Device for protecting an electric current transmission line, linking two electrical stations, from an abnormal variation in the characteristics of the current

摘要

The input signal (I) from the transmission line is transformed, by means of a filter (SF) and a voltage/frequency converter (VF) forming part of a transmitter (SD), into a signal transmitted by a frequency-modulated carrier wave (RW). A receiver (RC) receives this signal and shapes it in a shaping circuit (S1) whose output signal is demodulated by a frequency/voltage converter (FV). The signal thus obtained serves to actuate the protection relay (RY). An abnormal condition detection circuit (DET) connected to the output of the shaping circuit (S1) includes a frequency division circuit (S2), a multivibrator (MV), two logic multiplier circuits (A1, A2), a counter (CTR) with two directions of counting, a clock signal generating circuit (TG) and a logic decision circuit (LG). The output signal (LP) from the abnormal condition detection circuit (DET) controls the operation of the protection relay (RY) while enabling a distinction to be made between the normal and abnormal variations in the frequency of the carrier wave, so as to avoid the untimely activation of the protection relay (RY) in the event of a disturbance in the transmission of the radio carrier wave (RW). <IMAGE>