Analysis of earth resistivity frequency dependence: Test method and its practical application

Abstract

The first step in planning and designing of the proper grounding system, is the earth resistivity measurement. Measurements are carried out before the construction of the power facility. However, it is not an uncommon situation that during construction, subsequent leveling and raising of the ground level is performed. For this purpose, it is customary to use the land from the locations far away. Delivered soil has largely different electromagnetic characteristics (electric conductivity, permittivity and dielectric constant) in relation to the soil on which the previous measurement of the earth resistivity was conducted. Since the value of the earth resistivity directly affects the grounding system electrical parameters - grounding system impedance, touch and step voltages - additional measurements are required and according to this appropriate corrections of the grounding system In this paper, we propose a practical method for earth resistivity measurement. The method is applicable in the design phase, and also for the revision of the installed grounding system. A practical example of a power facility (RP 400 kV Mladost, Elektromreža Srbije), based on laboratory measurements of the soil samples earth resistivity and grounding system impedance measurement, clearly shows what consequences might occur by leveling and raising of the ground level using ash coal dump.

Keywords

• earth resistivity
• test method
• laboratory conditions