are there any transformer need 3 REF protection?

[dav08a]

Dear all,

The Areva P643 has 3 REF protection function. However, in the real world, would there be any transformer need 3 REF protection?

i normally see Yy0d11 transformer (which will need 2 REF protection function), but i never see Yyy transformer.

therefore, is it safe to say only 2 REF function will be used (for a single transformer)?

 

[inpran]

dav08a,
Areva's P64x relays are differential protection relay in general. As you put it, even I haven't come across an YNynyn transformer yet. In which case what you say would be right.

But were the relay had to be used for protecting, for instance, a Reactor provided with bushing CT on either side of a phase used for REF protection, then you would need 3 functions, one for each phase.

 

[slavag]

Why not?
Ydd ( 3 winding transformer) transformer with two zig-zag transformers on the delta sides.
or Yyd, someting like to 110/35/6.6kV.

 

[Marmite]

When a 3 winding transformer is just used to feed loads you can get away with 2 sets of CT inputs, but if there is a fault current infeed from another source then there is a possibility of circulating current between the two sets of paralleled LV CT's without producing any bias current. It may also be advantageous to detect which winding has tripped the REF as you may be able to disconnect the single cores between the Tx and the switchgear (which are the most likely cause of the trip)and do a partial restoration.
Regards
Marmite

 

[dav08a]

thank you all. it is very helpful.

 

[YERUK123]

Hi ,

I have come across a power Transformer where all the windings have REF Prtn and the Vector Group of the Transformer Being YNyn0yn0d11 . This Transformer is used in one of the Water pumping Station.

Regards