MV/LV Transformer output

[mastergate]

I have a configuration with 3 MV/LV transformers: 2 working and 1 standby with an auto-transfer scheme(I attached a single line diagram)

http://files.engineering.com/getfile.aspx?folder=e062394a-d37e-480e-a04a-715eb5e58a41&file=SLD1.bmp

- In normal operation, buscouplers 1 and 2 are open
- Standby transformer can feed either busbar 1 or 2 (interlocks)
i.e When the standby transformer is working it feeds only one side, through buscoupler (CB).
- Distance between transformers and busbar : ~ 20m
- applicable code: IEC

I'm asking if in this case if an additionnal CB at the standby transformer output is necessary or not?


Please advise.

 

[inpran]

@BENSAID: I feel there is no requirement for an additional CB at the standby transformer output.

Case 1: Stand by transformer is feeding the left side via Buscoupler 1. In case there is a bus fault, tripping of buscoupler 1 breaker (and the incoming side breaker) will isolate the transformer. Same is the case with stand by transformer feeding the right side via buscoupler 2 breaker. In this case, tripping of buscoupler 2 breaker will isolate the transformer from the fault.

Case 2: In case there is a transformer fault, then tripping of buscoupler breakers 1/2 will isolate the fault from the healthy bus.

Bus-coupler breakers itself act as standby transformer breaker.

 

[ScottyUK]

Are there any loads on the centre bus section?


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If we learn from our mistakes I'm getting a great education!

 

[jghrist]

Are the incomers and bus couplers breakers or motor operated switches only?

 

[mastergate]

thanks for your replies.

ScottyUK : there is no load on the centre bus section

jghrist : breakers motor operated