05 operational policies of the power system in Vietnam

Operational policies of the power system in Vietnam

(1) The power system is considered to be under normal operational policies when it meets the following conditions:

- Generation capacity and load are in a balanced state;

- There is no implementation of load shedding due to electrical faults;

- The load level of transmission lines and transformers in high voltage, ultra-high voltage grids are all below 90% of the rated value;

- Power plants and other electrical equipment operate within allowable parameter ranges;

- The system frequency is within the allowable range for normal operational policies as stipulated in Article 4 of this Circular;

- Voltage at nodes in high voltage, ultra-high voltage grids is within the allowable range as stipulated in Article 6 of this Circular for normal operational policies;

- The reserve sources of the national power system are in a ready state to ensure the maintenance of frequency and voltage of the national power system within the normal operational frequency and voltage range; automatic equipment operates within the allowable range so that when unusual incidents occur, load shedding due to electrical faults is not required.

(2) The power system operates under warning policies when one of the following conditions arises or exists:

- Secondary frequency reserve and quick start reserve levels are lower than the requirements for normal operational policies;

- The load level of transmission lines and transformers in high voltage, ultra-high voltage grids is from 90% upward but does not exceed the rated value;

- Voltage at any node in the high voltage, ultra-high voltage grid is outside the allowable range under normal operational policies but within the allowable voltage range for a single incident in the power system as stipulated in Article 6 of this Circular;

- There is a possibility of natural disasters or unusual weather conditions that may affect the security of electricity supply;

- There is a possibility of security or defense issues threatening the ability to ensure electricity supply.

(3) The power system operates under emergency policies when one of the following conditions arises or exists:

- The system frequency is outside the normal operational policy's allowable range but within the frequency range allowed for a single incident in the power system as stipulated in Article 4 of this Circular;

- Voltage at any node in the high voltage, ultra-high voltage grid is outside the allowable voltage range for a single incident scenario as stipulated in Article 6 of this Circular;

- The load level of any electrical equipment in the high voltage, ultra-high voltage grid or any electrically connected equipment surpasses the rated value but under 110% of the rated value, where such an overload-related equipment failure could lead to extremely urgent operational policies.

(4) The power system operates under extremely urgent policies when one of the following conditions arises or exists:

- The system frequency is outside the frequency range allowed for a single incident in the power system as stipulated in Article 4 of this Circular, or after all reserve sources are mobilized, the frequency continues to tend to fall below 49.5Hz;

- The load level of any equipment in the high voltage, ultra-high voltage grid or electrically connected equipment is from 110% of the rated value or higher, where such an overload-related equipment failure could lead to partial disintegration of the power system;

- Voltage at any node in the high voltage, ultra-high voltage grid drops low, activating the low voltage load-shedding relay; the transmission grid voltage is more than 10% below the nominal voltage level, or the system's reactive power reserve is insufficient, and the voltage in the high voltage, ultra-high voltage grid tends to drop below the threshold with the risk of voltage collapse in the system.

(5) The power system operates under restoration policies when generators, high voltage, ultra-high voltage grids, and electrical loads have been reconnected and synchronized to return to a normal working status.

Circular 05/2025/TT-BCT is effective from the date of signing.

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