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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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**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**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**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**WRIM Current and Torque Versus Speed**RMWG Wits, 16 Nov 2006**“Vapour” Starter – Two Stage**RMWG Wits, 16 Nov 2006**Liquid Resistor Start – Low Electrolyte Concentration**RMWG Wits, 16 Nov 2006**Eddy-Current Starter Start**RMWG Wits, 16 Nov 2006**Fundamental Design**RMWG Wits, 16 Nov 2006**Fundamental Design (cont.)**RMWG Wits, 16 Nov 2006**Fundamental Design (cont.)**RMWG Wits, 16 Nov 2006**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**Non-linearity Issues – Current Density**RMWG Wits, 16 Nov 2006**Current Density Spectrum 2**RMWG Wits, 16 Nov 2006**Current Density Spectrum**RMWG Wits, 16 Nov 2006**Current Density Spectrum (cont.)**RMWG Wits, 16 Nov 2006**Current Density Spectrum (cont.)**RMWG Wits, 16 Nov 2006**Leakage Effects**RMWG Wits, 16 Nov 2006**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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