GB700474A - Improvements in speed control systems for multiphase statorfed a.c. commutator motors - Google Patents

Abstract

700,474. Control of A.C. motors. LAURENCE, SCOTT, & ELECTROMOTORS, Ltd., WOODS, J. V., and SCHWARTZ, K. K. April 8,1952 [April 27, 1951], No. 9945/51. Class 38(3) [Also in Group XXXV] Relates to single phase speed control of a polyphase commutator motor 1 which has a three phase main voltage control transformer 2 (for example an induction regulator) the secondary winding 2S of which is connected to the commutator brushes of the motor. As shown, a single phase variable voltage transformer 3 has its secondary winding 3S connected in the motor secondary circuit, its primary winding 3 Pr being connected across a fixed supply such as a phase winding SP of the motor stator. The speed regulation thus obtained by the transformer 3 is independent of the speed level provided by the adjustment of the transformer 2. In order to reduce unbalance of current the single phase control may be obtained from an auto transformer coupled to the rotor circuit of the motor through an auxiliary transformer the primary winding of which is connected between a centre tapping and an adjustable slider of the auto transformer, Fig. 1a (not shown). The injected voltage may thus be used for increasing or decreasing the speed according to the position of the adjustable slider. The motor may have a tapped auxiliary polyphase stator winding in place of the main control transformer, the single phase transformer having its secondary winding connected to a tapping in the auxiliary stator winding and included by way of an adjustable slider in the secondary circuit of the motor, Fig. 2 (not shown). The primary winding of the single phase transformer is supplied at a fixed voltage which may be derived from the auxiliary stator winding. In a further example the main control transformer has a tapped secondary winding, the single phase transformer being auto-wound and connected across one phase of the part of the tapped secondary winding which is in use, Fig. 3 (not shown). The adjusting slider of the single phase transformer may then be connected in the secondary circuit of the motor. One primary winding of the main control transformer may be supplied from the single phase transformer. The application to the control of a series polyphase motor is referred to, the supply voltage being controlled by a single phase variable voltage transformer which has an adjusting contact connected to a tapping in one primary phase winding of the main polyphase supply transformer, Fig. 4 (not shown), which may be, in turn, of the variable voltage type.