Abstract
Modern partial discharge (PD) calibrators often have their lowest range below 1 pC. However, traceable calibration services below 1-pC charges are not widely available, or their uncertainties are relatively high because of low signal levels. We have applied a commercial charge-sensitive preamplifier for the low-level calibration of PD calibrators. This calibration method both improves the signal-to-noise ratio and performs the analog integration of the PD pulse. The drooping response of the preamplifier is corrected using software. Comparison with a reference PD calibrator supports an expanded uncertainty less than 1% down to 0.1 pC and 3% for 0.01 pC.
Highlights
M ODERN commercial partial discharge (PD) calibrators often have their lowest charge level as 0.1 pC
At the moment, National Metrology Institutes (NMIs) provide traceable calibration services for apparent charge starting from 0.5 pC, and the smallest relative uncertainty at this level is 3%
Performance test of a PD calibrator should be performed periodically, and it should include the determination of the calibrator charge, rise time of the step voltage, and the pulse repetition rate
Summary
M ODERN commercial partial discharge (PD) calibrators often have their lowest charge level as 0.1 pC. With the numerical integration method, the amplitude of the measured impulse voltage can be only a few millivolts with charges below 1 pC. This low impulse voltage is very difficult to measure accurately with a digitizer. Hauschild and Lemke [4] have pointed out that on low PD level below 10 pC, the use of an electronic integrator will significantly amplify the voltage and improve the signal-to-noise ratio Earlier, their use with charges ≥100 pC has been verified and compared to the existing methods [5]. CSPs are characterized using the reference method, and their use is compared to the commonly used numerical integration method
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