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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If both are reversed, iinterpole will continue in the original direction. Excessive current will flow when DC voltage is first applied unless current is limited in some way.

As the armature begins to turn, counter EMF increases; and, since the counter EMF opposes the applied voltage, the armature current is reduced.

Navy Electricity and Electronics Training Series (NEETS), Module 5, through – RF Cafe

By reversing either field or armature connections. Increasing shunt-field circuit resistance increases motor speed. What is the purpose of starting resistors? The field strength varies with changes in armature current.

Increasing the armature circuit resistance decreases motor speed.

Gramme-ring wound armatures are seldom used for this reason. It may then be removed after counter EMF has been built up. Direction of armature current, and direction of magnetic flux in field. Unloaded operation of large machines is dangerous.

LOAD on a motor is the physical object to be moved by the motor. There are no differences. The speed and torque characteristics are a combination of the desirable characteristics of both series and shunt motors. Automatic starters are not covered in detail in this module.


These interpoles, being midway between main poles, are just opposite the armature poles shown in Windingss. Like poles of the armature and field then repel each other, causing armature rotation to continue. Electrical Engineering is a free introductory textbook to the basics of electrical engineering.

Shunt-motor speed varies only slightly with changes in load, and the starting torque is less than that of other types of DC motors. In practice the interpoles are made stronger than just sufficient to neutralize the armature flux, in order to aid in the reversal of current in the coils being commutated.

Adding resistance in series with the armature windings reduces initial current. If their polarities be made the same as those of the armature poles opposite to them, and if their strength be made equal to that of the armature poles, then the distortion of the main field at the commutating point, as in Fig.

Motor will slow down. 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.

When its speed is reduced by a load, the series motor interpooe greater torque.


To avoid the commutation difficulty actually encountered in old-style generators, narrow poles called interpoles or commutating poles are used, as indicated in Fig. Its speed varies widely between full-load and no-load. Its primary purpose was to provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer.

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Therefore, the interpole still has the proper polarity to provide automatic commutation. To limit armature current until counter EMF builds up. What current flows in the interpole windings? 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.

In a generator the interpoles must be of the same polarity as the main poles which they precede in the direction of rotation. Nearly all DC motors have drum-wound armatures. This causes the neutral plane to be shifted in the direction opposite to that of armature rotation.

The field strength is independent of the armature current. The DC motor is reversed by reversing the direction of the current in the armature. It must lnterpole a load connected to avoid damage from excess speed.

Such a diverter is called an inductive shunt. They remain in that position for all conditions of load.


The brushes are located on the no-load neutral plane. In fact, most DC interpolee can be made to act as DC motors, and vice versa. Interpoles and compensating windings are used to reduce the effect of armature reaction on motor operation. The armature poles are attracted to field poles of opposite polarity, causing the armature to rotate.