Ac Motors Flashcards

1
Q

What are the two basic classes of motors?

A

Ac
Dc

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2
Q

What voltages are Ac motors rated in?

A

120vac
208vac
240vac
480vac
600vac

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3
Q

What is two numbers for frames divided by?

A

16ths

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4
Q

What is three digits divided by one frames?

A

4ths first two numbers

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5
Q

Frame letter meanings

A

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

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6
Q

What are factors that cause motors to overheat?

A

High or low voltage supply

Slow or repeated starts

High ambient temperatures

Blocked vent holes

Voltage imbalance on three phase

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7
Q

Motor insulation is also known as?

A

Motor class

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8
Q

On motor class what do the letters stand for?

A

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

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9
Q

What is service factor?

A

The amount of overload a motor can take without overheating

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10
Q

On service factor 1.15 is what?

A

115 percent

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11
Q

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

A

High.

Unless a centrifugal clutch then it’s opposite

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12
Q

What are the two optional mounting positions for motors?

A

C- face - motor attaches directly to endbell

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

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13
Q

How do you protect fractional horsepower motors from overheating?

A

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

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14
Q

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

Built into windings

A

Thermostats
Thermistors
Resistance temperature detectors

Most common thermal overloads

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15
Q

What is the flow of electrons?

A

Electric current

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16
Q

Can single phase and three phase motors be interchangeable?

A

No

Should use three phase motor if available they are cheaper.

17
Q

What are the two main parts of a ac motor?

A

Rotor
stator (stationary part outer shell)

18
Q

What is a set of windings called?

A

Poles ( the number of poles determines horsepower)

19
Q

What is “slip”

A

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

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

20
Q

Why are three phase induction motor most commonly used?

A

High efficiency, low cost (workhorses of industry)

21
Q

Single phase induction motors.

A

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.

22
Q

Different techniques to help single phase induction motors to start.

A

Shaded pole
Split phase
Capacitor start
Permanent split capacitor

23
Q

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

A

Shaded - pole motor

24
Q

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

A

Split phase motor

25
Q

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

A

Capacitor start / capacitor start capacitor run motor

26
Q

What is the most common single phase motor?

A

Capacitor start motor

27
Q

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

A

Permanent split capacitor motor