Scribd
Upload
865 views1 page

Earthing Conductor Sizing Guide

This document provides calculations for sizing an earthing conductor based on inputs for material type, soil resistivity, fault current, and time. It performs the following calculations: 1) Determines material constants like resistivity and heat capacity based on the selected material of copper. 2) Calculates the cross-sectional area of the earth strip needed based on the fault current and time using a formula involving the material constant. 3) Applies a corrosion factor based on soil resistivity to get a final cross-sectional area and selects a standard size that meets this area.

Uploaded by

sreenath rao
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
865 views1 page

Earthing Conductor Sizing Guide

This document provides calculations for sizing an earthing conductor based on inputs for material type, soil resistivity, fault current, and time. It performs the following calculations: 1) Determines material constants like resistivity and heat capacity based on the selected material of copper. 2) Calculates the cross-sectional area of the earth strip needed based on the fault current and time using a formula involving the material constant. 3) Applies a corrosion factor based on soil resistivity to get a final cross-sectional area and selects a standard size that meets this area.

Uploaded by

sreenath rao
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
You are on page 1/ 1

CALCULATION OF EARTHING SYSTEM

Part - A Calculation for sizing the Earthing conductor


Page : 3 of 4

Project : UNIT : DAHEJ


LOCATION :
DOCUMENT NUMBER
REFERENCE DOCUMENT

Reference Standard : IS 3043

Inputs Results
Step : 1
Type of Earthing Conductor material :
Option = 4 as
1 For copper flat
2 For Aluminium
3 For Lead
4 For Steel (G.S. Flat)
Material Constants
B ( c ) Qc (J/ c mm3) 20 (mm) f i
Copper 234.5 3.45E-03 1.72E-05 395 40
Aluminium 228 2.50E-03 2.83E-05 325 40
Lead 230 1.45E-03 2.14E-04 300 40
Steel 202 3.80E-03 1.38E-04 500 40

For the conductor material selected, the following are the material constants :

Qc ==> Volumetric heat capacity of conductor material (J/ c mm3) = 0.0038


B ==> Reciprocal of temperature co-efficient of resistivity ( c ) = 202
at 0 c for the conductor
20 ==> Electrical resistivity of conductor material at 20 c (mm) = 0.000138
f ==> FInal temperature of conductor ( c ) = 500
i ==> Initial temperature of conductor ( c ) = 40

k = Qc ( B + 20 ) ( f - i )
ln 1+ = 80.6868322 ==> Constant
20 ( B + i )

Step :2
= I*t
Cross sectional area of Earth strip A ( mm2 )
k

where
I ==> Maximum R.M.S ground fault current = 25 KA

t ==> Operating time of fault clearing device = 0.5 secs


k ==> Factor dependant on material of earth conductor

Calculated Cross Section Area A= 219.09 ( mm2 )

Corrosion factor ( CBIP manual 302 : Earthing of AC system)


1) Soil resistivity up to 25 Ohm - Meter 30%
2) Soil resistivity >25 <100 Ohm - Meter 15%
3) Soil resistivity >100 Ohm - Meter 10%

Considering Corrosion factor of = 30 (%)

A= 284.82 ( mm2 )

===> Size of Earth strip chosen = 50 x 6 mm


Area of choosen Earth strip = 300 Sq mm

You might also like