GB1312643A - High voltage electric circuit breakers - Google Patents

Abstract

1312643 Electric switches GENERAL ELECTRIC CO 14 July 1970 [23 July 1969] 34090/70 Heading H1N [Also in Division H3] In order to avoid undesirable voltage surges when connecting a supply line 121, Fig. 1, to a load line, when the latter may have retained an appreciable charge, connection is made at a voltage peak of polarity similar to that of the charge. Voltage dropping capacitors 70, 72, connected across the supply line of one phase and earth, supply an input to a zero crossing detector 75 which produces a pulse 76 each time the voltage passes through zero, so providing a datum for timing. A closing logic circuit 78 receives these pulses and also the output from a trapped charge detector 83, which gives an output indicative of the polarity of the charge provided it is above a predetermined minimum magnitude. When a zero pulse of the same polarity as the charge is received, the circuit 78, through a circuit 100, giving an appropriate time delay, releases latch 43 to close sequential switches 28, 32, 22. The trapped charge indicator, Fig. 3, receives an input from the line 12 through voltage divider 80, 82, this input corresponding in polarity with the charge on the line. This is passed through amplifiers 156, 157, connected to give positive feedback through resistor 159 and consequently continuing to give an output on lead 85 of appropriate polarity once an input signal has been received. The closing logic circuit 78, Fig. 4, comprises two flip-flops 180, 181 such that when the polarities of their terminals A, B are as shown, neither can be turned on by a positive input on line 84, the reverse set of conditions also being true. The polarity of these terminals A, B is determined by the polarity on the line 85, i.e. the output of the charge detector, and thus only when the pulse received on line 84, from the zero crossing detector, is of the same polarity as that on line 85 is an output passed through line 88 to trip the closing latch.