TESTING OF THREE-PHASE IMs
Experimental investigation or testing of induction machines at the manufacturer’s and user’s site may be considered an engineering art in itself. It is also an indispensable tool in research and development of new induction machines in terms of new materials, sizing, topologies, control, or power supply and application requirements. There are national and international standards on the testing of IMs of low and large power with cage or wound rotor, fed from sinusoidal or PWM converter, and working in various environments. We mention here the International Electrotechnical Committee (IEC) and the National Electrical Manufacturers Association (NEMA) with their standards on induction machines (IEC34 series and NEMA MG1-1993 for large IMs) Temperature, losses and efficiency, starting, unbalanced operation, overload, dielectric limits, cooling, noise, surge capabilities, and electromagnetic compatibility tests are all standardized. A description of standard tests is not considered here as the reader may study the standards for himself; the space required would be too large and the diversity of different standards prescriptions is so pronounced that it may create confusion for a newcomer in the field. Instead, we decided to present here the most widely accepted tests and a few non-standardized ones which have been promoted recently, with strong international vigour. They refer to
• Loss segregation/power and temperature based methods • Load testing/direct and indirect approaches • Machine parameters estimation methods • Noise testing methodologies
22.1 LOSS SEGREGATION TESTS
Let us first recall here the loss breakdown (Figure 22.1) in the induction machine as presented in detail in Chapter 11.