GB471361A - Improvements in and relating to systems of electric motor control - Google Patents

Abstract

471,361. Automatic control systems; rectifying alternating currents. BRITISH THOMSON-HOUSTON CO., Ltd. March 2, 1936, No. 6301.. Convention date, March 1, 1935. [Classes 38 (ii) and 38 (iv)] [Also in Group XXXVII] Speed.-When a control arm 43 is moved from its central position, one of two reversing switches 45, 46, is closed to connect the field winding 14 of the generator of a Ward-Leonard system to a source 20, through a grid-controlled discharge device 21, a control arm 38 remaining in contact with a segment 56, and the grid of the device 21 being subjected to a bias voltage lagging the anode voltage by 90‹ and obtained from a transformer 25. No appreciable current flows through the device 21 and the motor 10 is not started. The control arm 38 is then moved over potentiometer resistance 35 to an extent corresponding to the desired speed of the motor, and a condenser 29 in the grid circuit of the device 21 is subjected to a corresponding voltage through a resistance 41 and a rectifier 42. The device 21 is thus rendered conducting and the generator field and motor speed build up. The grid circuit includes a voltage which is derived from a generator 19 driven by the motor 10 and opposes the condenser voltage. The motor accelerates in accordance with the rate at which the condenser charges until the voltage of the generator 19 matches the condenser voltage. The system then operates to maintain the speed uniform. When the control arm 38 is moved towards its central position the condenser 29 discharges through a resistance 40, and the motor decelerates, the voltage of the generator 19 again being matched to the condenser voltage. The connection of the generator 19 in the grid circuit is reversed with the reversal of the generator field 14 by means of contacts 32, 33, operated with the reversing contactors 45, 46. A second device similar to the device 21 may be provided to rectify the other half of the alternating voltage wave, or, as shown, the field 14 may be maintained during the negative half-wave bv a rectifier 47 connected in parallel with the field, and rendered conducting by the induced voltage in the field winding.