What is Earthing?
Equipment earthing is a connection done through a metal link between the body of any electrical appliance, or neutral point, as the case may be, to the deeper ground soil. The metal link is normally of MS flat, CI flat, GI wire which should be penetrated to the ground earth grid.
Equipment earthing is based on IS:3043-1987 Standards.
- Classification of electrical equipment IS: 9409-1980
- Important rules for safety and earthing practice is based on IE rules 1956
- Guide on effects of current passing through human body – IS:8437-1997
- Protection of buildings and structures from lightning – IS:2309-1969
- Earth: The conductive mass of the earth, whose electric potential at any point is conventionally assumed and taken as ZERO.
- Earth Electrode: A Conductor or group of conductors in intimate contact with and providing as electrical connection to earth.
- Earth Electrode Resistance: The electrical resistance of an earth electrode to the general mass of earth.
- Earthing Conductor: A protective conductor connecting the main earthing terminal to an earth electrode or other means of earthing.
- Equipotential Bonding: Electrical connection putting various exposed conductive parts and extraneous conductive parts at a substantially equal potential. Example: Inter connect protective conductor, earth continuity conductors and risers of AC/HV systems if any.
- Potential gradient: The potential difference per unit length measured in the direction in which it is max.
- Touch Voltage: The P.D. between a grounded metallic structure and a point on the earth’s surface separated by a horizontal reach of one Metre.
- Step Voltage: The P.D. between two points on the earth’s surface separated by a distance one pace (step) assumed to be one Metre.
- Earth Grid: A System of grounding electrodes consisting of interconnected connectors buried in the earth to provide a common ground from electrical devices and metallic structures.
- Earth Mat: A grounding system formed by a grid of horizontally buried conductors – Serves to dissipate the earth fault current to earth and also as an equipotential bonding conductor system.
Necessity of Equipment Earthing
-Safety of personnel
-Safety of equipment
-Prevent or at least minimize damage to equipment as a result of flow of heavy currents.
-Improvement of the reliability of the power system.
Classification of Earthing
The earthing is broadly divided as
1.System earthing (Connection between part of plant in an operating system like LV neutral of a power transformer winding) and earth.
2.Equipment earthing (safety grounding) connecting bodies of equipment (like electric motor body, transformer tank, switchgear box, operating rods of air break switches, LV breaker body, HV breaker body, feeder breaker bodies etc) to earth.
Permissible Values of Earth Resistance
-Power stations – 0.5 ohms
-EHT stations – 1.0 ohms
-33KV SS – 2 ohms
-DTR structures – 5 ohms
-Tower foot resistance – 10 ohms
What is the Basics for arriving at Permissible Earth Resistances?
As per IE rules one has to have a definite base for that as per IE rules one has to keep touch potential less than
1.Recommended safe value 523 volts
2. Ifault = maximum current in fault conditions,
3.Maximum fault current is 100 KVA the current in 100 KVA is about 100 A; where
percentage impedance is 4%
4.For a substation of 100 KVA transformer
0.26 ohms being quite low, quality work is to be done during construction, to obtain such a value of earthing system, and the expenditure for that will be very high. Hence the electrical inspectors are insisting about 1.0 ohms. This seems justifying for the urban areas. This value may be 2 ohms in case of rural areas, which is recommended by most of the authorities.
5.The earth electrode resistance value also carries importance in view of full protection by lightning arrestors against lightning. The earth electrode resistance value in that case is given by the formula
Flash over voltage of 11 KV = 75 KV
Lightning arrestor Displacement = 40 KA
Type of Earthing
Plate Type Earthing
In this, cast Iron plate of size 600 mm × 600 mm × 6.3 mm thick plate is being used as earth plate. This is being connected with hot dip GI main earth strip of size 50mm breadth × 6mm thick × 2.5 meter long by means of nut, bolts and washers of required size. The main earth strip is connected with hot dip GI strip of size 40mm × 3mm of required length as per the site location up to the equipment earth / neutral connection. The earth plate is back filled and covered with earthing material (mixture of charcoal & salt) by 150mm from all six sides. The remaining pit is back filled with excavated earth. Along with earth plate, rigid PVC pipe of 2.5 meter long is also provided in the earth pit for watering purpose for to keep the earthing resistance within specific limit.
Pipe Type Earthing
In this method hot dip GI pipe of size 40 mm dia × 2.5 meter is being used for equipment earthing. This pipe is perforated at each interval of 100mm and is tapered at lower end. A clamped is welded with this pipe at 100 mm below the top for making connection with hot dip GI strip of size 40mm × 3mm of required length as per the site location up to the equipment earth / neutral connection. On its open end funnel is being fitted for watering purpose. The earth pipe is placed inside 2700 mm depth pit. A 600mm dia “farma“ of GI sheet or cement pipe in two halves is are placed around the pipe. Then the angular space between this “farma” and earth pipe is back filled with alternate layer of 300mm height with salt and charcoal. The remaining space outside “farma” will be backfilled by excavated earth. The “farma” is gradually lifted up as the backfilling up progresses. Thus the pit is being filled up to the 300mm below the ground level. This remaining portion is covered by constructing a small chamber of brick so that top open end of pipe and connection with main earth pipe will be accessible for attending when necessary. The chamber is closed by wooden/stone cover. Water is poured into the pipe through its open end funnel to keep the earthing resistance within specific limit.
Other Types of Earthing: When the capabilities of certain equipment are limited, they may not with stand certain fault currents then the following types of earthing are resorted to limit the fault current.
3-Peterson coil earthing.
4-Earthing through grounding transformer.
Utangulizi wa Dunia ni nini? Kuunganisha vifaa ni uhusiano uliofanywa kupitia kiungo cha chuma kati ya mwili wa kifaa chochote cha umeme, au hatua ya neutral, kama ilivyo, kwa udongo wa chini ya ardhi. Kwa kawaida, kiungo cha chuma ni MS flat, CI flat, waya wa GI ambayo inapaswa kupenya kwenye gridi ya ardhi ya ardhi. Mashine ya kuunganisha ardhi ya vifaa ni msingi wa IS 3043-1987 viwango. "Kifungu cha vifaa vya umeme: IS 9409 - 1980: ""Sheria muhimu za usalama na mazoezi ya ardhi ni msingi wa sheria za 1956 - Mwongozo wa athari za sasa kupita kupitia mwili wa binadamu"" - IS 8347 - 1997: ""Ulinzi wa majengo na miundo kutoka umeme"" - IS 9409 - 1969: ""Mdundo wa umeme wa dunia, ambao uwezo wa umeme katika hatua yoyote ni kawaida kudhaniwa na kuchukuliwa kama ZERO.""" - Dunia Electrode: Conductor au kundi la conductors katika mawasiliano ya karibu na kutoa kama uhusiano wa umeme na ardhi. - Earth Electrode Upinzani: Upinzani wa umeme wa electrode ardhi kwa wingi wa jumla ya dunia. - Earthing Conductor: Mwongozo wa ulinzi kuunganisha kuu grounding terminal kwa electrode ardhi au njia nyingine ya grounding. - Equipotential Bonding: Kiunganishi cha umeme kuweka sehemu mbalimbali wazi conductive na sehemu conductive nje katika uwezekano sawa kimsingi. Mfano: Interconnect kinga conductor, ardhi mwendelezo conductors na risers ya AC au HVAC mifumo, kama yoyote. - uwezekano gradient: tofauti ya uwezekano kwa muda kitengo kipimo katika mwelekeo ambao ni max. - Voltage ya kugusa: P.D. kati ya muundo wa chuma grounded na uhakika juu ya uso wa dunia kutenganishwa na kufikia usawa wa mita moja. - Hatua Voltage: P.D. kati ya pointi mbili juu ya uso wa dunia kutenganishwa na umbali hatua moja (hatua) kudhaniwa kuwa mita moja. - Dunia Grid: Mfumo wa grounding electrodes linajumuisha connectors interconnected kuzikwa katika dunia kutoa ardhi ya kawaida kutoka vifaa vya umeme na miundo ya chuma. - Dunia Mat: Mfumo grounding iliyoundwa na gridi ya conductors horizontally kuzikwa <unk> Hutumika kuondoa dunia kosa sasa kwa dunia na pia kama equipotential bonding conductor mfumo. Uhitaji wa vifaa grounding - Usalama wa wafanyakazi - Usalama wa vifaa - Kuzuia au angalau kupunguza uharibifu wa vifaa kama matokeo ya mtiririko wa mikondo nzito. -Uboreshaji wa kuegemea ya mfumo wa umeme. Kuunganisha kwa ardhi: Kuunganisha kwa ardhi kunaweza kugawanywa katika sehemu mbili: Kuunganisha kwa ardhi (kuunganisha kati ya sehemu ya kiwanda katika mfumo wa uendeshaji kama vile LV neutral ya winding ya transformer ya nguvu) na ardhi. 2.Equipment grounding (salama grounding) kuunganisha miili ya vifaa (kama mwili wa umeme motor, transformer tank, switchgear sanduku, kazi vijiti ya hewa kuvunja swichi, LV breaker mwili, HV breaker mwili, feeder breaker miili, nk) kwa ardhi. "Kuna ""mashine"" ya umeme ya kiwango cha juu, ambayo inahitajika kwa ajili ya ujenzi wa nyumba za umeme, kama vile nyumba za umeme, nyumba za umeme, nyumba za umeme, nyumba za umeme, nyumba za umeme, nyumba za umeme, nyumba za umeme, nyumba za umeme, nyumba za umeme, nyumba za umeme." Kwa mujibu wa sheria za IE, mtu lazima awe na msingi maalum kwa ajili ya kwamba, kwa mujibu wa sheria za IE, mtu lazima kuweka kugusa uwezo chini ya 1. "Mfano: ""Mfumo wa chini wa 100KV"" ni sawa na ""mfumo wa chini wa 100KV"" na ""mfumo wa chini wa 100KV"" ni sawa na ""mfumo wa chini wa 100KV"" na ""mfumo wa chini wa 100KV"" ni sawa na ""mfumo wa chini wa 100KV"" na ""mfumo wa chini wa 100KV"" na ""mfumo wa chini wa 100KV"" ni sawa na ""mfumo wa chini wa 100KV""." Kwa hiyo wakaguzi wa umeme wanasisitiza kuhusu 1.0 ohm. Hii inaonekana kuhalalisha kwa ajili ya maeneo ya mijini. Kiwango hiki kinaweza kuwa ohm mbili katika maeneo ya vijijini, ambayo inashauriwa na mamlaka nyingi. 5.The ardhi electrode upinzani thamani pia hubeba umuhimu kwa kuzingatia ulinzi kamili na umeme arrestors dhidi ya umeme. "Kama kwa mfano, ""Flash over voltage"" (FV) ni ""F"" ya umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme wa umeme." Hii ni kuunganishwa na moto dip GI kuu ardhi strip ukubwa 50mm upana 6mm unene 2.5m kwa njia ya karanga, bolts na washers ya ukubwa required. Mstari wa ardhi kuu umeunganishwa na mstari wa joto wa GI wa ukubwa wa 40mm × 3mm wa urefu unaohitajika kulingana na eneo la tovuti hadi vifaa vya ardhi vya utatu. Bamba la ardhi limefunikwa na kufunikwa na vifaa vya ardhi (mchanganyiko wa makaa ya mawe na chumvi) kwa 150mm kutoka pande zote sita. Shimo lililobaki limejazwa tena kwa udongo uliochimbuliwa. Pamoja na sahani ya ardhi, bomba la PVC ngumu la mita 2.5 pia linatolewa katika shimo la ardhi kwa kusudi la umwagiliaji maji ili kuweka upinzani wa ardhi ndani ya kikomo maalum. Pipe Earthing: Pipe ya chini ya maji ya joto ya 40mm x 2.5mm kwa ajili ya kuunganisha vifaa. Bomba hili ni perforated katika kila muda wa 100mm na ni tapered katika mwisho wa chini. Pipe hii imefungwa kwa 100mm chini ya juu kwa kufanya uhusiano na mstari wa kuingiza moto wa GI wa ukubwa wa 40mm × 3mm wa urefu unaohitajika kulingana na eneo la tovuti hadi vifaa vya kuunganisha ardhi. Kwenye mwisho wake ulio wazi, mtungi unawekwa kwa ajili ya umwagiliaji maji. Bomba la ardhi linawekwa ndani ya shimo la kina cha 2700 mm. Pipa ya 600mm ya karatasi ya GI au bomba la saruji katika nusu mbili huwekwa kuzunguka bomba. Kisha nafasi ya pembe kati ya hii farma na bomba la ardhi ni nyuma kujazwa na tabaka mbadala ya urefu wa 300mm na chumvi na makaa ya mawe. Sehemu iliyobaki nje ya <unk>farma<unk> itajazwa tena na ardhi iliyochimbwa. "Shamba" hilo huinuliwa hatua kwa hatua kadiri ujenzi unavyoendelea. Kwa hivyo, shimo hilo linajazwa hadi 300mm chini ya kiwango cha ardhi. Sehemu hii iliyobaki imefunikwa kwa kujenga chumba kidogo cha matofali ili mwisho wa juu wa bomba na uhusiano na bomba kuu la ardhi uweze kupatikana kwa kuhudhuria wakati inahitajika. Chumba ni kufungwa na mbao-jiwe kifuniko. Maji ni kumwagika katika bomba kupitia funnel yake wazi mwisho kuweka upinzani grounding ndani ya kikomo maalum. Aina nyingine za Grounding: Wakati uwezo wa vifaa fulani ni mdogo, wanaweza si kusimama na baadhi ya makosa ya sasa, kisha aina zifuatazo za grounding ni resorted kupunguza makosa ya sasa. 3 - Peterson Coil Grounding 4 - Kuunganisha ardhi kupitia transformer grounding.