Consumer Earthing System PDF

CONSUMER EARTHING SYSTEM Purpose of Earthing 1. Safety for Human life/ Building/ Equipment To save human life from danger of electrical shock or death by providing an alternative path for the fault current to flow so that it will not endanger the user. To ensure that all exposed co...

CONSUMER EARTHING SYSTEM Purpose of Earthing 1. Safety for Human life/ Building/ Equipment To save human life from danger of electrical shock or death by providing an alternative path for the fault current to flow so that it will not endanger the user. To ensure that all exposed conductive parts do not reach a dangerous potential.  To protect buildings, machinery & appliances under fault conditions. To provide safe path to dissipate lightning and short circuit currents. To maintain the voltage at any part of an electrical system at a known value so as to prevent over current or excessive voltage on the appliances or equipment. 2. Over voltage protection Lightning, line surges or unintentional contact with higher voltage lines can cause dangerously high voltages to the electrical distribution system. Earthing provides an alternative path around the electrical system to minimize damages in the System. 3. Voltage stabilization: There are many sources of electricity. Every transformer can be considered a separate source. If there were not a common reference point for all these voltage sources it would be extremely difficult to calculate their relationships to each other. The earth is the most omnipresent conductive surface, and so it was adopted in the very beginnings of electrical distribution systems as a nearly universal standard for all electric systems. Conventional methods of earthing 1. Plate type Earthing: For plate type earthing normal practice is to use Type Dimension Cast iron plate 600 mm x 600 mm x12 mm Galvanized iron plate 600 mm x 600 mm x 6 mm Copper plate 600 mm x 600 mm x 3.15 mm buried at the depth of 8 feet in the vertical position and GI strip of size 50 mm x 6 mm bolted with the plate is brought up to the ground level. These types of earth pit are generally filled with alternate layer of charcoal & salt up to 4 feet from the bottom of the pit. 2. Pipe type Earthing: For Pipe type earthing normal practice is to use GI (Galvanized Iron) pipe [C-class] of 75 mm diameter, 3 m long welded with 75 mm diameter GI flange having 6 numbers of holes for the connection of earth wires and inserted in ground. These types of earth pit are generally filled with alternate layer of charcoal & salt or earth reactivation compound. Measurement of Earth Resistance Sphere of Influence  Step Voltage A Multidisciplinary Forensic Analysis of Two Lightning Deaths Observed in South Africa, August 2020, International Journal of Disaster Risk Reduction Factors affecting on Earth resistivity 1. Soil Resistivity It is the resistance of soil to the passage of electric current. The earth resistance value (Ohmic value) of an earth pit depends on soil resistivity. It depends on the physical composition of the soil, moisture, dissolved salts, grain size and distribution, seasonal variation, current magnitude etc. 2. Soil Condition Different soil conditions give different soil resistivity. Most of the soils are very poor conductors of electricity when they are completely dry. Soil plays a significant role in determining the performance of Electrode. Soil with low resistivity is highly corrosive. If soil is dry then soil resistivity value will be very high. If soil resistivity is high, earth resistance of electrode will also be high. 3. Moisture Moisture has a great influence on resistivity value of soil. The resistivity of a soil can be determined by the quantity of water held by the soil and resistivity of the water itself. Conduction of electricity in soil is through water. The resistance drops quickly to a more or less steady minimum value of about 15% moisture. And further increase of moisture level in soil will have little effect on soil resistivity. Therefore, it is essential to pour water in and around the earth pit to maintain moisture in dry weather conditions. Moisture significantly influences soil resistivity 4. Dissolved Salts Pure water is poor conductor of electricity. Resistivity of soil depends on resistivity of water which in turn depends on the amount and nature of salts dissolved in it. Small quantity of salts in water reduces soil resistivity by 80%. common salt is most effective in improving conductivity of soil. But it corrodes metal and hence discouraged. 5. Climate Condition Increase or decrease of moisture content determines the increase or decrease of soil resistivity. Thus in dry whether resistivity will be very high and in monsoon months the resistivity will be low. 6. Location of Earth Pit The location also contributes to resistivity to a great extent. In a sloping landscape, or in a land with made up of soil, or areas which are hilly, rocky or sandy, water runs off and in dry weather conditions water level goes down very fast. Though back fill compound retains moisture under normal conditions, it gives off moisture during dry weather to the dry soil around the electrode, and in the process loses moisture over a period of time. Therefore, choose a site that is naturally not well drained. Else, the earth pits located in such areas must be watered at frequent intervals, particularly during dry weather conditions. 7. Effect of current magnitude: Soil resistivity in the vicinity of ground electrode may be affected by current flowing from the electrode into the surrounding soil. The thermal characteristics and the moisture content of the soil will determine if a current of a given magnitude and duration will cause significant drying and thus increase the effect of soil resistivity 8. Area Available Single electrode rod or strip or plate will not achieve the desired resistance alone. If a number of electrodes could be installed and interconnected the desired resistance could be achieved. The distance between the electrodes must be equal to the driven depth to avoid overlapping of area of influence. Each electrode, therefore, must be outside the resistance area of the other. If the earth pits are close by, the resistance value will be high.