The Development of Precision 500/√3-kV Two-Stage Voltage Transformer With High-Voltage Excitation

Two-stage voltage transformer (VT) based on high-voltage excitation is usually less than 10 kV due to insulation limitation. To develop a two-stage VT with high-voltage excitation above 10 kV, this article designed two feasible structures. By calculating and comparing the lengths of the magnetic path, a better structural scheme was selected. The excitation winding and the precise ratio winding are in an "up-and-down" structure. This makes it work at a higher voltage possible. Moreover, a flexible compensation circuit was added to the secondary of this two-stage VT to acquire higher accuracy. Based on the principle, a 500/root 3-kV two-stage VT has been developed. The half-symmetry summation method was used to calibrate this two-stage VT. The measurement results indicate that the voltage coefficient is very low. The error is (-2.2 to +3.1) mu V/V for the ratio error and (-2.6 to -0.2) mu rad for the phase displacement in the range of (20%-120%) rated voltage.