Study on Power Frequency Impedance and Impulse Impedance Characteristics of Grounding Grid Based on CDEGS

Abstract

The grounding grid provides a fast discharge route for power frequency fault current and impulse fault current in converter station. The performance of grounding grid is directly related to personal safety, safety and reliable operation of power equipment in service. The power frequency resistance and impulse impedance are two indexes to measure the ability of the power frequency current and the impulse current to disperse in the grounding grid respectively, and there are great differences between the power frequency current and the impulse current in the dispersion of the grounding grid, the measures of lengthening the length of the vertical grounding body, changing the soil resistivity, the buried depth of grounding grid, the area of grounding grid and the cross-sectional area of grounding body are different in the effectiveness of reducing the power frequency impedance and the impact impedance. In this paper, based on the power system grounding analysis software CDEGS, the grounding network model of converter station is established, and the length of vertical grounding body is extended, the effectiveness of changing soil resistivity, grounding depth, grounding grid area and grounding body cross-sectional area to reduce power frequency impedance and impact grounding impedance is different, the conclusions are as follows: The power frequency impedance is higher than the impulse impedance, the power frequency impedance and the impulse impedance can be reduced effectively by extending the length of the vertical grounding body, enlarging the area of the grounding grid and the cross section of the grounding body. The power frequency impedance and the impulse grounding impedance have obvious linear relationship with the soil resistivity and the grounding depth, but the grounding depth has little influence. The method of enlarging the area of grounding grid has the most significant effect on reducing power frequency impedance and impulse grounding impedance.