GB745331A - Improvements in and relating to current limiting systems - Google Patents

Abstract

745,331. Automatic current control systems. CANADIAN GENERAL ELECTRIC CO., Ltd. Dec. 16, 1953 [Dec. 16, 1952], No. 35066/53. Class 38 (4). [Also in Group XXXVII] The current supplied to the motor of a Ward- Leonard set is limited by energizing two biased, self-saturating magnetic amplifiers in reversed sense in accordance with the current, and connecting their outputs in series opposition to control the excitation of the Ward-Leonard generator. The motor 1 is supplied by the generator 3 which is of reversible polarity, excited from amplidyne exciter 8 controlled by .a main field 9 and the limiter field 10. The current is detected by the voltage drop across an interpole winding 5. This voltage is applied to the control windings 24, 34 of the self-saturating magnetic amplifiers 20, 30 so as to aid and oppose respectively the self-magnetization. Bias windings 27, 32 oppose windings 24, 34. The amplifier loads, 21, 31 are connected in series opposition in series with the field 10 of the exciter. Hence when the motor current is below the level set by the bias windings 27, 32, the small outputs of the amplifiers 20, 30 are equal and opposite, and the field 10 is unexcited. Currents due to any slight unbalance are prevented by the reversely connected pair of contact rectifiers 18. When the motor current exceeds the limiting value the output of amplifier 20 rises rapidly but there is little change in the output of amplifier 30, and the field 10 is excited in a sense to reduce the motor current. When the generator polarity is reversed, amplifier 30 saturates instead of amplifier 20.