A New Partial Discharge Measuring System Calibrator

A new PD (partial discharge) measuring system calibrator is described. The device, battery operated, may be used either grounded or in a floating position, and generates securely mains-synchronized impulses by capacitive coupling. It allows the determination of the scale factor k and resolution time Tr in PD measuring systems, and it fulfils the requirements of International Standard IEC 60270. PD measuring instruments have mains-synchronized sweeps. Hence, in order to have stationary calibration impulses in the PD measuring instrument , the calibrator must generate mains-synchronized impulses. Usually, PD calibrators synchronize to mains frequency by a photodiode. In case of insufficient pick-up of power frequency light, these calibrators automatically select an internal quartz oscillator. When the internal oscillator is on, there is usually a slight difference between the oscillator frequency (fixed) and the mains frequency (variable), and consequently the impulses generated by the internal oscillator are not stationary in the PD measuring instrument (detector screen). This new calibrator avoids that problem because it generates securely mains-synchronized impulses by capacitive coupling, making unnecessary an internal quartz oscillator.