Deck 3: DC Compound Motors

Question 1

When starting a(n) ____________________ motor, it is recommended that the series field be shorted because the great starting current in this field may overbalance the shunt field and cause the motor to start in the opposite direction.

Answer 1

differential

Question 2

Briefly explain the difference between a cumulative compound motor and a differential compound motor.

Answer 2

When the series winding field is connected to aid the shunt winding field, the machine is a cumulative compound motor. When the series field opposes the shunt field, the machine is a differential compound motor. Using Fleming's left-hand rule for electromagnets, it can be seen that the two windings will either reinforce each other or try to cancel each other.

Question 3

It is conventional to reverse the current in the field circuits to reverse the rotation of a compound-wound motor.

Answer 3

False

Question 4

The speed regulation of a cumulative compound-wound motor is inferior to that of a shunt motor and superior to that of a series motor.

Question 5

The rotation of a compound-wound motor can be reversed by changing the direction of the current in the field circuits or the armature circuit. Briefly explain why it is conventional to reverse the current in the armature only rather than reversing the shunt field.

Question 6

When a motor is first connected, what conditions are checked using standardized tests?

Question 7

The speed of a cumulative compound motor can be controlled by using ____________________ in the armature circuit to reduce the applied voltage.

Question 8

Most speed controls have some type of feedback to sense the armature current, compare it to the set speed, and adjust the electronic conduction control to compensate for varying ____________________ to keep the motor speed regulated.

Question 9

The cumulative compound motor has a definite no-load speed and will not build up to destructive speeds if the load is removed.

Question 10

Connecting the compound motor is referred to as _____________________________.

Question 11

Because many drives need a fairly high starting torque and a constant speed under load, the ____________________ motor is suitable for these applications.

Question 12

The torque of a cumulative compound motor for a given current is less than it would be for a shunt motor.

Question 13

When operating a cumulative compound-wound motor, describe the change that occurs in the field flux when a load is applied.

Question 14

Because the field decreases with a load increase, a differential compound motor has a tendency for load instability.

Question 15

Briefly explain why a DC compound motor would be chosen for a particular application over a series motor or a shunt motor.