Electric tracion—Rotating electrical machines for rail and road vehicles—Part 3:Determination of the total losses of convertor-fed alternating current motors by summation of the component losses
1 Scope
This part of GB/T 25123 applies to machines complying with GB/T 25123.2.
The total losses of a convertor-fed motor may be determined by summation of the component losses derived from no-load and load tests. The total input power is the sum of the power at the fundamental frequency and at all other frequencies. In all practical cases the latter input includes the losses resulting from the voltage and current harmonics in the convertor supply by using suitable instrumentation it can be derived from measurement of the total and fundamental frequency power inputs when the machine is on load.
The losses supplied at the fundamental frequency cannot be measured directly and so are derived from measurement of the fundamental frequency load current and the fundamental frequency no-load power input.
2 Instrumentation
The extra loss due to operation on a convertor supply is obtained from the difference of the total and fundamental frequency power input on load.
The power inputs shall be measured simultaneously on each phase by a digital sampling instrument. Measurement on all three phases is preferred but the two wattmeter method is permissible as an alternative.
The total power is obtained from the product of voltage and current over a period of time and the fundamental power from a Fourier transform using the same sampling.
It is necessary to consider the accuracy of the whole instrument chain taking into account both amplification and phase shift errors over the desired frequency range. As the power factor of the harmonics is generally very low (less than 0.1 for voltage imposed asynchronous systems) particular attention is drawn to the need for minimum phase angle errors.
Wattmeters accurate within the following frequencies, at 0.08 power factor, were available:
— below 2 kHz ±0.5%;
— between 2 kHz and 20 kHz ±1.0%;
— between 20 kHz and 50 kHz ±2.0%.
Instruments often contain attenuators compensated and adapted to them, but if an external attenuator is used, it is desirable that it be accurate within the following limits given in Table 1.
Foreword II
1 Scope
2 Instrumentation
3 Summation of Losses
Annex A (Informative) The Equivalent Circuit of Asynchronous Motor
Annex B (Informative) Stray Load Loss
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