INVESTIGATION AND IMPROVEMENT ON THE EARTH RESISTANCE OF THE POWER SUBSTATION IN AMBROSE ALLI UNIVERSITY, EKPOMA NIGERIA

Abstract

Earthing of electrical appliances, installations and machinery is required to avoid the risk of electric shock to personnel as a damage to equipment. This is achieved by connecting the appliances or machinery through earth electrodes to the earth mass and connecting the electrodes together through low resistance conductors. In this project the earthing system of Ambrose Alli University 1000kVA MIKANO generator located in the power station was evaluated, Its earthing resistance was measured using Kyoritsu digital earth tester, It was discovered that the existing earthing system of the generator has degraded, which can endanger the life of the operating personnel and the generator. The earth resistance measured was 529 ohms thus, necessitating remediation measures. A pit 5 feet long, 3feet wide and 8 feet deep was excavated to place the earth electrode and earth mat. The earth mat was buried and galvanized earth rods of 6 fit with diameter of 32mm were driven into the ground at equidistant from each other. The pit was watered to increase the moisture content of the soil thereby enhancing its conductivity. The soil was treated with charcoal, magnesium sulfate salt, cow dung, poultry droppings. The combination of these materials enhanced conductivity of the earth electrode in the area around the earthing system. The mixture can also serves as an anti-corrosive agent, thereby ensuring longer life of the earth conductor owing to the fact that coal absorbs water and keeps the soil wet. Furthermore, coal is made up of carbon which is a good conductor, hence it minimizes earth resistance. Salt helps in forming electrolyte which increases the conductivity between the earth rod and ground. The resistance value was measured using a digital earth resistance tester. However, earthing resistance values varies with the time of the year; it is high during the dry season and low during rainy season. Lastly, the value of the earth resistance depends largely on the type and resistivity of soil. The measured minimum earth resistance of 10 ohms was used as a standard to evaluate the earthing resistances of the generator because of the high resistivity of the selected site.