A new digital relay to provide protection against unbalanced fault conditions

In this paper, a new digital relay monitoring the sinusoidal component of three phase instantaneous power is introduced for generator protection against unbalanced faults. It is designed such that the new relay can provide protection for all types of asymmetrical internal faults provided that it creates 1% or more unbalanced power based on the machine rated capacity. While the new relay produces high speed tripping for internal asymmetrical faults, it provides back-up protection for external unbalanced conditions.