A technique to increase the effective length of horizontal earth electrodes and its application to a practical earth electrode system

The ability of a horizontal earth electrode in reducing earth potential rise is limited because, beyond a certain length known as the effective length, no further reduction is obtained. In this paper, field experiments and computer simulations of a horizontal earth electrode is presented. The electrode was energised using different sources (dc, variable frequency ac and transients of different shapes), and current and voltage distributions along the length of the electrode were examined. Furthermore, by incrementally increasing the length of the test electrode, the effective length of the earth electrode was determined. The experimental and simulation results show reasonably close agreement and also that quite good prediction of the effective length is possible. A new proposed method to increase the effective length of the horizontal earth electrode was investigated by installing an additional insulated parallel conductor which is bonded to the horizontal electrode at points along its length. The results show that the current and voltage distributions are changed such that a greater length of buried conductor is utilised and that this contributes to an additional reduction in the earth impedance, and hence the earth potential rise at the point of current injection. Preliminary computer simulations show how this technique can also be extended to a practical earthing system for wind turbines with good effect.