Synthesis of Hydropower Plant Monitoring Experience using Conventional and Un-Conventional Partial Discharge Measurement Sensors


Dr Raja Kuppuswamy
Dynamic Ratings

Paper Authored by

Dr. Raja Kuppuswamy
Dynamic Ratings

Sandy Rainey
NCPA Hydroelectric Operations

Availability of a power plant depends crucially on the reliability of major high voltage components such as the generator, isolated phase bus (IPB) and the generator step-up transformer (GSU). These assets are interconnected and when they are monitored in isolation, it could result in false conclusions of the origin of the fault sources and false alarms. Conventional approach has been to use two capacitive couplers one near the monitored asset (generator / transformer) and another inside the bus duct to eliminate discharges outside the monitored asset. This solution has practical limitations.  We used direction sensitive high frequency partial discharge (PD) sensors across the isolation joint between the monitored asset and IPB enclosures as means to separate wanted and unwanted signals and locate problems within the bus-duct.  Working principle and problems detected are reported in the paper.

 It is generally accepted within the industry that terminal partial discharge (PD) measurements are less sensitive to electrical discharges deep within the stator windings. Typically, on large generators, electrical defects beyond 10-15% from the line-end of the stator winding cannot be detected. This equates to first 2 to 3 coils from the line-end.Therefore, other measures are necessary to expand the zone of detection. Large generators are typically equipped with 12 or more resistive temperature detectors (RTDs) embedded into the stator winding. The RTD acts as an RF-antenna placed into a winding that is sensitive to the high frequency component of an electromagnetic pulse caused by PD. The RTD is both capacitively and magnetically coupled to the PD pulse originated by a discharge. Using case examples, we show how RTD PD sensors have been useful in detecting problems deep within the windings and loose bars.

Raja Kuppuswamy is senior principal engineer at Dynamic Ratings (DR) Inc., based in Sussex, United States.  In 1996, he earned his PhD degree in high voltage engineering for his doctoral thesis on the study of the aging life-cycle of power transformer insulation using partial discharge pattern recognition techniques.

Over the next 22 years, he pioneered the development of eight partial discharge measurement and analysis tools based on ultra-high frequency, ultrasonic and traditional PD sensing technologies.

Prior to joining DR, he held product management, sales and technical services positions at ABB, Alstom, Crompton Greaves, Haefely in France, India, Sweden and Switzerland. He served in CIGRE, France and IEC, Switzerland technical committees on partial discharges. He is senior member IEEE, holds 4 patents and 120 scientific publications.