Tracking stator bar condition by on-line partial discharge measurements

A total of 24 new stator bar windings in hydrogenerators were equipped with 80 pF permanent couplers for on-line partial discharge measurements beginning in 1979. This paper summarizes some of the changes in the PD characteristics that have occurred over the years and correlates significant changes with the condition of the windings.

I. Introduction

On-line measurements of partial discharge activity in air cooled stator windings of hydrogenerators allow detection of the effects of load, temperature and humidity at constant voltage. This paper discusses the experience with 24 roebel bar stator windings rated 13.8 kV and insulated with tank treated epoxy mica from one manufacturer. The characteristics of the generators will be found in Table I. TABLE I H<sc>ydrogenerators with</sc> R<sc>oebel</sc> B<sc>ar</sc> W<sc>indings</sc>**

Station	Unit	Installed	MVA	P-F	RTD	Slots
Grand Rapids	1 - 3	1993-01	132	0.95	110	504
Grand Rapids	4	1968	132	0.95	110	504
Long Spruce	1 - 10	1977-79	130	0.79	120	684
Limestone	1 - 10	1990-92	156	0.79	120	540

**maximum stator RTD oC is listed, all windings have 3 circuits per phase