Into To 3 Phase Induction Motors Flashcards
(31 cards)
What is an electrical motor?
A device that converts electrical power into mechanical power
What is another term for torque?
Moment of force
Motor torque (always / sometimes) matches counter-torque of load.
Motor torque ALWAYS matches counter-torque of load
Which formula do we use to calculate torque?
T = F • r
T is torque in Nm
F is force in N
r is radius in m
What is the formula for calculating mechanical power?
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
How do we calculate mechanical power using hp?
Hp=
(T • n) / 7121
What is the formula for efficiency?
Eff =
Pout / Pin
OR
Pout / (Pout + Plosses)
What is the formula for %eff?
%eff =
( Pout / Pin ) •100
A motor has 2 types of losses. What are they?
Mechanical losses
• Friction
• Windage
Electrical losses
• Iron losses
• Copper losses
Is the shaft of a NEMA motor on the front or back of the motor?
The shaft is on the back of a NEMA motor
A motor is made up of 3 parts…..
Frame
Rotor
Stator
Which way does the shaft rotate, if looking from the front of the motor?
Counter-clockwise
The frame holds the stater and the rotor.
List four things that are included on the frame.
- The cast
- End brackets/bells
- Bearings in the end brackets
- Junction box (pecker head)
Drip-proof frames (aka open drip-proof frames) are used in
a) dirty environments
b) clean + dry, indoor environments.
b) clean and dry, indoor envoronmenta
Totally enclosed [TE] motors are used in dirty and wet environments.
3 types of TE motors are…
- Totally Enclosed Fan Cooled (TEFC)
- Totally Enclosed Non-Ventilated (TENV) in the textile industry
- Totally Enclosed Pipe-Ventilated (TEPV) in hazardous locations
List the four parts included in the stator.
- Laminated and slotted iron
- The conductors
- Conductor Insulation
- Protective sleeves and wedges for slots
What are the two types of stator windings?
• 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
What is synchronous speed?
- Stator speed
* The CONSTANT SPEED of the magnetic field in the stator
What is the difference between the stator speed and the rotor speed?
Slip speed
What are the two types of rotors available?
- Squirrel-cage rotors
* Wound rotors
What are the three parts of a rotor?
- Laminated iron
- Conductors
- Shaft
What do we call the aluminum or copper bars over squirrel cage rotor?
Rotor conductors
Or
Rotor bars
The rotor conductors are permanently shorted by the end rings.
True or False
True
What is the purpose of the end rings?
- They tie the rotor bars together.
* Creates a path for induced currents
