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Reply To: Protection Riddle No.57 – Protection of two power transformer with one relay

#1756
AMIR KHASHAYAR

    During the test , the relay and restraint function have operated properly . Because the ratio of second harmonics to fundamental component has been measured correctly , and reley has distiguished the inrush current nature . But , during real case , it’s because the other relay has been under load and steady state current , the fundamental component is large and the ratio of second harmonics to fundamental component is low or lower than setting . Thus , the restraint function is not active