Efficiency determination of standard asynchronous machines from start-up data

There are various methods to determine the efficiency of three phase induction machines. But all of them have in common that they are inaccurate or they are impracticable. In this paper the machine efficiency will be derived from start up data. For that purpose the time dependence of all stator currents and all stator voltages have to been measured. Normally it isn't possible to mount a speed sensor on the machine. For this reason only the speed at the end of the start up can be determined. Practical results with standard three phase induction machines with different power ranges from 3 kW up to 500 kW are presented.