Rational Temperature Guarantees for Large A-C Generators

Abstract

The paper is an argument for the standardization of temperature guarantees when the guarantee is based on internal temperatures as measured by thermocouples. It is recommended that in all cases the maximum safe operating temperature of the insulation be used as the temperature guarantee, instead of using a lower temperature. The standardized guarantee, 50-deg. rise by thermometer, is cited in comparison with the present wide range of temperature rises, from 60 deg. to 100 deg., that have been called for in specifications when the thermocouple method of measurement is used. Arguments are presented from the stand-point of both the designing and the operating engineer for the use of this standardized temperature rise. Curves are shown illustrating the temperature conditions in both stator and rotor of a typical large, high-voltage turbo-generator. Examples, based on these curves, are given to show that a low temperature rise guarantee for the stator does not necessarily result in margin for overloads. This margin for overloads is the main argument that can be advanced in favor of low temperature rises. The only way in which the purchaser can be certain of overload margin is to have the specifications call for the maximum rating desired, in which case the maximum safe operating temperature may logically be made the temperature guarantee.