Nonintrusive efficiency estimation for large power and high voltage induction motors

Nonintrusive efficiency evaluation method based on the air gap torque and rotor slot frequency is generally used in industry application. However, this method has the following problems: 1) the number of rotor slots should be given in advance; 2) with some special number of pole pairs and rotor slots, the stator and rotor slot harmonics may be aliasing, which may lead to great errors in identification results; 3) the solution of air gap torque needs a complicated solving procedure for flux linkage, which slows down the processing time for motor efficiency estimation; 4) the sampling frequency and the total duration of sampling can also affect the identification results significantly. To solve these problems, this paper firstly presents an on-line rotor slot number identification method based on Monte Carlo method, and the aliasing of the stator and rotor slot harmonics is avoided by determining the speed range of the different load conditions. Then, the transformation of integral for fast calculation of flux linkage is presented, and a corresponding criterion of the sampling frequency and the total duration of sampling is put forward to guarantee the correctness of identification. The above improving measures are applied to the estimation of the output power of large-power and high-voltage induction motors. To validate the presented method, experiments are carried out on a 5000 V, 80 kW induction motor, the accuracies of on-line efficiency estimation and speed identification at different load conditions are verified; and the developed efficiency estimation device is also installed on a 10 kV, 11 000 kW feeding pump motor in a power plant.