Electric Motor

In a DC motor, the armature turns and cuts through the lines of magnetic force produced by the _____.

• field poles

• brushes

• commutator

• rotor

Which of the following is TRUE regarding the neutral plane in a single-loop DC motor?

• At the neutral plane, the loop is parallel to the magnetic field.

• At this position, the commutator connects to the brushes.

• The neutral plane allows the motor to be self-starting.

• No torque is produced in the neutral plane.

The approximate horsepower of a 15,000W DC motor is _____.

• 10hp

• 20hp

• 30hp

• 40hp

Which of the following motors is the BEST choice for an application requiring adjustable speeds?

• Shunt DC

• Split-phase AC

• Capacitor-start AC

• Synchronous AC

A polyphase synchronous motor has three stator windings that are _____.

• 180° apart

• 120° apart

• 90° apart

• 45° apart

Which of the following motors is used to provide high starting torque and constant speed under load?

• Brushless

• Shunt

• Series

• Compound

The synchronous speed at which a four-pole, 50Hz induction motor operates is _____.

• 1,200 rpm

• 1,500 rpm

• 1,800 rpm

• 2,000 rpm

For a given number of poles, which of the following determines the speed of an AC motor?

• Frequency

• Current

• Voltage

• Frame size

The speed of a three-phase squirrel cage induction motor is controlled by the frequency of the applied voltage and the _____.

• diameter of the core

• shaft length

• number of poles

• brush voltage

A wound-rotor induction motor is used _____.

• for speed control and to limit starting current

• to start low inertia loads

• when reduced slip is required

• to increase power factor