Research and Analysis on the Testing of Ground Impedance of Large Grounding Grid through Straight-Line Method Considering the Influence of Earth

doi:10.11930/j.issn.1004-9649.201708029

Electric Power ›› 2018, Vol. 51 ›› Issue (7): 36-42.DOI: 10.11930/j.issn.1004-9649.201708029

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Research and Analysis on the Testing of Ground Impedance of Large Grounding Grid through Straight-Line Method Considering the Influence of Earth

YUAN Pei¹, HE Zhiqiang¹, HU Xiaohui², YE Huisheng¹, HUANG Haibo¹

1. State Grid Hunan Electric Power Corporation Research Institute, Changsha, 410007, China;
2. Wuhan Kangda Electric Co., Ltd., Wuhan, 430070, China

Received:2017-08-29 Revised:2018-01-15 Online:2018-07-05 Published:2018-07-31
Supported by:
This work is supported by State Grid 2018 Science and Technology Guideline Project (Research and application of key technology for active early warning, No.5216A0180003).

Abstract

Abstract: When measuring the ground impedance of a large grounding grid of a substation (or a power plant) using the straight-line method, a measurement error will be included in the result, causing the readings higher than the actual ground impedance. The measurement error is related to two factors. One is the non-uniform distribution of soil resistivity in the vicinity of the large grounding grid, making it difficult to find the zero-potential position. The other is the mutual coupling function through earth between the parallel test leads in long distance, resulting in non-negligible reactance compared to the ground impedance. This paper presents a new method for measuring the ground impedance of a large grounding grid considering the influence of non-uniform soil resistivity and mutual inductance. In the new method, the accurate zero potential position and the corresponding resistance are obtained on the basis of fitting of the measurement curves. Besides, the influence of mutual inductance is removed by the fitting of measured data of inductance under different length of test lines. By comparing the results with CDEGS software simulation, the difference between the measured and simulated results is less than 5%. It is possible to effectively eliminate the influence of non-uniform soil resistivity distribution and mutual coupling between test lines. The new method can effectively improve the accuracy of measurement.

Key words: large grounding grid, ground impedance, straight-line method, earth influence, fitting and simulation

CLC Number:

TM835

YUAN Pei, HE Zhiqiang, HU Xiaohui, YE Huisheng, HUANG Haibo. Research and Analysis on the Testing of Ground Impedance of Large Grounding Grid through Straight-Line Method Considering the Influence of Earth[J]. Electric Power, 2018, 51(7): 36-42.

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Research and Analysis on the Testing of Ground Impedance of Large Grounding Grid through Straight-Line Method Considering the Influence of Earth

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