BIASED CIRCULATING CURRENT PROTECTION FOR THREE PHASE GENERATORS
The biased circulating relays are useful because they allow non-similarity between two sets of C.T.s. the restraining coil is inserted in series with one of the phases, while the operating coil is connected to the central tapping and the neutral pilot wire as in fig 4. Only one biased relay is shown for simplicity. The advantage of biased relay is that when generator carries through heavy fault current the current transformers will fail to balance each other and if ordinary relay is used the relay will trip: but biased relay does not operate at one definite current setting, its operation increases with the through current passing into operating coil
Written by John on March 19th, 2009 with
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