Heating of a D-C armature

T. M. Linville (General Electric Company, Schenectady, N. Y.): The paper suggests the use of the contact thermocouple for measuring surface temperatures. The thermometer has the advantage of simplicity since any number of them can be placed in position rapidly and read repeatedly in succession with little chance of error. It is conceivable that a number of thermocouples could be attached to the rotor after shutdown and read repeatedly in succession without disturbing them. However, it has always appeared more satisfactory to use thermometers. Therefore, in connection with data relating internal and surface temperatures, it is recommended that thermometers be used to determine the latter. Other methods of measuring surface temperatures include the use of alloys having melting points about ten degrees apart, fastened to the armature in inaccessible spots and covered with thermal insulation, pyrometers, and (for commutators) thermocouples placed in a hole drilled in the face of brushes which are electrically and thermally insulated. In connection with the use of thermocouples, the leads may be brought out through copper and “copnic” slip rings without difficulty, using leaf brushes of the same material.