Electrical Engineering ⇒ Topic : Compound Motor

Cumulative compound motor   In this type of motor the speed falls appreciably as the torque increases, but on low torques the maximum speed is limited to a safe value. These motors are used :

• When a larg-e starting torque is required but when the load may fall so low that a series motor would race.
• When the load is of a fluctuating nature and a reduced speed is desirable on the heavy loads.

In such a case a flywheel is usually fitted so that when speed is so reduced the kinetic energy stored in the flywheel at high speeds is given up to assist the motor is driving the heavy load.

When the supply voltage is subject to fluctuations (as in traction system).

 Differential compound motor  The speed at low torque is limited by the shunt winding, as in the cumulative compound machine. At high torques, the speed may be arranged

to remain constant or, with a stronger series field, the speed may rise with increasing load.

• On very heavy loads the machine may tend to race.
• Its use is usually restricted to applications which require a constant speed.