PURPOSE:To monitor the working characteristic of a ratio-differential protective- relay directly without connecting an external instrumentation device to, by detecting difference current and phase difference always against current flowing into the relay. CONSTITUTION:A ratio differential protective-circuit 9 is worked by unbalanced current generated between current I1 and I2 from meter current-transformers 2, 4 when excess current flows to a transformer 1, and the output of trip signal is directed to breakers 3, 5. In a phase difference detecting circuit 12, by the count number of clock pulse T from a clock circuit 13 and pulse in the combined pulse signals i1, i2 of a pulse generating circuit, phase between the current I1 and I2 is detected. The input of the phase difference signal to a phase difference comparing circuit 14 is provided, and is displayed on a phase difference displaying circuit 16. In the same manner, in the current output I1 and I2 of the meter current-transformers 2, 4, difference current is detected by a difference current detector 11, and the input to a difference current comparing circuit 17 is provided, and is displayed by a difference current displaying circuit 19.
展开▼
