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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Kimberly To avoid the commutation difficulty actually encountered in old-style generators, narrow poles called interpoles or commutating poles are used, as indicated in Fig. It is 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 diverter around the interpole windings to permit shunting of a part of the windins armature current around those coils.

Its speed varies widely between full-load and no-load. The speed and torque characteristics are a combination of the desirable characteristics of both series and shunt motors.

By reversing either field or armature connections. Nearly all DC motors have drum-wound armatures. Interpoles and compensating windings are used to reduce the effect of armature reaction on motor operation.


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.

Shunt-motor speed varies only slightly with changes in load, and the starting torque is less than that of other types of DC motors. Gramme-ring wound armatures are seldom used for this reason.

Like poles of the armature and winsings then repel each other, causing armature rotation to continue.

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

When its speed is reduced by a load, the series motor develops greater torque. Direction of conductor movement rotationdirection windibgs flux, and the direction of current flow. As the load varies, the interpole flux varies, and commutation is automatically corrected as the load changes. The field strength varies with changes in armature current. In fact, most DC generators can be made to act as DC motors, and vice versa.


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 inherpole just equal to that of the interpole coils.

It may then be removed after counter EMF has been built up. This EMF opposes the applied voltage, and limits the flow of armature current. See the editorial for more information It must have a load connected to avoid damage from excess speed.

It maintains a constant speed under varying loads.


The brushes are located on the no-load neutral plane. 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.

They are the Gramme-ring and the drum-wound types. Unloaded operation of large machines is dangerous. Such a diverter is called an inductive shunt. They remain in that position for all conditions of load.

When the armature current is reversed, the current through the interpole is also wkndings. It is not necessary to shift ijterpole brushes when there is an increase or decrease in load. If both are reversed, rotation will continue in the original direction. The device to be driven by the motor.

Controlling the starting resistance in a DC motor is accomplished either manually, by an operator, or by any of several automatic devices. The interpole windings are connected in series with the armature windings, and therefore their correction ampere-turns increase or decrease in the same proportion as do the distorting ampere-turns of unterpole armature.

All trademarks, copyrights, patents, and other rights of ownership to images and text used on the RF Windingd website are hereby interpol. Such an improper division would cause the interpole field to fail to rise in proportion to the armature current to be commutated, and would probably cause the commutator to flash over at the brushes. Increasing the armature circuit resistance decreases motor speed.


What is the purpose of starting resistors?

To avoid the commutation difficulty actually encountered in old-style generators, narrow poles called interpoles or commutating poles are used, as indicated in Fig. In a generator the interpoles must be of the same polarity as the main poles which they precede in the direction of rotation.

Automatic starters are not covered in detail in this module. LOAD on a motor is the physical object to be moved by the motor. High torque ihterpole force at low speed.

If the ordinary resistance diverter were used, a sudden surge windkngs current caused by a sharp increase in load would not divide between the interpole path and the diverter path in inverse proportion to their respective resistances; but, because of the high reactance of the interpole path, a disproportionately large portion of the surge current would flow through the diverter. Increasing shunt-field circuit resistance increases motor speed.

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. There are no differences. Pages through Its starting torque is greater than other types of DC motors. The inductance of the coil tends to retard the reversal of the coil current by generating a prolonging voltage.

The field strength is independent of the armature current. Therefore, the interpole still has the proper polarity to provide automatic commutation. The DC motor is reversed by reversing the direction of the current in the armature. Only outside of coils cut flux inefficient. In practice the interpoles are made stronger than just inter;ole to neutralize the armature flux, in order to aid in the reversal of current in the coils being commutated.

As the armature begins to turn, counter EMF increases; and, since the counter EMF opposes the applied voltage, the armature current is reduced. The automatic devices are usually just switches controlled by motor speed sensors.