STAND-BY STAGE OF PROTECTION AGAINST SHORT-CIRCUITS Russian patent published in 1994 - IPC

FIELD: electrical engineering. SUBSTANCE: stand-by stage of protection against short-circuits has resistance relay, first element of operation delay. Resistance relay is provided with unit of change of setting of operation by voltage circuits. Novelty of stage lies in its fitting with supplementary element of enhanced automatic sensitivity, first and second logic AND gates, second element of operation delay, first logic OR gate. In case of short-circuit in zone determined by setting of relay 1 signal "1" emerges across its output and signal "0" across output of AND gate 10 which leads to triggering of element 8, to emergence of signal "0" at output of element 8 after its operation and of working signal "0" at output of OR gate 12. Triggering of element 13 is blocked by appearance of signal "0" at output of device 18 after operation of relay 1 and with emergence of working signal across output of filter 19 with fault to ground in protected network. In case of short- circuit in protected zone signals "0" will emerge across outputs of AND gate 15, elements 16, 14 when signal "1" emerges across output of unit 17 with its triggering if relay 1 operates due to short-circuit outside operation zone. It results in blocking of operation of protection stage with time delay of element 8 by second input of AND gate 10, in change of setting of relay 1 to bigger operational resistance, in improvement of its tunning-out from load currents and of current selectivity of its operation due to operation of units 2 and/or 3, 4, 5, 6, 7. In case of short-circuit in zone determined by new operational setting of relay 1 AND gate III operates, element 9 is triggered and after time delay of it signal emerges across output of OR gate 12. For provision of selective action of stand-by stage of protection after its selectivity was improved by operational resistance time of delay of element 9 is chosen from condition of its agreement with time of delay of stand-by stages pf preceding sections of protected network. Protection circuit returns to initial state after return of unit 17 and emergence of signal "0" at input 21 of element 14. Action of element 14 on input of one of elements of change of its characteristic can be sufficient depending on selected settings of relay 1 under condition of improved sensitivity and loading of protected connection for tuning away from these currents. EFFECT: increased speed of action, expanded protection zone. 9 cl, 9 dwg