Theoretical and empirical error analysis for the direct calibration of resonant partial discharge detection circuitry

An approximate expression for the inherent error associated with the direct calibration of conventional resonant PD (partial discharge) measurement circuitry has been derived. This relation defines an equivalent charge transfer ratio (ECTR), i.e. the ratio between actual and nominal charges transferred to an insulation test specimen, which explicitly shows the dependence of the direct calibration error on the magnitude of the calibrator coupling capacitor and the stray capacitance of the PD detection network. If the parasitic test loop capacitance is carefully estimated, then the ECTR can be determined and the direct calibration data scaled accordingly to yield a superior calibration. The expression is used to calculate the percent error for the calibration of a commercial resonant PD detector that is typical of industrial apparatus, and the results are compared to laboratory measurements and a computer model