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To establish a series of ppm-level high-voltage ratio standards up to 110 kV, we propose and have designed low-voltage-excitation two-stage voltage transformers (LVE-TSVTs) for high voltage. Ratio traceability for a 10 kV/100 V LVE-TSVT is vital in this scheme. This paper focuses on the voltage ratio traceability of the 10 kV LVE-TSVT by measuring the errors of the reference voltage and the voltage coefficient separately. A 1 kV double-TSVT with a 1 kV/100 V TSVT and a 100 V/10 V TSVT in cascade was developed and calibrated, and then was used to calibrate the error of the 10-kV LVE-TSVT at 10% rated voltage. The voltage coefficient was measured by comparing with a high-voltage capacitive divider through a current comparator bridge. The measurement was implemented in the range of 10%–120% rated voltage. The calibration results showed that the ratio errors of the 10-kV LVE-TSVT were less than $0.95 \times 10^{-6}$ in magnitude and $-1.26\,\,\mu $ rad in phase displacement at the 10% rated voltage. The expanded uncertainties are about $1.8 \times 10^{-6}$ in ratio and $2.2~\mu $ rad in phase, respectively, with coverage factor $k = 2$ .

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 cores. Three TSVTs, 10, 35, and $110/\sqrt {3} ~\textrm {kV}$ , were developed based on this scheme. The uncertainties of magnitude and phase of these TSVTs are all less than $3.2\times 10^{-6}$ and 1.1 $\mu $ rad, 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– $4\times 10^{-6}$ and $2~\mu $ rad in magnitude and phase, respectively, which reach class 0.0005 to class 0.001.