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2. Calculate Numbers of Plate/Pipe/Strip Earthing’s (Part-2)

CALCULATE NUMBERS OF PLATE/PIPE/STRIP EARTHINGS (PART-2)

(2)CALCULATE NUMBER OF PLATE EARTHING:

  • The Earth Resistance of Single Plate electrode is calculated as per IS 3040:

  • R=Ρ/A√(3.14/A)

  • Where ρ=Resistivity of Soil (Ω Meter), * A=Area of both side of Plate (m2), * Example: Calculate Number of CI Earthing Plate of 600×600 mm, System has Fault current 65KA for 1 Sec and Soil Resistivity is 100 Ω-Meters. * Current Density At The Surface of Earth Electrode (As per IS 3043): * Max. Allowable Current Density I = 7.57×1000/(√ρxt) A/m2 * Max. Allowable Current Density = 7.57×1000/(√100X1)=757 A/m2 * Surface area of both side of single 600×600 mm Plate= 2 x lxw=2 x 0.06×0.06 = 0.72 m2 * Max. current dissipated by one Earthing Plate = Current Density x Surface area of electrode * Max. current dissipated by one Earthing Plate =757×0.72= 545.04 Amps * Resistance of Earthing Plate (Isolated)(R)=ρ/A√(3.14/A) * Resistance of Earthing Plate (Isolated)(R)=100/0.72x√(3.14/.072)=290.14 Ω * Number of Earthing Plate required =Fault Current / Max.current dissipated by one Earthing Pipe. * Number of Earthing Plate required= 65000/545.04 =119 No’s. * Total Number of Earthing Plate required = 119 No’s. * Overall resistance of 119 No of Earthing Plate=290.14/119=2.438 Ω.

(3)CALCULATING RESISTANCE OF BARED EARTHING STRIP:

1)CALCULATION FOR EARTH RESISTANCE OF BURIED STRIP (AS PER IEEE):

  • The Earth Resistance of Single Strip of Rod buried in ground is

  • R=Ρ/PX3.14XL (LOGE (2XLXL/WXH)+Q)

  • Where ρ=Resistivity of Soil (Ω Meter), * h=Depth of Electrode (Meter), * w=Width of Strip or Diameter of Conductor (Meter) * L=Length of Strip or Conductor (Meter) * P and Q are Coefficients

2)CALCULATION FOR EARTH RESISTANCE OF BURIED STRIP(AS PER IS 3043):

  • The Earth Resistance of Single Strip of Rod buried in ground is

  • R=100XΡ/2×3.14XL (LOGE (2XLXL/WXT))

  • Where ρ=Resistivity of Soil (Ω Meter), * L=Length of Strip or Conductor (cm) * w=Width of Strip or Diameter of Conductor (cm) * t= Depth of burial (cm) * Example : * Calculate Earthing Resistance of Earthing strip/wire of 36mm Diameter, 262 meter long buried at 500mm depth in ground, soil Resistivity is 65 Ω Meter. * Here R = Resistance of earth rod in W. * r = Resistivity of soil(Ω Meter) = 65 Ω Meter * l = length of the rod (cm) = 262m = 26200 cm * d = internal diameter of rod(cm) = 36mm = 3.6cm * h = Depth of the buried strip/rod (cm)= 500mm = 50cm * Resistance of Earthing Strip/Conductor (R)=ρ/2×3.14xL (loge (2xLxL/Wt)) * Resistance of Earthing Strip/Conductor (R)=65/2×3.14x26200xln(2x26200x26200/3.6×50) * Resistance of Earthing Strip/Conductor (R)== 1.7 Ω