Patent GB-342087-A (GB)
Title: Improvements in and relating to electric motor control systems
IPC: H02P25/26
Filed: 1929-12-18
Abstract: 342,087. Master control of A.C. and D.C. motors ; electromagnetic switches. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London.- (Assignees of Hardesty, L. C. ; 303, Sanders Avenue, Scotia, New York, U.S.A.) Dec. 18, 1929, No. 38814. Convention date, Dec. 18, 1928. [Classes 38 (iii) and 38 (v).] Reversing arrangements.-The current of an induction motor 10, Fig. 1, when reversed while running is limited by a comparatively large plugging resistance 19, placed in the rotor circuit for a predetermined period, but short-circuited when the motor accelerates from rest. A contactor 24, controlling the plugging resistance 19, is energized responsively to the operation of contactors 12, 13, and time limiting devices 25, 26; and accelerating contactors 21, 22, 23, automatically short-circuit accelerating resistances 16, 17, 18 successively, in intervals of time determined by the time limiting devices 27, 28, 29, controlled by the plugging contactor 24. Thus the automatic operation of the contactors 21, 22, 23 is initiated when the contactor 24 operates. When the motor is reversed while running the master switch 14 is thrown from position 3 to 3<1>, de-energizing contactor 12 and closing contactor 13. The closing of contactor 13, and the opening of contactor 12 opens the timing switch 26 immediately, and closes the timing switch 25 after a time interval. When this happens the motor has come to rest; and as it speeds up in the opposite direction the contactor 24 is energized and the resistances 19, 18, 17, 16 are cut out. The time limiting devices 27, 28, 29, attached to the contactors 21, 22, 23 are such that they open instantly when the contactor opens, and close in an interval of time after the contactor closes ; the time limiting devices 25, 26 attached to the reversing and forward contactors 13, 12, controlled by the master switch 14, are such that they open instantly the contactor closes, and close in an interval of time after the contactor opens. The Specification as open to inspection under Sect. 91 (3) (a) comprises also the application of the invention to the control of direct current motors. This subject-matter does not appear in the Specification as accepted. Switches; retarding action of.-Fig. 2 shows the type of time controlled switch in which the switch arm 32 is connected to the associated contactor by a shaft 33, arm 34 and bolt 35 over which slides a collar 36, reduced in diameter so as to pass through a hole in the arm 34. The closing of the contactor compresses a spring 38, causing a bridge 31 to connect contacts 30, a movement regulated by the mechanical escapement consisting of the rack and pinion 40, 41, which engage only on upward movement, and gearing 42 .. 45 connected to a pendulum 48. On opening of the contactor, the spring 38 immediately breaks the contact. The other type of time controlled switch in which contact is broken immediately the associated contactor closes, and is made in a time interval after the associated contactor opens, operates with a similar mechanical escapement and is described with reference to Fig. 3 not shown.