1.1 operation sequence of transformer shutdown and transmission

The operation sequence of main transformer shutdown and power transmission is as follows: firstly stop the load side and then the power supply side in case of power failure; secondly, supply the power supply side first and then the load side during power transmission

a. If the power supply side is shut down first, it may cause protection misoperation or refuse to operate in case of fault, thus prolonging the fault removal time and expanding the scope of power failure.

b. Power is transmitted step by step from the power supply side. In case of failure, it is easy to check according to the power transmission range.

c. When the bus voltage transformer at the load side is equipped with a low-frequency load shedding device and is not installed with a current blocking device, the power supply side will be shut down first when the power is cut off, which may cause the low-frequency load shedding device to malfunction due to the feedback of large-scale synchronous motor.

1.2 classification of transformer working state

The working state of transformer after operation is divided into four states, namely, operation state, hot standby state, cold standby state and maintenance state.

Operation state: the circuit breaker and disconnector of the transformer are in the closing position;

Hot standby state: the transformer only disconnects the circuit breaker and the disconnector is still in the closing position;

Cold standby state: the circuit breaker and disconnector of the transformer are in the non operating state at the opening position;

Maintenance status: all circuit breakers and disconnectors of the transformer have been disconnected, and the non operation state of safety technical measures such as installing ground wire, hanging signboard and setting temporary barrier has been completed.