Influence of Auxiliary Impedance on Stray Load Loss Determination with Eh-Star Method
The eh-star method acc. to the new edition of standard IEC 60034-2 is a simple and economical alternative test for stray load losses assessment in induction machines also for higher efficiency above 96％. It is an asymmetrical single phase circuit, where two machine phases are connected in parallel through an auxiliary resistance R<,eh> without coupling of the machine and without needing any dynamometer. This auxiliary resistance shall be adjusted, so that the positive sequence current I1 stays below 30％ of negative sequence current I2. The determination of stray load losses must be done from the measured losses by decomposition into positive and negative sequence losses. Negative sequence losses at slip 2-s≌2 correspond to stray load losses, similar to the standardized reverse rotation test. For this evaluation, phase angles of measured currents and voltages must be known. This can be done by calculation with two different methods (A) and (A1), which yield identical results for ideal ohmic resistance R<,eh>. The sensitivity of both methods on the phase angle φ <,eh> of the impedance Z<,eh> = Z<,eh>e<jφ><,eh>, which is taken instead of R<,eh>, and on measurement errors of current, voltage and resistance is investigated, showing that method (A) is useful, whereas method (A1) should not be used. As a checking parameter, the calculated input power P<,cont> is a good indicator for the accuracy of the calculation model and of the measurement. The calculated input power P<,cont> should be identical with the measured input power P<,e, in> within 1％, which corresponds to a phase angle deviation from the ideal value φ<,eh> =0°by-10°≤φ<,eh> ≤10°In addition the sensitivity of the eh-star test on the winding temperature and on the measurement circuit is investigated.
M. Aoulkadi A. Binder
Department of Electrical Energy Conversion, Darmstadt University of Technology, Germany
国际会议
北京
英文
542-553
2007-06-10（万方平台首次上网日期，不代表论文的发表时间）