Ac Motors

Question 1

What are the two basic classes of motors?

Answer 1

Ac
Dc

Question 2

What voltages are Ac motors rated in?

Answer 2

120vac
208vac
240vac
480vac
600vac

Question 3

What is two numbers for frames divided by?

Answer 3

16ths

Question 4

What is three digits divided by one frames?

Answer 4

4ths first two numbers

Question 5

Frame letter meanings

Answer 5

T- long shaft
TS - short shaft
C- c-face motor
TC - c - face with long shaft
JM,JP - close coupled
U- France size horsepower relation ship
TZ - special shaft dimensions
TY- special mounting

Question 6

What are factors that cause motors to overheat?

Answer 6

High or low voltage supply

Slow or repeated starts

High ambient temperatures

Blocked vent holes

Voltage imbalance on three phase

Question 7

Motor insulation is also known as?

Answer 7

Motor class

Question 8

On motor class what do the letters stand for?

Answer 8

A- 221 degrees
B- 266 degrees
F- 311 degrees
H 356 degrees

Question 9

What is service factor?

Answer 9

The amount of overload a motor can take without overheating

Question 10

On service factor 1.15 is what?

Answer 10

115 percent

Question 11

On a speed torque curve when speed is low torque is what?

Answer 11

High.

Unless a centrifugal clutch then it’s opposite

Question 12

What are the two optional mounting positions for motors?

Answer 12

C- face - motor attaches directly to endbell

D - flange - has a mounting flange allows motor to be noted directly onto the driven machinery

Question 13

How do you protect fractional horsepower motors from overheating?

Answer 13

Manual thermal overload (MTO)
Or automatic thermal overload (ATO)

Question 14

How to keep large horsepower motors from overheating? (Three phase motors)

Built into windings

Answer 14

Thermostats
Thermistors
Resistance temperature detectors

Most common thermal overloads

Question 15

What is the flow of electrons?

Answer 15

Electric current

Question 16

Can single phase and three phase motors be interchangeable?

Answer 16

No

Should use three phase motor if available they are cheaper.

Question 17

What are the two main parts of a ac motor?

Answer 17

Rotor
stator (stationary part outer shell)

Question 18

What is a set of windings called?

Answer 18

Poles ( the number of poles determines horsepower)

Question 19

What is “slip”

Answer 19

The difference between the synchronous speed and the actual rotor speed.

(Must be some slip for induction motor to operate) 1-5 percent

Question 20

Why are three phase induction motor most commonly used?

Answer 20

High efficiency, low cost (workhorses of industry)

Question 21

Single phase induction motors.

Answer 21

The rotating magnetic field does not exist until running rpm is reached. No starting torque so manufactures have to include design mechanisms to cause the motor to start.

Question 22

Different techniques to help single phase induction motors to start.

Answer 22

Shaded pole
Split phase
Capacitor start
Permanent split capacitor

Question 23

What motor has a copper loop called a shading ring surrounding a portion of each starter pole?

Answer 23

Shaded - pole motor

Question 24

What motor has two sets of stator windings one start and one run. Start windings positioned 90 degrees to run windings and shift the magnetic field by 25 degrees. Has a switch built in to disconnect start windings when motor is at 3/4 synchronizes speed

Answer 24

Split phase motor

Question 25

Motor with start and run windings and includes a capacitor in series with start winding? Stairs magnetic field shifted to 82 degrees

Answer 25

Capacitor start / capacitor start capacitor run motor

Question 26

What is the most common single phase motor?

Answer 26

Capacitor start motor

Question 27

What motors uses identical main and auxiliary windings with a capacitor but used continuously and requires no start switch?

Answer 27

Permanent split capacitor motor