Circular No. 30/2019/TT-BCT amends and supplements certain Articles of Circular No. 25/2016/TT-BCT dated November 30, 2016, issued by the Minister of Industry and Trade on the transmission power system and Circular No. 39/2015/TT-BCT dated November 18, 2015, issued by the Minister of Industry and Trade on the distribution power system.

           

CIRCULAR

Amending and supplementing certain articles of Circular No. 25/2016/TT-BCT dated November 30, 2016 of the Minister of Industry and Trade on the transmission power system and Circular No. 39/2015/TT-BCT dated November 18, 2015 of the Minister of Industry and Trade on the distribution power system.

Based on the Electricity Law dated December 3, 2004, and the Law Amending and Supplementing Certain Provisions of the Electricity Law dated November 20, 2012;

Pursuant to Decree No. 98/2017/NĐ-CP dated August 18, 2017, of the Government stipulating the functions, tasks, powers, and organizational structure of the Ministry of Industry and Trade;

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 this Circular to amend and supplement certain articles of Circular No. 25/2016/TT-BCT dated November 30, 2016 of the Minister of Industry and Trade on the transmission power system and Circular No. 39/2015/TT-BCT dated November 18, 2015 of the Minister of Industry and Trade on the distribution power system.

Article 1.Amend and supplement some articles of Circular No. 25/2016/TT-BCT dated November 30, 2016, issued by the Minister of Industry and Trade on the transmission electricity system.

1.Supplement Clause 5a following Clause 5, Clause 6a following Clause 6 of Article 3 as follows:

“5a. The rated capacity of the power plant is the total rated capacity of the generating units within the power plant under stable and normal operating conditions, as published by the manufacturer according to the design of the generating unit. For solar power plants, the rated capacity of the solar power plant is the maximum alternating current power that can be generated, calculated and announced, consistent with the direct current power of the solar power plant as planned.

6a. DIM (in English abbreviation: Dispatch Instruction Management) is the information management system for dispatch instructions between the control level with authority and the power plant or the Control Center of power plants.”

2.Amend Clause 10, Clause 35, Clause 49, Clause 53 of Article 3 as follows:

“10. Frequency control in the power system (hereinafter referred to as frequency control) is the process of controlling the power system to maintain its stable operation, including primary frequency control, secondary frequency control, and tertiary frequency control:

a) Primary frequency control is the immediate automatic control of the system frequency performed by a large number of generating units equipped with speed control systems;

b) Secondary frequency control is the subsequent control of primary frequency control carried out through the impact of the Automatic Generation Control (AGC) system to bring the frequency back to the long-term allowable range;

c) Tertiary frequency control is the subsequent control of secondary frequency control carried out by dispatch orders to ensure the stable operation of the power system in accordance with current regulations and to ensure the economic allocation of generating capacity among generating units.

35. Short-term voltage flicker level (P_st) and long-term voltage flicker level (P_lt) ) are measured values according to the current national standards. In cases where the measured values P_st st_lt and P

49. lt are not included in the national standards, they shall be measured according to the current International Electrotechnical Commission (IEC) standard published by the International Electrotechnical Commission.

53. Power System Stabilizer (PSS) (in English abbreviation: Power System Stabilizer) is a device that provides additional signals to the automatic voltage regulator (AVR) to reduce power oscillations in the power system.

3.Automatic load shedding

“Article 7. Phase Balance

1. In normal operating conditions, the reverse sequence component of phase voltage shall not exceed 3% of the rated voltage for the rated voltage levels in the transmission network.

2. The reverse sequence component of phase voltage on the transmission network may exceed the value specified in Clause 1 of this Article at certain times but must ensure that 95% of measured values over a measurement period of at least one week with a sampling frequency of once every ten minutes do not exceed the prescribed limit.

4.Amend Clause 1, Clause 2, and add Clause 6 to Article 8 as follows:

"1. Voltage Harmonics

a) Total harmonic distortion (THD) is the ratio between the effective value of the harmonic voltage and the effective value of the fundamental voltage calculated according to the following formula:

 

Where:

- THD: Total harmonic distortion;

- V (VND/year): is the total investment capital allocated annually for the usable area of social housing for rent, ensuring the preservation of capital, calculated according to the following formula:_i: Effective value of the ith harmonic voltage and N is the highest order of harmonics to be evaluated;

- V (VND/year): is the total investment capital allocated annually for the usable area of social housing for rent, ensuring the preservation of capital, calculated according to the following formula:₁: Effective value of the fundamental voltage (50 Hz).

b) The maximum allowable total harmonic distortion caused by high-order harmonics for voltage levels of 220 kV and 500 kV must be less than or equal to 3%.

2. Current Harmonics

a) Total harmonic distortion of current (TDD) is the ratio between the effective value of the harmonic current and the effective value of the fundamental current under load conditions and maximum generation capacity calculated according to the following formula:

 

Where:

- TDD: Total harmonic distortion of current;

- I_i: Effective value of the ith harmonic current and N is the highest order of harmonics to be evaluated;

- I_L: Effective value of the fundamental current (50 Hz) under load and maximum generation capacity (load, maximum generation capacity is the average of 12 loads, maximum generation capacity corresponding to the previous 12 months, in cases where new connections or load, maximum generation capacity corresponding to the previous 12 months cannot be obtained, then use the load, maximum generation capacity throughout the measurement period).

b) The maximum allowable total harmonic distortion caused by high-order harmonics for voltage levels of 220 kV and 500 kV must be less than or equal to 3%.

6. Peak spikes of harmonic waves on the transmission network exceeding the harmonic distortion specified in Clauses 1 and 2 of this Article are permitted but must ensure that 95% of measured harmonic voltage and harmonic current values over a measurement period of at least one week with a sampling frequency of once every ten minutes do not exceed the prescribed limit."

5.Amend Article 12 as follows:

“Article 12. Short Circuit Current and Fault Clearance Time

1. Maximum Allowable Short Circuit Current

a) The maximum allowable short circuit current and the maximum fault clearance time by main protection in the transmission system is specified in Table 6 as follows:

Table 6

Maximum Allowable Short Circuit Current

and Maximum Fault Clearance Time by Main Protection

b) Main protection of electrical equipment is the primary protection and is installed and adjusted to act first, ensuring the selectivity criteria, reliability of action, and action time of the protection system when a fault occurs within the protected range of the protected equipment;

c) For 110 kV busbars of 500 kV and 220 kV substations in the transmission network, the maximum allowable short circuit current is 40 kA.

2. Switchgear on the transmission network must have sufficient capability to interrupt the maximum short circuit current through the switchgear for at least 10 years from the expected date of commissioning and withstand this short circuit current for a minimum duration of one second or more.

3. For hydroelectric and thermal power plants with a capacity greater than 30 MW, the total value of the unsaturated transient reactance of the generator (X_{For coal-fired thermal power plants where the enterprise holds 100% of the registered capital and uses 100% of its own capital to invest in the project approved by the competent authority, E is determined as 100%;}’-%) and the short-circuit reactance of the transformer winding (U_k-%) calculated in per unit system (pu relative to the rated apparent power of the generator) shall not be less than 40%.

If these requirements are not met, the project investor shall be responsible for calculating, investing in, and installing additional reactance so that the total value of X_{For coal-fired thermal power plants where the enterprise holds 100% of the registered capital and uses 100% of its own capital to invest in the project approved by the competent authority, E is determined as 100%;}’’, U_k and the additional reactance calculated in per unit system (pu relative to the rated apparent power of the generator) shall not be less than 40%.

4. Electrical projects connected to the transmission system with a short circuit current value at the connection point higher than the maximum allowable short circuit current value specified in Table 6, the investors of such projects shall be responsible for applying measures to reduce the short circuit current at the connection point to a value lower than or equal to the maximum allowable short circuit current value specified in Table 6.

5. Transmission companies shall notify customers using the transmission network of the maximum short circuit current value at the connection point at present and in the next 10 years to coordinate during investment and installation of equipment, ensuring that the switchgear has sufficient capability to interrupt the maximum short circuit current at the connection point for at least 10 years from the expected date of commissioning.

6.Amend Clause 3 of Article 28 as follows:

"3. In case the customer's proposed connection scheme does not comply with the approved power development plan, the transmission company shall inform the customer requiring connection to make adjustments and supplements to the plan in accordance with regulations."

7.Amend Clause 1 of Article 31 as follows:

"1. Customers using transmission grids shall be responsible for investing, installing, managing, and operating information systems within their management scope, ensuring the connection of these systems to the information systems of Transmission Units and Control Centers with control authority; ensuring full, reliable, and continuous communication and data transmission (including SCADA system data, PMU data, fault recording data) to serve power system operation and electricity market operations. The minimum communication means serving dispatching and operation work in the transmission grid system, including direct communication channels, telephones, faxes, and DIM, must operate reliably and continuously."

8.Amend Clause 1 and Clause 2 of Article 32 as follows:

"1. Transformer stations with voltage levels of 220 kV or higher, power plants with installed capacity over 30 MW, and power plants connected to the transmission grid but not yet connected to the Control Center shall be equipped with Gateway or RTU and establish two physically independent connections with the SCADA system of the Control Center with control authority."

"2. Transformer stations with voltage levels of 220 kV or higher, power plants with installed capacity over 30 MW, and power plants connected to the transmission grid and controlled from the Control Center shall be equipped with Gateway or RTU and establish one connection with the SCADA system of the Control Center with control authority and two connections with the control system at the Control Center."

9.Amend Article 36 as follows:

"Article 36. Automatic Load Shedding System"

"1. Customers using transmission grids shall cooperate with relevant units to install equipment and ensure the operation of the automatic load shedding system in their power systems according to calculations and requirements of the Control Center with control authority."

"2. The automatic load shedding system must be designed and adjusted to meet the following requirements:"

"a) Reliability not less than 99%;"

"b) The failure to shed any load shall not affect the operation of the entire power system;"

"c) The sequence of shedding and the amount of power shed must comply with the allocation level set by the Control Center with control authority and may not be changed under any circumstances without permission from the Control Center with control authority."

"3. The sequence of restoring power supply must follow the dispatch orders of the Control Center with control authority."

10.Amend Clause 2 of Article 37 as follows:

"2. Requirements for Control Center Connection"

a) Information system connection requirements

"- There shall be one data transmission link connecting to the information system of the Control Center with control authority. In cases where there are multiple Control Centers with control authority, the Control Centers shall be responsible for unifying the method of sharing information;"

"- There shall be two data transmission links (one working link and one backup link) connecting to the control and information systems of power plants and substations controlled remotely by the Control Center;"

"- Communication means serving dispatching work, including direct communication, telephones, faxes, DIM, and computer networks, must function well;"

b) SCADA system connection requirements

- One connection to the SCADA system of the Dispatching Authority with control rights. In case there are multiple dispatching authorities with control rights, these authorities shall be responsible for sharing information;

"- There shall be two connections with the terminal RTU/Gateway, control systems of power plants and substations, and circuit breakers on the grid controlled remotely by the Control Center;"

"c) The Control Center must be equipped with monitoring screens and connected to security surveillance cameras at power plants, substations, and circuit breakers on the grid, linking back to the Control Center."

11.Amend Clause 3 of Article 38 as follows:

"3. Power generation units of power plants must have the ability to participate in primary frequency control when the frequency deviates from the deadband of the speed governor system and must provide the full primary frequency control power of the unit within 15 seconds and maintain this power for at least 15 seconds. The primary frequency control power of the unit is calculated based on actual frequency deviation and settings required by the System Operation Unit and Electricity Market."

12.Amend Article 42 as follows:

“Article 42. Technical Requirements for Wind Power Plants and Solar Power Plants

1. Wind power plants and solar power plants must be capable of maintaining operation to generate effective capacity under the following modes:

a) Free generation mode: Operating to generate maximum possible electrical capacity according to the primary energy source changes (wind or sun).

b) Generation capacity control mode:

Wind power plants and solar power plants must be able to limit generation capacity according to dispatch orders in the following cases:

- In case the primary energy source fluctuation is lower than the value specified in the dispatch order, generate the maximum possible capacity;

"- When the primary energy source fluctuates by or more than the limit value according to dispatch orders, the power output should be adjusted to the limit value according to dispatch orders with an error range of ± 01% of the rated power."

"2. Wind power plants and solar power plants must maintain power generation operation for a minimum time corresponding to the operational frequency ranges specified in Table 8 as follows:"

Table 8

Minimum Time to Maintain Operation to Generate Electricity of Wind Power Plants and Solar Power Plants

Corresponding to System Frequency Ranges System Frequency Range

"3. When the system frequency exceeds 50.5 Hz, wind power plants and solar power plants can reduce active power according to the relative slope of the static characteristic curve (droop characteristics) within the range of 2% to 10%. The setting value of the relative slope of the static characteristic curve is calculated and determined by the Control Center with control authority."

" 4. Wind power plants and solar power plants must be able to adjust reactive power according to the characteristics described in Point a and Point b of this Clause:"

"         a) If the power plant generates active power greater than or equal to 20% of the rated active power and the voltage at the point of interconnection is within ± 10% of the nominal voltage, the power plant must be able to continuously adjust reactive power within the power factor range of 0.95 (corresponding to the mode of generating reactive power) to 0.95 (corresponding to the mode of absorbing reactive power) at the point of interconnection with the rated power."

5. Voltage Control and Reactive Power Control Mode:

"5.  Voltage control mode and reactive power adjustment:"

- Voltage control mode according to set voltage value, voltage adjustment characteristic (voltage/reactive power relationship characteristic);

"- Voltage control mode according to the adjustable voltage characteristic (voltage/reactive power relationship characteristic);"

- Power factor control mode.

b) If the high-voltage side transformer boost voltage of the power plant is within ± 10 % of the nominal voltage, wind power plants and solar power plants must be capable of adjusting the low-voltage side transformer boost voltage with a deviation not exceeding ± 0.5 % of the rated voltage (compared to the set voltage value) whenever the generator unit's reactive power remains within the permissible operating range and complete the adjustment within 05 seconds.

"b) If the voltage at the point of interconnection is within ± 10% of the nominal voltage, wind power plants and solar power plants must be able to increase the low-side voltage of the step-up transformer with a deviation not exceeding ± 0.5% of the rated voltage (compared to the set voltage) whenever the reactive power of the generator unit remains within the permissible operating range and complete the adjustment within 05 seconds."

6. Wind power plants and solar power plants must maintain their operation and electricity generation corresponding to the voltage range at the point of interconnection with the grid at all times as follows:

 

b) Voltage from 0.3 pu to below 0.9 pu, the minimum maintenance time is calculated according to the following formula:

= 4 x U - 0.6

T_{Maximum Downhill Gradient} - T (seconds): Minimum generation time;

Where:

- U (pu): Actual voltage at the high-voltage side of the transformer boost of the power plant expressed in per unit (relative units);_{Maximum Downhill Gradient} c) Voltage from 0.9 pu to below 1.1 pu, wind power plants and solar power plants must maintain continuous operation to generate electricity;

- U (pu): The actual voltage at the point of interconnection expressed in per unit (relative unit).

đ) Voltage from 1.15 pu to below 1.2 pu, wind power plants and solar power plants must maintain operation to generate electricity for 0.5 seconds.

7. Phase imbalance, total harmonic distortion, and voltage flicker levels caused by wind power plants and solar power plants at the high-voltage side of the transformer boost must not exceed the values prescribed in Articles 7, 8, and 9 of this Circular.

8. Wind power plants and solar power plants must invest in equipment, control systems, and automatic systems to ensure stable, reliable, and secure connection with the Automatic Generation Control (AGC) system of the System Operator and Electricity Market to serve remote control of plant capacity according to dispatch orders from the System Operator and Electricity Market.

7. The phase imbalance, total harmonic distortion, and voltage flicker levels caused by wind power plants and solar power plants at the point of interconnection shall not exceed the values specified in Articles 7, 8, and 9 of this Circular.

8. Wind power plants and solar power plants must invest in equipment and control systems to ensure stable, reliable, and secure connection with the Automatic Generation Control (AGC) system of the System Operator and Electricity Market for remote control of plant capacity according to dispatch orders from the System Operator and Electricity Market.

13.Amend Point a Clause 2 Article 59 as follows:

“a) The secondary frequency regulation reserve and fast start reserve level shall be lower than the required level during normal operating conditions.”

14.Amend Point b Clause 3 Article 64 as follows:

“b) Shedding loads on individual transmission lines using automatic load shedding relays or shedding loads according to dispatch orders.”

15.Add Clause 2a after Clause 2 Article 69 as follows:

“2a. Provide information on primary energy sources (hydrological data for hydropower plants, coal-oil-fuel data for thermal power plants, meteorological observation data for wind and solar power plants), forecasted capacity and output of the plant, and transmit such data to the System Operator and Electricity Market.”

16.Amend Article 72 as follows:

“Article 72. Types of ancillary services

Ancillary services in the power system include:

1. Secondary frequency control.

2. Fast start reserve.

3. Voltage regulation.

4. Forced generation reserve to ensure power system security.

5. Black start capability.

17.Amend Article 73 as follows:

“Article 73. Technical requirements for ancillary services

1. Secondary frequency control: Generating units providing secondary frequency control services must be able to begin supplying frequency regulation capacity within 20 seconds after receiving the AGC signal from the System Operator and Electricity Market, and supply the full registered secondary frequency regulation capacity within 10 minutes and maintain that level for at least 15 minutes.

2. Fast start reserve: Generating units providing fast start reserve must be able to reach rated capacity within 25 minutes and maintain that level for at least 8 hours.

3. Voltage regulation: Generating units providing voltage regulation services must be able to change reactive power outside the adjustment range specified in Clause 2 Article 38 of this Circular, as required by the System Operator and Electricity Market.

4. Forced generation reserve to ensure power system security: Generating units providing forced generation reserve to ensure power system security must be able to reach rated capacity within 1 hour and maintain that level for at least 8 hours (excluding startup time).

5. Black start capability: Generating units providing black start services must be capable of self-starting from a cold state without requiring power from the national grid and must be able to connect and supply power to the grid after successful startup.

18.Amend Article 74 as follows:

        “Article 74: Determination of Demand and Operation of Ancillary Services hỗ trợ

1. The general principles for determining the demand for ancillary services include:

1. Ensuring the maintenance of reserve power and capacity levels in the power system to meet operational and security standards of the power system;
2. Ensuring minimum costs appropriate to the conditions and constraints within the national power system.
   2. The entity operating the power system and electricity market shall calculate and submit to Vietnam Electricity Corporation the demand for ancillary services for the national power system according to the process for determining demand and operating ancillary services issued by the Electricity Regulatory Authority.
   3. Before November 1st each year, Vietnam Electricity Corporation shall submit to the Electricity Regulatory Authority for approval the demand for ancillary services for the national power system for the following year to serve as the basis for planning the purchase and mobilization of ancillary services in the national power system operation plan for the following year.”

19.Amend Point b Clause 1 Article 85 as follows:

“b) When an imbalance occurs on the power system, the entity operating the power system and electricity market shall mobilize generating units to provide ancillary services and adjust the generation capacity of the generating units based on the order of mobilization of the generating units in the system to bring the power system back to balance and maintain the reserve level as prescribed.”

20.Supplement Clause 4 Article 90 as follows:

“4. Transmission entities shall report in accordance with Clause 1, Clause 2, and Clause 3 of this Article in writing via official mail and email.”

21.Supplement Clause 5 Article 91 as follows:

“5. Entities operating the power system and electricity market shall report in accordance with Clause 1, Clause 2, Clause 3, and Clause 4 of this Article in writing via official mail and email.”

Article 2.1. Amend and supplement Clause 1 Article 37 as follows:

1.Supplement Clause 3a after Clause 3 Article 3 as follows:

“3a. The rated capacity of the power plant is the total rated capacity of the generating units in the power plant under stable and normal operating conditions and published by the manufacturer according to the design of the generating unit. For solar power plants, the rated capacity of the solar power plant is the maximum alternating current power that can be generated by the plant calculated and announced in the approved technical design, consistent with the direct current power of the solar power plant as planned.”

2.Revised and supplemented Article 5 as follows:

“Article 5. Voltage

1. The nominal voltage levels in the distribution network include 110 kV, 35 kV, 22 kV, 15 kV, 10 kV, 06 kV, and 0.38 kV.

2. Permissible voltage deviation during normal operation on the distribution network:

a) The permissible voltage deviation at the busbar on the distribution network operated by the Distribution Entity compared to the nominal voltage is +10% and -05%;

b) The permissible voltage deviation at the point of connection compared to the nominal voltage is as follows:

- At the point of connection with the Customer using electricity is ±05%;

- At the point of connection with the power plant is +10% and -05%;

- In the case where the power plant and customer using electricity are connected to the same busbar, line on the distribution network, the voltage at the point of connection managed and operated by the Distribution Entity shall be determined to ensure compliance with the technical requirements for operating the distribution network and to ensure the quality of voltage for customers using electricity as prescribed.

3. For unstable networks after a fault, the permissible voltage deviation at the point of connection with the Customer using electricity directly affected by the fault may range from +5% to -10% compared to the nominal voltage.

4. During a system fault or recovery from a fault, the permissible voltage fluctuation on the distribution network may range from ±10% compared to the nominal voltage.

5. During the time of a fault, the voltage at the location of the fault and nearby areas may drop sharply to zero in the phase affected by the fault or increase beyond 110% of the nominal voltage in unaffected phases until the fault is eliminated.

6. Voltage fluctuations at the point of connection on the distribution network caused by variations in customer load or switching operations within the power plant shall not exceed 2.5% of the nominal voltage and must remain within the permissible voltage range specified in Clause 2 of this Article.

7. If the Customer using the distribution network requests higher voltage quality than stipulated in Clause 2 of this Article, the Customer using the distribution network may negotiate with the Distribution Entity or the Distribution and Retail Entity. The Distribution Entity or the Distribution and Retail Entity shall take the opinion of the Control Authority with control rights before reaching an agreement with the customer.”

3.Revised Article 6 as follows:

“ Article 6. Phase Balance

1. In normal working conditions, the reverse component of phase voltage shall not exceed three percent of the rated voltage for 110 kV voltage level or five percent of the rated voltage for medium and low voltage levels.

2. The reverse component of phase voltage on the distribution network may exceed the value specified in Clause 1 of this Article at certain times but must ensure that ninety-five percent of measured values over a measurement period of at least one week with a sampling frequency of ten minutes per time do not exceed the prescribed limit.

4. Amend and supplement Article 7 as follows:

“Article 7. Harmonic Waves

1. Harmonic Voltage Waves:

a) Total harmonic distortion (THD) is the ratio between the effective value of the harmonic voltage and the effective value of the fundamental voltage calculated according to the following formula:

 

Where:

- THD: Total harmonic distortion;

- V (VND/year): is the total investment capital allocated annually for the usable area of social housing for rent, ensuring the preservation of capital, calculated according to the following formula:_i: Effective value of the ith harmonic voltage and N is the highest order of harmonics to be evaluated;

- V (VND/year): is the total investment capital allocated annually for the usable area of social housing for rent, ensuring the preservation of capital, calculated according to the following formula:₁: Effective value of the fundamental voltage (50 Hz).

b) The maximum allowable harmonic wave distortion voltage on the distribution network is specified in Table 1a as follows:

Table 1a

Maximum Allowable Harmonic Wave Distortion Voltage

2. Harmonic Current Waves:

a) The total harmonic distortion current is the ratio between the effective value of the harmonic current wave and the effective value of the fundamental current at the load or maximum generation capacity calculated according to the following formula:

 

Where:

- TDD: Total harmonic distortion of current;

- I_i: Effective value of the ith harmonic current and N is the highest order of harmonics to be evaluated;

- I_L: Effective value of the fundamental current (50 Hz) at the load, maximum generation capacity (load, maximum generation capacity is the average of twelve load values corresponding to the twelve months prior, in cases where new connections or load values for the twelve months prior cannot be obtained, the load and maximum generation capacity during the entire measurement period will be used).

b) Power plants connected to the distribution network must ensure that they do not cause harmonic current wave distortion exceeding the values specified in Table 1b as follows:

Table 1b

Maximum Allowable Harmonic Current Wave Distortion for Power Plants

 

c) Electrical loads connected to the distribution network must ensure that they do not cause harmonic current wave distortion exceeding the values specified in Table 1c as follows:

Table 1c

Maximum Allowable Harmonic Current Wave Distortion for Electrical Loads

3. Peak distortions of harmonic waves on the distribution network may exceed the total harmonic distortion specified in Clauses 1 and 2 of this Article but must ensure that ninety-five percent of measured harmonic voltage and harmonic current values over a measurement period of at least one week with a sampling frequency of ten minutes per time do not exceed the prescribed limit.

5. Amend Article 8 as follows:

“Article 8. Voltage Fluctuations

1. Under normal operating conditions, the level of voltage fluctuations at all connection points shall not exceed the limits specified in Table 2 as follows:

Table 2

 Voltage Fluctuation Level

2. The short-term voltage fluctuation level (P_st) and long-term voltage flicker level (P_lt) is measured according to the current national standard. In cases where the measured value P_st st_lt is not included in the national standard, it is measured according to the current IEC standard published by the International Electrotechnical Commission.

6. Amend Article 9 as follows:

“Article 9. Short Circuit Current and Fault Clearance Time

1. The maximum allowable short circuit current on the distribution network and the maximum fault clearance time of the main protection are specified in Table 3 as follows:

Table 3

 Maximum Allowable Short Circuit Current and Maximum Fault Clearance Time

2. Switchgear on the distribution network must have sufficient capability to interrupt the maximum short circuit current through the switchgear for at least ten years from the expected date of commissioning and withstand this short circuit current for a minimum of one second.

3. For medium voltage lines with multiple sections where coordination between switchgear protections on the network is difficult, the fault clearance time of the main protection at some switching positions may exceed the value specified in Clause 1 of this Article but must be less than one second and must ensure safety for equipment and the network.

4. For electrical projects connected to the distribution system with short circuit current values at the connection point higher than the maximum allowable short circuit current values specified in Table 3, the project investors are responsible for applying measures to reduce the short circuit current at the connection point to below or equal to the maximum allowable short circuit current values specified in Table 3.

5. Distribution companies are responsible for informing customers about the maximum short circuit current value at the connection point to coordinate in investment and installation of equipment to ensure that the switchgear has sufficient capability to interrupt the maximum short circuit current at the connection point for at least ten years from the expected date of commissioning.

7. Add Article 17a after Article 17 as follows:

"Article 17a. Disclosure of Information on Power Supply Reliability, Energy Losses, and Customer Service Quality

1. Before the tenth day of each month, distribution companies are responsible for publishing on their electronic information websites the information on power supply reliability, energy losses, and customer service quality of the previous month.

2. Before January 31 of each year, distribution companies are responsible for publishing on their electronic information websites the information on power supply reliability, energy losses, and customer service quality of the previous year."

8. Amend Clause 2 of Article 28 as follows:

"2. If the connection plan proposed by the customer does not comply with the approved power development plan, the distribution company or the distribution and retail company is responsible for notifying the customer using the distribution network to adjust and supplement the plan according to regulations."

9. Amend Article 32 as follows:

“Article 32. Requirements for Harmonic Wave Distortion

The harmonic wave distortion at the point of connection to the distribution network must comply with the requirements stipulated in Article 7 of this Circular.”

10. Amend Clause 1 and Clause 2 of Article 38 as follows:

“1. Power plants connecting to the distribution network with a capacity of 10 MW or more (regardless of the connection voltage level) and 110 kV substations not yet connected to the Control Center shall be equipped with Gateway or RTU and establish two physically independent connections with the SCADA system of the Dispatching Authority having control rights. In cases where power plants or substations have multiple dispatching authorities with control rights, these dispatching authorities shall share information to facilitate coordinated operation of the power system.

2. Power plants connecting to the distribution network with a capacity of 10 MW or more, and 110 kV substations already connected to the Control Center shall be equipped with Gateway or RTU established with one connection to the SCADA system of the Dispatching Authority having control rights and two connections to the control system at the Control Center.”.

11. Amend and supplement Article 40 as follows:

“Article 40. Requirements for wind power plants and solar power plants connecting to the distribution network from medium voltage level and above

1. Wind power plants and solar power plants must be capable of maintaining operation to generate effective capacity under the following modes:

a) Free generation mode: Operating to generate maximum possible electrical capacity according to the primary energy source changes (wind or sun).

b) Generation capacity control mode:

Wind power plants and solar power plants must be able to limit generation capacity according to dispatch orders in the following cases:

- In case the primary energy source fluctuation is lower than the value specified in the dispatch order, generate the maximum possible capacity;

"- When the primary energy source fluctuates by or more than the limit value according to dispatch orders, the power output should be adjusted to the limit value according to dispatch orders with an error range of ± 01% of the rated power."

"2. Wind power plants and solar power plants must maintain power generation operation for a minimum time corresponding to the operational frequency ranges specified in Table 8 as follows:"

Table 8

Minimum Time to Maintain Operation to Generate Electricity of Wind Power Plants and Solar Power Plants

Corresponding to System Frequency Ranges System Frequency Range

"3. When the system frequency exceeds 50.5 Hz, wind power plants and solar power plants can reduce active power according to the relative slope of the static characteristic curve (droop characteristics) within the range of 2% to 10%. The setting value of the relative slope of the static characteristic curve is calculated and determined by the Control Center with control authority."

" 4. Wind power plants and solar power plants must be able to adjust reactive power according to the characteristics described in Point a and Point b of this Clause:"

"         a) If the power plant generates active power greater than or equal to 20% of the rated active power and the voltage at the point of interconnection is within ± 10% of the nominal voltage, the power plant must be able to continuously adjust reactive power within the power factor range of 0.95 (corresponding to the mode of generating reactive power) to 0.95 (corresponding to the mode of absorbing reactive power) at the point of interconnection with the rated power."

5. Voltage Control and Reactive Power Control Mode:

"5.  Voltage control mode and reactive power adjustment:"

- Voltage control mode according to set voltage value, voltage adjustment characteristic (voltage/reactive power relationship characteristic);

"- Voltage control mode according to the adjustable voltage characteristic (voltage/reactive power relationship characteristic);"

- Power factor control mode.

b) If the high-voltage side transformer boost voltage of the power plant is within ± 10 % of the nominal voltage, wind power plants and solar power plants must be capable of adjusting the low-voltage side transformer boost voltage with a deviation not exceeding ± 0.5 % of the rated voltage (compared to the set voltage value) whenever the generator unit's reactive power remains within the permissible operating range and complete the adjustment within 05 seconds.

b) If the voltage at the point of connection is within the range of ± 10% of the rated voltage, wind power plants and solar power plants must have the capability to adjust the voltage on the low-voltage side of the step-up transformer with a deviation not exceeding ± 0.5% of the rated voltage (relative to the set voltage value) whenever the reactive power output of the generator remains within the permissible operating range and complete within a time not exceeding five seconds.

6. Wind power plants and solar power plants must maintain their operation and electricity generation corresponding to the voltage range at the point of interconnection with the grid at all times as follows:

 

b) Voltage from 0.3 pu to below 0.9 pu, the minimum maintenance time is calculated according to the following formula:

= 4 x U - 0.6

T_{Maximum Downhill Gradient} - T (seconds): Minimum generation time;

Where:

- U (pu): Actual voltage at the high-voltage side of the transformer boost of the power plant expressed in per unit (relative units);_{Maximum Downhill Gradient} c) Voltage from 0.9 pu to below 1.1 pu, wind power plants and solar power plants must maintain continuous operation to generate electricity;

- U (pu): The actual voltage at the point of interconnection expressed in per unit (relative unit).

đ) Voltage from 1.15 pu to below 1.2 pu, wind power plants and solar power plants must maintain operation to generate electricity for 0.5 seconds.

7. Phase imbalance, total harmonic distortion, and voltage flicker levels caused by wind power plants and solar power plants at the high-voltage side of the transformer boost must not exceed the values prescribed in Articles 7, 8, and 9 of this Circular.

8. Wind power plants and solar power plants must invest in equipment, control systems, and automatic systems to ensure stable, reliable, and secure connection with the Automatic Generation Control (AGC) system of the System Operator and Electricity Market to serve remote control of plant capacity according to dispatch orders from the System Operator and Electricity Market.

7. Phase imbalance, total harmonic distortion, and voltage flicker levels caused by wind power plants and solar power plants at the point of connection shall not exceed the values prescribed in Articles 6, 7, and 8 of this Circular.

8. Wind power plants and solar power plants must invest in equipment and control systems to ensure stable, reliable, and secure connection with the Automatic Generation Control (AGC) system of the System Operator and Electricity Market for remote control of plant capacity according to dispatch orders from the System Operator and Electricity Market.

12. Amend and supplement Article 41 as follows:

“Article 41. Requirements for Solar Power Systems Connecting to the Distribution Network at Low Voltage Level

Solar power systems are permitted to connect to the low-voltage grid when meeting the following requirements:

1. Connection Capacity

a) The total installed capacity of solar power systems connecting to the low-voltage level of the low-voltage substation shall not exceed the installed capacity of that substation;

b) Solar power systems with a capacity of up to 20 kWp may be connected to a single-phase or three-phase grid according to agreement with the Distribution Company and Retail Electricity Company;

c) Solar power systems with a capacity of 20 kWp or more must be connected to a three-phase grid.

2. At any time while connected to the grid, solar power systems permitted to connect to the low-voltage grid must have the ability to maintain continuous operation during the minimum time corresponding to the frequency ranges specified in Table 5a as follows:

Table 5a

Minimum Time to Maintain Operation to Generate Electricity

System Frequency Range

3. When the system frequency exceeds 50.5 Hz, solar power systems with a capacity of 20 kWp or more must reduce their active power output according to the following formula:

Where:

- ΔP: The level of active power reduction (MW);

- P_{t s}: The active power output at the moment before the reduction (MW);

- f_{For power plants invested under the Build-Operate-Transfer (BOT) model, n is determined according to the operational period of the power plant stipulated in the BOT contract.}: The system frequency at the moment before the reduction (Hz).

4. Solar power systems must have the ability to maintain continuous operation within the voltage ranges at the point of connection as specified in Table 5b as follows: 

Table 5b

Minimum Time to Maintain Operation to Generate Electricity

corresponding to the voltage ranges at the point of connection

5. Solar power systems connected to the low-voltage grid shall not inject reactive power into the grid and operate in a mode consuming reactive power with a power factor (cosj) greater than 0.98.

6. Solar power systems connected to the low-voltage grid shall not cause a direct current intrusion into the distribution network exceeding 0.5% of the rated current at the point of connection.

7. Solar power systems connected to the low-voltage grid must comply with the regulations on voltage, phase balance, harmonic waves, voltage flicker, and grounding modes stipulated in Articles 5, 6, 7, 8, and 10 of this Circular.

8. Solar power systems must be equipped with protective devices ensuring the following requirements:

a) Automatically disconnect from the distribution network in case of internal system faults;

b) Automatically disconnect when a grid outage occurs and refrain from feeding power back into the grid during such outages;

c) Shall not reconnect to the grid automatically until the following conditions are met:

- The grid frequency remains within the range of 48Hz to 51Hz for a minimum of 60 seconds;

- All phases' voltages at the point of connection remain within the range of 85% to 110% of the rated voltage for a minimum of 60 seconds.

d) For solar power systems connected to a three-phase low-voltage grid, customers requesting connection must agree and unify protection system requirements with the Distribution Company but must minimally include protections specified in Points a, b, and c of this Clause, overvoltage, undervoltage, and frequency-based protections.”.

13. Amend Clause 2 of Article 42 as follows:

"2. Requirements for Control Center Connection"

a) Requirements for information system connection:

"- There shall be one data transmission link connecting to the information system of the Control Center with control authority. In cases where there are multiple Control Centers with control authority, the Control Centers shall be responsible for unifying the method of sharing information;"

- There must be two data transmission links (one working link, one backup link) connecting to the control and information system of the power plant, substation which is remotely controlled by the Control Center;

- Communication means serving dispatch operations, including direct communication, telephone, fax, and computer networks, must function properly.

b) Requirements for SCADA system connection:

- One connection to the SCADA system of the Dispatching Authority with control rights. In case there are multiple dispatching authorities with control rights, these authorities shall be responsible for sharing information;

- There must be two connections to the RTU/Gateway terminal, the control system of the power plant, substation, and switching equipment on the grid controlled remotely by the Control Center.

"c) The Control Center must be equipped with monitoring screens and connected to security surveillance cameras at power plants, substations, and circuit breakers on the grid, linking back to the Control Center."

14. Supplement Clause 3 of Article 43 as follows:

“3. In cases where, at the time of submitting the application for connection to the medium voltage and 110 kV levels, there is insufficient information and documentation as required under Clause 2 of this Article, the customer using the distribution network shall be responsible for agreeing with the Distribution Company on providing such information and documentation and clearly stating it in the connection agreement.”.

15. Amend the name of Article 44 as follows:

“Article 44. Procedures for negotiating grid connection for Customers using distribution networks who request grid connection at 110 kV voltage level and Customers owning power generation units who request grid connection to medium voltage networks.”.

16. Amend Point c Clause 2 Article 44 as follows:

“c) Solicit opinions from the Control Authority with control rights and related units regarding the impact of the grid connection on the power system, regional distribution network, requirements for connecting to the information system and the SCADA system of the Control Authority with control rights, requirements for relay protection, automation, and other technical requirements related to equipment at the connection point;”.

17. Amend Clause 2 Article 45 as follows:

“2. For customers using electricity with their own substation connected to the medium voltage network: Within two working days from receiving complete valid documents from the customer, the Distribution Unit or the Distribution and Retail Unit shall be responsible for site survey, negotiation, and signing the Grid Connection Agreement with customers having their own substations connected to the medium voltage network.”

18. Amend Clause 2 Article 51 as follows:

“2. For customers using electricity with their own substation connected to the medium voltage network: Within five working days from the date of receiving complete valid energization documents of customers with their own substations connected to the medium voltage network as stipulated in Article 48 of this Circular, the Distribution Unit shall be responsible for coordinating with the customer to complete trial energization, acceptance, and formal energization for customers requesting grid connection.”

19. Amend Clause 2, Clause 6 Article 52 as follows:

“2. In case both parties cannot reach an agreement on the results of inspection and the cause of violation, both parties must agree on the scope of inspection for the customer to hire an independent testing unit to conduct re-inspection and testing. If the inspection results of the independent testing unit show that the violations are caused by the customer's equipment and the customer does not accept the remediation solutions or fails to complete the remediation within the time committed to the Distribution Unit, the Distribution Unit has the right to disconnect the customer's equipment from the distribution network. The remediation period shall be agreed upon by both parties; if both parties cannot agree on the remediation period, disputes shall be resolved according to the regulations on power operation activities and electricity usage, and dispute resolution for power purchase and sale contracts issued by the Ministry of Industry and Trade.

6. During operation, if there is a risk of unsafe operation of the power system due to equipment owned by the customer at the connection point, the Distribution Unit must immediately notify the Control Authority with control rights and the Customer using the distribution network with their own substation to rectify and eliminate the risk of unsafe operation of the power system. In case the technical issue cannot be resolved or there is suspicion that the customer's equipment affects the distribution network negatively, the Distribution Unit has the right to require the customer to re-inspect and test the equipment under their management according to Clause 1 and Clause 2 of this Article.”

20. Supplement Point d Clause 2 Article 64 as follows:

“d) Power generation units are responsible for providing primary energy source information (hydrological information for hydropower plants, coal-oil-fuel information for thermal power plants, meteorological observation information for wind and solar power plants), forecasted capacity and output of the plant, and transmitting data to the Control Authority for system operation planning according to the National System Operation Planning Procedure issued by the Electricity Regulatory Authority.”

21. Amend Article 79 as follows:

“Article 79. Load Control ;

1. Electrical load control in the power system includes measures:

a) Stopping, reducing electricity supply levels;

b) Shedding electrical loads;

c) Adjusting electrical loads of customers participating in demand management programs.

2. The dispatch authority has the right to control and the Distribution Units implement load control according to the provisions of the National Power System Dispatch Procedures and the Content and Implementation Procedures for Demand Management Programs issued by the Ministry of Industry and Trade.

22. Amend Clause 1 of Article 82 as follows:

“1. Automatic load shedding is the shedding caused by frequency, voltage, and power level relays to selectively cut off loads in order to keep the power system operating within permissible limits and prevent widespread blackouts.”

23. Supplement Clause 4 of Article 99 as follows:

“4. The Electricity Corporation and Distribution Units shall report in accordance with Clauses 1, 2, and 3 of this Article in writing via official correspondence and email.”

Article 3.Repeal certain Articles and Clauses of Circular No. 25/2016/TT-BCT dated November 30, 2016, issued by the Minister of Industry and Trade on the transmission power system and Circular No. 39/2015/TT-BCT dated November 18, 2015, issued by the Minister of Industry and Trade on the distribution power system.

1. Repeal Clause 8, Clause 9, Clause 36 of Article 3 and Chapter IV of Circular No. 25/2016/TT-BCT dated November 30, 2016, issued by the Minister of Industry and Trade on the transmission power system.

2. Repeal Chapter IV and Article 101 of Circular No. 39/2015/TT-BCT dated November 18, 2015, issued by the Minister of Industry and Trade on the distribution power system.

Article 4.Effectiveness

1. This Circular takes effect from the year 03 the 01 year 2020.

2. During implementation, if any issues arise, relevant units shall reflect them to the Electricity Regulatory Authority for consideration and resolution within their jurisdiction or report to the Ministry of Industry and Trade for resolution./.