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AC Machines

AC Machines. 6077SA NUE 046. 3 Phase Induction Motor Construction. 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.

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AC Machines

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  1. AC Machines 6077SA NUE 046

  2. 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:

  3. 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

  4. Construction Fixed Stator (stationary) Rotor (The bit that Rotates)

  5. Construction Frame can bemade from cast • Iron • Steel • Aluminium End caps/shields bolted to each end of frame

  6. Drip Proof • Designed for air flow into motor • Not waterproof • Not suitable for flame proof atmospheres

  7. Totally Enclosed • No airflow between motor inside and outside atmosphere • Waterproof • Easier to adapt to for flame proof atmospheres

  8. Open • Designed for air flow into motor • Not waterproof • Very rare due to OH&S considerations

  9. 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

  10. 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

  11. Rotors Two Main Types • Wound rotor • (not common) • Squirrel cage • (most common)

  12. Squirrel Cage Rotor

  13. Squirrel Cage Rotor • Aluminium • Copper • Copper alloy Can be Cast Copper/Copper alloy bars inserted into the laminations and welded/brazed to shorting ring

  14. 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.

  15. Motor Terminals

  16. Motor Terminals

  17. Motor Terminals U1 V1 W1 V2 W2 U2

  18. Motor Terminals U1 V1 W1 V2 W2 U2

  19. Motor Terminals U1 V1 W1 V2 W2 U2 To Make Star Connection

  20. Motor Terminals U1 V1 W1 V2 W2 U2 To Make Delta Connection

  21. 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

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