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6077SA
NUE 046
3 Phase Induction Motor
Construction
At the end of this section you will be able to:
 Identify the basic components of a 3Ø induction
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


motor
List the types of rotors used
Test motor windings for suitability to connect to
the supply
Connect in both star and delta
List the steps for dismantling it
3Ø Induction Motors
Why are they so common in industry?

Simple in construction

Only one moving part

Don’t have brush gear and commutators

Now with VSD technology, Variable speed
 Speed of machine fixed to supply frequency
Construction
Fixed Stator
(stationary)
Rotor (The bit that Rotates)
Construction
Frame can be made from cast
 Iron
 Steel
 Aluminium
End caps/shields bolted to each end of frame
Drip Proof
 Designed for air flow into motor
 Not waterproof
 Not suitable for flame proof atmospheres
Totally Enclosed
 No airflow between motor inside and outside atmosphere
 Waterproof
 Easier to adapt to for flame proof atmospheres
Open
 Designed for air flow into motor
 Not waterproof
 Very rare due to OH&S considerations
Core Laminations
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

Carries the stator windings
Made of silicone steel 0.3 to 0.5mm thick
Insulated from one another to reduce eddy current
loss
Stator windings
3 identical phase windings that are displaced by 120°
electrical around the stator
 Each winding consists of series, parallel connected
coils to achieve the number of poles required.
 2, 4, 6, & 8 poles per phase are common
 Windings are generally connected in delta but can be
connected in star

Rotors
 Wound rotor
 (not common)
 Squirrel cage
 (most common)
Two Main Types
Squirrel Cage Rotor
Squirrel Cage Rotor
Can be Cast
Rotor bars (slightly skewed)
• Aluminium
• Copper
• Copper alloy
End ring
Copper/Copper alloy bars inserted into the
laminations and welded/brazed to shorting ring
Wound Rotor
Slip ring




Same number of poles as stator.
One end of coil is connected to a star point
Other end is terminated on a slip ring
Resistance is added to change the mechanical and
electrical characteristics of motor.
Motor Terminals
Motor Terminals
Motor Terminals
U1
V1
W1
V2
W2
U2
Motor Terminals
U1
V1
W1
V2
W2
U2
Motor Terminals
U1
V2
V1
W2
W1
U2
To Make
Star
Connection
Motor Terminals
U1
V2
V1
W2
W1
U2
To Make
Delta
Connection
Electrical Testing
 Each winding should have the same
resistance
 ie 1-10
 Voltage between windings =400V
 Insulation test level =1000V
 IR reading no less than 1M