A comparison of measurements of voltage transformer (VT) voltage ratio and phase displacement was performed between the National Center for High Voltage Measurement (NCHVM), China and the National Measurement Institute (NMI), Australia, with two voltage transformers provided by the NCHVM being used as the travelling standards. Voltage ratios of the 10 kV/100 V transformer measured by the two institutes differed by less than 5 μV/V and the phase displacement by less than 6 μrad, while voltage ratios of the (110/p3 kV)/100 V transformer differed by less than 16 μV/V and 13 μrad. These results confirmed that measurement results of the two institutes agreed within detailed measurement uncertainties evaluation. The comparison further enhances the confidence in both methods, which are widely used for calibration of voltage transformers in the electricity industry.

Capacitive leakage and adjacent interference are the main influence sources of the measuring error in the traditional series step-up method. To solve the two problems, a new algorithm was proposed in this study based on a three-ports network. Considering the two influences, it has been proved that response of this three-ports network still has characteristics of linear superposition with this new algorithm. In this threeport network, the auxiliary series voltage transformers use a two-stage structure that can further decrease measurement uncertainty. The measurement uncertainty of this proposed method at 500/√3 kV is 6.8 ppm for ratio error and 7 μrad for phase displacement ( k = 2). This new method has also been verified by comparing its results with measurement results of the PTB in Germany over the same 110/√3 kV standard voltage transformer. According to test results, the error between the two methods was less than 2.7 ppm for ratio error and 2.9 μrad for phase displacement.