1. Electrical Earthing D.K.Pathirana

2. Applications of earthing Protect human against lightning and earth fault condition Protect the premises against lightning and earth fault condition Provide low resistance and safe path for lightning and fault current All metallic enclosure and extraneous conductive parts are at equipotential LV System Earth

3. Functions of Earthing Equipment Earth : Path for fault current, lower touch voltage, protection against electric shock Lighting Earth : Low resistance path to diverse the current under lightning attack. Telecom Earth : Signal Earth, reduce noise and interference, stabilize DC supply voltage and prevent electric shock Computer Earth : reduce interference, maintain supply voltages

4. Two classes of protection Class I protection – use of barrier/insulation and connection of protective conductor to equipment metallic enclosure in order to protect against electric shock Class II protection – beside of the basic insulation, addition layer of insulation apply to the enclosure. Therefore no extraneous conductive part. The additional layer is independent to the basic insulation so that under failure of basic insulation, it offers additional protection

5. Types of Earthing Supply System – Neutral Earth System Earth Electrical Safety Earth Lightning Earth Generator Earth Protection Earth (i.e. surge arrestor) Telecom / Computer Earth Shielding Earth Integrated Earthing System (Advocated) Electrostatic Earth (Clean Room / Hospital)

6. Earthing Arrangements TN System TNS System TN C S System TN C system TT System IT System

7. TN-S System

8. TN-C System

9. TN-C-S System

10. TT System

11. IT System

12. Factors affect to the earth impedance Soil Weather Electrode type Electrode size Near by utilities Electrode in parallel Distance between electrode

13. Soil Resistivity The resistivity of earth may vary over extremely wide limits, depending on the composition of the soil and the moisture content. Factors that affect resistivity Type of earth (eg, clay, loam, sandstone, granite) Stratification; layers of different types of soil (eg, loam backfill on a clay base) Moisture content Temperature Chemical composition and concentration of dissolved salt

14. WENNER method ρ w = 2 π d R S-ES

15. SCHLUMBERGER method ρ s = ( π (d2 – A2/4) R S-ES ) / A

16. Types Of Earth Electrodes Solid Copper Copper clad steel rod ( copper shrunk onto the core) Copper Bonded steel core (coper is molecularly bonded to nickel plated steel rod)

17. Earth Resistance Of An Electrode soil exhibits a resistance to the flow an electrical current not an “ideal” conductor resistance (can never be zero) between the earth electrode and “true Earth”. The resistance between the earth electrode and “true Earth”

18. Rods Driven Vertically Into The Ground Rg = ( /2L)[ln(8L/d)-1] where, ρ - Soil Resistivity in Ωm L - Buried Length of the electrode in m d - Diameter of the electrode in m

19. Combined Resistance Of n No Of Electrodes In which Where R=resistance of one rod Ω S = distance between adjacent rods m ρ = resistivity of soil Ω-m λ =is a factor selected from Table 2 or 3 of BS 7430 ‘n is the no of electrodes as given in Tables 2 and3

20. Resistance Of A Vertical Electrode With Infill Of Bentonite Or Concrete Where, c – resistivity of the infill material d – diameter of electrode in m D – diameter of infill L – driven length of electrode

21. Where, L – length of the strip ‘h - the depth buried w - width of the strip P and Q are coefficient for strip or round conductor in Table 5 Approximate Resistance for a Strip or a round conductor

22. Questions ?

23. Thank You