Interturn Short-Circuit Detector for Turbine-Generator Rotor Windings

An effective new method of detecting interturn short circuits on round rotor windings is described. The approach used is to measure the rate of change of the air-gap flux density wave when the rotor is at operating speed and excitation is applied to the field winding. The measurements are obtained by the use of a small stationary search coil positioned near the rotor surface. The voltage outputs are recorded by Polaroid pictures from an oscilloscope screen and can be analyzed based on the information presented. The sensitivity obtained from these methods is far superior to previous methods. The data obtained at operating speed identify the coils and slots which have shorted turns, and provide a good indication of the number of turns shorted in a coil if more than one short exists.