| 摘要 |
1455280 Protective arrangements GENERAL ELECTRIC CO 31 Dec 1973 [2 Jan 1973 (2)] 60271/73 Heading H2K A circuit breaker having a protective circuit for three phase lines, which opens circuit breaker contacts in the lines under overcurrent conditions or faults to earth and comprises a power supply circuit 200, a signal sensing circuit 100 having an earth fault sensing part and an overcurrent sensing part, an earth fault control circuit 300, an instantaneous time control circuit 400, a short time delay control circuit 500, a long time delay control circuit 600 and an output circuit 700 containing a trip coil 12 for tripping a latch 10 of the circuit breaker, wherein the power supply circuit 200 has separate inputs each connected respectively to one of the phase and has a common output, the signal sensing circuit has connected respectively to each phases a first transformer 102, 104, 106 and a second transformer 122, 124, 126, and a third transformer 114 having respective primary windings but a common secondary winding coupled to the input of the earth fault control circuit 300, for each phase the respective secondary winding of the first transformer, the respective primary winding of the second transformer, the respective primary winding of the third transformer and the respective power supply input being connected together in series. The earth fault sensing part of the signal sensing circuit 100 is connected via the third transformer 114 to the earth fault control circuit whose transistors, under fault conditions, are gated by capacitor 174 to charge capacitor 310 to trigger unijunction transistor 710 to fire SCR 726 to energize the trip coil 12. The overcurrent sensing part of the sensing circuit 100 is coupled via the first and second transformers, full wave rectifier bridges and an OR circuit comprising diodes 134, 136, 138 so that a voltage representative of the highest peak line current is fed to transistor 156 whose emitter is connected to the instantaneous time control circuit 400, the short time delay control circuit 500 and the long time delay control circuit 600. According to the magnitude of the overcurrent the transistors of one of these control circuits will switch to trigger unijunction transistor 710 to fire SCR 726 to energize the trip coil 12, the greater the overcurrent the shorter the time delay within the available ranges. To protect the solid state control circuits from damage under high ambient temperatures a thermistor 542 is connected across their supply. |
