A method of measuring loss distribution in electrical machines

The paper discusses the need for new measurement techniques for the investigation and evaluation of machine behaviour. The disadvantages of former methods of core-loss measurement are dealt with, and an improved thermal method is described, based on the principle that the initial rate of rise of temperature at any point is proportional to the loss generated at that point. It is shown theoretically that, to achieve sufficient accuracy, measurements must be made over a short period of time, and this requirement is met by the use of a chopper-type d.c. amplifier and recorder to measure the e.m.f. generated in thermocouples. The measuring equipment is described and the effects of stray a.c. pick-up are discussed. Examples of applications are given which show that not only can the core-loss distribution be measured but also the effects of changes of geometry or materials can be studied by tests on a single production machine.