Relay protection circuit

  
Operating power protection devices, there is a DC power supply operating power and AC operation into two categories.
Relay protection circuit - schematic

Since the AC operating power with less investment, operation and maintenance is simple and convenient and reliable secondary circuit, so it is widely used in small factories. (1) Direct-action protection circuit uses off circuit breaker manually operated mechanism within the overcurrent release (trip coil) YR as a direct-acting overcurrent relay , a relay connected into a two-phase or two-phase two-relay device type. During normal operation, the current YR by far less than the operating current, and therefore no action. In a second phase short circuit when the circuit, YR movements to trip the circuit breaker QF, this mode of operation is simple by economic, but the protection of low sensitivity, in fact seldom used, as shown in FIG. (2) to shunt trip protection circuit shown in Figure b. Normal operation, the current relay KA normally closed contact will short-circuit trip coil YR stream. YR no current through the circuit breaker QF is not so trips. When the primary circuit phase short circuit, the current relay KA action, the normally closed contacts disconnect, short-circuit trip coil YR partial stream branch is removed, the so-called "de-streaming", so that the current transformer secondary current all through YR, QF causing the circuit breaker tripped, the so-called "de-shunt trip." Wiring this mode of operation is relatively simple, reliable and sensitive, but requires current relay KA breaking contacts can force big enough. GL15,16 on the market and other types of GL25,26 current relay, which contacts a large capacity, short break current unitary division of 150A, fully able to meet short circuit "to shunt trip" requirements. Therefore, this mode of operation to shunt trip power supply system in the factory now applied quite widely.




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