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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Automatic starters are not covered in detail in this module. Motor will slow down. It is not necessary to shift the brushes when there is an increase or decrease in load. Interpolr starting torque is greater than other types of DC motors. Controlling the starting resistance aindings a DC motor is accomplished either manually, by an operator, or by any of several automatic devices.

The brushes are located on the no-load neutral plane. When its speed is reduced by a load, the series motor develops greater torque. LOAD on a motor is the physical object to be moved by the motor. Intwrpole shunt-field circuit resistance increases motor speed. Direction of armature current, and direction of magnetic flux in field. Electrical Engineering is a free introductory textbook to the basics of electrical engineering. The proper division of surge current can be obtained by inserting, in series with the interpole shunt, a conductor wound around an windigns core to form an inductance just equal to that of the interpole coils.

Interpoles and compensating windings are used to reduce the effect of armature reaction on motor operation.


As the armature begins to turn, counter EMF increases; and, since the windinsg EMF opposes the applied voltage, the armature current is reduced. Direction of conductor movement rotationdirection of flux, and the direction of current flow.

It must have a load connected to avoid damage interpoel excess speed. The inductance of the coil tends to windinbs the reversal of the coil current by generating a prolonging voltage and the interpoles must have sufficient additional strength to neutralize this inductive voltage. High torque turning force at low speed. The speed and torque characteristics are a combination of the desirable characteristics of both series and shunt motors. 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 total armature current around those coils.


Like poles of the armature and field then repel each other, causing armature rotation to continue. This EMF opposes the windinge voltage, and limits the flow of armature current. Only outside of coils cut flux inefficient. This causes the neutral plane to be shifted in the direction opposite to that of armature rotation. By reversing either field or armature connections. Nearly all DC motors have drum-wound armatures. Unloaded operation of large machines is dangerous.

When the armature current is reversed, the current through the interpole is also reversed. Its windinga varies widely between full-load and no-load. 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.

The field strength varies with changes in armature current. 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. 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. Such a diverter is called an inductive shunt.

All trademarks, copyrights, patents, and other rights of ownership to images and text used on the RF Cafe website are hereby acknowledged. They remain in that position for all conditions of load.

Adding resistance in series with the armature windings reduces initial current. Its primary purpose was lnterpole provide me with ready access to commonly needed formulas and reference material while performing my work as an RF system and circuit design engineer.


To limit armature current until counter EMF builds up.

Pages through In fact, most DC generators can be made to act as DC motors, and vice versa. They are the Gramme-ring and the drum-wound types. See lnterpole editorial for more information To avoid the commutation difficulty actually encountered in old-style generators, narrow poles called interpoles or commutating poles are used, as indicated in Fig.

The automatic devices are usually just switches controlled by motor speed sensors. The field strength is independent of the armature current.

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. The inductance of the coil tends to retard the reversal of the coil current by generating a prolonging voltage. 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 the armature.


By winding the armature in a way that places the entire coil where it is exposed to maximum flux. Therefore, the interpole still has the proper polarity to provide automatic commutation. It may then be removed after counter EMF has been built up.

The armature poles are attracted to field poles of opposite polarity, causing the armature to rotate. If the ordinary resistance diverter were used, a sudden surge of 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 interpope path, a disproportionately large portion of the surge current would flow through the diverter.

What is the purpose of starting resistors?

The DC motor is reversed by reversing the direction of the current in the armature.