GB360440A - Improvements in and relating to electric motor control - Google Patents

Abstract

360,440. Control of A.C. motors. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London, and HEINRICH, A. F., 34, Lancaster Road, Rugby. Aug. 6, 1930, No. 23595. [Class 38 (iii).] In the alternating-current motor described in Specification 288,987, [Class 35, Dynamo-electric generators &c.], wherein speed regulation is effected by varying the effective secondary turns, the necessary variation is effected automatically. In the case of a lift motor having secondary winding parts which can be connected in series or in parallel, the change from series to parallel connection is effected at the synchronous brush position, but only when decelerating, the series connection being used at all other times. The Figure shows the circuit and control arrangements for such a motor. The primary winding P is connected to the supply system through one or the other of the reversing switches 1, 2 which carry interlocks 11, 21 in the circuit of a coil 4a operating a switch 4 which connects the elements S1, S2 of the secondary winding in series or parallel. The commutator winding R feeds the secondary winding through two movable brush sets and only one brush B1, B2 of each set is shown. The switch 4 is normally constrained by a spring to occupy the series position shown. A is an interlock on the brush gear of the motor which is closed when the brush gear is in a subsynchronous position and open otherwise, and B is an interlock with the reverse action. 5 is a pilot contactor having an operating coil 5a and a retaining interlock 51, Switches A, B are so positioned that A opens shortly before B closes when the brush gear is moved towards the high-speed position and B opens shortly before A closes when the brush gear is moved towards the low-speed position. Also contacts c, d of the switch 4 are arranged to close before contact e is opened when moving from the series to the parallel connection, and e is closed before c, d are opened when changing from parallel to series. In operation, with the brush gear in the low-speed position and either of the switches 1, 2 closed, interlock 11 or 21 is also closed, but as B is open the energizing coil 5a of contactor 5 is open circuited so that coil 4a is de-energized and the switch 4 remains in the series position. As the brush gear is moved past the synchronous position A opens and B closes so that contactor 5 is closed by the energization of the coil 5a and the interlock 51 also closes. If the brush gear is moved towards the low-speed position, B opens, but the retaining interlock 51 keeps the coil 5a energized so that contactor 5 remains closed. When A closes, coil 4a is energized and the switch 4 moves into the other position to connect the winding S1' S2 in parallel. In the case of a constant horse-power motor, the series connection may be used always for under synchronous running so that the interlock A and contactor 5 can be omitted. In the case of a fan motor, the series connection may be used always for over synchronous running so that the interlock B and contactor 5 can be omitted. Interlock A, B may comprise switches having lever arms carrying rollers which are actuated by cams or ramps on one or both brush rockers. If the switch 4 is to be operated in some position other than the synchronous, there must be no overlap between the closing of contacts c, d and the opening of e to avoid short-circuiting the brushes B1, B2.