Capacitive couplers with increased sensitivity for on-line PD measurement in stator windings

Capacitive couplers traditionally used for on-line PD measurement in rotating machines have been 80 pF. Recently it has been found that increasing the capacitance of 80 pF couplers can increase detection sensitivity. This paper presents theoretical analysis, laboratory tests and field test experience to compare traditional 80 pF couplers and higher-capacitance couplers for on-line PD measurement in rotating machines. The frequency bandwidth of various capacitive couplers is characterized and tested in relation to the PD detection sensitivity. This investigation concludes capacitive couplers with a higher capacitance than 80 pF are more sensitive for on-line PD measurement in rotating machines. They can detect more partial discharges and higher PD magnitudes than 80 pF couplers