Design and Voltage Supply of High-Speed Induction - Aaltodoc
Design and Voltage Supply of High-Speed Induction - Aaltodoc
Design and Voltage Supply of High-Speed Induction - Aaltodoc
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104<br />
8.6 Conclusion<br />
Circulatory currents in the stator winding were suspected <strong>of</strong> causing some <strong>of</strong> the discrepancy<br />
between electromagnetic loss measured <strong>and</strong> calculated. Stator winding <strong>of</strong> a high-speed motor was<br />
prepared for the measurement <strong>of</strong> individual str<strong>and</strong> currents <strong>of</strong> the filamentary winding.<br />
Circulatory current loss coefficients were measured at different frequencies up to 450 Hz with a<br />
sinusoidal input current. The measurement proved circulatory currents flowing in the parallel<br />
str<strong>and</strong>s <strong>of</strong> the filamentary winding <strong>and</strong> causing significant power loss. At 450 Hz, the effective<br />
circulatory current loss factor was 1.37. This means a 37 % increase in power loss in the stator<br />
winding due to the circulatory currents.<br />
A model to estimate the value <strong>of</strong> the loss coefficient at the frequency <strong>of</strong> 835 Hz was made. This is<br />
the supply frequency used in the measurements in Chapter 5. The estimated value for the effective<br />
circulatory current loss factor was used to scale the calculated values <strong>of</strong> the power loss in the stator<br />
winding. This was done for the motor with a copper coated rotor. After this scaling, the calculated<br />
electromagnetic loss agrees well with the measured one. Thus, taking the circulatory currents into<br />
account improves the validity <strong>of</strong> the model in the design <strong>and</strong> optimization <strong>of</strong> high-speed machines.