Apparatus ad Terram Coniunctio: Quid Est & Cur Hoc Importat

Quid est Earthing?

Equipment earthing est coniunctio per ligamen metallicum inter corpus cuiusque apparati electrici, vel punctum neutrale, ut casus sit, ad solium terrae profundius. Ligamen metallicum normaliter constat ex lamina MS, CI, et filo GI, quod debet penetrari in terram.
Equipment earthing fundatur in normis IS:3043-1987.

1. Classificatio apparatorum electricorum IS: 9409-1980

2. Regulae importantiores pro securitate et praxi earthing fundantur in regulis IE 1956

3. Ductor de effectibus currentis transiens per corpus humanum – IS:8437-1997

4. Protectio aedificiorum et structurarum ab fulgure – IS:2309-1969

5. Terra: Massa conductiva terrae, cuius electric potential in quopiam loco conventionaliter assumitur et accipitur ut ZERO.

6. Electrode Terrae: Conductor Conductor vel gruppus conductorum in intima contiguitate cum terra et praebens connexionem electricam ad terram.

7. Resistentia Electrodi Terrae: Resistentia electrica electrodi terrae ad massam generalem terrae.

8. Conductor Earthing: Conductor protector connexus termino principali earthing ad electrodum terrae vel alios modos earthing.

9. Equipotential Bonding: Connexio electrica ponens varias partes conductivas expostas et extraneas partes conductivas in potenti fere aequali.
   Exemplum: Inter connect conductor protector, conductores continuitatis terrae et ductus systematum AC/HV si quid.

10. Potential gradient: Diferentia potentialis potential difference per unitatem longitudinis mensura in directione qua maxima est.

11. Touch Voltage: P.D. inter structuram metallicam territam et punctum super superficie terrae separatum passu horizontali unius Metri.

12. Step Voltage: P.D. inter duo puncta super superficie terrae separata distanti passu (gradu) assumpto unius Metri.

13. Earth Grid: Systema electroditorum terrae constans ex connectoribus interconnectis sepultis in terra ad praebendum commune fundamentum ab apparatis electricis et structuris metallicis.

14. Earth Mat: Systema terrae formatum per reticulum conductorum horizontaliter sepultorum – Servit ad dissipandum currentem terrae in terram et etiam ut systema conductorum equipotentialium.

Cur Earthing est importante

Earthing est importante ad assecurandum:

1. Securitas personarum

2. Securitas apparatorum

3. Prevenire aut saltem minimare damnum apparatorum propter fluxum currentium magnarum

4. Melioratio fidei systematis electrici.

Classificatio Earthing

Earthing latissime dividitur in

1. System earthing (Coniunctio inter partem plantae in systemate operante sicut LV neutralis winding power transformer) et terra.

2. Equipment earthing (safety grounding) connecting corpora apparatorum (sicut electric motor body, tankus transformatoris, switchgear box, operating rods of air break switches, LV breaker body, HV breaker body, feeder breaker bodies etc) ad terram.

Valores Permissibiles Resistentiae Terrae

Valores rationabiles resistentiae terrae sunt:

• Stationes electricae – 0.5 ohms

• Stationes EHT – 1.0 ohms

• 33KV SS – 2 ohms

• Structurae DTR – 5 ohms

• Resistentia pedis turris – 10 ohms

Quid sunt Fundamenta ad Permittendas Resistantias Terrae?

Secundum regulas IE oportet habere certum fundamentum pro eo secundum regulas IE oportet tener potentialem tactum minorem quam

1. Valorem recommendatum 523 volts

2. Ifault = maximum current in fault conditions,
   

    

3. Maximum current in fault conditions 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 the earthing system, and the expenditure for that will be very high.
   Hence the electrical inspectors are insisting about 1.0 ohms. This seems to justify 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, and a lightning arrestor Displacement = 40 KA.

Typus Earthing

Typos Plate Earthing

In hoc, cast Iron plate of size 600 mm × 600 mm × 6.3 mm thick plate est usus ut plate terra. Haec est coniuncta cum hot dip GI main earth strip of size 50mm breadth × 6mm thick × 2.5 meter long per nut, bolts et washers of required size. Main earth strip est coniuncta cum hot dip GI strip of size 40mm × 3mm of required length as per the site location up to the equipment earth / neutral connection.

Earth plate est back filled et covered with earthing material (mixture of charcoal & salt) by 150mm from all six sides. The remaining pit est back filled with excavated earth. Along with earth plate, rigid PVC pipe of 2.5 meter long est etiam provisa in the earth pit for watering purpose for to keep the earthing resistance within specific limit.

Typus Pipe Earthing

In hoc methodo hot dip GI pipe of size 40 mm dia × 2.5 meter est usus pro equipment earthing. Hoc tubum est perforatum at each interval of 100mm et est tapered at lower end. A clamped est welded cum hoc tubo at 100 mm below the top for making connection cum 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 est being fitted for watering purpose. The earth pipe est placed inside 2700 mm depth pit. A 600mm dia “farma“ of GI sheet or cement pipe in two halves est are placed around the pipe.

Then the angular space between this “farma” and earth pipe est back filled cum alternate layer of 300mm height cum salt and charcoal. The remaining space outside “farma” erit backfilled by excavated earth. The “farma” est gradually lifted up as the backfilling up progresses.

Thus the pit est being filled up to the 300mm below the ground level. This remaining portion est covered by constructing a small chamber of brick so that top open end of pipe and connection cum main earth pipe erit accessible for attending when necessary. The chamber est closed by wooden/stone cover. Water est 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 sunt limited, they may not with stand certain fault currents then the following types of earthing sunt resorted to limit the fault current.

1. Resistance earthing

2. Reactance earthing

3. Peterson coil earthing.

4. Earthing through grounding transformer.

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