Figure —Armature reaction. Now you have two fields — the main field, view A, and the field around the armature coil, view B. View C of figure shows . These interpoles, being midway between main poles, are just opposite the The interpole windings are connected in series with the armature. Stator of a DC machine. ▫ Stator is the stationary part. ▫ Main poles as field winding. ▫ Further windings. ▫ Interpole. ▫ Compensation eliminate unwanted effects.

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There are no differences. All trademarks, copyrights, patents, and other rights of ownership to images and qindings used on the RF Cafe website are hereby acknowledged. What is the purpose of starting resistors? The inductance of the coil tends to retard the reversal of the coil current by generating a prolonging voltage and the interpoles must have sufficient additional strength to neutralize this inductive voltage.

Its starting torque is greater than other types of DC motors. See the editorial for more information It must have a load connected to avoid damage from excess speed. Interpoles and compensating windings are used to reduce the effect of armature reaction on motor operation.

Direction of armature current, and direction of magnetic flux in field. It maintains a constant speed under varying loads. What current flows in the interpole windings? Nearly all DC motors have drum-wound armatures.



It windingss very difficult for a designer to calculate the exact number of turns to be placed on the interpoles, and it is sometimes necessary to connect an adjustable intedpole around the interpole windings to permit shunting of a part of the total armature current around those coils.

The proper division of surge current can be obtained by inserting, in series with the interpole shunt, a conductor wound around an iron core to form an inductance just equal to that of the interpole coils.

When its speed is reduced by a load, the series motor develops greater torque. If both are reversed, rotation will continue in the original direction.

Pages through The DC motor is reversed by reversing the direction of the current in the armature. Motor will slow down.


By reversing either field or armature connections. The field strength is independent of the armature current. Therefore, the interpole still has the proper polarity to provide automatic commutation. The speed and torque characteristics are a combination of the desirable characteristics of both series and shunt motors.

Only outside of coils cut flux inefficient.

As the armature begins to turn, counter EMF increases; and, since the counter EMF opposes the applied voltage, the armature current is reduced. The field strength varies with changes in armature current. High torque turning force at low speed.


Unloaded operation of large machines is dangerous. When the armature current is reversed, the current wkndings the interpole is also reversed. They are the Gramme-ring and the drum-wound types. They remain in that position for all conditions of load. These interpoles, being midway between main poles, are just opposite the armature poles shown in Fig. Adding resistance in series with the armature windings reduces initial current.

It is not necessary to shift the brushes when there is an increase or decrease in load. Dindings the armature circuit resistance decreases motor speed. The external resistance in series with the armature is decreased or eliminated as the motor comes up to normal speed and full voltage is applied across the armature.

This causes the neutral plane to be shifted in the direction opposite to that of armature rotation. In a generator the interpoles must be of the same polarity as the main poles which they precede in onterpole direction of rotation.