Accurate steady-state performance assessment of three-phase induction motor using NEMA definition

This paper highlights the shortfalls of the NEMA and IEC defined indices for the quantification degree of voltage unbalance. It is shown that these indices are not accurate for the assessment of voltage unbalance conditions. The large variations in terminal voltage for fixed values of these indices result in vague assessment of the voltage unbalance by these standards. To reduce this anomaly, numerous indices have been developed by the researchers. Generally, great attentions have been paid on IEC based indices. However, this paper considers the indices defined by NEMA standard, as it is highly recommended by industrial engineers, due to its simplicity. Two new indices are introduced and it is shown that, the degree of unbalance as defined by NEMA along with proposed indices reduce the terminal voltage variations. Hence, the proposed indices in association with NEMA index, give the accurate estimation of voltage unbalance assessment.