The Development of Two-Stage Voltage Transformer With Accuracy Class 0.001

This paper presents a new structure of a two-stage voltage transformer (TSVT) with toroidally wound ring cores excited by low voltage for high-voltage measurement. In the new TSVT, two high-voltage windings are wound on two separate groups of toroidally wound ring cores, respectively. This avoids the insulation problem in the traditional TSVT structure for high voltage and high accuracy, in which, the high-voltage excitation and ratio windings need to be wound together around overlapped V cores. Three TSVTs, 10, 35, and 110/√3 kV, were developed based on this scheme. The uncertainties of magnitude and phase of these TSVTs are all less than 3.2 × 10^-6 and 1.1 μrad, respectively, at reference voltage. Comparative measurements with a high-voltage capacitive divider and a current comparator illustrate that in the range of 20%-120% rated voltage, variations of no-load errors of new TSVTs are as follows: 2-4 × 10^-6 and 2 μrad in magnitude and phase, respectively, which reach class 0.0005 to class 0.001.