Download - AC Machines
6077SANUE 046
3 Phase Induction MotorConstruction
Identify the basic components of a 3Ø induction 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
At the end of this section you will be able to:
3Ø Induction Motors 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
Why are they so common in industry?
ConstructionConstruction
Fixed Stator (stationary)
Rotor (The bit that Rotates)
ConstructionConstructionFrame can be made from cast
IronSteelAluminiu
m
End caps/shields bolted to each end of frame
Designed for air flow into motorNot waterproofNot suitable for flame proof atmospheres
Drip Proof
No airflow between motor inside and outside atmosphere
WaterproofEasier to adapt to for flame proof atmospheres
Totally Enclosed
OpenOpenDesigned for air flow into motorNot waterproofVery rare due to OH&S considerations
Core Laminations 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
RotorsWound rotor(not common)Squirrel cage (most common)
Two Main Types
Squirrel Cage RotorSquirrel Cage Rotor
Squirrel Cage RotorSquirrel Cage Rotor
• Aluminium• Copper• Copper alloy
Can be Cast
Copper/Copper alloy bars inserted into the laminations and welded/brazed to shorting ring
Rotor bars (slightly skewed)
End ring
Wound RotorWound Rotor 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.
Slip ring
Motor Terminals
Motor Terminals
Motor Terminals
U1 V1 W1
V2 W2 U2
Motor Terminals
U1 V1 W1
V2 W2 U2
Motor Terminals
U1 V1 W1
V2 W2 U2
To Make Star
Connection
Motor Terminals
U1 V1 W1
V2 W2 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