Verification of a Capacitive Voltage Divider with 6-μrad Uncertainty up to 100 kV

A reference setup for system calibration of industrial transformer loss measurement (TLM) systems consists of three main components, a voltage divider, a current transformer, and a power meter, and their phase displacements should each not be more than 10 $\mathrm {\mu }$ rad to achieve an overall system uncertainty of better than 20 $\mathrm {\mu }\text{W}$ /VA. We have extensively verified the uncertainty level of the current-comparator-based capacitive voltage divider (CVD) used in the TLM reference setup of the Van Swinden Laboratorium (VSL), both from the component level and the system as a whole. Different practical conditions relevant for on-site measurements are considered, e.g., measurement cable lengths, cable types, and grounding. The verification measurement results show an agreement of better than $(6 \pm 6) \times 10^{-6}$ in ratio error and $(4 \pm 6)~\mathrm {\mu }$ rad in phase displacement between the CVD component and system calibrations up to 100 kV. Requirements for achieving this agreement are adequate grounding of the CVD and the use of triax cable between the high-voltage (HV) capacitor and the CVD low-voltage electronics in case large distances have to be covered on-site. The $(4 \pm 6)~\mathrm {\mu }$ rad agreement in phase displacement is well within the required 10 $\mathrm {\mu }$ rad limit for voltage measurements as part of on-site TLM system calibrations with 20 $\mathrm {\mu }\text{W}$ /VA overall uncertainty at low power factors.