GB721398A - Improvements in or relating to electrical phase-sensitive devices and the like - Google Patents

Abstract

721,398. Valve relay circuits. WATFORD ELECTRIC & MANUFACTURING CO., Ltd. Aug. 17, 1953 [Aug. 25, 1952], No. 21335/52. Class 40 (6). In a phase sensitive device in which one or other of two gas-filled valves V1, V2 is fired when the input to the grids leads or lags the anode supply, a third valve V3 is arranged with its anode supply in quadrature so that, when short pulses of current occur in the associated valve V2, long pulses occur in the valve V3. The invention is stated to prevent chatter in relays and is used for the connection and disconnection of power factor correcting capacitors. The valves V2, V1 are energized in antiphase, Fig. 3, and are normally maintained non-conducting by bias derived from potentiometers P1, P2. A current transformer CT feeds pulses 33, 34 over a peaking transformer T2 which occur when there is no positive potential on the anodes when the system is operating at unity power factor. If the current lags the voltage, the pulse 33 fires valve V1 which remains conducting for most of the remaining half-cycle, providing adequate current to operate relay K1. When the current leads, the pulse 34 fires valve V2 near the end of the half cycle causing a short pulse of current to flow in valve V2. A voltage pulse is applied to valve V3 which is energized from phase C and neutral N and is thus in quadrature with the voltage from phases A and B. Current flows for at.least a quarter-cycle, increasing as the current leads further. Relays K1, K2 operate a reversible motor operating cams to connect and disconnect power factor correcting capacitors.