Frequency Converter applications

Induction motor powered by frequency converter may require additional testing following a fault identified as a stator related anomaly. If the inner phase insulation is damaged or weak, the rapid voltage rise seen from many frequency converters can result in inner phase currents sufficient to cause the frequency converter failure. This article is designed to give the analyst additional motor circuit evaluation test data, using the motor circuit evaluation for de-energized testing, to better isolate the cause of the failure to the frequency converter or motor. It is applicable only for induction motors with >3 leads exposed at the connection box.

Frequency converters are now finding wide use in mining applications. Most of these frequency converters use adjustable frequency outputs that are produced by rectifying the AC power supply to DC and then inverting this DC voltage back into AC using a high frequency carrier and pulse width modulation (PWM) to produce adjustable frequency, adjustable voltage supply to the motor.

Actually in the plant the generator, compressor, gas turbines are all on a single shaft. I have a doubt that if we are using static frequency converter then we can start with giving low frequency to the stator... and if the frequency is low then can magnetic locking between stator and rotor can take place directly (without excitation) and after that we can increase the frequency to stator & after reaching say 75% speed the turbine will be self-sustaining and the static frequency converter supply can be cut off with the rotor being driven by the gas turbines then at this point if we give the excitation it can run as a Synchronous Generator.