Influence of High Voltage DC Transmission on Measuring Accuracy of Current Transformers

When the high-voltage direct current (HVDC) transmission is running under the monopole-ground-circuit operation mode, slight dc will be coupled into the nearby alternating current (ac) power grids and so has some negative influences, called dc bias phenomenon, on current transformers (CT). In this paper, based on the Preisach magnetization theory, a digital simulation method of CT is established, and then, its correctness has been verified by error calibration experiments. After that, the inherent mechanism of dc bias phenomenon is analyzed and concluded by simulating the coupling relationships among the magnetic flux density of iron core, exciting current, and coupling dc. Most importantly, we have built a coupling dc monitoring network for Jingpin to the south of Jiangsu (J2SJ) HVDC Project in China’s Jiangsu Province, and based on the monitoring data and analysis results of CT’s error varying with coupling dc, the actual influence of J2SJ HVDC on CT measuring accuracy is evaluated quantitatively.