What are the methods for switching operations of station transformers?

Let's take an auxiliary power system with two station transformers as an example. When one station transformer needs to be out of service, there are two operation methods: non-interruptive power supply and instantaneous power interruption. Generally, the method of instantaneous power interruption on the low-voltage side is preferred.

The operation method for instantaneous power interruption on the low-voltage side is as follows:

• Open the 380V power incoming circuit breaker of the corresponding section of the auxiliary power for the station transformer to be out of service.
• Open the 380V incoming isolating switch of the station transformer to be out of service.
• Close the auxiliary power section circuit breaker.
• Open the bus isolating switch of the station transformer to be out of service.
• Open the high-voltage fuse of the station transformer to be out of service.

The operation method for non-interruptive power supply on the low-voltage side is as follows:

• Apply to the dispatching for paralleling the high-voltage side of the station transformers (for example, close the 35kV bus tie circuit breaker).
• Measure that the voltage difference between the busbars of section Ⅰ and section Ⅱ of the auxiliary power is qualified, then close the auxiliary power section circuit breaker to make section Ⅰ and section Ⅱ of the auxiliary power operate in parallel.
• Open the 380V power incoming circuit breaker of the corresponding section of the auxiliary power for the station transformer to be out of service.
• Open the 380V incoming isolating switch of the station transformer to be out of service.
• Open the bus isolating switch of the station transformer to be out of service.
• Open the high-voltage fuse of the station transformer to be out of service.