Correction of Current Transformer Transient Performance

Abstract

If a current transformer (CT) saturates while transforming the heavy primary current, in each period, there are sections when the magnetic core is unsaturated and transformation is correct, and when it is saturated, it causes enormous errors. The key to correct the errors is to detect instants of saturation and moments when the saturation ends. This paper presents simple and efficient methods of doing that. In addition, it shows the way how to predict up to three samples after saturation with the acceptable degree of accuracy, thus artificially expanding the unsaturated section. It may substantially facilitate operation of protective devices. The ultimate solution of the problem is to estimate the values of the fundamental frequency component amplitude and the decaying dc component in each period. This paper presents the method of doing that on the ground of four consecutive samples taken during the unsaturated section. If the primary current consists of the fundamental and dc exponential components only, the accuracy of the method is excellent. Neglecting contamination of the current signal with harmonics and noise, it is possible to reconstruct the CT primary current based on the measured values of fundamental and dc components.

CT saturation correction based on the estimated CT saturation time constant

“…(1) four previous samples from the unsaturated time span are to be available. The other algorithms for the estimation of ie are described in [13].…”

Electromotive Force Characteristics of Current Transformer According to the Magnetic Properties of Ferromagnetic Core

“…The saturation phenomenon may impair the reliability of CT if an appropriate alternative for saturation detection or correction is not applied to resolve the problem. A few approaches have been proposed to reduce the effect of CT satu-ration [13][14][15]. To measure the large current, a Rogowski coil is used, which is representative of several devices.…”

Estimation of the inductive current transformer derating for operation with distorted currents

“…In these conditions and for transients inductive instrument transformers are characterized by significantly worst metrological properties than at rated frequency of sinusoidal primary signal [1][2][3][4][5][6][7]. The increase of transformation error for distorted voltage/current will increase the error of indirect measurements of power and electric energy.…”