Improved Stepup Method to Determine the Errors of Voltage Instrument Transformer With High Accuracy

Improvements in the method of determining voltage instrument transformer (IT) errors are described in this paper. Two auxiliary ITs are used in series and separately to test the standard voltage IT under test on the voltage of U and 2U to measure the errors variation between these two voltages. The experimental results showed that the measurement uncertainty of the method was below 5×10-6and 4 μrad at an applied voltage of 110/√3 kV. This method is used to finish the traceability of the standard ITs up to 1000 kV.