Distance protection

[apprenteng]

Hallo guys,
Just wondering which side of CTs for distance protection shoul be shorted. If the VTs used are located on the busbar should the shorted side be towards the bus for the relay to look forward?

 

[davidbeach]

Shorted side - do you mean the wye point? The wye point is typically on the side of the CT facing the protected zone.

 

[cvejicv]

It depends which dist. prot. u r using. Or should I say - according to manufact. specs. For Areva relays - it is defined by manufac., for Siemens relays - you can specify by software. ABB relays also - you can spec by means of software. So, just check the manual.

 

[veritas]

apprenteng

There are actually two different issues here. One is polarity and the other is commoning of the CT's. I have always seen CT's being starred (commoned) on the line side for distance relays. This is not to say that commoning on the busbar side will not work - it is all about a matter of convention and once decided upon - to stick to it.

With regards to CT polarity - one has to ensure that current flowing from the busbar into the feeder is seen as forward current by the relay. Again it is a matter of convetnion whether P1 or P2 faces the busbar. Let's suppose it is P1. Then s1 must be connected to the "positive" CT input (a CT input on the relay has a "positive" and a neutral). The CT neutral inputs are typically commoned and connected to the CT common.

Hope this helps.

Veritas