GB969915A - Improvements in or relating to electrical circuit-breakers - Google Patents

Abstract

969,915. Arcing preventing in switches. CENTRAL ELECTRICITY GENERATING BOARD, and W. E. J. FARVIS. July 17, 1962 [July 18, 1961], No. 26010/61. Heading H2B. [Also in Division H3] An apparatus for controlling the instant of operation of a circuit-breaker includes means responsive to input signals representative of the instantaneous value of the alternating current to be interrupted and of the phase of the current with respect to the voltage and providing a circuit-breaker operating signal at the instantaneous optimum operating time with respect to a current zero. In the arrangement of Fig. 1, current and voltage signals are applied respectively to comparators 13 and 14 which give outputs to a gate circuit 15 when the instantaneous values of the signals are zero. The circuit 15 gives a square output pulse which is started and stopped by the output pulses from 14 and 13 so that the length of the output pulse from 15 is representative of the phase angle between the current and voltage and determines the number of pulses given from an oscillator 16 and stored in a counter 17. The alternating current signal is also applied through a halfwave rectifier 18 to an amplitude discriminator 19 (see Division H3) which gives an output representative of the peak amplitude of the line current to be broken. The information concerning phase angle (from 17) and current amplitude is fed to a logic matrix 21 which in conjunction with a system of delay channels 23 causes a triggering pulse to be sent to the circuit-breaker operating mechanism at the appropriate time in the current cycle as determined by the magnitude of the current and its phase angle. A timing pulse generator 20 triggers and resets the various circuit elements. This apparatus may control an air-break, airblast, oil, or vacuum circuit-breaker. Fig. 6 shows a suggested circuit-breaker arrangement in which the energization of spiral coils 63, 65 causes the repulsion of conductive discs 62, 64 so that initially both contacts 52, 53 move together until the movement of the contact 53 abruptly ceases due to the disc 64 abutting a stop 66. The contact 52 moves to its open position under the control of the over-centre spring toggle mechanism shown. The energization of the coils may be provided by the discharge of a charged capacitor, the discharge being initiated through a spark-gap in response to the output from the delay channels 23.