Can someone help me with the control circuit of this situation; there are two tranformers each supplying half of the 400V bus bar with a bus coupler. Under normal operation all transformers are on load and the tie circuit breaker is open. The aim is to develop a circuit that will automatically close the tie circuit breaker once we lose one of the transformers. The operation of the circuit breakers is always two out three.

 

Please post a schematic of what you have now. You probably could use a relay to switch it.

 

Can someone help me with the control circuit of this situation; there are two tranformers each supplying half of the 400V bus bar with a bus coupler. Under normal operation all transformers are on load and the tie circuit breaker is open. The aim is to develop a circuit that will automatically close the tie circuit breaker once we lose one of the transformers. The operation of the circuit breakers is always two out three.

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The power circuit schematic is attached. Thanx.

 

I don´t see the mode of failure very clearly. Losing one of the transformers means that you lose the 6.6kV input but the xformer is still working, or that the transformer itself stops working for example because of a breaker tripping?

Now that I think about it it probably doesn´t matter. The course of action should be like this: Voltage before CB1 fails OR voltage before CB2 fails, then turn off CB1 or 2 and turn on CB3. If voltage recovers, wait some time and then open CB3 and close CB1 or 2.
The action of the breakers will need to be carefully timed, so that you don´t get a short between the two transformers, which they most likely will not be happy about.

 

Thanks a lot, i will consider a note of timing the breakers very seriously.