Detection of Hidden Inter-laminar Insulation Defects in Stator Core

Inter-laminar shorts occur in stator core of turbine generators while in service. Surface defects can be identified by high ring flux test but hidden defects inside the slot are difficult to find by this method. Detection technique of these invisible inter-laminar shorts in the bar filled slots of stator core is the main contribution of the paper. The mathematical calculations that must be done for the flux test and the usage of patter shapes of the fault current signals are detailed. Investigation study in locating the hidden inter-laminar defects in 250 MW, 16 kV turbine generator by low flux technique is presented. Correctness of the analysis is ensured by repeating the test after repair. This method is helpful to remove ambiguity in localization of the hidden defects and enables proactive plan of rectification.