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Earthing in electrical network

Earthing in electrical network



Earthing of electrical house hold items and industrial earthing

Earthing of electrical house hold items and industrial earthing



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    Earthing in electrical network Earthing in electrical network Presentation Transcript

    • EARTHING To save human life from danger ofelectrical shock or death To protect buildings, machinery &appliances under fault conditions. To ensure that all exposed conductiveparts do not reach a dangerous potential. To provide safe path to dissipate lightningand short circuit currents. To maintain the line voltage constant toprevent over current or excessive voltage onthe appliances or equipment .
    • Earth Resistance Value Major power station= 0.5 Ohm. Major Sub-stations= 1.0 Ohm Minor Sub-station = 2 Ohm Neutral Bushing. =2 Ohm Service connection = 4 Ohm Medium Voltage Network =2 Ohm L.T.Lightening Arrestor= 4 Ohm L.T.Pole= 5 Ohm H.T.Pole =10 Ohm Tower =20-30 Ohm
    • Nos. of Earthing Single phase 1 HP motor –01 earth Socket/geyser/heater/fan/1phase appliance–01 earth Three phasemotor/generator/transformer/gadgets –02earth Metallic support of O/H line after every 03poles –02 earth Stay wire for overhead line -01 earth Neutral and frame earthing-separately
    • While doing Earthing Distance –from the equipment not morethan 1.5 meter Cross section of earth continuity conductor-not less than 14 SWG copper wire Cross section of earth wire-not less thanhalf of the main wire Voltage between Earth Pit conductors toNeutral of Mains Supply 220V AC 50 Hz itshould be less than 2.0 Volts.
    • Factors Affecting Earth Resistance Soil resistivity Soil condition Moisture Dissolved salts Climate conditions Physical composition Location of earth pit Effect of grain size Effect of current magnitude Area available
    • Type Of Earthing Plate earthing :where digging is easy Pipe earthing :very common, used fordomestic, small substations Strip earthing :where earth bed haverocky soil Rod earthing: done is sandy area/smalllamp post
    • Pipe Earthing GI pipe [C-class] of75 mm diameter 10 feet long weldedwith welded flathaving 4 numbers ofholes for connections Earth pits aregenerally filled withalternate layer ofcharcoal & salt orearth reactivationcompound.
    • Strip Earthing Strip earthing :whereearth bed have rocky soil Copper strip size 5 SWGor 25mmX1.6mm isburied in horizontaltrenches Earth resistance remainshigh i.e. 5 ohm
    • Plate Earthing Cast iron plate of size 600mm x600 mm x12 mm. OR Galvanized iron plate of size600 mm x600 mm x6 mm.OR Copper plate of size 600mm * 600 mm * 3.15 mm Plate burred at the depth of8 feet in the verticalposition and GI strip of size50 mmx6 mm bolted withthe plate is brought up tothe ground level. Earth pit are generallyfilled with alternate layer ofcharcoal & salt up to 4 feetfrom the bottom of the pit.
    • Insulation Resistance and Megger
    • Earth resistance test Three pointmethod The distance ofCurrent Spikefrom EarthElectrode D =60 ft, Then,distance ofPotential Spikewould be 62 %of D = 0.62Di.e. 0.62 x 60 ft= 37 ft.
    • Difference between Insulation Resistance andEarth resistance Insulation Resistance :measuredbetween earth and conductor, value intens/thousand/mega ohm, in built DCgenerator Earth resistance: measured for aearthed body or neutral point by earthresistance tester, value less than 10 ohm
    • Specification Of Earthing as per ISISr. Capacity Size of earth wire Size Of Earth ElectrodeCu GI Cu GI1 01- 10 HP 8 SWG 8 SWG 60cmX60cmX3.18mm 60cmX60cmX6.35mm2 10 – 15 HP 8 SWG 6 SWG 60cmX60cmX3.18mm 60cmX60cmX6.35mm3 15 – 30 HP 6 SWG 4SWG 60cmX60cmX3.18mm 90cmX90cmX6.35mm4 30 – 50 HP 4SWG 25mmX3 mm 90cmX90cmX6.35mm 90cmX90cmX6.35mm
    • Method used to reduce earth resistance Soldering/welding nuts and bolts By pouring water Increase in plate area By pouring salt and charcoal ,ratio 1:5 Depth of plate Installation of parallel electrode
    • Preventive Maintenance Of Earthing System Check half yearly in dry season Check for earth pit no Repair of damage/broken pit cover Tighten the earth connections Replace broken earth leads Corroded part change immediately Pass earth conductor through GI pipe Mandatory : bi-yearly and recorded
    • Typical Earthing In House Wiring