GB1300453A - Electrical fault protection system and circuitry - Google Patents

Abstract

1300453 Protective arrangements NOVOCHERKASSKY ORDENA TRUDOVOGO KRASNOGO ZNAMENI POLITEKHNICHESKY INSTITUT IMENI SERGO ORDZHONIKIDZE 5 Nov 1970 52616/70 Heading H2K In a differential protective system in which the currents to and from a protected alternating current arrangement 1 are summed to energize a differential starting element 5. the sum of these currents during the times they have one polarity and the sum of these currents during the times they have the opposite polarity are applied to relays 7 and 8 respectively to produce output signals when the sums exceed a predetermined value. When under external fault conditions the two output signals are simultaneously present during the first cycle of the fault, they cause a signal to inhibit the action of the element 5. In the arrangement shown, under external fault conditions, the output signals from the relays 7 and 8 are applied to an AND gate 11 which provides a signal to an INHIBIT gate 15. At the same time an OR gate 12 supplies a signal to a slow-to-reset relay 13 which supplies output signals to a slow-to-operate relay 14 and a NOR gate 16. The INHIBIT gate 15 supplies a signal to a memory circuit 17 until the operation of the relay 14 causes the gate 15 to cease to pass the output signal from the AND gate 11. The memory circuit 17 provides a signal to cause an INHIBIT gate 6 to block any output from the element 5. The NOR gate 16 provides a signal to restore the memory circuit 17 when the fault is cleared. In the event of an internal fault, the AND gate 11 does not initially provide an output signal, the fault currents all having the same initial polarity. Hence there is no output signal from the gate 11 to pass through the gate 15 to the memory circuit 17 before the relay 14 operates to cause the gate 15 to assume its inhibiting action. So the memory circuit 17 provides no signal to the gate 6 and the signal from the differential element 5 passes through the gate 6 to effect the disconnection of the protected arrangement.