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Eddy-Current Starters for Wound Rotor Induction Motors Robert Melaia (robm@lhm.co.za) (melaia@mweb.co.za)

LHMarthinusen. ELECTRICAL & MECHANICAL ENGINEERS. TELEPHONE: +27 11 615 6722 FAX: +27 11 616 6808 www. lhm.co.za. Eddy-Current Starters for Wound Rotor Induction Motors Robert Melaia (robm@lhm.co.za) (melaia@mweb.co.za). Eddy-Current Starters for Wound Rotor Induction Motors (WRIMs).

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Eddy-Current Starters for Wound Rotor Induction Motors Robert Melaia (robm@lhm.co.za) (melaia@mweb.co.za)

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  1. LHMarthinusen ELECTRICAL & MECHANICAL ENGINEERS TELEPHONE: +27 11 615 6722FAX: +27 11 616 6808 www. lhm.co.za Eddy-Current Starters for Wound Rotor Induction MotorsRobert Melaia(robm@lhm.co.za)(melaia@mweb.co.za) RMWG Wits, 16 Nov 2006

  2. Eddy-Current Starters for Wound Rotor Induction Motors (WRIMs) • Wound Rotor Induction Motors – Fundamentals and Requirements. • Starting devices / methods for WRIMs. • Theory of Eddy-Current Starters. • Fundamental design of Eddy-Current Starters. • Eddy-Current Power Density and Distribution: Non-linearity. • Intricacies about Eddy-Current Starters: Optimisation. • Current Density Spectrums. • Leakage Effects. • Conclusion. RMWG Wits, 16 Nov 2006

  3. Starters for Wound Rotor Induction Motors (WRIMs) • Liquid resistor starters • Traditional switched resistor networks • Electronically switched resistors (Pulse Width Modulated) • Vapour starters • Saturistors • Eddy-current starters • Built-in implementations of rotor resistance devices: Idle-bar rotors. RMWG Wits, 16 Nov 2006

  4. WRIM Current and Torque Versus Speed RMWG Wits, 16 Nov 2006

  5. “Vapour” Starter – Two Stage RMWG Wits, 16 Nov 2006

  6. Liquid Resistor Start – Low Electrolyte Concentration RMWG Wits, 16 Nov 2006

  7. Eddy-Current Starter Start RMWG Wits, 16 Nov 2006

  8. Fundamental Design RMWG Wits, 16 Nov 2006

  9. Fundamental Design (cont.) RMWG Wits, 16 Nov 2006

  10. Fundamental Design (cont.) RMWG Wits, 16 Nov 2006

  11. Eddy-Current Transfer Analysis Methods • Thomson’s classical eddy-current theory • Rosenberg’s Assumption • Agarwal’s Methods • Poynting Vector • Finite Difference Method • Boundary Integral Method • Finite Element Method • Miscellaneous Numerical Methods RMWG Wits, 16 Nov 2006

  12. Non-linearity Issues – Current Density RMWG Wits, 16 Nov 2006

  13. Current Density Spectrum 2 RMWG Wits, 16 Nov 2006

  14. Current Density Spectrum RMWG Wits, 16 Nov 2006

  15. Current Density Spectrum (cont.) RMWG Wits, 16 Nov 2006

  16. Current Density Spectrum (cont.) RMWG Wits, 16 Nov 2006

  17. Leakage Effects RMWG Wits, 16 Nov 2006

  18. Conclusion - Practicality • Simple: No moving parts • Low Maintenance: As above • Variations of Impedances with Tappings • Smooth, (almost) Stepless variation of resistance with motor speed • Heat energy is distributed mainly in the iron core • Good for smaller (up to 800 kW) small to medium loads • Not ideally suited for long runup times • Ideal retrofit where supply can accommodate some additional current • No control functions – just impedance variation with tapping setting • Not a pure resistance – has an inductive component • Good low-maintenance replacement for low and medium load torque applications with short to medium runup times. RMWG Wits, 16 Nov 2006

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