A Formula for Class F Induction Motor Specified Temperature

In this paper, a formula to estimate the specified (full-load) temperature of insulation class F induction motors is proposed. The formula is structured via an extensive investigation conducted on a database which consists of 141 small- and medium-sized induction motors, in the range of 1-500 hp, provided by the Laboratoire des Technologies de l'Énergie, Institut de Recherche, Hydro-Québec. The same is done on another tests set of 46 (aged) induction motors of the same insulation class that is provided by BC Hydro. To validate the proposed formula, the stator I²R loss is calculated based on the corrected stator resistance as per the measured full-load temperature, IEEE assumed temperature, and the proposed temperature formula. A comparison is conducted using the absolute normalized percentage error resulted from both the IEEE and the proposed formula. The new formula demonstrates better accuracy. This formula shows the potential to replace the existing IEEE formula for Class F induction machines in the 1-500 horsepower range.