Diagnosis of rotor winding shorts through signal reflection

Inter turn shorts are of major concern in rotor windings of high speed turbine generators (TG) which result in excess vibration, over excitation energy and higher temperature. Recurrent Surge Oscilloscope (RSO), a condition assessment test tool is getting popular in Indian power industry for shorted turns identification and localization in field windings. This paper objective is to detect inter turn short circuits in TG rotor windings by recurrent surge oscilloscope (RSO) which works on time domain reflectometry (TDR) principle. Rotor winding is modeled as equivalent electric circuit of transmission line with cascade sections of RLC network for electric and magnetic field transfer. A delay line unit is constructed to get hands-on experience of RSO method and to understand the resultant signal reflection waveforms. Test data of RSO on 30MW, 11KV TG faulty rotor is presented before and after fault rectification. Some more experiments have been conducted by deliberate shorts creation and interpretation of the reflection signals are discussed. This study shows that RSO is a sure shot test in detection of inter turn shorts over the traditional approaches for right refurbishment action.