A vertical electrode is one of the most widely-used electrodes to construct a grounding device. As an increase in the length of a vertical electrode leads current into deeper soil, it is possible to effectively reduce grounding resistance. In practice, however, the length of a vertical electrode is limited to below a certain threshold according to working conditions.
When the soil resistivity is high, it is difficult to provide a reference grounding resistance with a vertical electrode, in which case a composite grounding device with multiple vertical electrodes interconnected with one horizontal grounding body is used. The composite grounding device is one of the grounding devices that have been widely applied to today’s grounding equipment construction. Therefore, obtaining a mathematical model for the grounding resistance of a composite grounding device is an essential issue in the design of a grounding system using it.
In the past, many studies on composite grounding devices have been carried out, and only one-sided problems have been dealt with, such as individual vertical and horizontal grounding resistances, shielding effect between them when multiple vertical electrodes are connected in parallel, and adoption of the utility coefficient to the mathematical model of the grounding resistance of the composite grounding device, etc. However, a complete mathematical model of the grounding resistance of a composite grounding device has not been obtained.
Kim Tae Song, a researcher at the Faculty of Electronics, has obtained a mathematical model that accurately reflects the logical relationship between the ratio of the distance between vertical electrodes to the electrode length and the grounding resistance of a composite grounding device, and verified its validity through computer simulations and field measurements in soil conditions with different resistivity.
The proposed mathematical model comprehensively reflects the influence of factors on the grounding resistance of composite grounding devices and it can be effectively used in the design of composite grounding devices using multiple vertical electrodes.