Patent GB-469053-A (GB)
Title: Improvements in or relating to electric motor control systems
IPC: H02P1/20
Filed: 1936-03-07
Abstract: 469,053. Master control of D.C. motors. ELECTRICAL APPARATUS CO., Ltd., and BARBOUR, R. H. March 7, 1936, No. 6942. [Class 38 (iii)] In a control system of the type in which the motor is accelerated by means of electromagnetically controlled contactors operated sequentially by means of relays, one or more of the contactors other than the first is associated with a relay comprising a contactor coil, an armature controlling the circuit of the coil, a holding coil which, when energized, holds the armature in the position in which the circuit is open, and a transformer winding in series with the holding coil, so arranged. that on actuation of the preceding contactor the holding coil and transformer winding are short-circuited. Owing to the effect of the transformer winding current continues to flow in the holding coil for a period dependent on the magnitude of the current flowing in it at the moment before it is short-circuited, the associated contactor being held inoperative until the holding coil is de-energized. In the system shown, the motor M with series field winding 13 is connected to the line 11, 12 through a line contactor C<1>, forward and reverse contactors Mf, Mr, overload coils 14, 15 and starting resistances R<2> ... R<5>, which are adapted to be short-circuited in sequence by contactors C<2> . . . C<5>. The line contactor C<1> is normally closed, its operating coil m<1> being energized through contacts 3, 330 and contact segments x<1> ... x<3> on the controller drum D in the " off " position of the drum. When the contactor C<1> closes, an auxiliary contact a closes a maintaining circuit for the coil m<1>. Under overload conditions, switches L<3> open and the coil m<1> is de-energized. Each of the accelerating contactors C<3>. . . C<5> is associated with a relay comprising a setting coil S<3> ... S<5>, a holding coil H<3> ... H<5> and a transformer winding T<3> . . . T<5>, each holding coil being connected in series with its associated transformer winding. The relays, so far as their holding and setting coils are concerned, are of the type described in Specification 202,509, [Class 38 (iii)]. The relay associated with the contactor C<2> has holding and setting coils H<2>, S<2> but no transformer winding. The setting coils and series connected holding coils and transformer windings associated with the contactors C<3> . . . C<5> are energized in parallel across adjustable resistances r<2> ... r<4> connected in parallel with the main resistances R<2> ... R<4>, so that as each contactor closes, the relay windings associated with the next contactor are short-circuited. The transformer windings are mounted on a common core, successive windings being connected in opposite senses. When the drum D is moved to its first position in forward or reverse direction one or other of the forward or reverse contactor coils 25f, 25r is energized to close the forward or reverse contactors Mf, Mr and start the motor through the resistances R<2> . . . R<5>, applying to the setting coils S<3>. . . S<5> sufficient current to maintain open the circuits of the coils m<3> . . . m<5>. The circuit of the setting coil S<2>, which is closed in the " off " position of the drum D, is opened at the contacts x<2>, x<3> shortly before the drum reaches its second position. The holding coil H<2> associated with the contactor C<2> holds up its armature as long as the current through the resistance R<2> is greater than the value obtaining when the motor is at rest. If the holding coil H<2> has released its armature, the winding m<2> is energized at the second position of the controller, and the contactor C2 closes to short-circuit the resistance R<2>. Movement of the controller to the subsequent positions causes the contactors C<3> . . . C<5> to close in succession as soon as the current in the associated holding coils has died down, the setting coils having been short-circuited by the closing of the preceding contactor. Limit switches L<1>, L<2> are included in series with the contactor coils 25f, 25r to prevent overrunning. There is also a slow-down limit switch L which opens the circuits of the coils m<2> ... m<5> and reinserts the resistances at a certain point, thus causing the work being driven'to slow down before the ultimate limit switches are reached.