Operation of high power cycloconverter-fed gearless drives under abnormal conditions

This paper presents the behavior of large power mills (more than 10 MW each) fed by cycloconverters. Special attention is dedicated to the protection philosophy to avoid operational interruptions which can produce huge production losses and equipment damage. Several failure possibilities are considered: control failure, complete power outage, if a thyristor fails and cannot block reverse voltage, etc. Simulation studies and field measurements show that large currents and torque can occur under certain circumstances and that motor foundations must be able to support them. As a general conclusion, it can be said that proper protective design effectively avoids equipment damage.