40 Questions and Answers on Power Grid Dispatching

1. What is a dispatch instruction?

The so-called dispatching instruction refers to the decision that must be enforced issued by the superior duty dispatcher to the subordinate duty personnel of the dispatching system, including all normal operation, adjustment and accident handling instructions that the duty dispatcher is authorized to issue.

2. What are the principles for adjusting voltage as stipulated in the dispatching regulations?

(1) Voltage regulation method: within the voltage tolerance range, the supply voltage is adjusted so that the voltage value at peak load of the power grid is higher than the voltage value at valley load. (2) The reactive power regulation of the power grid should be based on the principles of stratification, zoning and local balance, avoiding the transmission of reactive power through long-distance lines or multi-stage transformers. (3) The accident reserve capacity in the reactive power source should be mainly reserved in the operating generators, phase regulators and reactive static compensation devices, so that when a voltage collapse accident occurs due to insufficient reactive power, the reactive output can be quickly increased to maintain the stable operation of the power grid.

3. What is the task of power system dispatching management?

The task of power system dispatching management is to organize, command, guide and coordinate the operation of the power system to ensure the realization of the following basic requirements:

(1) In accordance with the objective laws and relevant regulations of the power system, ensure the safe, stable, reliable and economical operation of the power system. (2) Adjust the power quality (frequency, voltage and harmonic components, etc.) indicators to meet the standards stipulated by the state. (3) Follow the principle of optimal resource allocation, give full play to the capacity of power generation, transmission and power supply equipment in the system, and meet the power needs of the economy, society and people's lives to the greatest extent. (4) In accordance with the principle of "openness, fairness and justice", and in accordance with relevant contracts or agreements, safeguard the legitimate rights and interests of all parties involved in power generation, power supply and power consumption.

4. What situations should the equipment under the jurisdiction of the local dispatch and power plant encounter? Should they be reported immediately to the provincial dispatch duty dispatcher?

(1) Damage to important power generation and supply equipment or major damage or theft. (2) Personal injury or death or power outage to important users. (3) Unplanned shutdown or fault tripping of 220 kV transformers or lines. (4) Fault tripping of any section of 220 kV busbar. (5) Power grid load loss (including accidental load shedding, load shedding and power restriction by safety automatic devices, and accidental line pulling). (6) Power oscillation and asynchronous oscillation in the regional power grid. (7) Mis-dispatch or mis-operation accidents within the dispatching jurisdiction. (8) Accidents of flooding of power plant buildings and collapse of dams at hydropower plants. (9) Severe weather or sudden weather changes are forecast.

5. What are the definitions of "line maintenance" and "busbar cold standby" in the dispatching regulations?

Line maintenance: Line switch and line high voltage side switch are opened. Line PT or CVT low voltage side is disconnected. And the grounding switch is closed at the line outlet (or the grounding wire is hung). Bus cold standby: It means that the bus side switches are all in the open position.

6. What are the management regulations for grounding switches?

(1) All grounding switches (ground wires) operated by the provincial dispatching duty dispatcher other than the line outlet switches under the jurisdiction of the provincial dispatching department shall be operated and managed by the provincial dispatching department. (2) Grounding switches (ground wires) within the line outlet switches shall be operated and managed by the station operation duty personnel. (3) The working ground wires installed on the line by maintenance personnel shall be operated and managed by maintenance personnel.

7. When should itemized instruction tickets be used? When should comprehensive instruction tickets be used?

For operations involving the coordination of two or more units or where the next operation can only be determined based on the impact on the power grid after the previous operation, item-by-item instructions must be used: for single or multiple operations involving only one unit that do not require the coordination of other units, comprehensive instructions can be used.

8. What are the main tasks of accident handling?

(1) Rapidly limit the development of the accident. Eliminate the root cause of the accident. Eliminate the threat to personal and equipment safety. Prevent the system from being damaged or disintegrated. (2) Use all possible means to maintain normal power supply to users. (3) Rapidly restore power to users who have lost power. In particular, priority should be given to restoring power to power plants, substations, and important users for security purposes. (4) Adjust the operation mode of the power grid to restore it to normal.

9. In what cases can power not be forced to be sent after the line trips?

(1) Cable lines (according to the fault recording distance measurement, the fault is within the cable range). (2) There is live work on the line. (3) Obvious signs of fault have been found. (4) Test run line. (5) The line transformer group switch is tripped. The transformer cannot be forced to operate. (6) Other lines that are clearly specified as not to be forced to operate.

10. When a line is overloaded, what measures should the dispatcher take to eliminate the overload?

(1) The power plants at the receiving end of the power grid increase their active and reactive outputs, and the power plants at the sending end appropriately reduce their active outputs. (2) Increase the operating voltages at the sending and receiving ends. (3) Change the way the power grid is connected so that the current is forced to be distributed. (4) Remove the load from the receiving area. (5) Limit power or shut down the power supply in the receiving area.

11. What is the operating range of the knife switch as stipulated in the dispatching regulations?

(1) When there is no ground fault in the power grid, close the voltage transformer. (2) When there is no lightning activity, close the lightning arrester. (3) Close the capacitive current of 220 kV and below busbars and equipment directly connected to the busbars, and close the 500 kV busbars that have been tested and allowed. (4) When there is no ground fault in the power grid, close the transformer neutral point grounding knife switch. (5) When the bypass knife switch connected in parallel with the switch is closed, the bypass current of the switch can be closed. (6) Close the busbar circulating current of 3/2 connection. Other knife switch operations shall be carried out according to the on-site regulations of the plant and station.

12. What is the repetition system and what is the recording system?

Repeating instruction system: Operation duty personnel who receive operation notices, operation instructions and listen to operation reports must repeat them. Operation instructions can only be executed if they are repeated correctly. The order is not considered to be executed until the person who gives the order receives the report that the person who directly receives the order has completed the order. Recording system: All dispatching operations, operation notices, and accident handling must be recorded; the on-duty dispatcher and on-site operation personnel must keep good operation records.

13. What are the main methods of voltage regulation?

(1) Change the excitation of generators and phase regulators, and start or stop capacitors and reactors. (2) Change the transformer tap. (3) Change the load distribution between power plants and within power plants. (4) Phase adjustment of pumped storage units. (5) Start or stop units. (6) Change the grid connection method, start or stop parallel transformers. (7) Limit the load in areas with too low voltage.

14. What issues should the on-duty dispatcher pay special attention to before filling out the operation instruction ticket and issuing the operation instruction?

(1) Impact on the operation mode, active power output, reactive power output, power flow distribution, frequency (ACE), voltage, power grid stability, communication and dispatching automation of the power grid. If necessary, online safety calculation and analysis of the power grid should be carried out and accidents should be anticipated. (2) When there is a significant impact on equipment and power supply quality outside the jurisdiction of the dispatcher, the relevant units should be notified in advance. (3) Correctness of the operation sequence, strictly prevent asynchronous parallel connection, load opening and closing of knife switches and closing of switches with ground wires, etc. (4) Adaptability of relay protection, safety automatic devices and transformer neutral point grounding methods. (5) Line "T" connection.

15. Under what circumstances can the on-duty dispatcher not fill out the operation instruction ticket, but should keep a record?

(1) Close or open a single switch or circuit breaker (including grounding circuit breaker). (2) Start or stop a set of protection and safety automatic devices. (3) Start or stop the unit AGC, AVC, PSS. (4) Start and stop the generator set. (5) Handle accidents.

16. What does the “operation instruction ticket system” include according to the regulations?

(1) For all normal operations, the on-duty dispatcher shall fill out the operation instruction ticket two hours before issuing the instruction, check the correctness of the operation steps against the main wiring diagram of the plant station, and inform the relevant units of the operation steps. The operation notice for the start-up of new equipment shall be issued 24 hours in advance. (2) The operation notice can be transmitted to the site by telephone, fax, network, etc. Both parties must repeat and verify the consistency of the content. (3) The site shall write out the switching operation ticket according to the steps of the dispatch notice, and make good preparations for the operation. (4) In drafting, reviewing, announcing and executing the operation instruction ticket, the on-duty dispatcher shall fully understand the content, arrangement, requirements and reasons for the change of operation mode in the maintenance ticket, clarify the purpose of the operation, determine the operation tasks, solicit opinions from the on-site operation when necessary, and make good preparations for accidents. (5) Fill out the operation ticket. The equipment double number and dispatch terminology must be used correctly; the content of the operation instruction ticket must be clear and unambiguous. The on-duty dispatcher must issue the operation instruction according to the operation instruction ticket that has been checked and correctly announced. (6) Before the new equipment is started and powered on. The on-duty dispatcher shall check with the on-site operation personnel to ensure that the wiring method, equipment name and number are correct. The dispatcher is not allowed to direct the operation on-site when starting up new equipment.