4 Types of DC Motors and Their Characteristics

Types of D.C. Motors

Like generators, there are three types of d.c. motors characterized by the

connections of field winding in relation to the armature viz.:

(i) Shunt-wound motor in which the field winding is connected in parallel

with the armature .The current through the shunt field

winding is not the same as the armature current. Shunt field windings are

designed to produce the necessary m.m.f. by means of a relatively large

number of turns of wire having high resistance. Therefore, shunt field

current is relatively small compared with the armature current.

The shunt-connected motor offers simplified control for reversing. This is especially beneficial in regenerative drives.

 (ii) Series-wound motor in which the field winding is connected in series with

the armature Therefore, series field winding carries the

armature current. Since the current passing through a series field winding is

the same as the armature current, series field windings must be designed

with much fewer turns than shunt field windings for the same m.m.f.

Therefore, a series field winding has a relatively small number of turns of

thick wire and, therefore, will possess a low resistance.

Series-connected motors generally are not suitable for use on most variable speed drive applications.

(iii) Compound-wound motor which has two field windings; one connected in

parallel with the armature and the other in series with it. There are two

types of compound motor connections (like generators). When the shunt

field winding is directly connected across the armature terminals

it is called short-shunt connection. When the shunt winding is so

connected that it shunts the series combination of armature and series field

it is called long-shunt connection.

The compound machines (generators or motors) are always designed so that the

flux produced by shunt field winding is considerably larger than the flux

produced by the series field winding. Therefore, shunt field in compound

machines is the basic dominant factor in the production of the magnetic field in

the machine.