Figure 1 shows the typical wiring diagram of the distributed power supply connected to the 10 (6) kV-35 kV distribution network via a dedicated line. The user’s high-voltage main incoming circuit breaker (2DL in Figure 1) should be equipped with staged (directional) overcurrent protection and fault decoupling. If the access to the power grid requires full-line quick-action protection, fiber-optic longitudinal differential protection should be configured.
The distributed power feeder circuit breaker (3DL in Figure 1) of the user’s high-voltage bus can be configured with staged (directional) overcurrent protection and reclosing.
The protection action configured at the user’s high-voltage main incoming circuit breaker (2DL in Figure 1) is to trip the 3DL or 2DL circuit breaker in Figure 1, the protection action configured at the distributed power feeder circuit breaker (3DL in Figure 1) of the user’s high-voltage busbar is to trip the 3DL circuit breaker in Figure 1 to cut off all power points when a fault occurs. When there are multiple distributed power supply lines, the protection configured at the user’s high-voltage main incoming circuit breaker (2DL in Figure 1) can trip each distributed power supply feeder switch at the same time.
The protection configured at the user’s high-voltage mains incoming circuit breaker (2DL in Figure 1) should meet the following requirements;
(1) When the user’s electricity load is greater than the installed capacity of the distributed power supply, the current protection should be blocked in the direction, and the positive direction of the protection action should point to the line. The current setting of the converter-type distributed power supply can be set according to 110%~120% of the rated current of the distributed power supply.
(2) Requirements that should be met for fault decoupling:
① Fault delisting includes low/overvoltage protection, low/overfrequency protection, etc.;
② The action time should be less than the action time of the public substation fault disconnection, and there is a certain level difference;
③ The action time should avoid the clearance time of other interval faults on the system and the user bus, and at the same time consider meeting the requirements of the reclosing time of the system.
The protection configured under the distributed power feeder circuit breaker (3DL in Figure 1) of the user’s high-voltage bus shall meet the following requirements:
(1) The current protection should meet the protection requirements of the public substation feeder circuit breaker (1DL in Figure 1), set according to the direction of the distributed power source, and can be blocked by the direction if necessary;
(2) Whether the distributed power supply feeder circuit breaker (3DL in Figure 1) of the user’s high-voltage bus is coincident after tripping can be determined according to the user’s needs. If reclosing is used, it can be checked for no-voltage or synchronous reclosing. Its delay should be coordinated with the reclosing at the feeder circuit breaker (1DL in Figure 1) of the public substation, and it should have a post-acceleration function.