Influence of stator winding structure on the relation between PD value and maximum discharge quantity in deterioration diagnosis of hydro-generators

In this study, the authors investigated on-line deterioration diagnosis of hydro-generators. Simultaneous measurement was done under off-line condition by using an on-line PD monitor and an off-line PD measuring system. When a stator had wave-winding structure, a good correlation between the maximum electric discharges of the offline PD measuring system and PD values of the online PD monitor was seen. On the other hand, when the stator had lap-winding structure, the correlation was not clear. PD values were small due to weak capacitive coupling of lap-winding structure. Then, PD measurement of hydro-generators with wave-winding structure was done under on-line and off-line conditions by using the PD monitor. Online PD values were slightly higher than offline PD values. From the results mentioned above, on-line PD monitoring is considered to be useful for diagnosis of hydro-generators with wave-winding structure.