Single phase tripping
Single phase tripping
(OP)
In a delta-wye 33/11kV system, what will be the imbalance current detected by the 11kV substation relay in the event one of the downstream protective device operated on single-pole tripping ? Say the load current is 60A, is the relay seeing 40A (i.e.{60+60}/3) when one phase is out, and 20A (i.e. 60/3) when two phases is out as imbalance current ? Will the imbalance current treated as "earth fault" current by the relay ? Any simple formulae to calculate ? Thanks.






RE: Single phase tripping
Alan
----
"It's always fun to do the impossible." - Walt Disney
RE: Single phase tripping
If the earth fault relaying operates on residual current, it will not distinguish unbalance from an earth fault. If the relaying uses a core-balance CT connection around all circuit conductors, then it will not be affected by the unbalance.
RE: Single phase tripping
May I suggest reading "Negative-Sequence Overcurrent Element Application and Coordination in Distribution Protection" by Ed Schweitzer. This is freely downloadable at selinc.com/literature
RE: Single phase tripping