GB1357891A - Electric motor control apparatus - Google Patents

Abstract

1357891 Control of DC motors DEWHURST & PARTNER Ltd 23 July 1971 [23 April 1970] 19610/70 Heading H2J A reversible compound D.C. motor having an armature 10, series field winding 12 and shunt field winding 14, is controlled by a main contactor having contacts 20, 22, 24, a first control contactor having normally-open contacts 26 and change-over contacts 28 and a second control contactor having change-over contacts 30, the arrangement being such that operation of the control contactors to a first position, corresponding to the hoist direction of a crane including the motor, energizes the winding 14 from a source 18 through a resistor 42, and the combination 10, 12 from a source 16, whilst operation to a second position corresponding to the lower direction fully energizes the winding 14, removes the winding 12 from the circuit and reverses the connections of the source 16 to the armature 10, which is shunted by a resistor 38 for absorbing most of the regenerative current produced by the motor (should it overrun) that would otherwise be applied to the source 16. Operation of the contactors to a third (off) position, in which the main contactor is opened, places a short circuit across the series combination 10, 12 so that a braking torque is produced which assists an electro-mechanical brake 44 operable when the contacts 24 open. The source 16 may comprise an engine-driven generator whose speed or excitation may be controlled when controlling the contactors, whilst the source 18 may comprise a battery. The contact positions for the various operating conditions are described, Figs. 2A, 2B and 2C (not shown).