The measurement of the rate of change of fquency provides two
improvements in frequency relaying. The fist improvement is the
reduction of the dynamic error in the pick-up time of the relay. The
second is the improvement in the effectiveness of the underfrequency
relays. Power su ly continuity in a power system can also be improved
by using relays 9t a t also estimate the rate of change of frequency and
restore generation load balance as quickly as possible.