Calibration of partial discharge measuring systems by a reference impulse charge generator

The calibration of a partial discharge measuring system is carried out to determine its scale factor. This operation is performed in the complete test circuit by injecting across the terminals of the device under test a known charge generated by a traceable calibrator. The paper presents the calibration of four different partial discharge measuring systems, carried out by using a programmable reference impulse charge generator developed at the Istituto Nazionale di Ricerca Metrologica. The device is composed of an arbitrary waveform generator and a series capacitor. By this instrument, the performances of the four systems (linearity, response to opposite polarity pulses, response to pulse train and pulse resolution time) are deeply investigated and compared. The results obtained show that the tests prescribed by the standards do not fully characterize the partial discharge measuring system behaviour. Additional checks should be carried out to better evaluate their performances, with particular reference to measuring systems which include advanced analysis tools.