Harmonic voltage measurement error of the capacitor voltage transformer

Abstract

This paper explores the mechanism for the harmonic voltage measurement error (HVME) of a capacitor voltage transformer (CVT) in a comprehensive way and develops a practical error correction method to improve the harmonic measurement performance of a CVT. The harmonic equivalent circuit (HEC) of CVTs with different types of dampers are established and the parameter value calculation methods of the circuit elements are presented. Characteristics of the individual inherent resonance mode of the HEC, including the resonant frequency, the resonant type and the circuit elements involved, are analyzed systematically. Centered on resonance mode formulation, an universal error correction method for CVTs in measuring harmonic voltage is proposed based on the piecewise fitting of the transformation ratio. A physical experimental platform available for low-voltage CVTs is developed in laboratory, which utilizes a 10-kV harmonic generator and a step-up transformer to provide harmonic signals with high voltage level. Moreover, a novel experimental scheme for testing the HVME of high-voltage CVTs is proposed based on alternating current/direct current (AC/DC) filters. Experiments are conducted on these experimental platforms to test the HVME of a 35-kV CVT in laboratory and a 525-kV CVT in a back-to-back DC converter station. The experimental results verify the validity of the built HECs of CVTs, the resonant mode analysis results and the resonant frequency calculation method. Finally, the effectiveness of the proposed harmonic error correction method is proved by several examples.

Internal insulation condition identification for high-voltage capacitor voltage transformers based on possibilistic fuzzy clustering

“…u 0k and t 0k of the monitoring dataset are relative to the normal operation condition, which should be close to the optimal values, if any faults occur to the monitored CVT, u 0k and t 0k would drop down from the optimal value, which means the monitored CVT is out of the normal operation condition. According to the definitions of typicality t ik and membership u ik , if all the typicalities of the monitoring data points is less than the optimal value significantly, it could by judged as an unknown fault happens, and all the u ik would be 1 c at the same time (c is the number of the preset typical fault type). Otherwise there must be some known faults happens to the monitored CVT and the membership u mk would be greater than all the other memberships, which means the monitored CVT is operating in the m-th typical fault condition.…”

“…The capacitor voltage transformers (CVTs) have already been the most widely used voltage transformer in the high voltage (HV) and ultra-high voltage (UHV) power system [1][2][3] . The internal structure of CVTs is much more complicated compared with the conventional electromagnetic potential transformers (PTs), which leads to worse long-term stability and susceptibility to external electromagnetic interference 4,5 .…”

Characteristics of commutation failure based on fault recording

“…As a result of the bad frequency response of the capacitor voltage transformer (CVT), the fault recording cannot fully reflect the actual voltage fluctuations of the AC bus in the convert station, which has a certain impact on the accuracy of the analysis of characteristics of the AC bus voltage. It is expected to install a CVT with a better frequency response on the AC bus of the converter station to improve the measuring accuracy of voltage [9–11].…”

The online diagnosis of internal insulation fault of capacitance voltage transformers based on machine learning

“…Capacitance voltage transformers (CVT) compared with electromagnetic potential transformers (PT) have better antiferromagnetic resonance ability, lower manufacturing cost, smaller volume, and lighter weight. So CVT is widely used in high voltage lines of 110kV and above 1 . In a long-time operation, CVT is easily prone to abnormal states like deterioration of insulation performance and low correctness of measurement error influenced by the environment because of its complicated internal structure.…”