MBCH12 Relay

[khadisa]

Please, I want to wire an MBCH12 (ALSTOM) differential relay to protect a 132/11KV, 15MVA, Yy0 transformer. It is to replace an old relay.
In the present scheme the primary and secondary CTs are wired in star while interposing CTs on both primary and secondary are wired in star/delta.
The literature show terminal 27 of the relay connected to neutral. In the present scheme, no neutral goes to the relay. What do I connect to the terminal? Can I leave the terminal unconnected?

 

[davidbeach]

Why not just eliminate the interposing CTs and directly connect the main CTs to the relay?

 

[khadisa]

I have an REF relay in the primary circuit and a floating delta on both primary and secondary ICTs is used for zero sequence filtering.

 

[a430]

Hello davidbeach.

What i understand is that there is a terminal to be connected to a star point, that is terminal 27, and even if he eliminated the interpossing CTS that terminal will be left unconnected since inputs to the relay will both be in delta.

 

[khadisa]

Your understanding is wrong a430.
The main CTs on primary and secondary are wired in star. So without the ICTs I have something to connect to terminal 27.

 

[unclebob]

From what I see in my books, when you have to protect a series reactor, neutrals are bounded together and wired to terminal 27. All three phases 27 are then jumped together.
Primary and secondary CT's are wired in Y.

I guess you can rewire all your CT's in Y to gain neutral wires for terminal 27. No ICT used. I would try that to see
if it works for a xfo.

 

[a430]

Hello Khadisa/Unclebob.

If i understand what you are trying to say, your transformer is star/star and therefore your CTs should be in delta both sides.

 

[unclebob]

Yes. But terminal 27 would'nt be used (no neutral wires).
Since you have no 30 degree shift to account for, the CT's can be both Y-Y or D-D. Use of Y-Y gives neutral wires for terminal 27.

 

[davidbeach]

I am not familiar with the particular Alstom relay given in the original post, but any decent numeric transformer differential relay can do all of the phase shifting and zero sequence filtering in the relay. Using a decent numeric differential relay, you can have all of your input CTs in wye without regard to the transformer winding configurations. The relays can handle other combinations also, but the event reporting works best, or at least provides the most information, when the CTs are connected in wye.

 

[khadisa]

Thanks to everybody, I have got a drawing on how to connect the relay from the manufacturers (AREVA).

 

[ScottyUK]

Care to share it for the benefit of others?


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I don't suffer from insanity. I enjoy it...

 

[khadisa]

I am sorry for the omission.

The MBCH12 relay come in single phase units. So, the terminals 27 of the three relays are linked and nothing is connected to them.

 

[ScottyUK]

Thanks khadisa.



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I don't suffer from insanity. I enjoy it...