Soil structure effect on transformer DC bias

Abstract

This paper studies the exciting current of transformer affected by DC bias in the Tibet soil structure when the UHVDC system is working in monopole state. Firstly, the model calculating the ground potential for a typical frozen soil of the Tuotuo River substation was described, and then the ground potential around the UHVDC grounding electrode for five-layer soil in summer and winter was calculated. According to the soil parameters, the magnetic bias current of the transformer were calculated. Results indicate that the distance is less than about 4 km and the earth potential is variable in different season. The substation electrode design parameters are complex, so building substation is very inconvenient. And when the distance is adjusted from 4 km to 8km, the earth potential is changed from 400 V to 200 V, the exciting current decreased from 45mA to 5mA, the waveform unbalance will also decrease.