2-12
COUNTER-ELECTROMOTIVE FORCE is generated in a dc motor as armature coils cut the
field flux. This emf opposes the applied voltage, and limits the flow of armature current.
In SERIES MOTORS, the field windings are connected in series with the armature coil. The field
strength varies with changes in armature current. When its speed is reduced by a load, the series motor
develops greater torque. Its starting torque is greater than other types of dc motors. Its speed varies widely
between full-load and no-load. Unloaded operation of large machines is dangerous.
In SHUNT MOTORS, the field windings are connected in parallel (shunt) across the armature coil.
The field strength is independent of the armature current. Shunt-motor speed varies only slightly with
changes in load, and the starting torque is less than that of other types of dc motors.
