GB637644A - Improvements in and relating to power factor correction arrangements for intermittently energized inductive electric loads - Google Patents

Abstract

637,644. Supply systems for resistance welding. BRITISH THOMSON-HOUSTON CO., Ltd. Nov. 28, 1945, No. 32174. Convention date, Nov. 29, 1944. Addition to 535,933 and 543,800. [Class 38 (iv)] [Also in Group XXXVII] In a supply system for a resistance welding transformer 1 or other intermittently energized inductive load, switching means are provided for connecting power factor correction capacitors 23 to the supply circuit 2 during the periods of energization of the load. The capacitors are charged through rectifier 28 in the off load periods and, upon energization of the load circuit, the switching means operates to connect them to the supply circuit at the moment the supply voltage wave is passing through its maximum value. Transformer 1 is supplied through ignitrons 3, 4 under the control of a timer 18 which, in addition to controlling the excitation circuits of these tubes, also controls, over transformer 52, the excitation circuits of ignitrons 26, 27 by which the capacitors are connected to the supply circuit. Ignitrons 26, 27, which have holding anodes 32, are fired 'by the discharge of condensers 33 into the ignition circuits over thyratrons 34, the control grid circuits of which include resistors 45, 48, 49 across which components of control voltage are developed. Resistor 48 provides a hold-off voltage derived from a supply circuit 42, transformer 58 and anode 60 of a rectifier 54. whilst the other anode of the rectifier which is fed from the timercontrolled transformer 52 provides in the resistor 49 a turnon voltage. This last voltage prepares the thyratrons for conduction, which occurs when the resistors 45 are energized by a peaking transformer 47. This transformer is supplied from circuit 42 through a phase-shifter 64-47 so adjusted that the thyratrons 34 conduct when the voltage wave of circuit 2 is passing through a maximum. Over-voltage protection of capacitors 23 is provided by a spark-gap 81 which, upon breaking down, energizes a trip coil 83 on a supply circuit-breaker 84.