GB108430A - Improvements in and relating to Electric Motor Control and Apparatus therefor. - Google Patents

Abstract

108,430. British Thomson-Houston Co., and Hastings, H. C. Feb. 3, 1917. Master control systems.-In an electric motor control system with contactors operating in succession and with electro-magnetic auxiliary switches the magnetic force in which varies with the speed or back electromotive force of the motor, each auxiliary switch is mechanically interlocked with one contactor and controls the closing of the next contactor. The stator S of an induction motor is connected to the mains L<1>, L<2>, L' by a contactor 1 and resistances are cut out of the circuit of the rotor R by contactors 2, 3, 4, 5. The contactors have operating-coils C<1> - - C<5> and the first four contactors are interlocked with auxiliary. switches S<1> - - S<4>, the switches being held open when the contactors are open. The switches have windings A<1> - - A<4> connected across the slip rings K<1>, K<2> of the rotor which are set to drop their cores at different voltages. When the controller M is moved to its first position, the contactor 1 is closed and the motor starts. The auxiliary switch S<1> is released by the contactor but is held up until the current in the coil A<1> drops to a suitable value. The switch S<1> then drops and, on the controller being moved to the second position, the contactor 2 is closed. Contactors 3, 4, 5 are closed similarly. The controller may be moved to the full ' on ' position and the contactors will then close automatically. An ohmic resistance is connected in series with each auxiliary switch winding so that its current is practically independent of the frequency of the rotor currents. In an arrangement for use with direct-current motors, the windings of the auxiliary switches are connected across the motor armature and the switches are closed by the lifting of the cores as the back electromotive force rises.