Accurate performance assessment of IM with approximate current unbalance factor for NEMA definition

The indices, namely, line voltage unbalance ratio (LVUR) and voltage unbalance factor (VUF), defined by NEMA and IEC, respectively, were highly recommended amongst the industrial engineers and researchers to quantify the condition of voltage unbalance. However, the existence of infinite voltage sets for fixed value of these indices produces erroneous estimation of voltage unbalance conditions. In this paper, three new indices, namely, maximum current deviation (MCD), combined maximum current deviation (CMCD), and effective current deviation (ECD), based on current measurement, are introduced. The proposed indices are used with LVUR to assess the effects of voltage unbalance. It is found that the information of proposed indices, along with LVUR, makes precise and unique assessment. Additionally, the various performance parameters are evaluated using these proposed indices and it is shown that the index ECD is more capable to reduce the variation in performance parameters for fixed value of LVUR. Hence, the index ECD is suggested to incorporate with LVUR to make unique and accurate assessment of voltage unbalance.