Precision Calibration System for Partial Discharge Calibrators

Jussi Havunen,Jari Hällström

doi:10.5324/nordis.v0i26.3264

Abstract

Partial discharge calibrators need to be periodically calibrated traceable to national standards. VTT MIKES, the National Metrology Institute (NMI) of Finland, has official expertise to calibrate the apparent charge of PD calibrators from 1 pC to 100 nC according to IEC 60270. Recently, VTT MIKES has developed techniques to measure charges as low as 0.01 pC with 3 % uncertainty (k = 2). VTT MIKES has participated to an intercomparison of four NMI’s in 2018 and the results indicate that VTT MIKES can both expand their official measurement capabilities and lower their uncertainties. This paper presents VTT MIKES’s precision calibration system for PD calibrators. Additionally, an overview of commercial PD calibrators’ performance is provided and compared to the requirements of IEC 60270. Data is based on the calibrations performed during the last 10 years.

Highlights

Partial discharges (PD) are unwanted in high-voltage insulation systems because they may lead to flashover and unrecoverable damage of solid insulation
PD calibrators are widely available commercial devices that periodically need to be calibrated traceable to national standards
At the moment VTT MIKES has official competence to calibrate the apparent charge of PD calibrators from 1 pC to 100 nC according to IEC 60270 using numerical and analog integration

Summary

Introduction

Partial discharges (PD) are unwanted in high-voltage insulation systems because they may lead to flashover and unrecoverable damage of solid insulation. In addition to the technical requirements, the standard defines that performance tests should be performed periodically to PD calibrators. These tests should include the determination of the calibrator charge, rise time of the step voltage, and the pulse repetition rate. At the moment VTT MIKES has official competence to calibrate the apparent charge of PD calibrators from 1 pC to 100 nC according to IEC 60270 using numerical and analog integration. The charge-sensitive preamplifier (CSP) based analog integration method for low charges is not yet described in our CMCs. The high signal-tonoise ratio of the CSP makes it possible to calibrate the step voltage parameters with low uncertainty. All PD calibrations are traceable to SI via Finnish national standards of capacitance, DC voltage and resistance

Generation of reference charge

Measurements: numerical integration method

Measurements: analog integration method

Current performance

Findings

Conclusions