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Power Systems protection - how are modern relays connected

  1. Apr 15, 2013 #1
    Hi, I have a PS&P assignment where we are designing the protection for a substation - its an overview of the type of protection etc.

    I have a star delta 42MVA (cyclic rating) 132:22 kv TX...

    I've done some research and want to use an SEL487E relay.

    Since this is star delta (star nueltral is floating) I have a 30deg phase shift. This is traditionally accounted for by configuring the CT's in delta on the HV side and star on the LV side, yielding a net phase shift of zero.... This is fine for electromechanical relays and I get why it's done.

    BUT - I think that since I have an electronic relay I can just have 6 completely independent CT's on each incoming/outgoing phase and feed a current to the relay.CT's are not connected at all - no differential element etc. Obviously I would account for the ratio in the TX by choosing CT ratios and tell the relay the setup, expected phase shift etc.

    -----Is this setup done in practice or would the CT's still be configured opposite to the transformer wingdings??
    ------If this is done, can I use the same CT's for over-current protection????

  2. jcsd
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