Accuracy testing of an inductive voltage transformer under rated fundamental voltage and superimposed harmonics
Publication Name
CIGRE Science and Engineering
Abstract
Measurement of harmonics in high-voltage networks has become increasingly important due to the increasing presence of harmonic voltages produced by power electronics in renewable energy generation plants. While new types of wideband voltage measurement devices are being deployed, the majority of voltage measurement instruments in the present high-voltage networks are still either the traditional inductive voltage transformers (IVTs) or the capacitive voltage transformers (CVTs). The traditional voltage transformers are designed for measuring at the power frequency and accuracy tests on these transformers are only performed at the fundamental frequency in accordance with international standards. It has been shown that frequencies of the harmonics from the renewable power plants can be as high tens of kilohertz at some system voltage levels. This poses challenges for measuring the harmonics utilising the majority of voltage transformers in the networks if the accuracy of these transforms for measuring harmonics has not been determined. Therefore, determination of the accuracy of the transformers for harmonic voltages with traceable measurements becomes critical. While the bandwidth of the high-voltage CVTs have been found to be insuf cient for accurately measuring harmonics beyond a few hundred hertz, some IVTs, however, are believed to be potentially capable of accurately measuring harmonics of much higher frequencies. In this paper, the ratio accuracy and the phase displacement of a 33 kV IVT used in a gas insulated substation were measured under harmonic voltages up to 50th order, i.e. 2500 Hz. Since the accuracy of an IVT is usually signi cantly dependent of the applied voltage, tests were performed not only with the harmonic voltages, which are normally signi cantly lower than the rated fundamental voltage, but also with harmonic voltages superimposed on the rated fundamental voltage. Accuracy results obtained with different levels of harmonic voltages under different test conditions are presented. The test results showed that maximum ratio error and maximum phase displacement of this particular IVT were +4.5% and-1.2 crad respectively, under the rated fundamental voltage superimposed with harmonics of up to 2500 Hz, and did not differ signi cantly from those measured with the individual harmonic voltages alone. The paper also describes the measurement system used for performing the accuracy tests, which included a high-voltage capacitive divider, two precision digitisers and measurement software that allows synchronisation of the two digitisers. The measurement uncertainties are also discussed.
Open Access Status
This publication is not available as open access
Volume
2023
Issue
31