Measurement of temperature in rotating electric machines

The paper discusses the advantages and disadvantages of standard and special methods of measuring temperatures, and also points out that the Standardization Rules on temperature tests are indefinite. The maximum temperature affecting the insulation is the factor to be determined in the measurement of temperature of electric machines. Thermometer and rise by resistance measurements have serious limitations under certain conditions, and the tests may either give erroneous results or must be carefully interpreted with due regard to the conditions under which they are taken. Thermocouple and exploring coil methods are discussed in more detail, since their application in temperature testing of electric machines, is comparatively new. A very convenient method of employing thermocouples is described and results showing the heat distribution in an electric generator are given. These results not only are valuable to the designer of machines, but also present important data concerning the shut down of machines after temperature tests. The question of the temperature of the air that actually cools a machine is discussed under “Room Temperatures.” Thermometer measurements are further discussed in regard to their application to machines, showing the lack of uniformity of results on account of the various coverings and pads that may be used. The method of stopping the rotating element is also referred to in regard to taking shut-down temperatures. The conclusion gives various recommendations to be considered in the revision of the Standardization Rules concerning temperature measurement.