Key Topic 62: Motors & Generators

Question 1

3-62I1: What occurs if the load is removed from an operating series DC motor?

A. It will stop running.
B. Speed will increase slightly.
C. No change occurs.
D. It will accelerate until it falls apart.

Answer 1

D. It will accelerate until it falls apart.

Question 2

3-62I2: If a shunt motor running with a load has its shunt field opened, how would this affect the speed of the motor?

A. It will slow down.
B. It will stop suddenly.
C. I will speed up.
D. It will be unaffected.

Answer 2

C. I will speed up.

Question 3

3-62I3: The expression “voltage regulation” s it applies to a shunt-wound DC generator operating at a constant frequency refers to:

A. Voltage fluctuations from load to no-load.
B. Voltage output efficiency.
C. Voltage in the secondary compared to the primary.
D. Rotor winding voltage ratio.

Answer 3

A. Voltage fluctuations from load to no-load.

Question 4

3-62I4: What is the line current of a 7 horsepower motor operating on 120 volts at full load, a power factor of 0.8, and 95% efficient?

A. 4.72 amps.
B. 13.03 amps.
C. 56 amps.
D. 57.2 amps.

Answer 4

D. 57.2 amps.

Question 5

3-62I5: A 3 horsepower, 100 V DC motor is 85% efficient when developing its rated output. What is the current?

A. 8.545 amps.
B. 20.345 amps.
C. 26.300 amps.
D. 25.000 amps.

Answer 5

C. 26.300 amps.

Question 6

3-62I6: The output of a separately-excited AC generator running at a constant speed can be controlled by:

A. The armature.
B. The amount of field current.
C. The brushes.
D. The exciter.

Answer 6

B. The amount of field current.