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Induction Machine

Induction Machine. Induction Machine (N. Tesla 1888). Principle of operation Construction Characteristics: slip rotor current power torque Classification Control. Principle of operation. o. squirrel-cage rotor. o. o. Three-Phase Supply Voltage. A. B. C. N. 60 120. S. A.

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Induction Machine

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  1. Induction Machine

  2. Induction Machine (N. Tesla 1888) • Principle of operation • Construction • Characteristics: • slip • rotor current • power • torque • Classification • Control

  3. Principle of operation o squirrel-cage rotor o o

  4. Three-Phase Supply Voltage A B C N 60 120 S A 120 C B

  5. C B Resultant Stator Flux Rotating Magnetic Flux A A C B 0 60

  6. It’s electromagnetic induction !!!

  7. Induction Motor • electromagnetic induction • rotating magnetic flux induces an alternating • current in the rotor • motor action • interaction of the induced rotor-current with • the rotating field produces motor torque

  8. Direction of Rotation i N The rotor follows the rotating magnetic flux !

  9. How to change the direction of rotation? • change the direction of rotation of the rotating magnetic flux • change the phase sequence of the applied voltage

  10. Synchronous Speed • speed of the rotating magnetic flux • ns = fs / (P/2)

  11. Slip Speed n, Slip s • n = ns - nr • s = ( ns - nr ) / ns • if nr then n and s • for nr = ns s = 0

  12. fr : frequency of the induced voltage in the rotor • fr= P n / 120 n = ns -nr

  13. Rotor Current 1 -------- slip ---.2 - 0 0 ------ speed ---- 100%

  14. Rotor Current Phasor } Ir cos (theta): horizontal component s = .05 s = .2 SGAP = EBRIr (cos 0 + j sin 0) s = 1

  15. Interpreting the Circle Diagram s = .05 Assume s = .05; If Tload nr s Ir Ir cos0 sufficient to carry the load s = .2 s = 1

  16. Power-Flow Diagram Pgap Pmech Pin Pshaft Pscl Pcore Prcl Pf,w Pstray

  17. Mechanical Power vs Torque Pmech = TDnr / 5252 (hp) shaft speed r/min developed torque lb-ft mechanical power developed in rotor hp

  18. Torque vs Speed o breakdown TD Torque o o rated value locked rotor 1 slip 0

  19. Torque-Speed Characteristics T D C A - B Speed

  20. Can slip at maximum torque be changed? Elevator Tmax Speed

  21. Induction Generator Induction Motor Turbine Increasing rotor speed above ns will reverse direction of PGAP ==> power is transferred in reverse direction, from rotor to stator

  22. Induction Motor Starting • Autotransformer Starting • Y-Delta Starting • Series Impedance • Solid State Starting

  23. Breaking (rotating rotor induces currents to be dissipated in stator circuit) • DC Injection • Capacitor Breaking

  24. Single-Phase Induction Motor • There is no rotating magnetic flux • How to produce needed rotating flux? • Quadrature Field

  25. Quadrature-Axis Flux (flux induced by rotor current) Stator or direct-axis flux Quadrature-axis or rotor flux

  26. Phase Splitting Single phase Phase Splitter

  27. Split-Phase Motors • Resistance-Start Split-Phase Motors • Capacitor-Start Split-Phase Motors

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