Elecrical Earthing System
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 seminar surveyer Active In SP Posts: 3,541 Joined: Sep 2010 05-10-2010, 10:34 AM   Earthing.ppt (Size: 91.5 KB / Downloads: 253) Introduction What is Earthing -The process of earthing is to connect all the objects which could become charged to the general mass of the earth, to provide a path for electrical current and to hold the parts as close as possible to earth potential. -For tying the electrical supply system to earth, supply transformer neutral conductor (Y point of 3 phase Supply) is connected to earth using an earthing electrode or the metal sheath and armouring of a buried conductor. Why Earthing required -The purpose of grounding system is to provide a low impedance electrical contact between the neutral of an electrical system and earth -1. To provide safety during normal or fault condition. -2. To stabilize the voltage during transient conditions and therefore to minimize the probability of a flashover during transients. -3. To dissipate lightening strokes -Due to impedance of the system, the potential of the grounding system may become different than the potential at various points on earth during abnormal operating condition or fault condition. -Due to this potential difference a touch and step voltages are subjected by the persons which generate an electrical current through his body. This flow of current is a source of danger. -Electrical body current below 116/(sqrt(t) mili amps, where t is shock duration time -Vtouch, allowable = 0.116(1.5 + 1000)/ (sqrt(t) -Vstep, allowable = 0.116(6.0 + 1000)/ (sqrt(t)