Novel approach to the measurement of iron and stray load losses in induction motors

Successful design of electrical machines hinges on a knowledge of the likely temperature rise within the machine. The ability to predict an accurate temperature distribution, in turn, requires a knowledge of the iron loss distribution, thermal characteristics of the materials, and the cooling conditions, all of which are very difficult to quantify. A temperature-time method is proposed to evaluate accurately the iron loss density distribution in the stator of an induction motor by measurement of temperature gradients in the machine. This method is used to determine the iron loss density distributions, under various load conditions, in a specially constructed 3- phase, 4-pole, 4 kW frameless induction motor. Accurate stray load losses are then computed from the resulting loss density distributions. The experimental results were validated against those obtained with standard test procedures, as well as predicted results from finite element analysis.