victim is at a height, prepare to catch them when they fall.
2. If the electrical circuit cannot be cut off
   • In this case, it is necessary to distinguish whether the victim is in contact with low-voltage or high-voltage electricity to apply the appropriate methods:
     • If it is low voltage, the rescuer must stand on a dry wooden table, chair, or board, wear slippers or rubber boots, and wear rubber gloves to pull the victim away from the electrical circuit. If these items are not available, you can grab the victim’s dry clothes to pull them away, or use a dry wooden or bamboo stick to push the wire away or push the victim away. You can also use insulated pliers, a hammer, or an axe with a wooden handle to cut the wire causing the accident. Absolutely do not touch the victim directly, as this will also electrocute the rescuer.
     • If it is a high-voltage circuit, it is best for the rescuer to wear insulated boots and gloves. Use an insulating pole to push or knock the victim away from the electrical circuit. You can use a metal wire grounded at one end and throw the other end onto all three phases to create a short circuit, causing the line to be de-energized, then separate the person from the electrical circuit.

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II. RESCUING THE VICTIM AFTER SEPARATION FROM THE ELECTRICAL CIRCUIT

Immediately after the victim is separated from the electrical circuit, treatment should be based on the following symptoms:

1. The victim has not lost consciousness
   • When the person who was electrocuted has not lost consciousness, is only momentarily unconscious, the heart is still beating, and breathing is weak, the victim should be moved to a well-ventilated, quiet place to recover. Then, call a doctor or gently take them to the nearest medical facility for monitoring and care.
2. The victim has lost consciousness
   • When the victim has lost consciousness but is still breathing shallowly and has a weak heartbeat, place the victim in a well-ventilated, quiet place (if it is cold, a place sheltered from the wind), loosen their clothing and belt, clear any saliva from their mouth, let them smell ammonia, urine, and rub their whole body to warm them up. Send someone to call a doctor to provide care.
3. The victim has stopped breathing
   • If the victim is no longer breathing, the heart has stopped beating, and the whole body is convulsing as if dead, move the victim to a well-ventilated area, loosen their clothing and belt, and clear any saliva from their mouth. If the tongue has fallen back, pull it forward. Begin artificial respiration and mouth-to-mouth resuscitation immediately. This must be done continuously and persistently until a doctor decides otherwise.

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III. METHODS OF ARTIFICIAL RESPIRATION AND MOUTH-TO-MOUTH RESUSCITATION

There are two methods of artificial respiration:

1. Placing the victim in a prone position
   • Place the victim on their stomach, with one hand under their head and the other extended straight. Turn their face towards the extended arm. Clear any saliva from their mouth and pull the tongue forward (if it has fallen back). The rescuer should kneel over the victim’s back, with their knees on either side of the victim’s hips. Place both hands on the sides of the victim’s ribs, with the thumbs close to the spine. Press down while counting “1-2-3,” then slowly release and straighten up, counting “4-5-6.” Repeat this 12 times per minute, in a steady rhythm with your own breathing. Continue until the victim can breathe on their own or until a doctor makes a decision. This method is often used when there is only one rescuer.
2. Placing the victim in a supine position
   • Place the victim on their back. Place a soft pillow or rolled-up clothing under their lower back so their head is slightly tilted back. Open their mouth, clear any saliva, and pull the tongue forward. One person should sit beside them to hold the tongue. If the mouth is clamped shut, use a blunt, hard object to pry it open. The rescuer should sit at the victim’s head, about 20-30 cm away. Take both of the victim’s hands (near the elbows) and slowly raise them above their head until their hands almost touch. After 2-3 seconds, gently bring the victim’s hands down and press them against their chest. After 2-3 seconds, repeat these movements. Try to do this 16-18 times per minute. Do it very evenly, counting “1-2-3” for inhalation and “4-5-6” for exhalation. Continue until the victim can breathe normally on their own or until a doctor makes a decision. This method allows more air into the lungs than the prone position method, but it requires two people.

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IV. MOUTH-TO-MOUTH RESUSCITATION COMBINED WITH EXTERNAL CHEST COMPRESSIONS

(This is the most effective and widely used rescue method today)

Lay the victim on their back, loosen their clothing and belt, and clear any saliva from their mouth. Tilt the victim’s head back slightly. The rescuer should stand (or kneel) next to the victim, place one hand on top of the other on the left side of the chest (the location of the heart), and then use their body weight to press down quickly and firmly, compressing the victim’s chest by 3-4 cm. After about 1/3 of a second, release the hands to allow the victim’s chest to return to normal. Do this about 60 times per minute. At the same time as the chest compressions, a second person must perform mouth-to-mouth resuscitation. It is best to place a piece of gauze or a handkerchief over the victim’s mouth. The rescuer should sit next to the victim’s head, use one hand to pinch the victim’s nose, and the other to hold the victim’s mouth open (if the tongue has fallen back, pull it out). Take a deep breath to fill your lungs with air, then place your mouth tightly over the victim’s mouth and blow until their chest rises (or cover their mouth and blow into their nose if blowing into the mouth is not possible). Give the victim 14-16 breaths per minute. The important thing is to coordinate the two actions rhythmically, otherwise one action will counteract the other. The coordination method is: for every 1 breath, perform 4 chest compressions (corresponding to one breath every 4 seconds and one heartbeat per second). Continue until the victim can breathe on their own or until a doctor says to stop.

If there is only one rescuer, you can do the following: Alternate the actions, giving 2-3 breaths and then switching to 4-6 chest compressions. Remember that rescuing an electric shock victim is an urgent task; the faster, the better. Depending on the circumstances, you must proactively use the appropriate rescue method. You must be very calm and persistent in the rescue. A victim should only be considered dead if their skull is fractured or their entire body is burned. Otherwise, the victim should be considered alive.

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PART 5: HIGH-VOLTAGE ELECTRICAL SAFETY PROTECTION

A high-voltage power grid is an electrical grid with a nominal voltage of 1,000V or more. Currently, Vietnam uses the following high-voltage levels: 22kV; 66kV; 110kV; 220kV and 500kV. A high-voltage power grid project includes the high-voltage grid and the safety protection corridor for the high-voltage grid.

I. Concept

• Protecting the safety of high-voltage grid projects includes managerial and technical measures, and defines the responsibilities of relevant agencies, organizations, and individuals to ensure the safety of the projects, the grid, residential areas, and workers.

II. Decree No. 106/2005/ND-CP dated August 17, 2005

of the Government detailing a number of articles of the Electricity Law on the safety protection of high-voltage grid projects has stipulated:

• a. Construction of high-voltage grid projects in electrical safety documents
  • After the high-voltage grid project has been approved by the competent state authority for the construction site, the investor must notify the local People’s Committee, organizations, households, and individuals who are land users, owners of houses, construction works, and other assets located within the safety corridor of the high-voltage grid in writing within 15 days. Compensation, support for land, assets on land, and other support for land users during the construction of the project shall be carried out in accordance with regulations on compensation, support, and resettlement. Any works created after receiving the project implementation notice that violate the high-voltage grid safety corridor as prescribed must be dismantled and will not be compensated or supported.
  • In cases where it is necessary to build overhead power lines through works of major political, economic, cultural, security, national defense, and communication importance, places where large numbers of people regularly gather, historical-cultural relics, and scenic spots ranked by the state, the following conditions must be ensured:
    • • The section of the overhead power line passing over these works and locations must have enhanced electrical and construction safety measures;
    • • The distance from the lowest point of the conductor at maximum sag to the natural ground level must not be less than the following regulations:

VOLTAGE UP TO	35 KV	66 – 110 KV	220 KV
Distance	11 m	12 m	13 m

 

• • The section of the underground cable connected to the overhead power line from the ground up to a height of 2m must be placed in a protective pipe.
  • Upon completion of the high-voltage grid project, the project owner must immediately notify the People’s Committee of the province or centrally-run city where the grid project is located for coordinated management.
• b. Safe clearance for electric discharge according to voltage level
  • Houses and works that have been permitted to exist within the safety protection corridor of overhead power lines must not violate the safe clearance for electric discharge according to the voltage level and must comply with the regulations on the safety protection of overhead power lines when repairing or renovating houses and works.

VOLTAGE	UP TO 22 KV		35 KV		66 – 110 KV	220 KV
	INSULATED WIRE	BARE WIRE	INSULATED WIRE	BARE WIRE	BARE WIRE
Safe clearance for electric discharge	1.0 m	2.0 m	1.5 m	3.0 m	4.0 m	6.0 m

 

• • It is forbidden to carry out any work in the protection corridor of overhead power lines if using equipment, tools, or means that could violate the safe clearance for electric discharge according to the voltage level. In special cases, due to urgent requirements of national defense and security, there must be an agreement with the grid project management unit on the necessary safety measures.

VOLTAGE	UP TO 22 KV	35 KV	66 – 110 KV	220 KV	500 KV
Safe clearance for electric discharge	4.0 m	4.0 m	6.0 m	6.0 m	8.0 m

 

• • The safe clearance for electric discharge according to the voltage level at intersections between overhead power lines and roads, railways, and inland waterways is the minimum distance from the conductor at maximum sag to the highest point of the protected object and is specified in the following table:

VOLTAGE	UP TO 35 KV	66 – 110 KV	220 KV	500 KV
SAFE DISCHARGE CLEARANCE
To the highest point (4.5 m) of road transport vehicles	2.5 m	2.5 m	3.5 m	5.5 m
To the highest point (4.5 m) of railway transport vehicles and works	3.0 m	3.0 m	4.0 m	7.5 m
To the highest point (7.5 m) of electric railway transport vehicles and works	3.0 m	3.0 m	4.0 m	7.5 m
To the vertical clearance according to the technical grade of the inland waterway	1.5 m	2.0 m	3.0 m	4.5 m

 

• c. Safety protection corridor for overhead power lines
  • The safety protection corridor of an overhead power line is the space along the line and is limited as follows:
    • The length of the corridor is calculated from the point where the line leaves the protection boundary of one station to the point where the line enters the protection boundary of the next station.
    • The width of the corridor is limited by two vertical planes on either side of the line, parallel to the line, with a distance from the outermost conductor to each side when the conductor is in a static state as specified in the following table:

VOLTAGE	UP TO 22 KV		35 KV		66 – 110 KV	220 KV	500 KV
	INSULATED WIRE	BARE WIRE	INSULATED WIRE	BARE WIRE	BARE WIRE
Distance	1.0 m	2.0 m	1.5 m	3.0 m	4.0 m	6.0 m	7.0 m

 

• • • The height of the corridor is calculated from the bottom of the tower foundation to the highest point of the structure plus the vertical safety distance specified in the following table:

VOLTAGE	UP TO 22 KV	66 – 110 KV	220 KV	500 KV
Distance	2.0 m	3.0 m	4.0 m	6.0 m

 

• d. Safety protection corridor for various types of power cables in electrical safety documents
  • on the ground or suspended in the air is the space along the power cable and is limited on all sides by 0.5 m from the outer surface of the outermost cable.
• e. Trees in the safety protection corridor of overhead power lines
  • For power lines with a voltage up to 35kV in cities, towns, and townships, the distance from any point of a tree to the conductor in a static state must not be less than the distance specified in the following table:

VOLTAGE	UP TO 35 KV
Distance	Insulated wire	Bare wire
	0.7 m	1.5 m

 

• • For power lines with voltages from 66kV to 500kV in cities, towns, and townships, trees must not be taller than the lowest conductor. The distance from any point of a tree to the conductor when the conductor is in a static state must not be less than the distance specified in the following table:

VOLTAGE	66 TO 110 KV	220 KV	500 KV
Distance	Bare wire
	2.0 m	3.0 m	4.5 m

 

• • For power lines outside of cities, towns, and townships, the vertical distance from the highest point of a tree to the height of the lowest conductor in a static state shall not be less than the distance specified in the following table:

VOLTAGE	UP TO 35 KV		66 TO 110 KV	220 KV	500 KV
Distance	Insulated wire	Bare wire	Bare wire
	0.7 m	2.0 m	3.0 m	4.0 m	6.0 m

 

• • Rice, crops, and other plants may only be planted at a minimum distance of 0.5m from the edge of the tower foundation or stay wire foundation.
• f. Houses and buildings within the protection corridor of overhead power lines
  • Conditions for houses and buildings to exist within the safety protection corridor of high-voltage power grids up to 220kV:
    • Roofs and exterior walls must be made of non-combustible materials;
    • Metal roofs, building frames, and exterior walls must be grounded according to grounding technical regulations;
    • Must not obstruct access for inspection, maintenance, and replacement of parts of the high-voltage grid structure;
    • The distance from any part of the house or building to the nearest conductor when the conductor is in a static state must not be less than the distance specified in the following table:

VOLTAGE	UP TO 35 KV	66 TO 110 KV	220 KV
Distance	3.0 m	4.0 m	6.0 m

 

• • • The electric field strength must be ≤ 5 kV/m at any point outside the house 1m above the ground and ≤ 1 kV/m at any point inside the house 1m above the ground.
  • For houses and constructions legally built before the construction of the overhead power line that do not meet the specified conditions, the investor of the high-voltage grid project is responsible for the costs and implementation of renovations to meet those conditions.
  • In case only a part is demolished and the remaining part can still exist, be used, and meets the specified conditions, compensation will be provided for the value of the demolished part of the house or construction and the cost of renovation to complete the house or construction to a technical standard equivalent to that before demolition. In case it is not possible to renovate to meet the above conditions and it must be dismantled or relocated, compensation for the house or construction and support for relocation will be provided according to the laws on compensation, support, and resettlement.
• g. Safety protection corridor for underground power cables in electrical safety documents
  • The safety protection corridor for underground power cables is limited as follows:
    • The length of the corridor is calculated from the point where the cable leaves the protection boundary of one station to the point where it enters the protection boundary of the next station.
    • The width of the corridor is limited by:
      • The outer surface of the cable trench for cables laid in a trench;
      • Two vertical planes on either side of the underground power cable, at a distance from the outer surface of the cable sheath or the outermost cable, for cables laid directly in the ground or in water, as specified in the following table:

TYPE OF POWER CABLE	DIRECTLY BURIED IN GROUND		LAID IN WATER
Distance	Stable ground	Unstable ground	Areas with no boat traffic	Areas with boat traffic
	1.0 m	1.5 m	20.0 m	100.0 m

 

• • • The height is calculated from the ground or water surface to:
      • The outer surface of the cable trench foundation for cables laid in a trench;
      • A depth of 1.5m below the lowest point of the cable sheath for cables laid directly in the ground or in water.
• h. Safety protection corridor for electrical substations in electrical safety documents
  • The safety protection corridor of an electrical substation is the space surrounding the substation and is limited as follows:
    • For substations without walls or fences, the protection corridor is limited by the space surrounding the substation with a distance to the nearest live parts of the substation as specified in the following table:

VOLTAGE	UP TO 22 KV	35 KV
Distance	2.0 m	3.0 m

 

• • • For substations with fixed walls or fences, the width of the protection corridor is limited to the outer surface of the wall or fence;
• i. Signs and signals in electrical safety documents
  • The management unit of the high-voltage grid project must install warning signs and prohibition signs in accordance with the law.
  • Power poles must be painted white and red from a height of 50m and above and must have signal lights on top of the poles in the following cases:
    • Power poles 80m or taller;
    • Power poles over 50m but under 80m in height but in a location with special requirements;
    • In case the high-voltage power line is within a limit of 8,000m from the nearest airport runway for landing and takeoff, the painting of poles and placement of warning lights shall be in accordance with the regulations of the state management agency for aviation;
    • Along underground power cables in the ground, the project owner must place markers or signs.
• j. Management and operation of high-voltage grid projects in electrical safety documents
  • Responsibilities of the operation management unit:
    • Inspect and promptly detect violations, take remedial measures or propose to competent authorities for handling.
    • Inspect, maintain, and service the power lines on schedule. Do not overload the lines passing over houses and buildings.
    • Keep statistics and report as required.
  • Personnel managing, operating, and repairing the power grid must comply with safety regulations.
  • Tree cutting and trimming to ensure the safety of the high-voltage grid project shall be carried out by the grid project operation management unit and must notify the management unit or the tree owner and compensate for damages as prescribed.
• k. Prohibited acts in electrical safety documents
  • Entering an electrical substation, dismantling or climbing on parts of the grid project without authorization.
  • Theft, throwing objects at, or causing damage to parts of the grid project.
  • Using the grid project for other purposes without the agreement of the grid project management unit.
  • Flying kites or other flying objects near the grid project. Installing clotheslines, antennas, scaffolding, signs, advertising light boxes, and other objects that could come into contact with the grid project if they fall.
  • Blasting, opening mines, storing flammable, explosive, or corrosive chemicals that could damage parts of the grid project, and other acts that affect the safety of the grid project…

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PART 6: NECESSARY MEANS AND TOOLS FOR ELECTRICAL SAFETY

I. PROTECTION FROM DANGER OF ACCIDENTAL CONTACT WITH CONDUCTORS

To avoid accidental contact with live conductors, exposed parts of the electrical network, or electrical connections that people may come into contact with must be well shielded or fenced off.

Electrical conductors in homes, public places, etc., should be completely covered. In production areas (where only personnel serving electrical equipment are present), they can be covered with a mesh or a perforated protective plate. Fences or covers should have locks to prevent unnecessary opening. The covers must be sufficiently mechanically strong.

Electrical conductors placed in passageways indoors must be shielded and protected at the following heights:

• 10 kV and below – 2.5m
• 35 kV and below – 2.75m
• 110 kV and below – 3.5m

Outdoor electrical conductors must be shielded and protected at the following heights:

• 35 kV – 3m
• 110 kV – 3.75m
• 154 kV – 4m
• 220 kV – 4.5m

Transformers and other electrical equipment, if the bottom edge of the insulator is less than 2.5m above the floor, must be fenced. The height of the fence must not be less than 1.7m.

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II. SOME NECESSARY MEANS AND TOOLS FOR ELECTRICAL SAFETY

1. Protective equipment in electrical safety documents

Protective equipment is divided into the following groups:

• Insulating equipment to prevent voltage (step, contact, working) includes: insulating poles, insulating pliers, tools with insulated handles, insulating gloves, insulating shoes, insulating boots, insulating mats.
• Portable voltage testers, clamp meters.
• Portable grounding protection, barriers, warning signs.

Protective equipment to prevent the effects of electric arcs, hot metal fragments, and mechanical damage: protective goggles, canvas gloves, tools for protection against toxic gases.

Insulating protective equipment is further divided into 2 types: primary and secondary.

• Primary insulating protective equipment has insulation that is guaranteed not to be punctured by the equipment’s voltage and can be used to directly touch live parts.
• Secondary protective equipment: they cannot provide protection on their own but are supplementary to the primary equipment.

Primary protective equipment is made of a material with more durable insulating properties than secondary protective equipment.

Protective equipment must be maintained according to established rules. In indoor distribution stations, there must be a designated area at the entrance for protective equipment. Protective equipment must be regularly inspected and periodically tested with increased voltage, corresponding to each type of protective equipment as specified in the Vietnamese Standards.

2. Insulating equipment, voltage avoidance

• Insulating pole
  • Insulating poles are used directly to operate disconnect switches, install portable grounding, and perform high-voltage tests.
  • An insulating pole consists of 3 parts: the insulating part, the working part, and the handle. The length of the pole depends on the voltage (figure 10.1.a).
  • When using a pole, stand on an insulating platform, wear gloves, and insulating shoes. Poles used indoors can be used outdoors in dry weather, but using them in reverse requires permission from the procedure.
• Insulating Pliers
  • Insulating pliers are used to install and remove fuses, and to push on rubber insulating caps. Pliers are a primary protective means used with voltages below 35kV.
  • Insulating pliers also consist of 3 parts: the working part, the insulating part, and the handle (figure 10.1.b).
• Dielectric gloves, boots, pads (figure 10.1.c, d, e)
  • Used with electrical equipment, these tools are specially manufactured with a structure that complies with the procedure. They should absolutely not be considered protective equipment if they are not specifically manufactured for use with electrical equipment.
• Insulating Platform (figure 10.1. f,g).
  • The insulating platform has dimensions of approximately 75cm x 75cm but not exceeding 150cm x 150cm, made of assembled wooden planks. The gap between the planks should not exceed 2.5 cm. The height of the platform from the wooden floor to the ground floor should not be less than 10cm.
• Tools with insulated handles (figure 10.1. h,i).
  • The length of the insulated part must not be less than 10 cm and made of a material that is not affected by sweat, gasoline, kerosene, acid, and is not chipped.

3. Portable voltage testing devices in electrical safety documents

Portable voltage testing devices are used to check for the presence of voltage and for phase identification. The tool has a neon lamp that lights up when a capacitive current passes through it. The size of the device depends on the voltage. When using the testing device, only insert it into the equipment being tested to the extent necessary to see the light. Touching the equipment is only necessary when the object being tested is de-energized.

4. Portable temporary grounding protection equipment

• Portable temporary grounding protection is a safety measure when working in places where the power has been disconnected but there is a possibility of accidental re-energization or the sudden appearance of voltage.
• It consists of conductors for short-circuiting phases and needs to be grounded with clamps to connect to the live parts. The clamps must be able to withstand the electrodynamic force during a short circuit.
• The conductors are made of copper with a cross-section of not less than 25mm². The clamp must have a place to disconnect the short-circuit wire with a lever.
• Grounding should only be done after checking that the conductor is de-energized. First, connect the end of the grounding device to the ground, then test for voltage, and then connect the wire to the live part. When removing the grounding, do the reverse.
• To avoid forgetting the grounding, a thorough check is necessary. Grounding for shift work must be checked not only for quantity but also for their placement.
• For fixed grounding, to avoid mistakes, electronic or electromechanical interlocks are also used.

5. Portable temporary shielding devices, rubber covers

• Portable temporary shielding devices are used to protect repair workers from touching voltage. These items act as a partition, about 1.8m high. One person can easily carry them. The insulating liner placed to cover live parts must be made of a soft, non-flammable material. They can be used on equipment below 10 kV in cases where it is not convenient to use a screen.
• The rubber cover to insulate the disconnect switch must be made so that it is easy to cover and remove with pliers.

6. Electrical safety signs in electrical safety documents

• Used to warn of danger to people approaching live parts, to prohibit operations of equipment that could cause accidents, and to serve as reminders.

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III. PROCEDURE FOR CARRYING OUT WORK ON ELECTRICAL EQUIPMENT BY UNITS FROM OTHER PLACES

People from other places assigned to work on electrical equipment must comply with the following regulations:

Personnel in operations or in construction and installation units who have passed a knowledge test on safety technical procedures must have a certificate according to the prescribed form (the certificate is issued by the employee’s enterprise or by the enterprise to which they are assigned). In that case, they are considered equal to the employees of the enterprise to which they are assigned (except for the authority to be allowed to work).

If, due to production requirements, it is necessary to have permission to work on the required job, the electrical technical personnel sent from other places must pass an examination at the council of the enterprise they are sent to, at which time they are considered equal to the corresponding personnel of this enterprise to carry out that work. In addition, those who are sent by written order are:

1. The person who has the right to issue a work permit.
2. The work leader and direct supervisor. These people are required to study the records and the nature, characteristics of the enterprise’s electrical equipment, and listen to the necessary instructions. When there are people organizing and directing work in the enterprise’s electrical equipment like this, it is not necessary to appoint the enterprise’s operating personnel as special supervisors. Only in cases of carrying out work on electrical equipment with particularly dangerous conditions, as decided by the enterprise’s deputy technical director, is it necessary to appoint an electrical safety supervisor for people sent from other places.

When personnel from other places are sent to work on the electrical equipment of an enterprise, that enterprise is responsible for implementing safety measures to protect these personnel from electric shock. The enterprise that sends its personnel to work is responsible for the qualifications of the personnel sent to comply with the provisions of this procedure.

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PART 7: Further Reference

1. Group 3 Safety Training and Certification Service

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2. Group 3 Occupational Safety Test

• Group 3 Occupational Safety Multiple Choice Test

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3. Price List for Occupational Safety Training Services

• View details

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4. Download Document

• DOWNLOAD OCCUPATIONAL SAFETY TRAINING DOCUMENT FOR THE ELECTRICAL INDUSTRY

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APPENDIX

Sample form for external units working on equipment managed by the electricity sector that require a supervisor.

 

Characteristics:

Level I belongs to those who are involved in operating machinery but do not have a technical understanding of electricity, do not fully understand the dangers of electricity and the safety measures when working with electrical equipment.

Note: For workers working on electrical equipment above 1000 V, seniority is only counted when working at that machinery and equipment department.

Those belonging to level II must:

1. Have a basic understanding of substation and power line electrical equipment.
2. Fully recognize the dangers of electricity and the danger of approaching live electrical equipment.
3. Have a level of understanding of the basic methods to prevent danger when working with electrical equipment.
4. Know the principles and practice of first aid for electric shock victims.

Those belonging to level III must:

1. Have a basic technical understanding to become familiar with and operate electrical equipment and overhead lines above 1000 V.
2. Fully recognize the dangers when working on live electrical equipment (power lines and substations with voltages above 1000 V).
3. Have a level of understanding of safety techniques and especially the principle of being allowed to work on electrical machinery and equipment.
4. Understand the safety rules for their assigned part.
5. Know how to inspect and supervise workers working on electrical equipment and machinery.
6. Know how to give first aid to electric shock victims.

Those belonging to level IV must:

1. Have a basic understanding of electrical engineering.
2. Fully recognize the dangers when working on electrical equipment.
3. Understand this entire procedure, both the general part and the specific parts related to their profession, the principles of use and testing of safety tools applied to electrical machinery and equipment.
4. Understand the machinery to the extent of knowing which part to de-energize to carry out repairs. Be able to find that part in reality and check the compliance with safety measures.
5. Know how to organize supervision and monitoring of workers.
6. Know how to give first aid to electric shock victims.

Those with level V must:

1. Have a solid understanding of this procedure, both the general and specific parts, and the rules for using and testing safety equipment used in electrical machinery and equipment.
2. Fully understand the meaning and requirements of the items in this procedure.
3. Know how to organize the implementation of safety measures, inspect and monitor those tasks.
4. Have a solid understanding of the first aid method for electric shock victims.
5. Understand the diagrams and equipment of the department they are in charge of.