Analysis of Influence of DC Bias on Instrument Current Transformer
Tan Bingyua · Power System Technology · 2014
The relationship between the error of instrument current transformer(CT) and its core permeability is derived by T-shaped equivalent circuit based model of CT, and through experiments of ferromagnetic performance the variation law of the relationship between inductance and core permeability of CT under DC bias is attained. An AC/DC hybrid test method is designed to simulate actual DC bias phenomenon, and based on the test data the influence of DC bias on the error of instrument CT is analyzed. Analysis result show that DC bias does not affect the saturation characteristic of the core, and with the increase of DC offset the ratio error curve of CT overall shifts to negative direction while the phase angle error curve of CT overall shifts to positive direction, and the harmonic components at the secondary side of the CT increase, in which even harmonic components increase obviously.