40 Questions and Answers on Power Grid Dispatching

29. What is the general phenomenon of asynchronous oscillation?

(1) The current, voltage, and power meters of generators, transformers, and interconnection lines swing violently and periodically, with the voltage fluctuation at the center of the oscillation being the largest, and periodically decreasing or approaching zero. (2) The interconnection lines between power plants that have lost synchronization swing back and forth in power transmission. Although there is electrical connection, the frequency at the sending end increases, the frequency at the receiving end decreases, and there is swinging. (3) The generator emits a rhythmic sound, and the active and reactive power changes in sync, the voltage fluctuates greatly, the lights flicker, and some loads may be shed.

30. What is the general phenomenon of synchronous oscillation in power system?

(1) The current and power meter of the generator and the tie line change periodically, but the range of change is small, the generator beeps less, and the active power of the generator does not exceed zero. (2) The voltage fluctuations at the generator terminal and the grid are small, and there is no obvious local reduction. (3) The frequency of the generator and the grid does not change much, and the frequency of the entire grid decreases or increases synchronously.

31. Dispatching regulations stipulate that in the event of an accident, what should be done when the communication between the local dispatching, power plant, substation (or monitoring center) and the provincial dispatching is interrupted?

(1) Matters that do not require waiting for dispatching instructions according to regulations can be handled quickly on site. (2) After a line trips due to a fault, the switch that is put into the no-pressure reclosing switch does not reclose. When it is determined that there is no voltage on the line, it can be forced to reclose once immediately. (3) After the main transformer switch, bus tie switch, and line switch trip, as long as there is voltage on both sides of the switch, they can automatically restore synchronization and parallel connection. (4) After communication is restored, the relevant plant and station operation duty personnel should immediately report the handling situation during the communication interruption to the duty dispatcher to whom they belong. In the event of an accident, when the power plant, substation (or monitoring center) loses communication with the provincial dispatching station, the on-site operation duty personnel should take the initiative to contact the local dispatching station to which they belong. The local dispatching station can act on behalf of the provincial dispatching station and direct the handling.

32. What are the dispatching regulations' requirements for the protection of direct distribution lines (including charging standby lines) and the operation of reclosing switches?

(1) The longitudinal protection and backup protection on the receiving side of the direct distribution line (the side where the charging standby line is disconnected) are disabled. The switch non-full-phase protection is tripped. If the longitudinal protection on the power supply side is enabled, the longitudinal protection on the receiving side is enabled in signal mode. (2) The three-phase no-voltage reclosing switch is enabled on the power supply side of the direct distribution line, and the reclosing switch on the receiving side is disabled. The reclosing switches on both sides of the charging standby line are disabled. (3) The pressure plate for the start failure protection on the receiving side of the direct distribution line (the side where the charging standby line is disconnected) is disabled. Generally, it is not allowed to have a line with empty charging busbar.

33. What are the requirements of the dispatching regulations for each region to formulate low-frequency and low-voltage load reduction plans and implementation measures?

Each region should formulate a low-frequency, low-voltage load reduction plan and implementation measures based on the low-frequency, low-voltage load reduction plan of the power grid and the annual power grid load situation in the region, and submit it to the provincial dispatching department for review. The plan should include: (1) The installation location of the device, the name of the cut-off line and the number of loads (the cut-off load is not allowed to overlap, standby or automatically transfer). (2) The total number of loads cut in each round. (3) Those who need to send a safety power supply should specify the number of loads.

34. What is adjustable output? What is load reserve capacity?

Adjustable output - the actual output that can be achieved by operating and standby equipment. Including maximum output and minimum technical output. Load reserve capacity - the difference between the maximum adjustable output of the operating equipment and the total power consumption.

35. What is the definition of unit leading phase operation? What is spinning reserve?

Leading phase operation - the generator or phase regulator stator current phase leads its voltage phase. The generator absorbs system reactive power (power factor leading). Spinning reserve, specifically refers to the grid-connected operation with only partial load, which can increase output to rated capacity at any time.

36. What is a black start? What are the black start solutions?

Black start means that after the entire system stops operating due to a fault, the system starts up the units with self-starting capability or obtains power from the external power grid. The units without self-starting capability are started up to gradually expand the scope of system recovery and eventually achieve the recovery of the entire system. Black start plans include research plans, test plans and dispatching operation plans.

37. What are the definitions of circuit breakers and disconnectors?

Circuit breakers are switchgear that can close, carry and interrupt the normal current of the operating circuit, and can also close, carry and interrupt the specified overload current (including short-circuit current) within a specified time. Isolating switch - When in the open position, the contacts have an insulation distance that meets the specified requirements and an obvious disconnection mark; when in the closed position, it can carry the current under normal circuit conditions and the current under abnormal conditions (such as short circuit) within a specified time.

38. How should the allocation of components on the busbars be considered in double busbar operation?

(1) The principle of small busbar current. (2) The principle of each busbar having a power supply. (3) The principle of considering the distribution of neutral points. (4) The principle of separate layout of lines with the same geographical direction. (5) The principle of proper consideration of equipment numbering.

39. What is the meaning of power system stability? What are the categories?

From a broad perspective, the stability of the power system can be divided into: (1) the stability problem of synchronous operation of generators (depending on the size of the disturbance to which the power system is subjected, it can be divided into three categories: static stability, transient stability, and dynamic stability); (2) the voltage stability problem caused by insufficient reactive power in the power system; and the frequency stability problem caused by insufficient active power in the power system.

40. Please write down the principles for dividing the equipment under the jurisdiction of Shandong Power Grid Provincial Dispatching Office.

In the Shandong power system, the following equipment, except for those under the jurisdiction of the superior dispatching organization, is under the jurisdiction of the provincial dispatching organization: (1) Generators with a single unit capacity of 50Mw or more. (2) Main equipment of major power plants (500 kV transformers and busbars, 220 kV step-up transformers with unit connection, 220 kV busbars with single units of 600 Mw or more, important 220 kV busbars with unit capacity of 600 Mw or more, and reactive power compensation equipment). (3) Grid-connected wind farms with an installed capacity of more than 10 Mw. (4) Main equipment of 500 kV substations (main transformers, busbars, and reactive power compensation equipment). (5) 220 kV busbars with stability problems in 220 kV substations and important 220 kV busbars with outgoing lines of 6 or more. (6) 500 kV lines. 220 kV lines across regions (power supply areas). (7) Relay protection, safety automatic devices and related automation and communication equipment configured for equipment under the jurisdiction of the provincial dispatching system; unit grid-related protection and related regulation and control systems. Among the equipment under the jurisdiction of the provincial dispatching system, equipment whose operating status changes have a significant impact on the safe and stable operation and relay protection coordination of the North China main grid or adjacent grids is listed as grid dispatching management equipment. The grid dispatching management equipment within the Shandong Power System is determined by the grid dispatching regulations. Among the equipment under the jurisdiction of the provincial dispatching system, power generation and transmission equipment whose status changes have little impact on the system operation mode can be entrusted to local dispatching for management. For example: some power plant equipment, wind farms, and some cross-regional 220kV lines.