1. what is the power factor and whatis his losses
2. what is the working procedure of 51RNB AND 87 relay

Answer Posted / arun_sekar_1986

1.Power Factor is defined as the cosine angle between
voltage and current.
From Power triangle cosine angle is defined as the adjacent
by opposite side.
ie., cos angle=kW/kVA


2. 51-AC Time Overcurrent Relay is a relay with either a
definite or inverse time characteristic that functions
when the current in an ac circuit exceed a predetermined
value.

87-Differential Protective Relay is a protective relay that
functions on a percentage or phase angle or other
quantitative difference of two currents or of some other
electrical quantities.

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