Stray Load and Iron Losses in Small Induction Machines Under Variable Operating Frequency and Flux: A Simple Estimation Method

In this paper, an engineering approach to estimation of the fundamental stray load and iron losses in small induction machines (IMs) is proposed. This approach consists of experimental testing carried on several IMs of different efficiency class and rotor cage material, all rated 1.5 kW, followed by the derivation of simple empirical formulas for estimation of these two types of losses. The iron losses are evaluated as variable with respect to the operating frequency and flux, whereas the stray load losses are evaluated as variable with respect to the operating frequency, flux, and torque. Application of the proposed formulas does not require any additional tests other than those imposed by international standards, and, equally important, they do not include any constructional details of the IM. The validity of the formulas is verified by comparison of the estimated and measured losses in wide ranges of the operating frequency, flux, and torque. The proposed methods of estimation offer possibilities for application in the analysis of small IMs under various operating conditions with sinusoidal supply, as well as in developing advanced IM models and vector control algorithms.