neutral protection from residual connection OR zigzag ct
neutral protection from residual connection OR zigzag ct
(OP)
we have a new installation: a 25 kV feeder from a Y-D txfo, with a zigzag txfo. what is the common practice to protect that feeder from phase/ground faults. should I use residual CT connection from the overcurrent protection, or sould I use a CT from the neutral point of the zigzag. the overcurrent protection and the neutral overcurrent protection are done on the same relay -> multilin MIF II.
thanks
JL
thanks
JL






RE: neutral protection from residual connection OR zigzag ct
RE: neutral protection from residual connection OR zigzag ct
RE: neutral protection from residual connection OR zigzag ct
Thus, you will be able to use either or both of the methods (residual current or neutral CT)for earth fault protection.
As dpc mentioned, it is better if you could have two earth fault protection elements, one connected to the residual input and the other neutral CT input.
However, checkout the relay manual, many relays don't have provision for accepting two inputs.
In such a case, the neutral CT input becomes obvious choice. The residual connection always leaves a possibility of spurious earth fault protection operation, due to differences in the phase CT characteristics.
RE: neutral protection from residual connection OR zigzag ct
You can use MIFII with residual connection for ground fault protection. MIFII are include only one CT input for 51N function.
CT on neutral side of zigzag xfr. is possible connect to transformer protection.
Of course you need provide some coordination between these functions.
Regards.
Slava