AC Motors

Question 1

______ is higher when _____ is lower?

Answer 1

Current, resistance

Question 2

Name the 2 basic classes of electric motors:

Answer 2

1) AC
2) DC

Question 3

Frame sizes are often defined by what?

Answer 3

Letters and numbers

Question 4

Two digit frame sizes indicate the shaft center height in what inch increments?

Answer 4

1/16”

Question 5

Three digit frame sizes indicate the shaft center height in what inch increments?

Answer 5

1/4”

Question 6

What class motor is required to run a variable frequency drive?

Answer 6

Class F

Question 7

T or F:
T, TS, C, TC are all common suffix letters for AC motors?

Answer 7

True

Question 8

Name 4 reasons an AC motor will overheat:

Answer 8

1) High or low voltage supply
2) Blocked ventilation holes
3) High ambient temperatures
4) Voltage imbalance

Question 9

To prevent shorting, electric motor windings are coated in what?

Answer 9

Insulation

Question 10

Motor insulation is written as what on a motor nameplate?

Answer 10

Class

Question 11

What is the amount of overload a motor can continuously deliver without overheating?

Answer 11

Service factor

Question 12

A motor with 1.15 SF is able to deliver _____ percent of rated load without overheating?

Answer 12

115

Question 13

Name the 2 ways to mount a motor:

Answer 13

1) C-face
2) D-flange

Question 14

Which type of motor has an end bell and has threaded holes for attaching the motor to reducers and pumps?

Answer 14

C-face

Question 15

Name 2 types of motor protection:

Answer 15

1) Manual thermal overloads
2) Automatic thermal overloads

Question 16

Which type of motor protection requires a reset button on the thermal be pushed in order to start the motor?

Answer 16

Manual thermal overloads

Question 17

T or F:
On large HP 3 phase motors, overload devices operate as a function of heat as a result of the motor load?

Answer 17

True

Question 18

T or F:
The flow of electrons is electric current?

Answer 18

True

Question 19

The AC motor consists of what 2 main parts:

Answer 19

1) The rotor
2) The stator

Question 20

Which AC motor part is stationary and contains windings, which transform electricity into a magnetic field?

Answer 20

Stator

Question 21

Two or more sets of windings are called what?

Answer 21

Poles

Question 22

As the magnetic field generated by the stator crosses these bars, electromagnetic currents are induced into the bars, which creates a magnetic field in the what?

Answer 22

Rotor

Question 23

T or F:
If a motor reaches synchronous speed it will rotate?

Answer 23

False

Question 24

The difference between the synchronous speed and the actual speed is called what?

Answer 24

Slip

Question 25

For an induction motor to operate, there must be some what?

Answer 25

Slip

Question 26

Because of its high efficiency and low cost what is the most commonly used motor in industrial applications?

Answer 26

3 phase AC induction motor

Question 27

Better known as “workhorses of industry”

Answer 27

3-phase AC induction motor

Question 28

Name the 4 ways to help start a single-phase induction motor:

Answer 28

1) Shaded pole motor
2) Split phase motor
3) Capacitor start motor
4) Permanent split capacitor motor

Question 29

Which single phase motor has a copper loop called a shading ring surrounding a portion of each stator pole?

Answer 29

Shaded-pole motors

Question 30

Which type of single phase motor has both “starting” and “run” windings?

Answer 30

Split-phase motor

Question 31

Which single phase motor is the most common and uses a capacitor along side the start windings?

Answer 31

Capacitor start motor

Question 32

Which type of motor uses identical main and auxiliary windings in combination with a capacitor to provide starting torque?

Answer 32

Permanent split capacitor start

Question 33

Which type of motor is used for HVAC?

Answer 33

Permanent split capacitor start

Question 34

Which type of motor is used in fans and small appliances?

Answer 34

Shaded pole motor

Question 35

Which type of motor is used in a washing machine?

Answer 35

Split phase motor