Good substation earthing is essential for a safe and reliable power system. Methods to improve substation grounding with supporting measurements of earth resistance, and computational models to simulate the possible Ground Potential Rise (GPR) due to injected current surges are of particular interest.
The main objective of the initial work is to develop a reliable computational model for the impedance of substation earthing mats and the distribution of the surface potential that occurs when a power frequency fault current is injected into the earthing system. The commercial package CDEGS MALT has been found to be one of the best currently available, and part of the initial effort was to verify its performance. MALT is being tested with experimental results and also Earthing Standards and literatures formulas available. Extensive work have been done to study the effect of ï¿½proximity effectï¿½ on the surface potentials in and around the earthing system when comparing with the computer software computations.
Also, study of the potential distribution due to the insertion of a local high resistivity barrier have been carried out. The purpose of using local high resistivity is to skew the potential contours, so the earth potential rise immediately beyond the barrier can be reduced. As the power frequency current can penetrate very deep into the ground, the effectiveness of the high resistivity barrier needs to be examined. Effects of barrier geometry under various system conditions was analysed. Both solid barrier and barrier made of plates with various spacings of gaps were tested in the electrolytic tank and modelled in the CDEGS software.