Earthing Calculation IEEE

ITEM

DESCRIPTION

SYMBOL

VA V ALUE

Dimension of the grid in E alignment direction (m):

LE

123

2 3 4

Dimension of the grid in N alignment direction (m): Soil Soil resi resist stiv ivit ity y (Ohm (Ohm*m *m): ): Total enclosed area by ground grid (m2):

LN ρ

81 210 9963

5 6 7

CONDUCTOR SIZE  Symmetrical grid current (A): Duration of fault current (s): Material thermal capacity per unit volume in Joules/cm3/ºC:

8

Ground conductor thermal coefficient of resistivity at 0 ºC:

STEP 1

FIELD DATA 1

A

STEP 2

9 10 11 12 13 14 15

Ig tc TCAP α0

1000.00 0.3 3.42

Ground conductor thermal coefficient of resistivity at reference temperature of 20 ºC:

αt

0

Ground conductor resistivity at reference temperature of 20 ºC: Ko = 1 / α0

ρt

1.72

Ko Tm Ta Sm Sr

234 250 40 3.23 240

hs ρs

0.04

Maximum allowable temperature (ºC): Ambient temperature (ºC): Required conductor cross-section (mm2): Actual conductor cross-section (mm2):

0

STEP 3

16

TOUCH & STEP CRITERIA Su Surface layer thickness (m):

17 18

Surface layer resistivity (Ohm*m): Surface layer derating factor:

19

Cs

2,000 0.53

Tolera Tolerable ble touch touch voltag voltage e (V): (V):

Etouch50

546.10

20

Tolera Tolerable ble step step volt voltage age (V): (V):

Estep50

1549.03

21 22 23 24 25 26 27 28

INITIAL DESIGN  No. of parallel conductors in E alignment direction (m) No. of parallel conductors in N alignment direction (m) Spacing between parallel conductors in E alignment direction (m) Spacing between parallel conductors in N alignment direction (m) Number of ground rods: Le L ength of each ground rod (m): Grid burial depth (m): Total length of grid conductor (m):

29

Total effective length of grounding system conductor (m):

STEP 4

5 4 30.75 27.00 17.00 3.05 0.75 939

Nr Lr h Lc LT

990.85

Rg

1.1375

STEP 5

30

GRID RESISTANCE  Resistance of grounding system (Ω): STEP 6 AND 7

31

P

IgxRg
1

NO

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STEP 8

32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47

MESH & STEP VOLTAGES  Corrective weighting factor: Corrective weighting factor: Peripheral length of the grid (m): Geometric factor: Geometric factor: Geometric factor: Geometric factor: Geometric factor: Diameter of the conductor (m): Spacing factor for mesh voltage: Correction factor for grid geometry: Effective length for mesh voltage: Actual mesh voltage (V): Spacing factor for step voltage: Effective length for step voltage: Actual step voltage (V):

Kii Kh Lp na nb nc nd n d Km Ki Lm Em Ks Ls Es

1 1.32 408 4.60 1.01 1.00 1.00 4.65 0.02 1.20 1.33 1,020.68 330.33

0.23 748.32 86.40

STEP 9

48

Em
49

Es
 YES STEP 10

P

2

 YES

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APPLIED EQUATIONS

 A= L E × L N 

4

11

 K  0 =

14

S m =

18

1 α0

 I  g 





ln

K 0  T  m  K 0  T  a 10

t c αt  ρt 



4

TCAP  0 . 09

C  s = 1 −

2



1−

 ρ  ρ s



h s  0 .09

touch

19

20

 Ealignl ¿¿ ¿=  1000

 1. 5 × C  s × ρ s

 E  s te p=  1 0 00 6 C  s ρ s 

29

 L T = L C  N r  xL r 

30

 R g = ρ

[

1

 L T 



0.116



 t 

¿

0.1 1 6

 t 

1

 20 A



1

1

 20 /  A

1 h

]

32

Kii=1 (for grids with ground rods along the perimeter)

33

 K hh==  11hh//hh00  K  Lc

2

35

na =

36

nb =

(ho=1 m reference depth of grid)

 L  p

 

4

L p

  A

37

nc = 1 for rectangular grids

38

nd = 1 for rectangular grids

n= n a⋅n b⋅n c⋅n d 

39

 

4

S  π 

40

d =

41

 K m=

1000 1 2π

{[ ln

 D 2h  D2  16 h d  8 D d 

42

 K i = 0.644 0.148⋅n

43

 L M = L C 

44

 E m =

[

1 . 55 1 . 22

2

−



h 4 d 

]



 K ii  K h

L r 

  L E  L N  2

2

8

ln

π   2n− 1 

}

]

 L r  N r 

 ρ I  g  K m K i  L M  −

P

3

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45

P

 K  s =

π  2 h



h  D



 D

 1 −0 .5 −  n 2

46

 L s = 0.75⋅ LC  0 . 8 5⋅ L r ⋅ N r 

47

 E  s =

4

 ρ I  g  K  s K i  L s

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