Method for in-field evaluation of the stator winding connection of three-phase induction motors to maximize efficiency and power factor

The performance of the oversized three-phase induction motors can be improved, both in terms of efficiency and power factor, with the proper change of the stator winding connection, which can be delta or star, as a function of their load. A practical method is proposed to quickly and easily evaluate which stator winding connection is more appropriate for the actual motor load profile, in order to increase the motor efficiency and power factor. This new method is suitable for in-field evaluation, because it requires only the use of inexpensive equipment and has enough accuracy to allow a proper decision to be made. The automatic change of the stator winding connection, as a function of the motor line current, is also analyzed. When properly applied, these methods can lead to the improvement of the efficiency and power factor of permanently oversized motors, motors with a load variation between low load and near full load during their duty cycle, and/or motors driving high-inertia, low duty cycle loads. The proposed methods are particularly suitable to industrial plants where typically many electric motor systems are oversized and/or can have a wide load variation. In these conditions, the active and reactive electrical energy bill can be significantly reduced.