Step and Touch Potentials
At critical locations, such as the fence around your substation, hazardous step and touch voltages can occur. It is, therefore, crucial to measure step and touch voltage at locations in and around the substation to ensure safety for persons and animals.
The single-phase fault is simulated in the same way as when measuring ground impedance by injecting a current with a frequency variable current source and by grounding the remote end of your line.
Soil resistivity investigations are necessary to determine the soil structure the soil resistivity can change dramatically with changes in moisture, temperature, and chemical content. To determine the soil resistivity of a site, soil resistivity measurements need to be taken. The most widely used test for determining soil resistivity data was developed by Wenner and is called either the Wenner or four-pin method. Using four pins or electrodes driven into the earth along a straight line at equal distances of a, to a depth of b, current is passed through the outer pins while a voltage reading is taken with the two inside pins.
Based on the resistance R, as determined by the voltage and current, the apparent resistivity can be calculated
Electrodes and the connections to them may also be affected by corrosion, and it’s by no means unknown for earthing systems to sustain physical damage, either accidentally, as might occur during nearby building operations, or deliberately, in the form of theft and vandalism.
To prove that all connections to the earth grid under test are sound. Continuity testing of all earth connections should be carried out to a known reference point. The preferred reference point in a substation is the neutral earth bond on a power transformer.
Effective earthing is essential for the safe operation of every electrical system and the only way to ensure that earthing installations are effective and that they remain so, is to test them rigorously and regularly.
Most power distribution systems are designed so that, if an insulation failure or similar fault occurs, the resulting fault current is diverted to earth. This prevents exposed conductive parts from rising to a dangerous potential, while allowing the fault current to flow for long enough and at a high enough level for protective devices to operate and isolate the fault. It is clear from this description that a reliable, effective earth connection is essential for safe operation of the systems, and that if the earthing system fails or becomes inefficient, at best safety will be compromised and at worst there may well be a significant risk to life and property.