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Partial discharges occur because of insulation defects, when the electric field amplitude locally exceeds the dielectric strength of the cavities inside the insulating material. The thermal, chemical and electrical phenomena associated with the partial discharges are dangerous for insulation systems of high voltage equipment, as they can accelerate the aging process. Therefore, partial discharge tests are nowadays prescribed as routine tests for most of the high voltage devices. The calibration of a partial discharge measuring system is carried out to determine its scale factor before every test. The calibration is performed with partial discharge calibrator. IEC 60270 describes methods used for the evaluation of the actual charge generated by the calibrator. However, some factors that may influence the performance test results regarding the influence of circuit components, partial discharge measuring system’s linearity, bandwidth and pulse train response on calibration are not specified. This paper presents an improved method for performance testing of partial discharge calibrators. A reference partial discharge calibrator was used, and the traceability of calibration was established. Various effects on calibration procedure were investigated such as the influence of circuit components, partial discharge measuring system’s linearity, bandwidth and pulse train response on calibration. Performed tests in this paper showed that these factors cannot be neglected and therefore an improved method for performance testing of partial discharge calibrators is proposed which considers mentioned factors and minimizes their influence on the calibration procedure. |
