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Motors and Transformers > Three Phase Motors > Flashcards

Three Phase Motors Flashcards

1
Q

What are the three main three phase motors?

A

Squirrel Cage
Wound Rotor
Synchronous

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2
Q

What are the characteristics of a squirrel cage induction motor?

A

Small
Rugged
Very good speed regulation

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3
Q

What are the 4 main parts of a three phase motor?

A

Stator
Rotor
Frame with end shields
Bearings

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4
Q

What is the stator?

A

Stationary part that consists of the windings to connected to power
Pressed in laminated core

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5
Q

What is the rotating part?

A

Connected to the Load
Consists of rotor bars welded to 2 end rings to form a squirrel cage
has fins welded to it for air circulation
a steel shaft with key way is welded through its center

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6
Q

What is the frame?

A

Consists of all connections
Built for the environment

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7
Q

What are the bearings?

A

To reduce rotation friction

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8
Q

What are the three main types of bearings?

A

Ball
Roller
Sleeve

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9
Q

What is synchronous speed?

A

The speed of the rotating magnetic field in the stator

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10
Q

How is synchronous speed determined?

A

Determined by the supply voltage frequency and the number of poles of the motor

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11
Q

What is the formula for synchronous speed?

A

120 x F/ # of poles

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12
Q

What are the rpms of a 2, 4, and 6 pole motor?

A

2 Pole- 3600 rpm
4 Pole- 1800 rpm
6 Pole- 1200 rpm

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13
Q

What is slip?

A

Slip is the difference between synchronous speed and rotor speed

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14
Q

How is slip represented?

A

As a percentage

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15
Q

What percentage should slip be less then?

A

5%

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16
Q

What is the formula for %slip?

A

SS- rotor speed/ SS x 100

17
Q

What are the three types of motor starters?

A

Manual
Magnetic
VFD

18
Q

What is a motor starter?

A

A three phase contractor and an overload relay combined

19
Q

What is the top half of a motor starter?

A

The three phase contact

20
Q

What is the bottom half a motor starter?

A

The three phase overload relay

21
Q

What are 4 uses for motor starters?

A

Start motors
stop motors
reverse motors
protect motors

22
Q

What are the two main types of diagrams?

A

Wiring
Schematic

23
Q

What is a wiring diagram?

A

Shows actual location of all components and wiring

24
Q

What is a schematic diagram?

A

Shows the logic of the circuit without actual location of components and wiring. (AKA- Ladder or elementary diagram)

25
Q

What are the five rules of a schematic diagram?

A

1.) Only one load per line
2.) Pilot device (control) is wired before the load
3.) You must number the rungs from top to bottom
4.) You must contact Reference
5.) You must wire reference (Top to Bottom, Left to right)

26
Q

How do you wire a motor for high voltage?

A

Series connection

27
Q

How do you wire a motor for low voltage?

A

Parallel connection

28
Q

What are the components of a SCIM rotor?

A

Windings

29
Q

What is the power source supplying the SCIM connected to?

A

Stator

30
Q

What type of bearing uses oil as its method of lubrication?

A

Sleeve bearing

31
Q

What is the speed at which the magnetic field travels in the stator called?

A

Synchronous Speed

32
Q

What determines the speed at which the magnetic field travels in the stator?

A

Poles and Frequency

33
Q

What happens when the rotor of SCIM turns at the same speed at which the magnetic field travels in the stator?

A

No torque is developed

34
Q

When the SCIM is running at full load what is the current compared to the start current?

A

It is lower

35
Q

What is the power factor of a 3 phase SCIM operating unloaded?

A

Very Poor

36
Q

The interaction between between rotor magnetic field and stator magnetic field has a direct impact on the SCIMs what?

A

Torque

Motors and Transformers (4 decks)

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