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