When to use synchronous shutdown and when to use pressureless shutdown?

When two different power supplies need to be connected in parallel, they need to be closed at the same time, such as the grid connection of generators. Usually, the closing of the load is pressureless closing.

If there is power supply on both sides of the switch, it is necessary to close the switch at the same time.

The so-called synchronization means that the voltage and frequency on both sides of the switch are equal and the phase sequence and phase are the same. Only at this time will there be no surge current when the switch is closed. If the switch is closed in different periods and the surge current is too large, the switch will trip automatically and the switch will fail.

Because it needs to be closed at the same time, and the same time is only a moment, which is fleeting, and it is difficult for manual operation to grasp this moment, so now the closing signal is automatically issued by the microcomputer at the same time, and no one needs to send it. If this shutdown signal is sent by a person, it is called synchronous shutdown.

Extended data:

The operation experience of power system shows that most overhead line faults are "instantaneous" faults. When these faults occur, the relay protection action switch is turned off, and the arc is naturally extinguished soon. At this time, the insulation strength of the fault point is restored, and the normal power supply can be restored by closing the circuit breaker.

The advantages of reclosing are obvious: firstly, it can improve the reliability of power supply, especially for single-circuit lines; Colleagues can also improve the stability of parallel operation of power systems; It can also correct and remedy the misoperation caused by the misoperation of the circuit breaker mechanism itself or relay protection.

The disadvantages of reclosing are: when it coincides with a permanent fault, the power system is impacted by another fault, which may reduce the stability of parallel operation; At the same time, the circuit breaker is required to cut off the short-circuit current twice in a short time, which requires high arc extinguishing ability of the short-circuit breaker.

Reclosing should not act:

1) The personnel on duty will open the circuit breaker manually or by operating the remote control device.

2) Manual shutdown.

There are two starting methods for reclosing: starting without corresponding position (stealing jump) and starting by tripping of the protector.