Research on harmonic measurement based on reverse correction algorithm of CVT circuit model

Abstract

The voltage signals measured by Capacitor Voltage Transformer (CVT) are accurate in power frequency. However, it is difficult to accurately reflect components in non-power frequency due to the complex electrical structure and voltage transfer characteristics of CVT. Meanwhile, the core of intermediate transformer will be saturated when the sub-synchronous resonance occurs in power system. The voltage transfer characteristic of CVT changes with equivalent inductance of intermediate transformer core, resulting in increasing errors of harmonic measurement. The existing methods based on voltage transfer characteristic are difficult to dynamically calculate harmonic components of CVT when the voltage transfer characteristic changes. In this paper, the harmonic simulation of 35kV CVT circuit model is carried out, and the harmonic transfer characteristic of CVT is studied when the core of intermediate transformer is not saturated and saturated. Comparing the harmonic error of reduced voltage and voltage calculated by reverse correction algorithm in this paper, the results show that this algorithm can greatly reduce the harmonic measurement error from 91.6%, 201.1 % to 3.95%, 7.5% in the 100th harmonic frequency band. It is verified that this method can accurately calculate the real harmonic components of primary side voltage when the intermediate transformer core is in linear and nonlinear.