GB1302303A - - Google Patents

Abstract

1302303 Protective arrangements COMPAGNIE DES COMPTEURS 3 Nov 1970 [3 Nov 1969] 52200/70 Heading H2K Apparatus for responding to an opencircuit condition of one or more of a plurality of fuses Fa ... Fc connected in respective phases a ... c of an A.C. supply, comprises signal producing means for producing continuous logic signals which are functions of a voltage and/or a current in each phase and logic means responsive to at least one of the logic signals for each phase and the complement of at least one other of the logic signals for producing an output signal indicative of the open circuit condition. In the arrangement shown, the signal producing means are transformers TRA ... TRC, full-wave rectifiers P A ... P C and converters C A ... C C which produce rectangular waveforms of limited amplitude, the waveforms being filtered so as to obtain continuous logic quantities. The logic means comprise inverters R A ... R B connected to an OR gate OU 1 , a second OR gate OV 2 being connected directly to the converters C A ... C C . The OR-gate OU 2 provides a signal to an AND gate ET when any of the transformers TR is energized and the OR-gate OU 1 provides a signal to the AND gate ET when one or more of the transformers TR ceases to be energized, the AND gate then providing a signal to a relay RE which opens its contacts re 1 to deenergize the coil D of a main switch. In Fig. 3 (not shown) detection of an open circuit fuse is effected by comparing logic signals derived from two currents of different phases, the outputs of three AND gates being connected to a single OR-gate. In either of these arrangements the signals may be derived from voltages instead of currents. In further arrangements, Figs. 4 and 5 (not shown), logic signals derived from currents are compared with those derived from the voltages.