7/26/2019 Earthing Mat Design Calculation Sheet

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Prerequisites

TECHNICA

SYMBOL DESCRIPTIO

Energy of max earth faultMax allowable fusing temperature

Ambient Temperature

Thermal coecient of resisti!ity

"esisti!ity of earthing con#uctor

TCA$Thermal capacity of con#uctor per

Soil resistivity

Resistivity of the surface layer material

Thickness of the surface layer

Maximum fault clearing time

Total length of burie# con#uctors

Depth of the earthing gri#

Earth fault current

Current #i!ision factor

%&" ratio at the fault location

f 'ystem fre(uency

Duration of the fault

Total length of hori)ontal gri# con#uct

Length of gri# con#uctors on the peri

Total length of earthing electro#es & ro

Length of each earthing electro#e & ro#

A' Total area of the gri#

Maximum length of the gri#s in the x

Maximum length of the gri#s in the y #

Maximum #istance between any two p

'pacing between parallel gri# con#uct

Cross*sectional #iameter of a gri# con#

i+

tT

m

Ta

,r

-r

./

Sf

A is the minimum cross-sectional area of the

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A = 01213/4+1++5

/2555//+6

is the touch !oltage limit 789

is the step !oltage limit 789

0:23;;/4;/61

+32;:;3+/11+

0:2;556650;6

+3214;:;406;

/2///;454113

+/

02:+;:;13664

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DATA

N VALUE UNIT

35 ?C

6 ?C

/2//1

+ @>2 cm

0;1211111:

nit !olume6

/2//3 m

+ m

;6 m

;6 s

0/ m

6 m

+/ A

0

3

6/ H)

3 s

rs 0/ m

eter 6 m

s 3 m

+ m

+6

irections 6 m

irections 1 m

ints on the gri# ; m

rs : m

uctor + m

A+

s

?C*0

cm*3?C*0

m+

earthing grid conductor (mm2)

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emote earth 7>9

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x= /2/+1/304;

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+362105;6

+25:;:;555

TAis the #c time oBset constantT

A=

Dfis the #ecrement factor

Df=

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n is Geometric Factor

;

NOW

for square grids n= +2+:4;:;+63

for square and rectangular grids n= 02/+;+56/35

for square, rectangular and L-shaped grids n= +2++;;30655

/240+1/:0 for

/2;1;+0:6

+2;;5;45:

/206/116:

03

na=

nb

=0 for s(uare gri#s

nc=0 for s(uare an# rectangular gri#s

nd=0 for s(uare rectangular an# L*shape# gri#s

Kiis Irregularity factor

Ki=

Kiiis a weighting a!t"r "r earth e#e!tr"$es %r"$s "n the !"r

Kii=0 for gri#s with earth electro#es along the gri# perimeter or corn

Kii=

Khis a weighting factor for #epth of burial

Kh=

Kmis the geometric spacing factor

Km=

Lm

is the eBecti!e burie# length for gri#s with few or no earthing electr

7an# none on corners or along the perimeter9L

m=

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/2/3+;414

/2/+0+600

0/2/6

/2//65+:+

EA!"I#G GI$ $E%IG# I% %AFE

EA!"I#G GI$ $E%IG# I% %AFE

mis the mesh !oltage

m=

Ksis the geometric spacing factor

Ks=

Lsis the eBecti!e burie# length

Ls=

sis the maximum allowable step !oltage

s=

E%&'!50 kg(

E%&'!70 kg(

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otherwise /26

otherwise 0200++064

otherwise /260+0;:6

otherwise n= 02035+3:0

OR

!"#"$%&

nb

=

nc=

nd=

er &esh

ers

#es Lmis the eBecti!e burie# length for gri#s with e

electro#es on the corners an# along the perimL

m=

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rthing

eter

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or

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