AC/DC Motors: Quiz

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QUESTIONS

1. What is the function of the armature in a DC motor?

2. What is the function of the field in a shunt-type DC motor?

3. Explain how the forward and reverse motor starter circuits shown in Fig. 12-12 provides lockout protection so the motor can't he switched directly from the forward direction to the reverse direction.

4. What does the term induction mean in regard to an induction-type AC motor?

5. Explain how one can use a resistance test to detect the start and run winding of a split- phase AC motor.

6. What is counter EMF in a motor and what function does it provide?

7. Explain how one can change the speed of a DC shunt motor.

TRUE OR FALSE

1. The series field of a DC series motor is made of very fine wire so that its magnetic field will be as strong as possible.

2. The armature is the rotating part of the DC motor.

3. The brushes in a DC motor make contact between the stationary part of the motor and the armature.

4. The three-phase, wye-connected motor has more starting torque than the delta-connected, three-phase motor.

5. The synchronous AC motor uses DC voltage to provide extra field current so the motor does not have slip.

6. An induction-type AC motor needs slip to provide torque for the rotor.

7. Inrush current (LRA) is always larger than full-load current ( FLA).

8. The speed of a DC shunt-type motor is adjusted by changing the frequency of the supply voltage for the motor.

9. The direction of rotation for a split phase AC motor can be changed by changing the polarity of the supply voltage.

10. The direction of rotation for a three-phase AC motor can be changed by exchanging Li and L2 of the supply voltage.

MULTIPLE CHOICE

1. The _______ is connected in series with the start winding for a permanent split-capacitor (PSC) motor.

a. start capacitor

b. run capacitor

c. potential relay

2. The start winding is connected in _______ with the run winding for a split-phase AC single-phase motor.

a. series

b. parallel

c. series parallel

3. The _______ motor has the most torque of all of the single-phase AC motors.

a. split-phase

b. capacitor start, induction run

c. capacitor start, capacitor run

4. The speed of an AC motor can be increased by

a. decreasing the frequency of the supply voltage to the motor.

b. increasing the frequency of the supply voltage to the motor.

c. increasing the amount of voltage to the motor.

5. The single-phase induction motor needs a start winding

a. to create a phase shift that will provide starting torque.

b. to increase the speed of the motor.

c. to create additional running torque.

6. The shaded-pole single-phase motor _______

a. uses a relay to remove its start winding from the circuit after the motor starts.

b. uses a capacitor to remove the start winding from the circuit after the motor starts.

c. does not have a start winding since it has a shading pole to provide the phase shift for starting.

7. The rated of a four-pole AC motor is _______

a. 3600 rpm.

b. 1800 rpm.

c. 1200 rpm.

PROBLEMS

1. Calculate the rpm of a two-pole AC motor.

2. Draw the diagram of a delta-connected, three-phase motor that is connected for high voltage and low voltage and identify their terminals. Explain how one would reverse the direction of rotation for these motors.

3. Draw the wiring diagram of a wye-connected, three-phase motor that is connected for high voltage and low voltage and identify their terminals. Explain how one would reverse the direction of rotation for these motors.

4. Use this table to determine the locked-rotor current for a 2hp motor that has a NEMA code letter C.

5. Draw the wiring diagram for a split-phase, capacitor start, induction run, single-phase AC motor and identify its terminals.

6. Draw a sketch of a basic single-phase induction motor and identify the rotor, stator, and centrifugal switch.

7. Draw the wiring diagram for a PSC single-phase AC motor.

8. Draw the wiring diagram of a DC series, DC shunt, and any one of the DC compound motors and identify their terminals.

9. Determine the distance between the bolt holes for a 56 frame motor. (Use this table.)

10. Explain how one would troubleshoot a three-phase AC motor that fails to start and the motor windings don't make any noise or draw any current.

11. Explain how one would troubleshoot a single-phase AC motor that has a centrifugal switch and fails to start.

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