A new formulation for minimum input volt-ampere (VA)-slip relationship of three-phase induction motors

The magnetization component of input current of low-rating three-phase induction motor is large which results in poor power factor particularly at low-load conditions. The situation becomes critical when motor is fed from a distributed generating (DG) system. In this paper, the performance analysis of induction motor is carried out for minimum input VA. A distinct novel slip is found at which the input VA is minimum independent of the load conditions. This optimum slip is expressed in terms of motor per-phase equivalent circuit parameters. This novel relationship is valid for every induction motor. As compared to rated conditions, a drastic reduction in VA with a large improvement in power factor is observed. Although, a marginal change in output power and efficiency is recorded. All the analytical, simulated and experimental results match each other with a very fair degree of accuracy.