connecting protection relay of power transformer
connecting protection relay of power transformer
(OP)
Dear all experts
we are swapping a step-up power transformer of (35MVA 11kv/20kv) that has been defected due to low winding Insulation , but we are facing:
The old Transformer is provided with CT in side the primary winding of the Oil Transformer connected
to relay 87T (SEPAM 2000) but the new swapped transformer isn't provided with this internal C.T.
Proposal to solve the problem :
To connect the primary input of 87T relay( Sepam 2000) to the generator out put CTs in series with generator protection 87G(ALOSTOM) , in this way two protection relays (SEPAM & ALOSTOM) are connecting in series from on CT
what do you think about this connection ?
How can we make functional test (current injection) before charge the Transformer ?
we are swapping a step-up power transformer of (35MVA 11kv/20kv) that has been defected due to low winding Insulation , but we are facing:
The old Transformer is provided with CT in side the primary winding of the Oil Transformer connected
to relay 87T (SEPAM 2000) but the new swapped transformer isn't provided with this internal C.T.
Proposal to solve the problem :
To connect the primary input of 87T relay( Sepam 2000) to the generator out put CTs in series with generator protection 87G(ALOSTOM) , in this way two protection relays (SEPAM & ALOSTOM) are connecting in series from on CT
what do you think about this connection ?
How can we make functional test (current injection) before charge the Transformer ?






RE: connecting protection relay of power transformer
By "primary" do you mean high-side or low-side. Primary and secondary can be ambiguous but high- and low-sides aren't.
If the existing generator protection uses CTs at the generator and the existing transformer protection uses CTs at the transformer, how do you protect the bus between the generator and the transformer?
If your generator and transformer protection both have the CTs wired "right", the currents through the generator relay are 180 degrees out of phase from those going through the transformer relay. Can the transformer relay compensate for reversed polarity?
RE: connecting protection relay of power transformer
RE: connecting protection relay of power transformer
-Mr davidbeach 1) you may not noticed that I mentioned it's a step up transformer ,it is clear what I meant by "primary"
2) why the current at 87G and 87T will have 180 degree out of face?
Emad Shaaban
Tripoli Libya
RE: connecting protection relay of power transformer
Odds on, the CTs for the 87G are grounded toward the generator and the CTs for the 87T are grounded toward the transformer. There's the 180 degree phase shift.
RE: connecting protection relay of power transformer
I tried to get what you've meant by " ground toward Gen & ground toward Trans"
can you give me more clarification
I attached to sketches of the new and old CT connection .
first sketch
Emad Shaaban
Tripoli Libya
RE: connecting protection relay of power transformer
Emad Shaaban
Tripoli Libya
RE: connecting protection relay of power transformer
In your first sketch, is there really that unprotected gap? Or does the 87G actually use CTs on the transformer and the 87T use CTs on the generator so that the zones overlap?