Development and calibration of an HV impulse reference divider

Summary

Development and calibration of an HV impulse reference divider requires high technological skills, solid experience in HV measuring and testing techniques, metrological competence, and high accuracy equipment. For this reason, only a few companies in the world provide HV impulse reference dividers, and very few laboratories are able to calibrate them. Also, only quite limited guidance is given by international standards. The paper reports the experience in the development and calibration of a 500 kV LI, 400 kV SI reference divider, manufactured by AME Srl for the RSE metrological laboratory, accredited for calibration according to ISO/IEC 17025 and IEC 60060-2 standards. The latter standard provides detailed indications for the calibration of approved measuring systems used in test laboratories during the qualification of HV equipment (insulators, transformers, disconnectors), but not much guidance is given for the calibration of a reference divider. Only the requirements for overall uncertainty of the complete Reference Measuring System (RMS) are provided, but no specifications are given for the individual uncertainty contributions and related testing methods. The development of the reference divider was performed taking into account all metrological requirements. The components were chosen to ensure maximum thermal stability, highest voltage linearity, and excellent dynamic behaviour. The design solutions were chosen to minimize stray capacitance and inductance, and to reduce response and settling time of the divider’s step response. Checks were made during the manufacturing to find better design solutions and to optimize the values of circuital components. After the first qualification tests performed in HV laboratories of RSE and INRiM (Italian National Metrological Institute), the divider, together with the transmission system and the measuring instrument, was calibrated by VTT MIKES, the Finnish National Metrology Institute (NMI). The calibration was performed by comparison with a RMS with measuring uncertainty = 0.5 % for test voltage (Ut) value measurement. This figure is achieved by correcting the dynamic behaviour of the RMS using deconvolution techniques. The paper presents the reference divider features, the methodology used by AME during the development to obtain high metrological performance, and the contribution of INRiM during the divider qualification tests for the determination of measurement uncertainty. The paper reports also the main calibration results, together with instrumentation and methodologies applied by VTT MIKES to obtain low uncertainties.

Additional informations

Authors

SAMARDZIC, JANUARIO DOS REIS, GERMOND, STEIN, SETHURAMAN, CAMPBELL, BIELECKI

Keywords

Calibration, HV Reference Measuring Systems, Impulse Measurements