Transients and partial discharges recording in power reactors during normal operation

Transient conditions were studied in 50 MVARpsilas 400 kV power reactors employed in line compensations. The recording system was installed on a tap bushing and it was designed and constructed to provide linear output for frequencies ranging from 60 Hz to 500 kHz. The system output is fed to a fast digitizer that allows recording of all opening and closing circuit breaker operations. Grounding and over voltage protection was given a special attention, especially for recording system, preventing damage to electronic equipment, since all measurements were performed with the reactor directly connected to the 400 kV interconnected power system. Those records reveals that voltage transients above 2.3 pu are present during opening operations and that the energy trapped in the power reactor oscillates with the reactor winding capacitance producing a resonant circuit with natural frequencies above 1 kHz. Since testing of reactors is not normally performed in factory due to its large impedance, its behavior under such large transients and higher frequencies is not known and partial discharge (PD) during such transients can be deleterious and limit its usable life. In this paper construction details are presented regarding the measuring circuit, showing Impulse and 60 Hz response. The system was placed into service after calibration with a portable impulse generator that applied 300 kV switching impulse. During normal operation the system allowed PD measurements to be obtained at 60 Hz.