Interlaminar short circuits in slots of turbine generators: Detection and analysis

Short circuits occur in between steel leaves of magnetic core of turbine generators in service due to slot wall imperfections, inter laminar insulation damage and winding faults. Undetected defects for long time, results into hot spots, core fusion and fretting. EL CID - ELectromagnetic Core Imperfection Detector, a Condition Assessment Diagnosis (CAD) digital tool is engaged by machine diagnosticians to look at core damages. Power plant customers prefer this low induction precision identification method to high flux ring test for laminar shorts due to energy efficiency and safety provisions. This paper focuses on analysis of fault current signals of EL CID to locate core damages in the vicinity of slots. EL CID principles are briefed which works on Ampere's law and Faraday's law. Modern EL CID equipment features are highlighted. Fault classification with respect to induced current pattern is presented. Case studies of various waveform reports of EL CID before and after repair of core defects are presented.