Grid models were built using the integrated grid editor. of 5Дў Methodology Both case studies were modelled and analysed using SafeGrid earthing design software. Case 1 - Single potential control ring: Figure 2 Transmission tower earthing with double potential control rings.

Case 2 - Double potential control rings: Table 2 Case 2 earthing parameters Phase to earth fault current 162 A Depth of burial of control rings 0.25 m Top layer soil resistivity 393 О©.m Top layer soil depth 1.16 m Bottom layer soil resistivity 897 О©.m Case Studies The safety of two transmission tower designs has been assessed using analytical modelling software. Figure 1 Transmission tower earthing with single potential control ring. The requirement to evaluate and limit step and touch potentials around transmission line towers can govern the earthing system design and layout. Potential gradients which are expressed in terms of step and touch occur in the soil surrounding the towers need to be evaluated with respect to safety limits imposed by regulations and standards. During a phase to earth fault current flows back to the source via the overhead earth wires and through the earthing systems of the individual towers. Different tower earthing designs can occur from tower to tower due to the variation in parameters and conditions along the length of the line. Table 1 Case 1 earthing parameters Phase to earth fault current 400 A Depth of burial of control ring 0.25 m Top layer soil resistivity 100 О©.m Top layer soil depth 2 m Bottom layer soil resistivity 500 О©.m Individual tower earthing must consider the performance of the line and the individual tower.

Case 1 is an example from EPRI grounding system design guide. The tower earthing system is provided by an electrically interconnected system of conductors and rods, connectors, foundation and the local soil. 1 Transmission Line Tower Earthing Analysis using SafeGrid ElectroTechnik Pty Ltd Background The purpose of transmission line grounding is to (a) provide adequate lightning performance of the line and (b) effectively dissipate fault current avoiding the build-up of unsafe step and touch potentials around the tower base.

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