Suppression of overvoltages in high voltage induction motor

Generally in industrial plants, over voltages of impulse type are not considered; hence the impulse test of the equipment is not specified. This paper shows reduction of high voltages transients in a 6.6 kV systems, when a high voltage motor is operated though a vacuum switch. It also explains the failures of the motors. The voltage rate of change with time of the transients is about one micro second. A model was built in the MATLAB for simulating switching operations that are not easy to be tested in the real system or difficulty to record. A benchmark model suggested by CPRI, Bhopal, India is used as motor-equivalent circuits during switching operations. Measurement of switching in over voltages, current chopping and re-ignition over voltages has been done. Different techniques for their reduction have also been presented. Here a common protection system is used for all transient reduction. This is very economical from industrial point of view.