As shown in the illustrated alternator protection scheme diagram, what would cause the differential relay (DIFF) to trip the alternator circuit breaker? See illustration EL-0067.
ā¢ Current transformers (CTs) and what quantity they actually sense in the diagram ā¢ Purpose of a differential (DIFF) relay in generator protection ā¢ Difference between stator protection and field (rotor) protection on an alternator
ā¢ Look at where the DIFF relay gets its inputs in the illustration: are they coming from devices that measure current or voltage? ā¢ Ask yourself: what kind of fault inside a stator winding would create an imbalance that this relay is designed to detect? ā¢ Which part of the alternator windings are shown as being covered by the DIFF protection zone in the diagram?
ā¢ Verify which devices are feeding the DIFF relay ā are they labeled CT or PT? ā¢ Confirm that differential protection compares quantities at each end of the protected section and trips when there is a mismatch. ā¢ Check whether the diagram shows the DIFF relay connected to the stator phase windings or to the field (rotor) winding before choosing between the similar options.
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