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3rd Yr Electrical - Motors > Into To 3 Phase Induction Motors > Flashcards

Into To 3 Phase Induction Motors Flashcards

1
Q

What is an electrical motor?

A

A device that converts electrical power into mechanical power

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2
Q

What is another term for torque?

A

Moment of force

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3
Q

Motor torque (always / sometimes) matches counter-torque of load.

A

Motor torque ALWAYS matches counter-torque of load

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4
Q

Which formula do we use to calculate torque?

A

T = F • r

T is torque in Nm
F is force in N
r is radius in m

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5
Q

What is the formula for calculating mechanical power?

A

P =

(T • n) / 9.55

P is mech power in W
T is torque in Nm
n is rotational speed in rpm
9.55 is a contant

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6
Q

How do we calculate mechanical power using hp?

A

Hp=

(T • n) / 7121

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7
Q

What is the formula for efficiency?

A

Eff =

Pout / Pin

OR

Pout / (Pout + Plosses)

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8
Q

What is the formula for %eff?

A

%eff =

( Pout / Pin ) •100

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9
Q

A motor has 2 types of losses. What are they?

A

Mechanical losses
• Friction
• Windage

Electrical losses
• Iron losses
• Copper losses

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10
Q

Is the shaft of a NEMA motor on the front or back of the motor?

A

The shaft is on the back of a NEMA motor

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11
Q

A motor is made up of 3 parts…..

A

Frame

Rotor

Stator

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12
Q

Which way does the shaft rotate, if looking from the front of the motor?

A

Counter-clockwise

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13
Q

The frame holds the stater and the rotor.

List four things that are included on the frame.

A
  • The cast
  • End brackets/bells
  • Bearings in the end brackets
  • Junction box (pecker head)
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14
Q

Drip-proof frames (aka open drip-proof frames) are used in

a) dirty environments
b) clean + dry, indoor environments.

A

b) clean and dry, indoor envoronmenta

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15
Q

Totally enclosed [TE] motors are used in dirty and wet environments.

3 types of TE motors are…

A
  • Totally Enclosed Fan Cooled (TEFC)
  • Totally Enclosed Non-Ventilated (TENV) in the textile industry
  • Totally Enclosed Pipe-Ventilated (TEPV) in hazardous locations
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16
Q

List the four parts included in the stator.

A
  • Laminated and slotted iron
  • The conductors
  • Conductor Insulation
  • Protective sleeves and wedges for slots
17
Q

What are the two types of stator windings?

A

• Lap wound

  • has as many coils as slots
  • Coils are identical in size and orientation

• Concentric wound
- Have coils for each phase for each pole

18
Q

What is synchronous speed?

A
  • Stator speed

* The CONSTANT SPEED of the magnetic field in the stator

19
Q

What is the difference between the stator speed and the rotor speed?

A

Slip speed

20
Q

What are the two types of rotors available?

A
  • Squirrel-cage rotors

* Wound rotors

21
Q

What are the three parts of a rotor?

A
  • Laminated iron
  • Conductors
  • Shaft
22
Q

What do we call the aluminum or copper bars over squirrel cage rotor?

A

Rotor conductors

Or

Rotor bars

23
Q

The rotor conductors are permanently shorted by the end rings.

True or False

A

True

24
Q

What is the purpose of the end rings?

A
  • They tie the rotor bars together.

* Creates a path for induced currents

25
Q

Why are the rotor bars skewed?

A
  • To prevent the stator and rotor teeth from magnetic locking (torque pulsations or cogging)
  • To provide more uniform torque
  • To make motor operation more smooth and quiet
26
Q

What is the main difference between a SCIM and a WRM?

A

The construction of the rotor

27
Q

Where do the copper windings of a WRM terminate?

A

In the slip rings

28
Q

The stator currents for a WRM are

a) 100%
b) 150%
c) 200%

For the full load currents

A

b) 150%

29
Q

Why are WRM’s less common?

A

They need more maintenance

30
Q

Slip speed is typically ____% to ____% of synchronous speed.

A

Slip speed is typically 2% to 8% of synchronous speed.

31
Q

Nameplate values are always based on (no load / full load) conditions

A

Full load

3rd Yr Electrical - Motors (2 decks)

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