Performance of Earthing Systems of Operational/Live Stations under Impulse Conditions

-A number of impulse investigations on earthing systems have been performed in the field [1-6]. The studies were conducted on a few types of earth electrode: vertical rods, horizontal electrodes and the mesh and other geometries of electrodes. The type selected may depend on the type of soil encountered and the available depth or area available. Impulse voltages of up to 3MV with impulse currents of up to 30kA were applied on earth electrodes with different configurations. The experimental results from previous studies in the field [1-6] revealed that under high currents, a ‘non-linear’ soil behaviour would occur. However, so far the field measurements were conducted on the imitative earth electrodes, and not on the live operating systems. In this study, the performance and the electrical characteristics of earthing systems under impulse conditions were investigated. For the first time, the impulse tests were conducted on the earthing systems of operational stations, in which connected to the external paths and other equipments. Impulse voltages with increasing magnitudes up to 6kV were injected into the earth electrode. The results reveal that there is no flashover or damages on the equipments at the stations/sites under tests. It was also observed that the earthing systems are mainly inductive under impulse conditions of up to 6kV. It also includes the investigations on earthing systems using computer models [7]. The earth resistance values at power frequency and low-magnitude voltage and current of these selected sites were also obtained using Current Distribution Electromagnetic Interference Grounding and Soil Structure Analysis (CDEGS) [7]. The impedance values of the earthing systems were found to be ranging between 2.7Ω and 9.2Ω.