Circular No. 28/2014/TT-BCT on the procedures for handling incidents in the national power system

CIRCULAR

Specifies the procedures for handling incidents in the national power system.a

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Pursuant to Decree No. 95/2012/NĐ-CP dated November 12, 2012, of the Government, detailing the functions, tasks, powers, and organizational structure of the Ministry of Industry and Trade;

Pursuant to the Electricity Law dated December 3, 2004 and the Law Amending and Supplementing Some Articles of the Electricity Law dated November 20, 2012;

Based on Decree No. 137/2013/NĐ-CP dated October 21, 2013, issued by the Government, detailing the implementation of certain provisions of the Electricity Law and the Law Amending and Supplementing Certain Provisions of the Electricity Law;

At the proposal of the Director of the Electricity Regulatory Authority,

The Minister of Industry and Trade issues the Circular stipulating the procedures for handling incidents in the national power system.

PART I

GENERAL PROVISIONS

Article 1. Scope of Regulation

1. This Circular sets forth the principles and procedures for implementing incident handling in the national power system with the aim of quickly eliminating incidents and restoring normal operation of the national power system.

2. In cases of cross-border electricity trading, the handling of incidents on interconnection lines shall be carried out according to the dispatch agreements already signed.

Article 2. Applicability

1. National Power System Dispatch Unit (National Power System Dispatch Center).

2. Electricity Generation Unit.

3. Electricity Transmission Unit.

4. Electricity Distribution Unit.

5. Electricity Distribution and Retail Unit.

6. Customers using electricity directly from the transmission grid, customers using distribution networks with their own substations.

7. Operating personnel of the units.

8. Other related organizations and individuals.

Article 3. Explanation of Terms

Strategic multi-purpose hydropower plant

1. Incident report is a report on the incident prepared immediately after isolating the faulty element and temporarily restoring abnormal operating conditions in the power system by the operating personnel according to the model prescribed in Appendix 1 attached to this Circular.

2. Dispatching level with control authority is the Dispatch Level having the authority to command and dispatch the power system according to the分级控制权规定在由工业和贸易部发布的国家电力系统调度规程中。

3. Dispatch Level with inspection authority is the higher-level Dispatch Level having the authority to inspect, permit the lower-level Dispatch Level and the Operation Management Unit to exercise control rights to change the operating mode of the power system or electrical equipment according to the National Power System Dispatch Procedures issued by the Ministry of Industry and Trade.

4. Normal operating mode is the operating mode of the power system where operational parameters fall within the permissible range as stipulated in the Transmission System Regulations and Distribution System Regulations issued by the Ministry of Industry and Trade.

5. Dispatcher is the person directly commanding and dispatching the power system under their control, including:

a) National dispatcher;

b) Regional dispatcher;

c) Provincial or centrally-administered city distribution dispatcher;

d) District or county distribution dispatcher.

6. Operation Management Unit is the organization or individual responsible for managing and operating the lines or equipment connected to the national power system, including:

a) Electricity generation unit;

b) Transmission companies;

c) Electricity distribution unit;

d) Electricity distribution and retail unit;

e) Customers using electricity directly from the transmission grid, customers using distribution networks with their own substations.

7. Isolating switch (or breaker) incident is the line, substation, or equipment that has been de-energized due to automatic relay protection action.

8. Operations Staff is the person directly involved in controlling the process of electricity production, transmission, and distribution, including:

a) Shift leader, dispatcher at each Dispatch Level;

b) Shift leader, team leader, main operator, assistant operator at power plants or central control rooms for groups of power plants;

c) Main operator (or team leader), assistant operator at substations or central control rooms for groups of substations;

d) Distribution network operation operator.

9. Incident is an event where one or more pieces of equipment in the power system, due to one or more causes, operate abnormally, leading to power supply interruption, instability, safety hazards, and failure to ensure power quality.

10. Serious incident is an incident causing widespread power outage or fire/explosion resulting in casualties and property damage.

11. Hot repair is maintenance work performed on energized lines or equipment.

12. Substation is a transformer station, switching station, or reactive power compensation station.

13. Control center is a center equipped with information technology and telecommunications infrastructure to remotely monitor and control a group of substations, lines, or power plants.

Chapter II

REQUIREMENTS AND PRINCIPLES FOR HANDLING INCIDENTS IN THE NATIONAL POWER SYSTEM

Section 1

DRAWING UP THE WIRING DIAGRAM OF THE POWER SYSTEM

Article 4. Principles for establishing basic wiring diagrams in the power system

1. Ensuring safe and reliable power supply.

2. Ensuring stable operation of the entire national power system.

3. Ensuring power quality.

4. Ensuring the most economical operation of the national power system.

5. Ensuring that short-circuit currents do not exceed permissible values for equipment located at power plants or substations.

6. Ensuring the selectivity of protective relays.

7. Flexibility and convenience in operation and fault handling.

Article 5. Wiring at substations

1. At substations with a two-busbar diagram or a two-busbar diagram with a ring busbar and a sectionalized busbar, even-numbered circuit breakers connect to even-numbered busbars, odd-numbered circuit breakers connect to odd-numbered busbars, and tie circuit breakers normally operate in closed mode except in special cases due to operational requirements.

2. For substations with wiring diagrams other than those specified in Clause 1 of this Article, circuit breakers are designed to operate in a normally closed mode, while circuit breakers designed for standby operation are normally open. For substations with incomplete wiring diagrams, the operating management unit must perform calculations and propose technical solutions to be reviewed and approved by the Control Authority with the right to control to ensure overall safe operation of the power system.

Article 6. Ringing or opening ring circuits

1. Transmission lines with voltage levels of 110 kV or higher shall operate in a loop mode except in cases where the grid has a radial diagram or a loop diagram but must be opened due to short-circuit current limitation requirements, to prevent the spread of faults, or special methods have been calculated and considered by the Control Authority with the right to control based on ensuring safe and reliable power supply.

2. Loop operation in distribution networks shall not be conducted except in cases where closing the loop is necessary for load transfer or source switching to improve reliability of power supply, but it must ensure that it does not cause the spread of faults.

Section 2

PROTECTIVE RELAYS AND AUTOMATION

Article 7. Requirements for protective relays when putting equipment into operation

1. Electrical equipment and transmission lines may only be energized when all types of protective relays against all kinds of faults are put into service.

2. When protective relays are disconnected from service or some types of protective relays are damaged, the remaining protective relays must still provide full protection against all kinds of faults, with short-circuit clearing times for electrical equipment and transmission lines.

3. In cases where the requirements stipulated in Clause 2 of this Article cannot be met, the operator must implement one of the following measures:

a) Disconnect the electrical equipment or transmission lines, substations from operation;

b) Do not disconnect but must install temporary protection and obtain permission from the Control Authority with the right to control.

4. When removing fast-acting protection of connecting elements from service, appropriate temporary fast-acting protection, acceleration of backup protection, or adjustment of other protective relays must be implemented according to stability conditions.

Article 8. Installation of protective relays and automation

1. Electrical equipment in the power system must be equipped with protective relays and automation against all types of short circuits and failures during normal operation using relay protection devices, circuit breakers, or fuses, and automatic devices including automatic regulation and fault prevention devices.

2. Relay protection and automation equipment (including low-frequency load shedding relays) must be kept in operation mode continuously, except for relay equipment whose operating principle, system operating conditions, and selectivity require them to be taken out of service.

3. Fault recording and alarm devices must always be ready for operation.

4. The operation mode lacking protective relay or automation equipment must be specifically defined by the Control Authority with the right to control.

Article 9. Monitoring operation and rectifying defects of relay protection and automatic equipment

1. In cases where there is incorrect action or refusal to act of relay protection and automatic equipment, deficiencies discovered during operation must be examined, analyzed, and eliminated as soon as possible.

2. In cases where there is incorrect action or refusal to act of relay protection and automatic equipment, if damage is found in circuits or devices, it must be immediately reported to the Operation Management Unit and the Control Level with authority to control.

3. Isolation or reactivation of relay protection and automatic equipment into operation can only be carried out upon receiving permission from the Control Level with authority to control.

Section 3

REQUIREMENTS, PRINCIPLES AND CLASSIFICATION OF HANDLING NATIONAL ELECTRIC SYSTEM INCIDENTS

Article 10. General requirements for handling incidents in the national electric system

1. The Operation Management Unit shall be responsible for:

a) Issuing operational procedures and incident handling procedures for equipment within its management scope in accordance with the provisions of this Circular;

b) Regularly inspecting, maintaining, repairing equipment and control and protection systems of overhead lines, cable lines, substations, power plants, and control centers to ensure safe operation and minimize the likelihood of incidents.

2. The National Electric System Dispatching Unit shall be responsible for issuing operational procedures and incident handling procedures for the electric system under its control in accordance with the provisions of this Circular.

3. Annually, the National Electric System Dispatching Unit and the Operation Management Unit shall be responsible for organizing training and incident handling drills for operating personnel at least once.

4. Immediately after isolating the faulty element and temporarily restoring abnormal operation conditions in the national electric system, related units shall be responsible for:

a) Applying all necessary measures to repair equipment faults according to regulations to quickly restore the electric system to normal operation mode;

b) Investigating the cause of the incident and proposing preventive measures to avoid recurrence.

Incident Reporting Procedures

a) Immediately after isolating the faulty element and temporarily restoring abnormal operation conditions in the national electric system, the operating personnel at substations, power plants, and control centers shall be responsible for sending a quick incident report to the Control Level with authority to control according to the form prescribed in Appendix 1 issued together with this Circular;

b) Within 24 hours from the time of the incident, the Operation Management Unit shall be responsible for sending an incident report to the Control Level with authority to control the equipment according to the form prescribed in Appendix 2 issued together with this Circular;

c) Within 48 hours from the time of the incident, the Control Level with authority to control shall be responsible for sending an incident report to the Control Level with authority to check according to the form prescribed in Appendix 3 issued together with this Circular;

d) After resolving the incident, the National Electric System Dispatching Unit and the Operation Management Unit shall be responsible for sending an incident analysis report on the electric system under their control or operation management to the superior management unit according to the form prescribed in Appendix 4 issued together with this Circular when requested.

Forms of Sending Incident Reports:

a) Quick incident reports shall be sent via fax or email (Email) to the address provided by the Control Level with authority to control;

b) Incident reports and incident analysis reports shall be sent through the following methods:

- Sent via fax or email (Email) to the address provided by the Control Level with authority to control;

- Officially sent via express delivery (documents).

Article 11. Principles for Handling National Power System Incidents

1. Operating personnel shall be responsible for applying measures to handle incidents as prescribed to quickly eliminate the incident and prevent its spread.

2. Operating personnel shall be responsible for promptly restoring power supply to customers, particularly critical loads, and ensuring power quality in terms of frequency and voltage.

3. During the handling of incidents, the National Power System Dispatching Unit may operate the power system at frequencies and voltages different from those specified under normal operating conditions as set forth in the Transmission System Regulations and Distribution System Regulations issued by the Ministry of Industry and Trade, but must quickly implement solutions to restore the power system to its normal operating state, ensuring stable operation of the system.

4. Operating personnel must thoroughly understand the development of the incident, the status of equipment that has been isolated during the incident, analyze incident phenomena, and predict recovery time.

5. Incident command orders shall be transmitted verbally or through control signals.

6. Verbal incident command orders shall be directly conveyed by the superior dispatcher to subordinate operating personnel in accordance with the National Power System Dispatching Procedures Regulation issued by the Ministry of Industry and Trade. Command orders must be accurate, concise, and clear. The superior dispatcher issuing the order shall bear full responsibility for their order during the incident handling process.

7. During the incident handling period, the use of communication means for dispatch purposes for other purposes is strictly prohibited.

8. During the incident handling process, operating personnel must comply with the provisions of this Circular, technical standards, TCVN, procedures, specialized regulations, other legal regulations, and safety standards for electrical equipment as stipulated by the manufacturer.

Article 12. Hierarchical Levels for Handling National Power System Incidents

1. Equipment under the control of a certain dispatch level shall be commanded by that dispatch level to handle incidents on such equipment.

2. While handling incidents, the dispatch level with control authority may change the operational mode of equipment under its control before reporting to the dispatch level with inspection authority.

3. In emergency situations where delay is not possible, such as explosions or threats to human life and equipment safety at power plants, substations, or control centers, operating personnel at power plants, substations, or control centers may isolate incident elements according to the power plant, substation, or control center operation and incident handling procedures without seeking permission from the dispatch level with control authority and shall be responsible for their incident handling actions. After handling the incident, operating personnel at power plants, substations, or control centers must immediately report to the dispatch level with control authority.

Article 13. Responsibilities of Operating Personnel in Handling Incidents

1. Handle incidents in accordance with the operation and incident handling procedures of power plants, substations, and control centers.

2. Apply all necessary measures as prescribed to prevent the spread of incidents and restore power supply to customers as soon as possible.

3. In areas where incidents occur, promptly and accurately report incident phenomena and developments to superior operating personnel.

4. In areas where incidents do not occur, continuously monitor incident fluctuations through parameters on the power grid within their management scope, and report unusual phenomena to superior operating personnel.

5. After completing incident handling, superior operating personnel shall provide summary information about the incident handling situation that changes the normal operating mode of the system under the control of subordinate operating personnel in accordance with the information access rights stipulated in the National Power System Dispatching Procedures Regulation issued by the Ministry of Industry and Trade.

6. When there is an incident within the self-use power grid section of a power plant or substation, operating personnel at the power plant, substation, or control center shall be responsible for handling the incident and reporting to superior operating personnel to coordinate and prevent the incident from spreading further.

7. Report to the competent authority the cause of the incident and the estimated time for power restoration if the incident causes a power supply interruption.

Article 14. Work relations in handling incidents

1. Work relations between lower-level operators and higher-level operators

a) Lower-level operators must comply with orders from higher-level operators. For orders that pose a threat to human life and equipment safety, they may delay execution but must report to the higher-level operator;

b) Higher-level operators have the right to request the direct supervisor of the lower-level operator to replace such operator if there are sufficient reasons indicating that the lower-level operator lacks the capability to handle incidents or seriously violates technical standards and related procedures.

2. Work relations between lower-level operators and higher-level operators and the direct supervisor of the lower-level operator

a) The direct supervisor of the lower-level operator has the right to issue orders to the subordinate operator to handle incidents, provided that these orders do not conflict with orders from the higher-level operator and relevant technical standards, specifications, and regulations;

b) When the order from the direct supervisor conflicts with the order from the higher-level operator, the lower-level operator has the right to refuse to execute the direct supervisor's order and report to the higher-level operator, except in cases where there is a threat to human life and equipment safety;

c) If there are sufficient reasons indicating that the operator lacks the capability to handle incidents, the direct supervisor has the right to temporarily suspend the operator's work during their shift, handle the incident personally, or designate another operator to replace them, while simultaneously reporting to the higher-level operator.

3. Unauthorized persons without assigned duties are strictly prohibited from entering the control room when operators are handling incidents, except for senior leaders responsible and the direct supervisors of the unit. In necessary cases, operators or the direct supervisors of the unit have the right to request relevant specialized staff involved in incident handling to come to the unit's control room to handle the incident.

4. In case of serious incidents, operators must promptly report the incident to their unit's direct supervisor. The direct supervisor is responsible for reporting to senior leaders or related units.

Chapter III

INCIDENT HANDLING ON TRANSMISSION LINES

Section 1

INCIDENT HANDLING ON NON-POWERED 500 KV TRANSMISSION LINES IN THE AIR

Article 15. Transmission limits on 500 kV transmission lines

1. The transmission limit on 500 kV transmission lines is the smallest value among the following values:

a) The rated current of the 500 kV transmission line determined based on the smallest rated current of the conductor or connected electrical equipment, taking into account the impact of operational environmental conditions on the equipment;

b) The limit according to system stability conditions;

c) The voltage standard limit as stipulated in the Transmission System Regulation issued by the Ministry of Industry and Trade.

2. Operators at power plants, substations, or control centers must immediately report to the dispatching authority with control rights when operational parameters on the transmission line exceed permitted limits.

3. When transmission exceeds the permitted transmission limit, the dispatcher must handle the incident according to the extremely urgent mode prescribed in Article 53 of this Circular.

Article 16. Handling of Power Plant and Substation Operators at Power Plants, Substations, and Control Centers in Case of 500 kV Line Faults

1. When a 500 kV line circuit breaker trips due to a fault, the operator at the power plant, substation, or control center where the connected line is affected must immediately report to the Dispatch Authority with control rights the following information:

a) Time of the fault, name of the line and tripped circuit breaker, protective relay signal action;

b) Overloaded, overvoltage, or undervoltage conditions on the operating line or electrical equipment caused by the fault, local weather conditions;

c) Other related information.

2. Immediately after completing the fault handling, the operator at the power plant, substation, or control center must submit a quick fault report to the Dispatch Authority with control rights in accordance with Point a Clause 5 Article 10 of this Circular.

Article 17. Handling of Dispatchers in Case of 500 kV Line Faults

1. In case the automatic protective relay successfully recloses, the following actions must be taken:

a) Collect information from power plants, substations, and control centers at both ends of the faulty line;

b) Request operators at substations, power plants, and control centers to check the status of circuit breakers, protective devices, and automation systems;

c) Hand over the section of the line determined to have experienced a transient fault for visual inspection by the operation management unit with caution that the line is energized, and noting any suspected fault points (if present);

d) Complete the fault report according to the System Operation and Fault Handling Procedures issued by the Dispatch Authority with control rights.

2. In case the line is cut off due to a fault, the fault must be handled in the following sequence:

a) Preventing the expansion of the fault:

- Handle overload on the line and electrical equipment if overloaded due to the 500 kV line fault;

- Control voltage on the 500 kV grid if it exceeds permissible limits;

- Implement frequency control measures if the frequency is outside the permitted value;

b) Record the fault report from the operator at the power plant, substation, or control center;

c) Quickly analyze the fault based on the recorded information from substations, power plants, and control centers about protective relays and automation to decide whether to reclose or isolate the line in accordance with Article 18 of this Circular;

d) Complete the fault report according to the System Operation and Fault Handling Procedures issued by the Dispatch Authority with control rights.

3. In case the line experiences multiple faults and successfully recloses, the fault must be handled in the following sequence:

a) Within eight hours, if the line has experienced two successful reclosures, and the subsequent automatic reclosure point is close to the previous fault point, then issue an order to lock out the automatic reclosing relay circuit;

b) After eight hours from the time of the second successful reclosure, if no further fault occurs, issue an order to put the automatic reclosing relay back into service;

c) Within eight hours from the time of the second successful reclosure, if a fault occurs again, issue an order to isolate the line and hand over to the operation management unit for inspection and repair;

d) Complete the fault report according to the System Operation and Fault Handling Procedures issued by the Dispatch Authority with control rights.

Article 18. Reclosing of 500 kV Lines After Faults

1. When a single-phase fault occurs on a line, reclosing of the line once is allowed, including unsuccessful automatic reclosures.

2. In case the automatic protective relay does not operate:

a) It is not permitted to reclose the line when work is being performed on the line;

b) It is permitted to reclose the line once after preliminary checks of the equipment and protective devices confirm that the single-phase fault point is on the protected line and there is no additional information from the operation management unit indicating further fault damage on the line.

3. In case the single-phase automatic reclosure fails, reclosing of the line once is allowed after confirming the following information:

a) The unsuccessful single-phase automatic reclosure was due to transmission channel, secondary circuit, or unreliable protective relay operation, resulting in the line not actually being reclosed;

b) The single-phase automatic reclosure was successful at one end but tripped due to interlocking from the other end.

4. It is not permitted to reclose a section of the line if a short circuit involving two or more phases is confirmed, with clear indications from fault location devices on the same phases and close distances, and the function of single-phase automatic reclosure has locked all related circuit breakers. In this case, the dispatcher must isolate the line section as a safety measure, hand it over to the operation management unit for inspection and repair, and note any suspected fault points.

5. It is permitted to reclose the line a second time in cases of significant impact on stable and continuous power supply due to loss of connection on a 500 kV line, when it is confirmed that the single-phase automatic reclosure failed or the first reclosure was done by dispatch command. Before reclosing the line, the dispatcher must carefully consider all equipment and weather conditions at 500 kV substations, select the re-energization point to ensure safe operation of regional power systems.

6. It is not permitted to reclose the line during a typhoon with wind gusts of Force 10 or higher, floods causing landslides threatening the safety of the line, fires in areas through which the line passes, or equipment not meeting operational standards.

7. It is permitted to reclose the line if it is cut off due to interlocking from another location after the cause of the fault has been identified and eliminated.

8. After the operation management unit repairs the faulty elements on the 500 kV line, confirms they meet operational standards, and returns them to the Dispatch Authority with control rights for restoration, the dispatcher must base their instructions on actual operational conditions to bring the equipment and line back into operation.

Section 2

HANDLING OF FAULTS ON LINES WITH VOLTAGE RANGES FROM 35 KV TO 220 KV IN THE AIRBORNE POWER TRANSMISSION SYSTEM

Article 19. Handling Overloading on Overhead Transmission Lines with Voltage Levels from Above 35 kV to 220 kV

Clause 1. The transmission limit for overhead transmission lines with voltage levels from above 35 kV to 220 kV shall be determined as the smallest value among the following values:

Point a) The rated current of the conductor or electrical equipment connected to the line, taking into account the impact factor of the operating environmental conditions of the equipment;

b) The limit according to system stability conditions;

Point c) The limit according to the voltage standard specified in the Transmission System Regulations and Distribution System Regulations issued by the Ministry of Industry and Trade.

Clause 2. Operation staff at power plants, substations, or control centers must immediately report to the Control Authority with authority to control when the transmission exceeds the permitted limit on the line.

Clause 3. When the transmission on the line exceeds the permitted limit, the Dispatcher must handle the incident according to the extremely urgent mode prescribed in Article 53 of this Circular.

Article 20. Handling by Operation Staff at Power Plants, Substations, and Control Centers in Case of Incidents on Overhead Transmission Lines with Voltage Levels from Above 35 kV to 220 kV

Clause 1. When the circuit breaker trips, operation staff at power plants, substations, or control centers where the line is connected must immediately report to the Control Authority with authority to control the following information:

a) Time of the fault, name of the line and tripped circuit breaker, protective relay signal action;

b) Overloaded, overvoltage, or undervoltage conditions on the operating line or electrical equipment caused by the fault, local weather conditions;

c) Other related information.

Clause 2. Immediately after handling the incident, operation staff at power plants, substations, or control centers must submit a quick incident report to the Control Authority with authority to control as stipulated in Point a Clause 5 Article 10 of this Circular.

Article 21. Handling by Dispatchers in Case of Incidents on Overhead Transmission Lines with Voltage Levels from Above 35 kV to 220 kV

Clause 1. In case the protective relay automatically recloses successfully, the Dispatcher must perform the following tasks:

Point a) Collecting information from substations at both ends of the faulty line;

Point b) Requesting operation staff at substations, power plants, or control centers to check the status of circuit breakers, protective devices, and automatic devices;

Point c) Assigning the section of the line identified as having a transient fault to the Operating Management Unit for visual inspection, noting that the line is energized and identifying suspicious fault points;

d) Complete the fault report according to the System Operation and Fault Handling Procedures issued by the Dispatch Authority with control rights.

Clause 2. In case the protective relay automatically recloses unsuccessfully, the Dispatcher must take necessary measures to prevent the incident from expanding (overloading of the line or electrical equipment, voltage outside the permissible range). After the power system region stabilizes, quickly analyze the incident to restore the faulty line according to Article 22 of this Circular and complete the incident report according to the Power System Operation and Incident Handling Procedures issued by the Control Authority with authority to control.

Article 22. Provisions for Reclosing Overhead Transmission Lines with Voltage Levels from Above 35 kV to 220 kV after Incidents

Clause 1. When an incident occurs on a line with a voltage level from above 35 kV to 220 kV, reclosing the line is allowed up to two times, including unsuccessful automatic reclosures. For lines passing through densely populated areas and residential zones, reclosing the line for the second time is only allowed after the Operating Management Unit inspects and confirms that the line meets operational standards and ensures safety for people and electrical equipment.

Clause 2. Reclosing the line is not allowed during hot-line maintenance work.

Clause 3. Reclosing the line is not allowed in cases where the circuit breaker trips due to wind speeds of grade 6 or higher, floods leading to water levels exceeding safe distances from the design of the line, posing a threat to safety, fires in areas along the line, or non-compliant equipment.

Clause 4. Within eight hours, if the line experiences a transient fault after three successful reclosures (including automatic reclosures), operation staff must lock out the automatic reclosure relay. If the fault does not reappear within the next eight hours, the automatic reclosure relay can be put back into service. If the fault reappears within the next eight hours, operation staff must report to the Control Authority with authority to control to issue instructions:

Point a) Isolating the line and handing it over to the Operating Management Unit for inspection and repair;

Point b) If the line has sections, proceed to isolate and reclose each section, identify the faulty section, and implement safety measures, then hand it over to the Operating Management Unit for inspection and repair.

Clause 5. For lines with multiple branches, before energizing the entire line (excluding automatic reclosures), all main circuit breakers of branch transformers on the line must be disconnected. Before restoring the branch transformer, the tap position of the on-load tap changer of the transformer must be checked and adjusted to a suitable position relative to the line voltage.

Clause 6. For lines with permanent faults, before handing them over to the Operating Management Unit for inspection and repair, the Control Authority with authority to control must request operation staff at power plants, substations, or control centers to conduct preliminary checks on equipment connected to the line within the plant, substation, or control center fence. Operation staff must comply with technical standards, safety procedures, and other relevant regulations.

Clause 7. After the Operating Management Unit repairs the faulty elements on the line, confirms that they meet operational standards, and returns them to the Control Authority with authority to control for restoration, the actual operating mode must be taken into account to command operations to bring the equipment and line back into service.

Section 3

HANDLING INCIDENTS ON OVERHEAD TRANSMISSION LINES WITH VOLTAGE LEVELS FROM 35 KV AND BELOW

Article 23. Actions of Operating Personnel in Case of Faults on Overhead Lines with Voltage up to 35 kV

When a circuit breaker trips, operating personnel at power plants, substations, control centers, or distribution networks where the connected lines have faults must immediately report to the Control Authority with authority to control the following information:

1. Name of the tripped circuit breaker, number of trips, status of the circuit breaker.

2. Automatic protective relays that have operated, signals indicated, fault parameter records obtained from the equipped relays or other dedicated devices.

3. Status of line voltage.

4. Operational status of related equipment.

5. Local weather conditions.

Article 24. Actions of Dispatchers in Case of Faults on Overhead Lines with Voltage up to 35 kV

1. In case of successful automatic reclosing, information must be collected from substations at the ends of the faulty lines, the condition of the circuit breakers, protective and automatic devices checked, the faulty section identified and handed over to the Operation Management Unit for visual inspection with caution regarding live lines, suspected fault points, and completion of the Incident Report according to the System Operation and Incident Handling Procedures issued by the Control Authority with authority to control.

2. In case of unsuccessful automatic reclosing, necessary measures must be taken to prevent the fault from expanding (line or equipment overload), quickly analyze the fault to restore the faulty line in accordance with Article 25 of this Circular, and complete the Incident Report according to the System Operation and Incident Handling Procedures issued by the Control Authority with authority to control.

3. In case of ground fault points appearing on the network with ungrounded or arc suppression coil grounded neutral points, immediate measures must be taken to isolate the ground fault point and implement basic steps to identify and isolate the ground fault point for networks with insulated or arc suppression coil grounded neutral points as follows:

a) Based on the recorded parameters when the fault occurs to determine the faulty element, proceed to sectionalize and isolate the ground fault element for handling;

b) In case the faulty element cannot be immediately determined, the following steps must be carried out in sequence:

- Inspect elements belonging to the busbar and from the busbar to the substation fence;

- Divide the network with the ground fault point into regions for inspection;

- Sequentially operate to disconnect each element within the region with the ground fault point according to the principle of disconnecting less critical elements first until the faulty element is identified;

- After identifying the faulty element, proceed to sectionalize and isolate the ground fault element for handling.

4. In urgent cases that cannot be delayed (fire along the line route or non-compliant equipment posing a threat to human life and equipment safety; or flooding leading to water levels higher than the design level of the line threatening safety, and other information reported by the Operation Management Unit), command the line disconnection operation according to procedures and bear responsibility for the fault handling operation.

Article 25. Provisions on reclosing overhead power lines with voltage up to 35 kV

1. In case of line fault, reclosing the line is permitted not more than three times, including unsuccessful automatic reclosing attempts. For lines passing through residential areas, the Operating Management Unit shall decide to energize the line based on actual conditions to ensure safety for people, electrical equipment, and successful reclosing.

2. Reclosing the line is not allowed during hot-line maintenance time.

3. In cases of wind force six or higher, the Dispatching Officer of the Control Level has the authority to control and manually lock out the automatic reclosing function of circuit breakers. If there is a fault on the line, re-energization shall be carried out after preliminary visual inspection by the Operating Management Unit without detecting any abnormalities.

4. Within eight hours, if the line experiences a transient fault after four successful reclosings (including automatic reclosings), the Operating Personnel must lock out the reclosing relay circuit. If no further fault occurs within the next eight hours, the reclosing relay shall be returned to service. If another fault occurs within the subsequent eight hours, the Operating Personnel must report to the Control Level with authority to issue orders:

a) Isolate the line and hand over to the Operating Management Unit for inspection and repair;

b) If the line has sections, proceed to section the line to reclose each section to identify the faulty section and take safety measures, then hand over to the Operating Management Unit for inspection and repair.

5. For lines with sections, if the first attempt at reclosing fails, the Operating Personnel must report to the Control Level with authority to issue orders:

a) Section the line at the specific point defined, isolate the faulty section, and quickly restore power supply to customers;

b) Use protective relay signals, fault reporting devices, and short-circuit current measurements (if available) to section the line;

c) Implement safety measures to permanently isolate the faulty section and hand it over to the Operating Management Unit for inspection and repair.

Section 4

HANDLING FAULTS IN POWER CABLES

Article 26. Handling Overload and Ground Faults in Power Cables

1. Power cables with voltage below 35 kV may be operated in overload condition, with the duration and permissible overload current depending on the previous load of the cable according to the manufacturer's specifications and considering actual operating conditions. For power cables with voltage 35 kV or higher, overload operation is not permitted unless the manufacturer specifies allowable overload duration.

2. In case of a grid with isolated neutral, the permissible duration for a single-phase ground fault in power cables is according to the manufacturer's specifications and considering actual operating conditions. Upon detection of a single-phase ground fault, the Operating Management Unit must immediately locate and repair the fault in the shortest possible time.

Article 27. Actions of Operating Personnel at Power Plants, Substations, and Control Centers in Case of Power Cable Faults

1. When the circuit breaker of the power cable trips, the Operating Personnel at the power plant, substation, or control center where the faulty power cable is connected must record and immediately report to the Control Level with authority the following information:

a) Name of the tripped circuit breaker and the protective relay that acted based on the signal indication in the central control room;

b) The power line, power cable, or electrical equipment currently in operation experiencing overload, overvoltage, or undervoltage (if caused by the fault).

2. Immediately after completing the fault handling, the operator at the power plant, substation, or control center must submit a quick fault report to the Dispatch Authority with control rights in accordance with Point a Clause 5 Article 10 of this Circular.

Article 28. Handling by the System Dispatcher in Case of Power Cable Line Incident

1. Implement necessary measures to prevent the incident from expanding.

2. Request the Operator at the power plant, substation, or control center to conduct preliminary checks on the equipment connected to the faulty power cable line within the power plant or substation fence.

3. Fully comply with all safety procedures and measures as prescribed before handing over the power cable line to the Operating Unit for inspection and repair, noting the grounding closure time according to specific regulations for each type of cable.

4. Restore the faulty power cable line in accordance with Article 29 of this Circular.

5. Complete the Incident Report in accordance with the Power System Operation and Incident Handling Procedures issued by the Controlling Authority.

Article 29. Restoration of Power Cable Lines After Tripping Due to Incident

1. For power cables:

It is not permitted to reclose the power cable when relay protection against various types of short circuits within the range of the power cable has been activated. The System Dispatcher may only permit reclosing the power cable in the following cases:

a) The Operating Unit has inspected and confirmed that the power cable meets operational standards or determined that the power cable tripped due to a second fault and has been rectified;

b) After analyzing the relay protection incident, it is determined that the short circuit was transient and outside the range of the power cable.

2. For hybrid overhead and cable lines:

a) Reclosing is permitted for lines with voltage levels of 220 kV and above after the Operating Unit has identified and rectified the incident on the overhead section of the line;

b) Reclosing is permitted once for lines with voltage levels of 110 kV where the cable is merely a short section of the overhead line (including automatic reclosure) upon recommendation by the Operating Unit. If reclosing is unsuccessful, restoration of the hybrid line shall be carried out in accordance with Clause 1 of this Article;

c) Reclosing is permitted once for lines with voltage levels of 35 kV and below (including automatic reclosure). If reclosing is unsuccessful, the Operator must segment (if segmentation is available) and reclose the overhead line in accordance with regulations and perform insulation testing on the cable section of the line.

3. Reclosing is permitted once for cable lines with voltage levels of 35 kV and below with multiple overhead switching stations (automatic reclosure is not allowed). If reclosing is unsuccessful, the Operator must segment (if segmentation is available) and reclose the overhead line in accordance with regulations and perform insulation testing on the cable section of the line.

4. The Operating Unit is responsible for coordinating with the Controlling Authority to calculate and propose lines that are permitted to automatically reclose once.

Chapter IV

HANDLING INCIDENTS AT SUBSTATIONS AND POWER PLANTS

Section 1

HANDLING INCIDENTS WITH GENERATORS

Article 30. Handling Generator Warning Signals

When a generator issues a warning signal (stator overload, rotor overload, minimum excitation, or other warnings), handle as follows:

1. For the Shift Supervisor at the power plant or control center:

a) Handle the generator warning signal in accordance with the Generator Operation and Incident Handling Procedures issued by the Operating Unit;

b) Immediately report to the Controlling Authority the time required to handle the warning and any recommendations for handling the warning.

2. For the System Dispatcher:

a) Approve the handling recommendation of the Shift Supervisor at the power plant or control center in emergency situations threatening generator incidents or propose appropriate handling solutions for the power system;

b) Immediately implement frequency or voltage control measures when changing active power (P) or reactive power (Q) of the generator depending on the system's frequency and voltage;

c) Handle power system incidents in emergency mode if the frequency or voltage exceeds permissible limits.

Article 31. Handling when the generator trips due to an incident

1. For the Shift Supervisor at the power plant or control center:

a) Handle the generator incident according to the Generator Operation and Incident Handling Procedure issued by the Operating Management Unit;

b) Immediately report to the Dispatching Authority with control rights the following information:

- The name of the generator set affected by the incident, the protective relay that has been activated based on the signal indication in the central control room;

- The impact of the generator incident at the power plant;

c) Complete the Incident Report promptly as stipulated in Point a Clause 5 Article 10 of this Circular.

2. For the System Dispatcher:

a) Handle the electrical system incident in warning, emergency, or extreme emergency mode caused by the generator incident;

b) Bring the generator back into operation according to Article 32 of this Circular;

c) Complete the Incident Report according to the Electrical System Operation and Incident Handling Procedure issued by the Dispatching Authority with control rights.

Article 32. Restoring the generator after an incident

1. In cases where the Shift Leader of the power plant or control center conducts a preliminary check and confirms that the protective action was due to an external incident affecting the generator, and there are no abnormal conditions and it meets the operational standards, the Shift Leader permits the Dispatcher to bring the generator back into operation.

2. In cases where the Shift Leader of the power plant or control center confirms that the protective action was due to an internal incident within the generator or related equipment, the Shift Leader reports to the Dispatcher with control rights to permit isolation operations for repair. The generator can only be brought back into operation after the Operating Management Unit confirms that it meets the operational standards.

Section 2

HANDLING INCIDENTS WITH THE TRANSFORMER

Article 33. Handling transformer overload

1. If there is no specific manufacturer's specification regarding the rated capacity of the transformer, the transformer may be overloaded beyond the rated current according to the following limits:

a) Short-term overload for oil-filled transformers:

b) Short-term overload for dry-type transformers:

c) Long-term overload for all types of transformers is allowed up to 5% above the corresponding voltage level if the voltage at that level does not exceed the rated voltage.

2. Power plant, substation, and control center operators handle transformer overloads in the following sequence:

a) Report to the Dispatching Authority with control rights the following information:

- Start time and load carrying levels exceeding 90%, 100%, and 110% of the rated value;

- Oil temperature and winding temperature of the transformer (continuously monitored, reported immediately upon change);

- Permitted duration of overload as specified in Clause 1 of this Article.

b) Check the operating condition of the transformer cooling system and handle according to the Transformer Operation and Incident Handling Procedure issued by the Operating Management Unit.

3. The Dispatcher handles transformer overloads under warning, emergency, and extreme emergency modes according to Articles 49, 51, and 53 of this Circular.

Article 34. Handling transformer overvoltage

1. If there is no specific requirement from the manufacturer, the transformer may operate under overvoltage as follows:

a) Under normal operating conditions:

- The transformer may operate long-term with voltage up to 5% higher than the rated voltage corresponding to the tap position, provided the transformer is not overloaded; up to 10% higher than the rated voltage corresponding to the tap position, provided the load through the transformer does not exceed 25% of the transformer's rated capacity;

- The transformer may operate short-term (less than 06 hours in 24 hours) with voltage up to 10% higher than the rated voltage corresponding to the tap position, provided the transformer is not overloaded.

b) Under incident conditions:

- On-load tap-changing transformers, autotransformers without taps or connected in series with regulating transformers may operate long-term with voltage up to 10% higher than the rated voltage, provided the transformer is not overloaded;

- For autotransformers with taps or connected in series with regulating transformers, the permissible increase in voltage is determined by the manufacturer's data.

c) Operation voltage must not exceed 20% above the rated voltage of the corresponding tap position. Operators at power plants, substations, or control centers must immediately isolate the transformer from operation to prevent damage.

2. Power plant, substation, or control center operators handle transformer overvoltage in the following sequence:

a) If the transformer has an on-load tap changer and can automatically adjust the tap position to avoid overvoltage beyond the permissible limit specified in Clause 1 of this Article, then report to the Dispatching Authority with control rights;

b) If the transformer has a fixed tap position, immediately report to the Dispatching Authority with control rights if the transformer exceeds the permissible overvoltage limit.

3. The Dispatcher controls the voltage according to the National Electrical System Dispatching Procedures issued by the Ministry of Industry and Trade to ensure that the transformer under their control does not exceed the permissible overvoltage.

Article 35. Handling abnormal phenomena in transformers

1. In cases where abnormal phenomena such as oil leakage, insufficient oil, excessive overheating, unusual sounds, localized heating at porcelain bushings, abnormal operation of on-load tap changers are detected in transformers, the operators at power plants, substations, or control centers must take all measures to handle the incident according to regulations, report to the Control Authority with authority to control, direct leadership, and record in the operation logbook.

2. When gas relays signal, the operators must conduct external inspections of the transformer, take gas samples from the relay for analysis and test the flammability of the gas:

a) If the gas ignites or contains products resulting from the breakdown of insulating materials, immediate reports must be made to the Control Authority with authority to control to isolate the transformer;

b) If the gas is colorless, odorless, and non-flammable, the transformer may continue to operate but enhanced monitoring of the transformer's condition is required.

Article 36. Situations requiring isolation of transformers from operation

1. Presence of loud, uneven noises and electrical discharge sounds within the transformer.

2. Abnormal and continuous increase in transformer temperature under normal cooling conditions without overload.

3. Oil leaking out through auxiliary oil tanks, explosion-proof glass breaking, or oil spraying through safety valves.

4. Oil level dropping below the specified level and continuing to decrease.

5. Sudden change in the color of the oil.

6. Porcelain parts cracked, broken, surface electrical discharges, oil pressure of sealed porcelain types not within the manufacturer's specifications, bushing overheating to redness.

7. Oil analysis results showing that the oil does not meet standards.

8. Other abnormal situations as required by the Operating Management Unit.

Article 37. Handling when a transformer trips due to fault

1. Operators at power plants, substations, or control centers shall handle as follows:

a) Immediately report to the Control Authority with authority to control the following information:

- Name of the tripped transformer, protective relays activated according to signals in the central control room;

- Impact of the transformer fault.

b) Handle the transformer fault according to the Transformer Operation and Fault Handling Procedures issued by the Operating Management Unit. Switch to emergency power supply if alternating current self-use power is lost due to the transformer fault;

c) Complete the Incident Report promptly as stipulated in Point a Clause 5 Article 10 of this Circular.

2. The dispatcher of the Control Authority with authority to control shall command handling as follows:

a) Handle the power system fault in warning, urgent, and extremely urgent modes due to the transformer fault according to Articles 49, 51, and 53 of this Circular;

b) Command isolating or returning the transformer to operation according to Article 38 of this Circular;

c) Complete the Incident Report according to the Power System Operation and Fault Handling Procedures issued by the Control Authority with authority to control.

Article 38. Restoration of Transformers After Incidents

1. In cases where the transformer is tripped by protection other than phase imbalance, gas, oil flow, or oil pressure, the dispatcher will command returning the transformer to operation after the operator has checked and reported that there are no abnormal signs externally on the transformer, and confirmed that the protection circuit did not act erroneously.

2. In cases where the transformer is tripped by the activation of two internal protection circuits of the transformer, namely phase imbalance and gas (or oil flow, oil pressure), the dispatcher will command returning the transformer to operation once the following conditions are met:

a) The Operating Management Unit has conducted tests, verified parameters, analyzed gas and oil samples, and rectified any detected abnormalities;

b) The Operating Management Unit has issued a document confirming that the transformer meets operational conditions and sent it to the Dispatching Authority with control rights.

3. In cases where only one of the internal protection circuits activates, the dispatcher will command isolating the transformer and handing it over to the Operating Management Unit for testing and checking the internal protection circuit of the transformer. The dispatcher can command returning the transformer to operation once:

a) Upon inspection, it is found that the activation of the internal protection circuit of the transformer was due to damage within the protection circuit which has been repaired;

b) Upon inspection of the internal protection circuit and no damage being found, the Operating Management Unit has complied with the provisions of Clause 2 of this Article.

4. In cases where stopping the operation of the transformer leads to a large area power outage, the dispatcher will command returning the transformer to operation once the following conditions are met:

a) The operating staff have inspected, confirmed, and reported that the transformer was disconnected due to one of the internal protective measures of the transformer and there are no external signs indicating damage to the transformer;

b) The operator reports that the transformer has been approved by the Operating Management Unit's leadership to return to operation.

Section 3

HANDLING OF FAULTS IN OTHER PRIMARY EQUIPMENT

Article 39. Handling Overloading of Secondary Electrical Equipment

1. The level of overloading and the permitted duration of overloading for secondary electrical equipment (circuit breakers, disconnect switches, current transformers, shunt capacitors, and other related equipment) must be based on the manufacturer's specifications.

2. Staff operating at power plants, substations, or control centers must immediately report to the Control Authority with authority to control the level of overloading and the permitted duration of overloading of the equipment.

3. Dispatchers handle overloading of secondary electrical equipment under their control according to the warning, emergency, and critical emergency procedures specified in Articles 49, 51, and 53 of this Circular.

Article 40. Handling Overvoltage of Secondary Electrical Equipment

1. The maximum permissible long-term operating voltage for secondary electrical equipment must be based on the manufacturer's specifications.

2. Staff operating at power plants, substations, or control centers must immediately report to the Control Authority with authority to control if the voltage on the electrical equipment exceeds the permissible limit.

3. Dispatchers control the voltage in accordance with the national system dispatching procedure regulations issued by the Ministry of Industry and Trade so that the secondary electrical equipment under their control does not exceed the permissible voltage limit.

Article 41. Handling Faults in Compensation Equipment

1. For staff operating at substations or control centers:

a) Handle faults in compensation equipment according to the operational and fault handling procedures issued by the Operating Management Unit;

b) Report to the Control Authority with authority to control information about protective relays and automatic actions, and the ability to return compensation equipment to operation.

2. For dispatchers at the Control Authority with authority to control:

a) Handle faults in transmission lines, substations, and related electrical equipment if the fault in the compensation equipment causes tripping;

b) Control voltage, power sources, and loads according to the national system dispatching procedure regulations issued by the Ministry of Industry and Trade if the voltage and current on the grid under their control exceed the permissible limits;

c) Analyze the protective relay actions of the compensation equipment to decide whether to put the compensation equipment back into operation or isolate it in the following cases:

- If internal damage within the compensation equipment is determined, command the isolation of the compensation equipment and hand over to the Operating Management Unit for repair. The compensation equipment can only be returned to operation when confirmed to meet operational standards by the Operating Management Unit;

- If external factors are determined, allow the compensation equipment to be returned to operation when conditions permit.

Article 42. Handling Faults in Circuit Breakers, Current Transformers, Voltage Transformers

1. For staff operating at power plants, substations, or control centers:

a) Handle faults according to the operational and fault handling procedures issued by the Operating Management Unit;

b) Immediately report to the Control Authority with authority to control about the fault, the operational status of the transmission line or other electrical equipment at the power plant or substation;

c) Handle the fault according to the orders of the Control Authority with authority to control;

d) Complete the quick fault report as stipulated in Point a Clause 5 Article 10 of this Circular.

2. For dispatchers at the Control Authority with authority to control:

a) Handle faults in transmission lines, electrical equipment, busbars;

b) Order staff operating at power plants, substations, or control centers to isolate faulty electrical equipment and hand over to the Operating Management Unit for repair. The equipment can only be returned to operation when confirmed to meet operational standards by the Operating Management Unit;

c) Complete the Incident Report according to the Power System Operation and Fault Handling Procedures issued by the Control Authority with authority to control.

Section 4

HANDLING FAULTS IN BUSBARS AT SUBSTATIONS AND POWER PLANTS

Article 43. Handling by Substation and Power Plant Operators in Case of Busbar Fault

When a busbar fault occurs, substation and power plant operators, and control center staff shall follow the procedures as follows:

1. Implement fault handling according to the operating and fault handling procedures issued by the Operating Management Unit.

2. Disconnect all busbar tie breakers if the busbar loses power.

3. Immediately report the busbar fault and the operational status of related equipment to the Dispatching Authority with control authority.

4. On-site inspection of the entire faulty busbar and related equipment to decide whether to isolate or put the busbar back into operation under the following conditions:

a) In case the fault does not occur on the busbar, ensure that the busbar and related equipment meet the conditions for resuming power supply, then report to the Dispatching Authority with control authority to permit re-energization.

b) In case the fault occurs on the busbar, request the Dispatching Authority with control authority to perform isolation operations on the faulty line or equipment.

5. Complete the quick fault report as stipulated in Point a Clause 5 Article 10 of this Circular.

Article 44. Handling by Dispatcher in Case of Busbar Fault

1. Implement appropriate control measures to prevent the fault from expanding.

2. Analyze the fault, determine the cause of the busbar power loss at the substation or power plant.

3. Command the isolation operation of the faulty line or equipment causing the busbar power loss at the substation or power plant.

4. Command the restoration of the busbar and connected lines or equipment after isolating the faulty element or repairing the faulty busbar.

5. Complete the Incident Report in accordance with the Power System Operation and Incident Handling Procedures issued by the Controlling Authority.

Section 5

HANDLING OF FULL SUBSTATION OR POWER PLANT BLACKOUT

Article 45. Handling by Substation Operator in Case of Full Substation Blackout

When a full substation blackout occurs, the substation operator shall follow the procedures as follows:

1. Implement incident handling according to the Operation and Incident Handling Procedures issued by the Operating Management Unit, switching to backup power sources to provide essential self-use power for the substation.

2. Disconnect all circuit breakers in the substation. For special cases where technical requirements prevent the complete disconnection of all circuit breakers, specific regulations must be established to accommodate such situations.

3. Inspect the status of all equipment in the substation.

4. Immediately report to the Dispatching Authority with control rights on the status of the circuit breakers.

5. Conduct a comprehensive inspection of the substation to decide whether to isolate or restore the substation to operation based on the following conditions:

a) In cases where the incident did not occur within the substation and the equipment is ready to receive power again, report to the Dispatching Authority with control rights for permission to reconnect power;

b) In case the fault occurs within the substation, request the Dispatching Authority with control authority to perform the isolation operation on the faulty line or equipment.

Article 46. Handling by Power Plant Operator in Case of Full Power Plant Blackout

When a full power plant blackout occurs, the power plant operator shall follow the procedures as follows:

1. Handle the incident according to the Operation and Incident Handling Procedures issued by the operation management unit, switching to the backup power source to restore essential self-use power for the power plant.

2. Disconnect all circuit breakers in the power plant substation. For special cases where technical requirements prevent the complete disconnection of all circuit breakers, specific regulations must be established by the Operating Management Unit.

3. Inspect the status of equipment within the power plant and the condition of generator units.

4. Immediately report to the dispatch authority with control over the state of circuit breakers and the condition of generator units.

5. Ensure that the equipment and generating units are ready to reconnect without fault.

6. Request the dispatch authority with control to isolate faulty lines or equipment (if applicable).

7. Request the Dispatching Authority with control authority to cooperate in quickly restoring the power plant's self-use system (if the fault affects the backup power source).

Article 47. Handling by Dispatcher in Case of Full Substation or Power Plant Blackout

1. Implement control measures to prevent the fault from expanding.

2. Analyze the fault, determine the cause of the full substation or power plant blackout.

3. Order the isolation operation of the faulty line or equipment causing the full substation or power plant blackout.

4. Order the restoration of the entire affected substation or power plant.

5. Complete the Incident Report in accordance with the Power System Operation and Incident Handling Procedures issued by the Controlling Authority.

Chapter V

HANDLING OF WARNING, EMERGENCY, AND EXTREME EMERGENCY MODES

Section 1

HANDLING OF WARNING MODE

Article 48. Warning Mode

The transmission system operates in warning mode when any of the following conditions exist:

1. Frequency reserve, spinning reserve, and fast-start reserve levels are lower than the specified levels for normal operation.

2. Load level of main transmission lines and substations exceeds 90% but does not exceed the rated value.

3. Possibility of natural disasters or abnormal weather conditions that may affect system security.

4. Possibility of security or defense issues that may threaten system security.

Article 49. Measures taken by the System Operator when the transmission system is in warning mode

1. Control the power output of operating power plants to be below their rated capacity, start up reserve generating units to ensure that the frequency regulation reserve level reaches or exceeds the prescribed level.

2. Control the power output of power plants (spinning reserve, fast-start) to ensure that the load-carrying capacity of major transmission lines and substations in the transmission network does not exceed 90% of their rated value.

3. Reduce transmission power on 500 kV and 220 kV lines in areas where natural disasters or abnormal weather conditions may occur, or where security and defense issues could threaten the security of the power system.

4. Provide information for the issuance of warning information on the official website when necessary measures have been implemented but the system cannot be returned to normal operation mode.

Section 2

EMERGENCY MODE HANDLING

Article 50. Emergency Mode

The transmission system operates in emergency mode if any of the following conditions exist:

1. The system frequency exceeds the allowable range for normal operation but remains within the permissible frequency range for partial system component failures as stipulated in the Transmission System Regulation issued by the Ministry of Industry and Trade.

2. The voltage at any node on the transmission network falls outside the allowable range for normal operation but remains within the permissible voltage range for partial system component failures as stipulated in the Transmission System Regulation issued by the Ministry of Industry and Trade.

3. The load-carrying capacity of any electrical equipment in the transmission network or connected to the transmission network exceeds its rated value but is less than 110% of the rated value, which, if overloaded, could lead to an extremely emergency operation mode.

Article 51. Measures taken by the System Operator when the transmission system is in emergency mode

1. Control the frequency and voltage according to the National Power System Dispatching Procedures Regulation issued by the Ministry of Industry and Trade to bring the frequency and voltage back within the allowable range for normal operation.

2. Handling overloading of transmission lines or electrical equipment

a) Control the power output of power plants (spinning reserve, fast-start) to prevent overloading of transmission lines or electrical equipment;

b) Change the grid configuration based on pre-calculated results to alter power flow on the power system and reduce transmission power on overloaded transmission lines or electrical equipment.

Section 3

EXTREMELY EMERGENCY MODE HANDLING

Article 52. Extremely Emergency Mode

The transmission system operates in extremely emergency mode if any of the following conditions exist:

1. The system frequency falls outside the permissible range for partial system component failures as stipulated in the Transmission System Regulation issued by the Ministry of Industry and Trade.

2. The voltage at any node on the transmission network falls outside the permissible range for partial system component failures as stipulated in the Transmission System Regulation issued by the Ministry of Industry and Trade.

3. The load-carrying capacity of any equipment in the transmission network or connected to the transmission network exceeds 110% of its rated value, which, if overloaded, could lead to partial collapse of the power system.

4. When the transmission network is in emergency operation mode, if the measures taken to stabilize the system fail, it could result in partial collapse of the power system, islanding, or system voltage collapse.

Article 53. Actions of the System Operator when the transmission system is in an extremely urgent state

1. Control the frequency and voltage according to the National Power System Dispatching Procedures Regulation issued by the Ministry of Industry and Trade to bring the frequency and voltage back within the allowable range for normal operation.

2. Handling overloading of transmission lines or electrical equipment

a) Control the power of power plants (spinning reserve, fast start) to prevent transmission lines from exceeding their capacity limits or electrical equipment from being overloaded over 110%;

b) Change the grid configuration based on pre-calculated results to alter power flow within the system to reduce transmission power on lines or electrical equipment that are overloaded over 110%;

c) Shed medium voltage or source-end loads according to regulations to prevent transmission lines from exceeding their capacity limits or electrical equipment from being overloaded over 110%.

Chapter VI

IMPLEMENTATION

Article 54. Implementation Organization

1. The Electricity Regulatory Authority shall be responsible for disseminating, guiding, and supervising the implementation of this Circular.

2. The Vietnam Electricity Corporation shall be responsible for directing subordinate units to implement this Circular.

Article 55. Effective Date

1. This Circular takes effect from November 5, 2014. Decision No. 13/2007/QD-BCN dated March 13, 2007 of the Minister of Industry regarding the National Power System Emergency Response Procedures ceases to be effective from the date this Circular takes effect.

2. During the implementation of this Circular, if there are any difficulties or new issues arise, relevant units shall have the responsibility to report to the Electricity Regulatory Authority for research, proposal, and submission to the Minister of Industry and Trade for amendments and supplements to this Circular as appropriate./.