Novel electronic device to improve the performance of variable-torque fixed-speed induction motors

In this paper, a novel ultra-compact, self-powered, high-efficiency, solid-state electronic device to reduce the energy consumption and improve the power factor at light load of direct-on-line, variable-torque, fixed-speed, three-phase, squirrel-cage induction motors, by means of a novel load-based stator-winding connection-mode management technique, is presented, including some technical and economic considerations on its use. This device also performs optimized motor soft-starting, advanced motor protection and fault diagnosis. The ultra-compact design enables the device to be installed inside the motor terminal box, saving space in the switchboard. In relation to the electromechanical star-delta starters, the proposed device offers higher reliability and requires half of the cables from the switchboard to the motor. Moreover, due to the independent per-phase switching control, the current and voltage transients produced during the switching instants are smoother, extending the motor lifetime. The energy savings potential in applications with long low load periods can be up to 15%.