A self-calibrating technique for starting 3-phase cage induction machines on single phase supply lines

A novel self-calibrating technique for starting 3-phase cage induction machines on a single-phase supply with no inrush currents is described. The method uses a simple starting circuit to bring the machine up to near its rated speed within a very short period of time by generating a very high starting torque. The already spinning motor is then connected to a single-phase supply to operate in a standard Steinmetz configuration, thus eliminating any inrush currents at starting. A self-calibration system built into the system starts the motor under the exact load conditions by determining the best transition time before connecting the motor to the mains supply. Numerical and analytical solutions for the transient behaviour of a 1.1 KW machine during starting under various operating conditions are presented and compared with experimental results. The method is simple and low in cost, and is particularly useful in rural applications where the supply lines are generally weak.