Reversal of Direct-Current Motors

Author: E.E. Kimberly

The torque, and hence the direction of rotation, of a d-c motor may be reversed by reversing either the field flux or the direction of armature current. If the reversal of rotation is accomplished by field reversal both the shunt field and the series field, if there is one, must be reversed. The direction of current through the inter-pole windings need not be reversed in order to maintain the proper polarity sequence, as discussed on page 131.

If reversal of rotation is accomplished by reversal of armature current, the direction of current through the interpole windings must also be reversed. In "plugging" service, such as found in some steel-mill applications in which the motor is reversed frequently, reversal is accomplished by armature and interpole reversal, rather than by field-flux reversal, because of the simpler control required. Automatic reversing switches controlled from a master switch are used in such service.