Characteristic Analysis of Current Transformer by Measurement of Induced Electromotive Force

Abstract

Background/Objectives: CT is a typical measurement instrument capable of measuring alternating current in industry. When the large current such as the inrush current flows into the CT, the induced electromotive force characteristics and the magnetic field saturation characteristic analysis of the EMF coil are essential.

Methods/Statistical analysis: For induction electromotive force analysis, the induced electromotive force is modeled mathematically and the numerical formula for numerical analysis of the electromagnetic field is derived. Also, various CTs were selected and the saturation characteristics of the magnetic body were analyzed by measuring the induced electromotive force.

Findings: The analytical results show that saturation characteristics and induced electromotive force characteristics are analyzed. When sinusoidal wave is applied to primary winding of CT, induced electromotive force is calculated by electromagnetic field analysis using complex approximation method. In addition, the schematic waveforms of the induced electromotive force by numerically calculated and measured were compared. When a large current like a surge current flow into the CT, the magnetic core is saturated and the sensing ability of the CT is lowered.

Improvements/Applications: Therefore, optimal design should be performed considering the dimension of the CT and the characteristic of the ferromagnetic core. Based on the experimental results of this paper, it may be helpful to design the magnetic core or winding of the CT used in the surge protection device.

Keywords: Current transformer, Electromagnetic induction, Electromotive force, Saturation characteristics, Surge protection device.