Single-Phase Motors

Question 1

In general, single-phase motors do not perform as well as three-phase motors of comparable horsepower. T or F?

Answer 1

True

Question 2

What are the most common fractional horsepower sizes for single-phase motors?

Answer 2

1/6 to 3/4 HP

Question 3

________ ________ Motors are classified by the way the two windings are used to start and run the motor.

Answer 3

Split-Phase Motors

Question 4

Name the basic components of a resistance split-phase motor.

Answer 4

The stator
The rotor
The frame
The centrifugal switch

Question 5

The stator winding consists of a laminated steel core with slots to hold the insulated windings. Describe the auxiliary winding.

Answer 5

The auxiliary (or start) winding is made of smaller conductors with fewer turns. It also has GREATER resistance and LESS reactance than the main winding.

Question 6

The start winding of a four pole motor has the windings how many degrees away from the main windings?

Answer 6

45 degrees from the main windings

Question 7

A centrifugal switch is mounted inside the motor and serves to disconnect the start winding when the motor nears full-speed. At what percent does the switch open?

Answer 7

75%

Question 8

In a single-phase motor, the run winding by itself produces a rotating magnetic field. T or F?

Answer 8

False. The run winding produces a pulsating magnetic field, not the rotating magnetic field required to start the rotor turning.

Question 9

In a resistance split-phase motor, what amount of degrees is the displacement between the main and starting windings?

Answer 9

Usually about 25-30 degrees

Question 10

Describe the cross field theory.

Answer 10

The cross field theory is used to explain motor operation once the motor is running. When the rotor is turning, the currents flowing in the rotor circuit LAG the induced rotor voltage by about 80 degrees. This is because the rotor has very little resistance and comparatively high inductive reactance.

Question 11

The starting torque of a resistance split-phase motor is around _____ to ______ of rated running torque.

Answer 11

125% to 150%

Question 12

A common use of a resistance split-phase motor is a washing machine. T or F?

Answer 12

True

Question 13

The resistance split-phase induction motor has what two starting characteristics?

Answer 13

Low starting torque
High starting current

Question 14

The best performance from a split-phase, single-phase motor is provided by what type of motor?

Answer 14

Dual Cap Motor/Two-Value Capacitor Motor

Question 15

What type of capacitor is connected to the RUN winding in a dual cap motor?

Answer 15

oil-filled continuous duty rated at 40uf

Question 16

The electrolytic capacitor and the oil capacitor are connected in series. T or F?

Answer 16

False. They’re connected in Parallel

Question 17

Two-Value Capacitor Motors are in-expensive, quiet, yet operate with a poor power factor. T or F?

Answer 17

False. They are the most expensive, quiet and operate with a good power factor.

Question 18

Name the terminals of an integral thermal protection device and what components it contains

Answer 18

P1, P2 and P3
They contain a circuit breaking component between P1 & P2
A current sensing component (heater) between P2 & P3
And sometimes a manual reset. If manual reset is not found, its an automatic reset.

Question 19

In regards to a high voltage connection for a dual voltage, reversible, thermally-protected, split-phase motor, what terminal connects to P3?

Answer 19

T1

Question 20

In regards to a Low-voltage connection for a dual-voltage, reversible split-phase motor, what terminals are connected to L2?

Answer 20

T2, T4, and T8

Question 21

Low-noise, high starting torque describes the characteristics of what split-phase motor?

Answer 21

Dual Cap Motor/Two Value Capacitor Motor