Quantitative Analysis of Saturation of Measurement Current Transformer by Direct Current Bias

The DC bias caused by single pole-ground mode or bipolar unbalanced mode of HVDC transmission or geomagnetic induced current phenomenon may lead to the measuring CT saturation, which may affect the measurement performance. Therefore, it is necessary to evaluate the saturation degree of the CT. By using the effective permeability, analyzing the equivalent model of CT under DC bias state and combining with the electromagnetic relationship between flux and voltage, the expression of the saturation degree, DC current and circuit parameters is analyzed and derived. By simulating different types of CT, the effectiveness of the analytical expression is verified, and the influence on the saturation degree is analyzed. The actual power system parameters are used for numerical analysis, and the rough estimation of the measurement error is used to show the specific application of the method for analyzing the DC bias magnetic conditions of the measuring CT.