An Approach for Insulation Diagnosis of Mica-Resin Coils

Used coils from a hydro-generator and an induction motor both in operation for many years, and also model coils subjected to accelerated agings were examined concerning the correlationship between the residual breakdown voltage VR and two nondestructive measurements Δ and Qm. It was found that VR could be expressed by the following equation, Uniformly degraded coils and partially and abnormally degraded coils could be classified by plotting the nondestructive measurements on X-Y coordinates where the X axis represents log Qm and Y axis, Δ.