Precision 500/√3 kV three‐stage VT with double excitation

To develop the highest standard for high‐voltage ratio at power frequency, this study describes a three‐stage voltage transformer (VT) with high‐ and low‐voltage double excitation. In this high‐voltage VT, all primary windings are wound as a ‘pyramid’ structure, making it work at higher‐voltage possible. Moreover, the two high excitation and ratio coils are located as vertically symmetrical distribution, good for solving the insulation problem between two primary windings. On the basis of this scheme, a precision 500/√3 kV three‐stage VT has been developed. Calibration based on ‘series summation’ indicates that in the range of 20–120% rated voltage, the error of the three‐stage VT is as follows: (−17.2 to + 7.1) × 10 −6 for the ratio error and −5.1 to −1.3 µrad for the phase error, which reaches accuracy class 0.002. Moreover, the uncertainty of this three‐stage VT is 8.7 × 10 −6 for ratio and 8.7 µrad for phase ( k = 2).