10.

Touch and Step Voltage Criteria for Power House, Transformer cum GIS and Pothead Yard

10.1) Input Data :

(i) System Voltage, Vs = 13.8 kV

(ii.1) System fault Current, If = 63 KA

(iii) Fault Duration, t = 1 sec

(iv.1) Length of Earth grid = 2533 metre

(iv.2) Width of Earth grid = 5 metre

(iv.3) Area of Earth grid, A = 12666 sq.metre

(v) Conductor Size for main grid = 1256 sq.mm

(vi) Depth of burial w.r.t. ground level, h = 0.6 metre

(vii.1) Number of earth mat conductors in 'X' direction = 634 No.

(vii.2) Length of earth mat conductors in 'X' direction = 4438 metre

(vii.3) Number of earth mat conductors in 'Y' direction = 2 No.

(vii.4) Length of earth mat conductors in 'Y' direction = 5071 metre

(vii.5) Total Length of Buried conductor, Lc = 12539 metre

(viii.1) Total no. of ground rods = 154

(viii.2) Total ground rod length, LR = 462 metre

(viii.3) Effective Buried Length for mesh voltage, LM = 13255.3 metre

(viii.4) Effective Buried Length for step voltage, LS = 9796.61 metre

(ix) Soil Resistivity, r = 607.41 W-metre

(x) Surface Resistivity, rs = 10000 W-metre

(xi) Spacing for Earthing Mat below ,D = 4 metre

(xii) Corrective weighting factor, Kii = 1

(xiii) Reference Depth of grid, h0 = 1 metre

(xvi) Thickness of tiles/Gravel/concrete etc, hs = 0.15 metre

Page 1 of 91
10.2) Calculation of Tolerable Etouch & Estep Voltage :

a) Tolerable Etouch70 :
From Eq.33 of IEEE Std 80-2000
Tolerable Etouch70= [(1000 + 1.5CS rS) 0.157/ ÖtS ]
Where,
Cs = Reduction factor for derating the nominal value of surface layer

Cs = 1 - 0.09 [(1-r/rs)/(2hs + 0.09)] ( From eq.27 of IEEE Std 80-2000 )

Cs = 0.783
tS = Duration of shock current in seconds , t = 0.5 sec
( from clause 16.2.2 of IEEE Std 80-2000 )
Substituting the above values,
Tolerable Etouch70 = 2830.62 Volts

b) Tolerable Estep70 = [(1000 + 6CS rS) 0.157/ ÖtS ] (from eq.29 of IEEE Std 80-2000)

Substituting the values,

Tolerable Estep70 = 10656.38 Volts

10.3) Calculation of Maximum Ground Potential Rise :

Max. Ground potential above remote earth, GPR = Ig x Rg Volts
Where,
Ig = grid current = If x Sf

Sf = Fault current division factor

Ig = 63 KA at Sf = 0.5
Substituting the values,

Ground Potential Rise, GPR = #REF! Volts

Since, GPR > Estep70 (as per Figure 33 of IEEE Std 80-2000),calculate Emesh and Attainable
Estep voltages

10.4) Calculation of Attainable Etouch Voltage :

From Eq.80 of IEEE Std 80-2000, for Grid rods in the periphery,

Attainable Etouch Voltage = [ r Km Ki I G / L M ]

Lr
LM = Lc + 1.55+1.22 LR From eq.91 of IEEE Std 80-2000
Lx+L
2 2
y

Where,
Lr = Length of each ground rod = 3 m
Lx = Maximum length of grid conductor in x-direction = 2533 m
Ly = Maximum length of grid conductor in y-direction = 5 m

Page 2 of 91
 LR = Total length of ground rods = 462 m
Subtituting the above values,

LM = 13255.32 m

As per Eq.81 of IEEE Std 80-2000, the Spacing Factor for Mesh Voltage,

1 D2 (D + 2h) h Kii 8
Km = ln + - + ln
2p 16hd 8Dd 4d Kh p(2n-1)

Equ. Diameter of Earth conductor, d = 0.0400 metre

Kh = 1 + h / h 0 ( From eq.83 of IEEE Std 80-2000 )

Kh = 1.26

No. of Parallel Paths, n = n a nb nc nd

Where, From eq.85 to 88 of IEEE Std 80-2000 Lp

na = (2 Lc)/Lp nb =
4 A
0.7 A
L x Ly L x Ly
nc = nd = 1
A
Where,
Lp = Peripheral length of the grid = 5076.5498 m
D = Maximum distance between any two points
on the grid = 4 m
Substituting the above values,

na = 4.94 nb = 3.358

nc = 1 nd = 1.00

n = 16.59

As per Eq.89 of IEEE 80-2000,

The corrective Factor, Ki = 0.644 + ( 0.148 x n )

Ki = 3.10
Substituting the values,
Km = 0.2757

Attainable Etouch Voltage = 2466.40 Volts

10.5) Calculation of Attainable Estep :

From Eq.92 of IEEE Std 80-2000,
Attainable Estep = [ r Ks Ki IG / L S ]

Page 3 of 91
 As per Eq.94 of IEEE Std 80-2000, the Spacing Factor for Step Voltage,

1 1 1 1
Ks = + + (1 - 0.5n-2)
P 2h D + h D

No. of Parallel paths, n = 16.59

As per Eq.89 of IEEE 80-2000,

The corrective Factor, Ki = 0.644 + ( 0.148 x n )
Ki = 3.10

Ks = 0.4140

As per Eq.93 of IEEE Std 80-2000,

Ls = 0.75 Lc + 0.85 LR

Ls = 9796.61235 m

Substituting the values,

Attainable Estep Voltage = 5011.99 Volts

CONCLUSION :
Tolerable
Etouch = 2830.62 Volts

Attainable
Etouch = 2466.40 Volts SAFE

Tolerable
Estep = 10656.38 Volts

Attainable
Estep = 5011.99 Volts SAFE

From the above results,it can be seen that the Attainable E touch and Attainable Estep voltages are
less than the Tolerable Etouch and Tolerable Estep voltages and hence SAFE

10.6) Soil resistivity for Power house, Transformer cum GIS, Potheadyard

Soil resistivity for Power house = 245.43 W-meter

Soil resistivity for Transformer Cavern = 693.66 W-meter

Soil resistivity for Pothead yard = 883.15 W-meter

Soil resistivity for Tailrace = 245.43 W-meter

Soil resistivity for Surge Chamber = 245.43 W-meter

Soil resistivity for Intake structure = 245.43 W-meter

Average Soil resistivity = 426.42 W-meter

Page 4 of 91
Page 5 of 91
10. Touch and Step Voltage Criteria for Power House

1 Input Data :

(i) System Voltage, Vs = 13.8 kV

(ii.1) System fault Current, If = 63 KA

(iii) Fault Duration, t = 1 sec

(iv.1) Length of Earth grid = 1776.9 meter

(iv.2) Width of Earth grid = 4.0 meter

(iv.3) Area of Earth grid, A = 7107 sq.meter

(v) Conductor Size for main grid = 1256 sq.mm

(vi) Depth of burial w.r.t. ground level, h = 0.6 meter

(vii.1) Number of earth mat conductors in 'X' direction = 711 No.

(vii.2) Length of earth mat conductors in 'X' direction = 4266 meter

(vii.3) Number of earth mat conductors in 'Y' direction = 2 No.

(vii.4) Length of earth mat conductors in 'Y' direction = 3558 meter

(vii.5) Total Length of Buried conductor, Lc = 8734 meter

(viii.1) Total no. of ground rods = 115

(viii.2) Total ground rod length, LR = 345 meter

(viii.3) Effective Buried Length for mesh voltage, LM = 9269.2 meter

(viii.4) Effective Buried Length for step voltage, LS = 6843.53 meter

(ix) Soil Resistivity, r = 5346.83 W-meter

(x) Surface Resistivity, rs = 10000 W-meter

(xi) Spacing for Earthing Mat below ,D = 2.5 meter

(xii) Corrective weighting factor, Kii = 1 meter

(xiii) Reference Depth of grid, h0 = 1

(xvi) Thickness of tiles/Gravel/concrete etc, hs = 0.15 meter

Page 6 of 91
 2 Calculation of Tolerable Etouch & Estep Voltage :

a) Tolerable Etouch70 :
From Eq.33 of IEEE Std 80-2000
Tolerable Etouch70= [(1000 + 1.5CS rS) 0.157/ ÖtS ]
Where,
Cs = Reduction factor for derating the nominal value of surface layer

Cs = 1 - 0.09 [(1-r/rs)/(2hs + 0.09)] ( From eq.27 of IEEE Std 80-2000 )

Cs = 0.893
tS = Duration of shock current in seconds, t = 0.5 sec
( from clause 16.2.2 of IEEE Std 80-2000 )
Substituting the above values,
Tolerable Etouch70 = 3194.88 Volts

b) Tolerable Estep70 = [(1000 + 6CS rS) 0.157/ ÖtS ] (from eq.29 of IEEE Std 80-2000)

Substituting the values,

Tolerable Estep70 = 12113.41 Volts

3 Calculation of Maximum Ground Potential Rise :

Max. Ground potential above remote earth, GPR = Ig x Rg Volts
Where,
Ig = grid current = If x Sf

Sf = Fault current division factor

Ig = 63 KA at Sf = 0.5
Substituting the values,

Ground Potential Rise, GPR = #REF! Volts

Since, GPR > Estep70 (as per Figure 33 of IEEE Std 80-2000),calculate Emesh and Attainable
Estep voltages

4 Calculation of Attainable Etouch Voltage :

From Eq.80 of IEEE Std 80-2000, for Grid rods in the periphery,

Attainable Etouch Voltage = [ r Km Ki I G / L M ]

Lr
LM = Lc + 1.55+1.22 LR From eq.91 of IEEE Std 80-2000
Lx+L
2 2
y

Where,
Lr = Length of each ground rod = 3 m
Lx = Maximum length of grid conductor in x-direction = 1777 m
Ly = Maximum length of grid conductor in y-direction = 4 m

Page 7 of 91
 LR = Total length of ground rods = 345 m
Subtituting the above values,

LM = 9269.16 m

As per Eq.81 of IEEE Std 80-2000, the Spacing Factor for Mesh Voltage,

1 D2 (D + 2h) h Kii 8
Km = ln + - + ln
2p 16hd 8Dd 4d Kh p(2n-1)

Equ. Diameter of Earth conductor, d = 0.0400 meter

Kh = 1 + h / h 0 ( From eq.83 of IEEE Std 80-2000 )

Kh = 1.26

No. of Parallel Paths, n = n a nb nc nd

Where, From eq.85 to 88 of IEEE Std 80-2000 Lp

na = (2 Lc)/Lp nb =
4 A
0.7 A
L x Ly L x Ly
nc = nd = 1
A
Where,
Lp = Peripheral length of the grid = 3561.7 m
D = Maximum distance between any two points
on the grid = 2.5 m
Substituting the above values,

na = 4.90 nb = 3.250

nc = 1 nd = 1.00

n = 15.94

As per Eq.89 of IEEE 80-2000,

The corrective Factor, Ki = 0.644 + ( 0.148 x n )

Ki = 3.00
Substituting the values,
Km = 0.1384

Attainable Etouch Voltage = 15103.57 Volts

5 Calculation of Attainable Estep :

From Eq.92 of IEEE Std 80-2000,
Attainable Estep = [ r Ks Ki IG / L S ]

Page 8 of 91
 As per Eq.94 of IEEE Std 80-2000, the Spacing Factor for Step Voltage,

1 1 1 1
Ks = + + (1 - 0.5n-2)
P 2h D + h D

No. of Parallel paths, n = 15.94

As per Eq.89 of IEEE 80-2000,

The corrective Factor, Ki = 0.644 + ( 0.148 x n )
Ki = 3.00

Ks = 0.4953

As per Eq.93 of IEEE Std 80-2000,

Ls = 0.75 Lc + 0.85 LR

Ls = 6843.525 m

Substituting the values,

Attainable Estep Voltage = 73201.86 Volts

CONCLUSION :
Tolerable
Etouch = 3194.88 Volts

Attainable
Etouch = 15103.57 Volts SAFE

Tolerable
Estep = 12113.41 Volts

Attainable
Estep = 73201.86 Volts SAFE

Page 9 of 91
 Earthmat Sizing Calculations

R0. 27/Dec/24 First Issued IS PSN

Rev No. Date Description Checked Approved

Document No SS-E-MAN-MP-SYS-005

Project 400/132/220/ 33kV Vasundhara Substation

Sub: Earthing Calculations

Owner/
MP POWER TRANSMISSION PACKAGE - 1 LTD
Customer

Contractor MEGHA ENGINERING & INFRASTRUCTURES LIMITED, HYDERABAD

Revision R0
Reference standard : IEEE Std 80-2013

A. Conductor Sizing

Input data :- Properties of MS is as per Item 10 Table1 of IEEE Std 80-2013

(i) Conductor material = CU

(ii) System Voltage = 220 kV

(iii) Fault Current, If = 40 kA,

(iv) Fault Duration, tc = 3 sec

(v) Max. Allowable Temperature, Tm = 1084 *0

C see Note

(vi) Ambient Temperature, Ta = 50 C

0

(vii) Thermal Co-eff.of resistivity at reference

Temperature, ar = 0.00394 *

(viii) Resistivity of Ground Conductor at ref.

Temperature, rr = 10 * mW-cm

(ix) Thermal Capacity Factor, TCAP = 3.4 * J/(cm3.oC)

(x) K0 = 234 *

Conductor Size :-
As per Eq.37 of IEEE Std 80-2000, conductor size is given by
If

A = TCAP x 10-4 X ln Ko + Tm
tc ar rr Ko + Ta

Conductor size, A = 602 sq.mm

Corrosion allowance 30% 783 sq.mm Corrosive
As per CBIP Table 3.9 publication /No 339

Conductor size selected considering corrosion 40 MM MS ROD

allowance
1256.6 Sqmm

The minimum rate of corrosion of steel used for earthing

conductor shall be considered as 0.12 mm per year @ 40Y 35.2
Area of Earthing conductor after life time corrosion 973

Note:- 1) * marked values are taken as per IEEE.80

2) Earthing conductor size of 75 X 12 mm is as per specifications.

3) Earthing conductor size of 75 X 12 mm and 40 mm dia MS rod is sustainable to

withstand at fault level 63 kA for 1 sec.

PAGE 11 OF 91
PAGE 12 OF 91
Reference standard : IEEE Std 80-2013

A. Conductor Sizing

Input data :- Properties of MS is as per Item 10 Table1 of IEEE Std 80-2013

(i) Conductor material = M.S.

(ii) System Voltage = 400 kV

(iii) Fault Current, If = 63 kA,

(iv) Fault Duration, tc = 1 sec

(v) Max. Allowable Temperature, Tm = 1510 *0

C see Note

(vi) Ambient Temperature, Ta = 50 C

0

(vii) Thermal Co-eff.of resistivity at reference

Temperature, ar = 0.00377 *

(viii) Resistivity of Ground Conductor at ref.

Temperature, rr = 15.9 * mW-cm

(ix) Thermal Capacity Factor, TCAP = 3.8 * J/(cm3.oC)

(x) K0 = 245 *

Conductor Size :-
As per Eq.37 of IEEE Std 80-2000, conductor size is given by
If

A = TCAP x 10-4 X ln Ko + Tm
tc ar rr Ko + Ta

Conductor size, A = 593 sq.mm

Corrosion allowance 30% 770 sq.mm Corrosive
As per CBIP Table 3.9 publication /No 339

Conductor size selected considering corrosion 40 MM MS ROD

allowance
1256.6 Sqmm

The minimum rate of corrosion of steel used for earthing

conductor shall be considered as 0.12 mm per year @ 40Y 35.2
Area of Earthing conductor after life time corrosion 973

Note:- 1) * marked values are taken as per IEEE.80

2) Earthing conductor size of 40 mm dia MS rod is as per specifications.

3) Earthing conductor size of 40 mm dia MS rod is sustainable to withstand at fault

level 63 kA for 1 sec.

PAGE 13 OF 91
PAGE 14 OF 91
1. 400/220/132/33kV Substation

1.1 Input Data :

(i) System Voltage, Vs = 400 kV

(ii.1) System fault Current, If = 63 KA

(iii) Fault Duration, t = 1 sec

(iv.1) Length of Earth grid = 290.000 meter

(iv.2) Width of Earth grid = 101.0 meter

(iv.3) Area of Earth grid, A = 29290 sq.meter

(v) Conductor Size for main grid = 1256 sq.mm

(vi) Depth of burial w.r.t. ground level, h = 0.6 meter

(vii.1) Number of earth mat conductors in 'X' direction = 30 No.

(vii.2) Length of earth mat conductors in 'X' direction = 3030 meter

(vii.3) Number of earth mat conductors in 'Y' direction = 12 No.

(vii.4) Length of earth mat conductors in 'Y' direction = 3480 meter

Total Length of Buried conductor = 6510 meter

(vii.5)
Effective Length of Buried conductor = 6510 meter

(viii.1) Total no. of ground rods = 250 No.

(viii.2) Total ground rod length, LR = 750 meter

(viii.3) Effective Buried Length for mesh voltage, LM = 7681.4 meter

(viii.4) Effective Buried Length for step voltage, LS = 5520.00 meter

(ix) Soil Resistivity, r = 40.000 W-meter

(x) Surface Resistivity, rs = 3000 W-meter

(xi) Spacing for Earthing Mat below ,D = 10 meter

(xii) Corrective weighting factor, Kii = 1

(xiii) Reference Depth of grid, h0 = 1 meter

(xvi) Thickness of tiles/Gravel/concrete etc, hs = 0.1 meter

Decrement factor for the entire duration of fault tf

1
(xvii) (Df) =

Page 15 of 91
1.2 Grid resistance of Substation

As per Eq.52 of IEEE Std 80-2013,

The total system resistance,

Where,
Rg = Ground resistance of grid conductors in W
Ground resistance of the grid, Rg

  
1 1  1 
Rg =
     1  
From eq.52 of IEEE Std 80-2013
L
 T 20 A  1  h  20  
 A 
Where,
r = Soil resistivity in W-m 40.00 ohm-m
Lt = Is the total buried length of conductors in m (Lc+Lr) 7260 m
A = Area covered by conductors in m2 29290 m2
h = is the depth of the grid in m 0.600

Rg = 0.1092 W

Grid resistance of Substation = 0.11 W

Page 16 of 91
 1.3 Calculation of Tolerable Etouch & Estep Voltage :

a) Tolerable Etouch70 :
From Eq.33 of IEEE Std 80-2013
Tolerable Etouch70= [(1000 + 1.5CS rS) 0.157/ ÖtS ]
Where,
Cs = Reduction factor for derating the nominal value of surface layer

Cs = 1 - 0.09 [(1-r/rs)/(2hs + 0.09)] ( From eq.27 of IEEE Std 80-2013 )

Cs = 0.694
tS = Duration of shock current in seconds , t = 0.5 sec
( from clause 16.2.2 of IEEE Std 80-2013 )
Substituting the above values,

Tolerable Etouch70 = 915.23 Volts

b) Tolerable Estep70 = [(1000 + 6CS rS) 0.157/ ÖtS ] (from eq.30 of IEEE Std 80-2013)

Substituting the values,

Tolerable Estep70 = 2994.82 Volts

1.4 Calculation of Maximum Ground Potential Rise :

Max. Ground potential above remote earth, GPR = Ig x Rg Volts
Where,
Ig = grid current = If x Sf I G= Df X I g

Sf = Fault current division factor

IG = 44.1 KA at Sf = 0.7

Substituting the values,

Ground Potential Rise, GPR = 4816.90 Volts

Since, GPR > Estep70 (as per Figure 33 of IEEE Std 80-2013),calculate Emesh and Attainable
Estep voltages

1.5 Calculation of Attainable Etouch Voltage :

From Eq.80 of IEEE Std 80-2013, for Grid rods in the periphery,

Attainable Etouch Voltage = [ r Km Ki I g / L M ]

Lr
LM = Lc + 1.55+1.22 LR From eq.91 of IEEE Std 80-2013
L 2x + L 2 y
Where,
Lr = Length of each ground rod = 3 m
Lx = Maximum length of grid conductor in x-direction = 290.00 m
Ly = Maximum length of grid conductor in y-direction = 101 m

Page 17 of 91
 LR = Total length of ground rods = 750 m
Subtituting the above values,

LM = 7681.44 m

As per Eq.81 of IEEE Std 80-2013, the Spacing Factor for Mesh Voltage,

1 D2 (D + 2h)2 h Kii 8
Km = ln + - + ln
2p 16hd 8Dd 4d Kh p(2n-1)

Equ. Diameter of Earth conductor, d = 0.0400 meter

Kh = 1 + h / h 0 ( From eq.83 of IEEE Std 80-2013 )

Kh = 1.26

No. of Parallel Paths, n = n a nb nc nd

Where, From eq.85 to 88 of IEEE Std 80-2013 Lp

na = (2 Lc)/Lp nb =
4 A
0.7 A
L x Ly L x Ly
nc = nd = 1
A
Where,
Lp = Peripheral length of the grid = 782 m
Substituting the above values,

na = 16.65 nb = 1.069

nc = 1 nd = 1.00

n = 17.79

As per Eq.89 of IEEE 80-2013,

The corrective Factor, Ki = 0.644 + ( 0.148 x n )

Ki = 3.28
Substituting the values,
Km = 0.5774

Attainable Etouch Voltage = 434.58 Volts

1.6 Calculation of Attainable Estep :

From Eq.92 of IEEE Std 80-2013,
Attainable Estep = [ r Ks Ki I g / L S ]

Page 18 of 91
 As per Eq.94 of IEEE Std 80-2013, the Spacing Factor for Step Voltage,

1 1 1 1
Ks = + + (1 - 0.5n-2)
p 2h D + h D

No. of Parallel paths, n = 17.79

As per Eq.89 of IEEE 80-2013,

The corrective Factor, Ki = 0.644 + ( 0.148 x n )
Ki = 3.28

Ks = 0.3271

As per Eq.93 of IEEE Std 80-2013,

Ls = 0.75 Lc + 0.85 LR

Ls = 5520.00 m

Substituting the values,

Attainable Estep Voltage = 342.63 Volts

CONCLUSION :
Tolerable
Etouch = 915.23 Volts

Attainable
Etouch = 434.58 Volts SAFE

Tolerable
Estep = 2994.82 Volts

Attainable
Estep = 342.63 Volts SAFE
The Maximum attainable touch & step vltage is less than tolerable limit . Hence earthing design is safe

Page 19 of 91
3. Calculation of Earth Grid Resistance for Switchgear room
3.1) Input Data :

(i) System Voltage, Vs = 400 kV

(ii.1) System fault Current, If = 25 KA

(iii) Fault Duration, t = 1 sec

(iv.1) Length of Earth Mat = 24.4 metre

(iv.2) Width of Earth Mat = 10.16 metre

(iv.3) Area of Earth Mat, A = 248 sq.metre

(v) Conductor Size for main grid = 300 sq.mm

(vi) Depth of burial w.r.t. Ground level, h = 0.6 metre

(vii.1) Number of earth mat conductors in 'Y' direction = 7 No.

(vii.2) Length of earth mat conductors in 'Y' direction = 71.12 metre

(vii.3) Number of earth mat conductors in 'X' direction = 4 No.

(vii.4) Length of earth mat conductors in 'X' direction = 97.6 metre

(vii.5) Length of Buried conductor, Lc = 168.72 metre

(viii.1) Total no. of ground rods

For 3.0 m long = 4

(viii.2) Total ground rod length, LR = 12 metre

(ix) (Average) Soil Resistivity, r = 307.28 W-metre

(x) Spacing for Earth Mat below Pump House,D = 3.5 metre
3.2) Calculation of Grid Resistance, Rgs : For Switchgear room

As per Eq.53 of IEEE Std 80-2000,

R1 R2 - Rm2
The total system resistance, Rgp =
R1 + R2 - 2Rm
Where,
R1 = Ground resistance of grid conductors in W
Ground resistance of the grid, R1

r 2 Lc k1 Lc
R1 = ln + - k2 From eq.54 of
p Lc a '
A IEEE Std 80-2000

Where,
r = Soil resistivity in W-m 307.28 ohm-m
Lc = Total length of all connected grid conductors in m 168.72 m
a' = a . 2h for conductors buried at depth h in m 0.1083 m
2a = Diameter of conductor in m 0.0195 m
A = Area covered by conductors in m2 247.904 m2
k1 = Coefficient from fig 25(a) of IEEE Std 80-2000 (curve-A) 1.314
k2 = Coefficient from fig 25(b) of IEEE Std 80-2000 (curve-A) 5.860

R1 = 9.4286 W

Ground resistance of the rod bed, R2

From eq.55 of IEEE Std 80-2000
r 4 LR 2 k1 . Lr
R2 = ln -1 + ( n R - 1 )2
2p nRLR b A

Where,
Lr = length of each rod in m 3 m
2b = diameter of rod in m 0.040 m
nR = number of rods placed in area A 4

R2 = 7.421 W

Mutual ground resistance between the grid and the rod bed, R m
From eq.55 of IEEE Std 80-2000

r 2 Lc k1 Lc
Rm = ln + - k2 + 1
p Lc Lr A

Rm = 8.0827 W

Subtituting the above values,

Rgs = 6.7821 W

3.3) CONCLUSION :

Grid Resistance = 6.7821 W

3. Calculation for Earth Grid Resistance of Surge Pool
3.1) Input Data :

(i) System Voltage, Vs = 11 kV

(ii.1) System fault Current, If = 40 KA

(iii) Fault Duration, t = 1 sec

(iv.1) Length of Earth Mat = 45.00 metre

(iv.2) Width of Earth Mat = 20 metre

(iv.3) Area of Earth Mat, A = 900 sq.metre

(v) Conductor Size for main grid = 600 sq.mm

(vi) Depth of burial w.r.t. ground level, h = 128 metre

(vii.1) Number of earth mat conductors in 'X' direction = 10 No.

(vii.2) Length of earth mat conductors in 'X' direction = 200 metre

(vii.3) Number of earth mat conductors in 'Y' direction = 5 No.

(vii.4) Length of earth mat conductors in 'Y' direction = 225 metre

(vii.5) Length of Buried conductor, Lc = 425 metre

(viii.1) Total no. of ground rods

For 1.0 m long = 6

(viii.2) Total ground rod length, LR = 6 metre

(ix) (Average) Soil Resistivity, r = 100 W-metre

(x) Spacing for Earth Mat below Pump House,D = 5 metre

3.2) Calculation of Grid Resistance, Rgs : For Surge Pool

As per Eq.53 of IEEE Std 80-2000,

R1 R2 - Rm2
The total system resistance, Rgs =
R1 + R2 - 2Rm
Where,
R1 = Ground resistance of grid conductors in W
Ground resistance of the grid, R1

r 2 Lc k1 Lc
R1 = ln + - k2 From eq.54 of
p Lc a '
A IEEE Std 80-2000

Where,
r = Soil resistivity in W-m 100 ohm-m
Lc = Total length of all connected grid conductors in m 425 m
a' = a . 2h for conductors buried at depth h in m 1.8809 m
2a = Diameter of conductor in m 0.0276 m
A = Area covered by conductors in m2 900 m2
k1 = Coefficient from fig 25(a) of IEEE Std 80-2000 (curve-A) 1.320
k2 = Coefficient from fig 25(b) of IEEE Std 80-2000 (curve-A) 5.838

R1 = 1.4212 W

Ground resistance of the rod bed, R2

From eq.55 of IEEE Std 80-2000
r 4 LR 2 k1 . Lr
R2 = ln -1 + ( n R - 1 )2
2p nRLR b A

Where,
Lr = length of each rod in m 1 m
2b = diameter of rod in m 0.040 m
nR = number of rods placed in area A 6

R2 = 2.774 W

Mutual ground resistance between the grid and the rod bed, R m
From eq.55 of IEEE Std 80-2000

r 2 Lc k1 Lc
Rm = ln + - k2 + 1
p Lc Lr A

Rm = 1.5434 W

Subtituting the above values,

Rgs = 1.4078 W

3.3) CONCLUSION :

Grid Resistance = 1.4078 W

Reference standard : IEEE Std 80-2000

3. CONDUCTOR SIZING FOR SWITCH YARD

Input data :- Properties of GS is as per Item 10 Table1 of IEEE Std 80-2000

(i) Conductor material = G.S.

(ii) System Voltage = 66 kV

(iii) Fault Current, If = 25 kA,

(iv) Fault Duration, tc = 1 sec

(v) Max. Allowable Temperature, Tm = 500 *0

C see Note

(vi) Ambient Temperature, Ta = 50 C

0

(vii) Thermal Co-eff.of resistivity at reference

Temperature, ar = 0.0016 *

(viii) Resistivity of Ground Conductor at ref.

Temperature, rr = 15.9 * mW-cm

(ix) Thermal Capacity Factor, TCAP = 3.28 * J/(cm3.oC)

(x) K0 (=1/a0) = 605

Conductor Size :-
As per Eq.37 of IEEE Std 80-2000, conductor size is given by
If

A = TCAP x 10-4 X ln Ko + Tm
tc ar rr Ko + Ta

Conductor size, A = 304 sq.mm

Conductor size selected considering corrosion 50 X 10

allowance as per Calculation GS. Strip

Note:- 1) * marked values are taken as per IEEE.80

PAGE 24 OF 91
4. TOUCH AND STEP VOLTAGE CRITERIA FOR SWITCH YARD
4.1) Input Data :

(i) System Voltage, Vs = 66 kV

(ii.1) System fault Current, If 25 KA

(iii) Fault Duration, t = 1 sec

(iv.1) Length of Earth grid = 51.6 metre

(iv.2) Width of Earth grid = 28 metre

(iv.3) Area of Earth grid, A = 1444.8 sq.metre

(v) Conductor Size for main grid = 500 sq.mm

(vi) Depth of burial w.r.t. ground level, h = 0.6 metre

(vii.1) Number of earth mat conductors in 'X' direction = 10 No.

(vii.2) Length of earth mat conductors in 'X' direction = 300 metre

(vii.3) Number of earth mat conductors in 'Y' direction = 6 No.

(vii.4) Length of earth mat conductors in 'Y' direction = 322 metre

(vii.5) Total Length of Buried conductor, Lc = 622 metre

(viii.1) Total no. of ground rods = 25

(viii.2) Total ground rod length, LR = 75 metre

(viii.3) Effective Buried Length for mesh voltage, LM = 742.53 metre

(viii.4) Effective Buried Length for step voltage, LS = 529.95 metre

(ix) Soil Resistivity, r = 50 W-metre

(x) Surface Resistivity, rs = 3000 W-metre

(xi) Spacing for Earthing Mat below switchyard,D = 6 metre

(xii) Corrective weighting factor, Kii = 1

(xiii) Reference Depth of grid, h0 = 1 metre

(xvi) Thickness of tiles/Gravel/concrete etc, hs = 0.15 metre

Page 25 of 91
 4.2) Calculation of Tolerable Etouch & Estep Voltage :

a) Tolerable Etouch70 :
From Eq.33 of IEEE Std 80-2000
Tolerable Etouch70= [(1000 + 1.5CS rS) 0.157/ ÖtS ]
Where,
Cs = Reduction factor for derating the nominal value of surface layer

Cs = 1 - 0.09 [(1-r/rs)/(2hs + 0.09)] ( From eq.27 of IEEE Std 80-2000 )

Cs = 0.773
tS = Duration of shock current in seconds = Fault duaration, t = 1 sec
( from clause 16.2.2 of IEEE Std 80-2000 )
Substituting the above values,
Tolerable Etouch70 = 1406.36 Volts

b) Tolerable Estep70 = [(1000 + 6CS rS) 0.157/ ÖtS ] (from eq.29 of IEEE Std 80-2000)

Substituting the values,

Tolerable Estep70 = 4683.43 Volts

4.3) Calculation of Maximum Ground Potential Rise :

Max. Ground potential above remote earth, GPR = Ig x Rg Volts
Where,
Ig = grid current = If x Sf

Sf = Fault current division factor

Ig = 12.5 KA at Sf = 0.5
Substituting the values,

Ground Potential Rise, GPR = 7267.63 Volts

Since, GPR > Estep70 (as per Figure 33 of IEEE Std 80-2000),calculate Emesh and Attainable
Estep voltages

4.4) Calculation of Attainable Etouch Voltage :

From Eq.80 of IEEE Std 80-2000, for Grid rods in the periphery,

Attainable Etouch Voltage = [ r Km Ki I G / L M ]

Lr
LM = Lc + 1.55+1.22 LR From eq.91 of IEEE Std 80-2000
Lx+L
2 2
y

Where,
Lr = Length of each ground rod = 3 m
Lx = Maximum length of grid conductor in x-direction = 51.6 m
Ly = Maximum length of grid conductor in y-direction = 28 m

Page 26 of 91
 LR = Total length of ground rods = 75 m
Subtituting the above values,

LM = 742.53 m

As per Eq.81 of IEEE Std 80-2000, the Spacing Factor for Mesh Voltage,

1 D2 (D + 2h) h Kii 8
Km = ln + - + ln
2p 16hd 8Dd 4d Kh p(2n-1)

Equ. Diameter of Earth conductor, d = 0.0252 metre

Kh = 1 + h / h 0 ( From eq.83 of IEEE Std 80-2000 )

Kh = 1.26

No. of Parallel Paths, n = n a nb nc nd

Where, From eq.85 to 88 of IEEE Std 80-2000 Lp

na = (2 Lc)/Lp nb =
4 A
0.7 A
L x Ly L x Ly
nc = nd = 1
A
Where,
Lp = Peripheral length of the grid = 159.2 m
D = Maximum distance between any two points
on the grid = 6 m
Substituting the above values,

na = 7.81 nb = 1.023

nc = 1 nd = 1.00

n = 7.99

As per Eq.89 of IEEE 80-2000,

The corrective Factor, Ki = 0.644 + ( 0.148 x n )

Ki = 1.83
Substituting the values,
Km = 0.5730

Attainable Etouch Voltage = 881.04 Volts

4.5) Calculation of Attainable Estep :

From Eq.92 of IEEE Std 80-2000,
Attainable Estep = [ r Ks Ki I G / L S ]

Page 27 of 91
Page 28 of 91
 As per Eq.94 of IEEE Std 80-2000, the Spacing Factor for Step Voltage,

1 1 1 1
Ks = + + (1 - 0.5n-2)
P 2h D + h D

No. of Parallel paths, n = 7.99

As per Eq.89 of IEEE 80-2000,

The corrective Factor, Ki = 0.644 + ( 0.148 x n )
Ki = 1.83

Ks = 0.3657

As per Eq.93 of IEEE Std 80-2000,

Ls = 0.75 Lc + 0.85 LR

Ls = 529.95 m

Substituting the values,

Attainable Estep Voltage = 787.82 Volts

CONCLUSION :
Tolerable
Etouch = 1406.36 Volts

Attainable
Etouch = 881.04 Volts SAFE

Tolerable
Estep = 4683.43 Volts

Attainable
Estep = 787.82 Volts SAFE

4.6) Calculation of Grid Resistance, Rg :

As per Eq.53 of IEEE Std 80-2000,

R1 R2 - Rm2
The total system resistance, Rg =
R1 + R2 - 2Rm
Where,
R1 = Ground resistance of grid conductors in W
R2 = Ground resistance of of all ground rods in W
Rm = Mutual ground resistance between the group of grid conductors, R1 and
group of ground rods, R2 in W

Ground resistance of the grid, R1

r 2 Lc k1 Lc
R1 = ln + - k2 From eq.54 of IEEE Std 80-2000

Page 29 of 91
p Lc a' A

Page 30 of 91
Where,
r = Soil resistivity in W-m 50 ohm-m
Lc = Total length of all connected grid conductors in m 621.6 m
a' = a . 2h for conductors buried at depth h in m 0.1230 m
2a = Diameter of conductor in m 0.0252 m
A = Area covered by conductors in m2 1444.8 m2
k1 = Coefficient from fig 25(a) of IEEE Std 80-2000 (curve-B) 1.100
k2 = Coefficient from fig 25(b) of IEEE Std 80-2000 (curve-B) 4.800

R1 = 0.5738 W

Ground resistance of the rod bed, R2

From eq.55 of IEEE Std 80-2000
r 4 LR 2 k1 . Lr
R2 = ln -1 + ( n R - 1 )2
2p nRLR b A

Where,
Lr = length of each rod in m 3 m
2b = diameter of rod in m 0.040 m
nR = number of rods placed in area A 25

R2 = 0.048 W

Mutual ground resistance between the grid and the rod bed, R m
From eq.55 of IEEE Std 80-2000

r 2 Lc k1 Lc
Rm = ln + - k2 + 1
p Lc Lr A

Rm = 0.5176 W

Subtituting the above values,

Rg = 0.5814 W

Grid Resistance, Rg = 0.5814 W

From the above results,it can be seen that the Attainable E touch and Attainable Estep voltages are
less than the Tolerable Etouch and Tolerable Estep voltages and hence SAFE

Page 31 of 91
2. Calculation of Earth Grid Resistance for Pump House
2.1) Input Data :

(i) System Voltage, Vs = 400 kV

(ii.1) System fault Current, If = 40 KA

(iii) Fault Duration, t = 1 sec

(iv.1) Length of Earth Mat = 40.0 metre

(iv.2) Width of Earth Mat = 10.8 metre

(iv.3) Area of Earth Mat, A = 432 sq.metre

(v) Conductor Size for main grid = 500 sq.mm

(vi) Depth of burial w.r.t. Raft level, h = 0.6 metre

(vii.1) Number of earth mat conductors in 'Y' direction = 21 No.

(vii.2) Length of earth mat conductors in 'Y' direction = 226.8 metre

(vii.3) Number of earth mat conductors in 'X' direction = 6 No.

(vii.4) Length of earth mat conductors in 'X' direction = 240 metre

(vii.5) Length of Buried conductor, Lc = 466.8 metre

(viii.1) Total no. of ground rods

For 3.0 m long = 10

(viii.2) Total ground rod length, LR = 10 metre

(ix) (Average) Soil Resistivity, r = 634.35 W-metre

(x) Spacing for Earth Mat below Pump House,D = 2 metre

2.2) Calculation of Grid Resistance, Rgp : For Pump house

As per Eq.53 of IEEE Std 80-2000,

R1 R2 - Rm2
The total system resistance, Rgp =
R1 + R2 - 2Rm
Where,
R1 = Ground resistance of grid conductors in W
Ground resistance of the grid, R1

r 2 Lc k1 Lc
R1 = ln + - k2 From eq.54 of
p Lc a' A IEEE Std 80-2000

Where,
r = Soil resistivity in W-m 634.3507 ohm-m
Lc = Total length of all connected grid conductors in m 466.8 m
a' = a . 2h for conductors buried at depth h in m 0.1230 m
2a = Diameter of conductor in m 0.0252 m
A = Area covered by conductors in m2 432 m2
k1 = Coefficient from fig 25(a) of IEEE Std 80-2000 (curve-A) 1.262
k2 = Coefficient from fig 25(b) of IEEE Std 80-2000 (curve-A) 6.056

R1 = 13.5040 W

Ground resistance of the rod bed, R2

From eq.55 of IEEE Std 80-2000
r 4 LR 2 k1 . Lr
R2 = ln -1 + ( n R - 1 )2
2p nRLR b A

Where,
Lr = length of each rod in m 1 m
2b = diameter of rod in m 0.040 m
nR = number of rods placed in area A 10

R2 = 7.237 W

Mutual ground resistance between the grid and the rod bed, R m
From eq.55 of IEEE Std 80-2000

r 2 Lc k1 Lc
Rm = ln + - k2 + 1
p Lc Lr A

Rm = 13.0302 W

Subtituting the above values,

Rgp = 13.5462 W

2.3) CONCLUSION :

Grid Resistance = 13.546 W

2. Calculation of Earth Grid Resistance for Pump House
2.1) Input Data :

(i) System Voltage, Vs = 400 kV

(ii.1) System fault Current, If = 40 KA

(iii) Fault Duration, t = 1 sec

(iv.1) Length of Earth Mat = 10.0 metre

(iv.2) Width of Earth Mat = 10 metre

(iv.3) Area of Earth Mat, A = 100 sq.metre

(v) Conductor Size for main grid = 500 sq.mm

(vi) Depth of burial w.r.t. Raft level, h = 0.6 metre

(vii.1) Number of earth mat conductors in 'Y' direction = 6 No.

(vii.2) Length of earth mat conductors in 'Y' direction = 60 metre

(vii.3) Number of earth mat conductors in 'X' direction = 5 No.

(vii.4) Length of earth mat conductors in 'X' direction = 50 metre

(vii.5) Length of Buried conductor, Lc = 110 metre

(viii.1) Total no. of ground rods

For 3.0 m long = 10

(viii.2) Total ground rod length, LR = 10 metre

(ix) (Average) Soil Resistivity, r = 634.35 W-metre

(x) Spacing for Earth Mat below Pump House,D = 2 metre

2.2) Calculation of Grid Resistance, Rgp : For Pump house

As per Eq.53 of IEEE Std 80-2000,

R1 R2 - Rm2
The total system resistance, Rgp =
R1 + R2 - 2Rm
Where,
R1 = Ground resistance of grid conductors in W
Ground resistance of the grid, R1

r 2 Lc k1 Lc
R1 = ln + - k2 From eq.54 of
p Lc a' A IEEE Std 80-2000

Where,
r = Soil resistivity in W-m 634.3507 ohm-m
Lc = Total length of all connected grid conductors in m 110 m
a' = a . 2h for conductors buried at depth h in m 0.1230 m
2a = Diameter of conductor in m 0.0252 m
A = Area covered by conductors in m2 100 m2
k1 = Coefficient from fig 25(a) of IEEE Std 80-2000 (curve-A) 1.370
k2 = Coefficient from fig 25(b) of IEEE Std 80-2000 (curve-A) 5.650

R1 = 31.0386 W

Ground resistance of the rod bed, R2

From eq.55 of IEEE Std 80-2000
r 4 LR 2 k1 . Lr
R2 = ln -1 + ( n R - 1 )2
2p nRLR b A

Where,
Lr = length of each rod in m 1 m
2b = diameter of rod in m 0.040 m
nR = number of rods placed in area A 10

R2 = 7.958 W

Mutual ground resistance between the grid and the rod bed, R m
From eq.55 of IEEE Std 80-2000

r 2 Lc k1 Lc
Rm = ln + - k2 + 1
p Lc Lr A

Rm = 29.0281 W

Subtituting the above values,

Rgp = 31.2506 W

2.3) CONCLUSION :

Grid Resistance = 31.251 W

2. Transformer cum GIS area
2.1 Input Data :

(i) System Voltage, Vs = 13.8 kV

(ii.1) System fault Current, If = 63 KA

(iii) Fault Duration, t = 1 sec

(iv.1) Length of Earth grid = 202 meter

(iv.2) Width of Earth grid = 15.7 meter

(iv.3) Area of Earth grid, A = 3821 sq.meter

Escape gallery (48 x 5m)and connecting tunnel
(41 x10m) from PH cavern to TR cavern is
considered
(v) Conductor Size for main grid = 1256 sq.mm

(vi) Depth of burial w.r.t. ground level, h = 0.6 meter

(vii.1) Number of earth mat conductors in 'X' direction = 69 No.

(vii.2) Length of earth mat conductors in 'X' direction = 1083 meter

(vii.3) Number of earth mat conductors in 'Y' direction = 7 No.

(vii.4) Length of earth mat conductors in 'Y' direction = 1414 meter

Total Length of Buried conductor Lc = 2992 meter

(vii.5)
Effective Length of Buried conductor (Power
house,Transfomer yard,Potheadyard, Surge = 21197 meter
Chamber,TRT,Intake Structure,MAT,CVT) Lc,

(viii.1) Total no. of ground rods = 43 No.

(viii.2) Total ground rod length, LR = 129 meter

(viii.3) Effective Buried Length for mesh voltage, LM = 21399.6 meter

(viii.4) Effective Buried Length for step voltage, LS = 16007.62 meter

(ix) Soil Resistivity, r = 693.657 W-meter

(x) Surface Resistivity, rs = 10000 W-meter

(xi) Spacing for Earthing Mat below ,D = 3 meter

(xii) Corrective weighting factor, Kii = 1

(xiii) Reference Depth of grid, h0 = 1 meter

(xvi) Thickness of tiles/Gravel/concrete etc, hs = 0.3 meter

(xvii) Decrement factor for the entire duration of fault tf = 1.101

Page 36 of 91
Page 37 of 91
2.2 Grid resistance of Transformer cavern

As per Eq.52 of IEEE Std 80-2013,

The total system resistance,

Where,
Rg = Ground resistance of grid conductors in W
Ground resistance of the grid, Rg

  
1 1  1 
Rg =
     1  
From eq.52 of IEEE Std 80-2013
L
 T 20 A  1  h  20  
 A 
Where,
r = Soil resistivity in W-m 693.66 ohm-m
Lt = Is the total buried length of conductors in m (Lc+Lr) 3121 m
A = Area covered by conductors in m2 3821 m2
h = is the depth of the grid in m 0.600

Rg = 5.1361 W

Grid resistance of Transformer cavern = 5.14 W

Page 38 of 91
 2.3 Calculation of Tolerable Etouch & Estep Voltage :

a) Tolerable Etouch70 :
From Eq.33 of IEEE Std 80-2013
Tolerable Etouch70= [(1000 + 1.5CS rS) 0.157/ ÖtS ]
Where,
Cs = Reduction factor for derating the nominal value of surface layer

Cs = 1 - 0.09 [(1-r/rs)/(2hs + 0.09)] ( From eq.27 of IEEE Std 80-2013 )

Cs = 0.879
tS = Duration of shock current in seconds, t = 0.5 sec
( from clause 16.2.2 of IEEE Std 80-2013 )
Substituting the above values,
Tolerable Etouch70 = 3148.23 Volts

b) Tolerable Estep70 = [(1000 + 6CS rS) 0.157/ ÖtS ] (from eq.30 of IEEE Std 80-2013)

Substituting the values,

Tolerable Estep70 = 11927 Volts

2.4 Calculation of Maximum Ground Potential Rise :

Max. Ground potential above remote earth, GPR = Ig x Rg Volts
Where,
Ig = grid current = If x Sf I G= Df X I g

Sf = Fault current division factor

IG = 34.6815 KA at Sf = 0.5
Substituting the values,

Ground Potential Rise, GPR = 178126.23 Volts

Since, GPR > Estep70 (as per Figure 33 of IEEE Std 80-2013),calculate Emesh and Attainable
Estep voltages

2.5 Calculation of Attainable Etouch Voltage :

From Eq.80 of IEEE Std 80-2013, for Grid rods in the periphery,

Attainable Etouch Voltage = [ r Km Ki I G / L M ]

Lr
LM = Lc + 1.55+1.22 LR From eq.91 of IEEE Std 80-2013
Lx+L
2 2
y

Where,
Lr = Length of each ground rod = 3 m
Lx = Maximum length of grid conductor in x-direction = 202 m
Ly = Maximum length of grid conductor in y-direction = 15.7 m

Page 39 of 91
 LR = Total length of ground rods = 129 m
Subtituting the above values,

LM = 21399.58 m

As per Eq.81 of IEEE Std 80-2013, the Spacing Factor for Mesh Voltage,

1 D2 (D + 2h)2 h Kii 8
Km = ln + - + ln
2p 16hd 8Dd 4d Kh p(2n-1)

Equ. Diameter of Earth conductor, d = 0.0400 meter

Kh = 1 + h / h 0 ( From eq.83 of IEEE Std 80-2013 )

Kh = 1.26

No. of Parallel Paths, n = n a nb nc nd

Where, From eq.85 to 88 of IEEE Std 80-2013 Lp

na = (2 Lc)/Lp nb =
4 A
0.7 A
L x Ly L x Ly
nc = nd = 1
A
Where,
Lp = Peripheral length of the grid = 435.4 m

Substituting the above values,

na = 13.75 nb = 1.327

nc = 0.8544821746 nd = 1.00

n = 15.59

As per Eq.89 of IEEE 80-2013,

The corrective Factor, Ki = 0.644 + ( 0.148 x n )

Ki = 2.95
Substituting the values,
Km = 0.2682

Attainable Etouch Voltage = 889.59 Volts

2.6 Calculation of Attainable Estep :

From Eq.92 of IEEE Std 80-2013,
Attainable Estep = [ r Ks Ki IG / L S ]

Page 40 of 91
 As per Eq.94 of IEEE Std 80-2013, the Spacing Factor for Step Voltage,

1 1 1 1
Ks = + + (1 - 0.5n-2)
p 2h D + h D

No. of Parallel paths, n = 15.59

As per Eq.89 of IEEE 80-2013,

The corrective Factor, Ki = 0.644 + ( 0.148 x n )
Ki = 2.95

Ks = 0.4598

As per Eq.93 of IEEE Std 80-2013,

Ls = 0.75 Lc + 0.85 LR

Ls = 16007.625 m

Substituting the values,

Attainable Estep Voltage = 2038.76 Volts

CONCLUSION :
Tolerable
Etouch = 3148.23 Volts

Attainable
Etouch = 889.59 Volts SAFE

Tolerable
Estep = 11926.82 Volts

Attainable
Estep = 2038.76 Volts SAFE

Page 41 of 91
3. Potheadyard area & DG set area
3.1 Input Data :

(i) System Voltage, Vs = 400 kV

(ii.1) System fault Current, If = 63 KA

(iii) Fault Duration, t = 1 sec

(iv.1) Length of Earth grid = 123 meter

(iv.2) Width of Earth grid = 32 meter

(iv.3) Area of Earth grid, A = 3936 sq.meter

(v) Conductor Size for main grid = 1256 sq.mm

(vi) Depth of burial w.r.t. ground level, h = 0.6 meter

(vii.1) Number of earth mat conductors in 'X' direction = 42 No.

(vii.2) Length of earth mat conductors in 'X' direction = 1344 meter

(vii.3) Number of earth mat conductors in 'Y' direction = 12 No.

(vii.4) Length of earth mat conductors in 'Y' direction = 1476 meter

Total Length of Buried conductor = 2820 meter

(vii.5)
Effective Length of Buried conductor (Power
house,Transfomer yard,Potheadyard, Surge = 21197 meter
Chamber,TRT,Intake Structure,MAT,CVT) Lc,

(viii.1) Total no. of ground rods = 58 No.

(viii.2) Total ground rod length, LR = 174 meter

(viii.3) Effective Buried Length for mesh voltage, LM = 21472.0 meter

(viii.4) Effective Buried Length for step voltage, LS = 16046 meter

(ix) Soil Resistivity, r = 10000.000 W-meter

(x) Surface Resistivity, rs = 10000 W-meter

(xi) Spacing for Earthing Mat below ,D = 3 meter

(xii) Corrective weighting factor, Kii = 1

(xiii) Reference Depth of grid, h0 = 1 meter

(xvi) Thickness of tiles/Gravel/concrete etc, hs = 0.3 meter

(xvii) Decrement factor for the entire duration of fault tf = 1.101

Page 42 of 91
3.2 Grid resistance of Potheadyard area & DG set area

As per Eq.52 of IEEE Std 80-2013,

The total system resistance,

Where,
Rg = Ground resistance of grid conductors in W
Ground resistance of the grid, Rg

  
1 1  1 
Rg =
     1  
From eq.52 of IEEE Std 80-2013
L
 T 20 A  1  h  20  
 A 
Where,
r = Soil resistivity in W-m 10000.00 ohm-m
Lt = Is the total buried length of conductors in m (Lc+Lr) 2994 m
A = Area covered by conductors in m2 3936 m2
h = is the depth of the grid in m 0.600

Rg = 73.1614 W

Grid resistance of Potheadyard area & DG set area = 73.16 W

Page 43 of 91
 3.3 Calculation of Tolerable Etouch & Estep Voltage :

a) Tolerable Etouch70 :
From Eq.33 of IEEE Std 80-2013
Tolerable Etouch70= [(1000 + 1.5CS rS) 0.157/ ÖtS ]
Where,
Cs = Reduction factor for derating the nominal value of surface layer

Cs = 1 - 0.09 [(1-r/rs)/(2hs + 0.09)] ( From eq.27 of IEEE Std 80-2013 )

Cs = 1.000
tS = Duration of shock current in seconds, t = 0.5 sec
( from clause 16.2.2 of IEEE Std 80-2013 )
Substituting the above values,
Tolerable Etouch70 = 3552.50 Volts

b) Tolerable Estep70 = [(1000 + 6CS rS) 0.157/ ÖtS ] (from eq.30 of IEEE Std 80-2013)

Substituting the values,

Tolerable Estep70 = 13543.92 Volts

3.4 Calculation of Maximum Ground Potential Rise :

Max. Ground potential above remote earth, GPR = Ig x Rg Volts
Where,
Ig = grid current = If x Sf
I G= Df X I g
Sf = Fault current division factor
IG = 34.6815 KA at Sf = 0.5
Substituting the values,

Ground Potential Rise, GPR = 2537346.77 Volts

Since, GPR > Estep70 (as per Figure 33 of IEEE Std 80-2013),calculate Emesh and Attainable
Estep voltages

3.5 Calculation of Attainable Etouch Voltage :

From Eq.80 of IEEE Std 80-2013, for Grid rods in the periphery,

Attainable Etouch Voltage = [ r Km Ki I G / L M ]

Lr
LM = Lc + 1.55+1.22 LR From eq.91 of IEEE Std 80-2013
Lx+L
2 2
y

Where,
Lr = Length of each ground rod = 3 m
Lx = Maximum length of grid conductor in x-direction = 123 m
Ly = Maximum length of grid conductor in y-direction = 32 m

Page 44 of 91
 LR = Total length of ground rods = 174 m
Subtituting the above values,

LM = 21472.01 m

As per Eq.81 of IEEE Std 80-2013, the Spacing Factor for Mesh Voltage,

1 D2 (D + 2h)2 h Kii 8
Km = ln + - + ln
2p 16hd 8Dd 4d Kh p(2n-1)

Equ. Diameter of Earth conductor, d = 0.0400 meter

Kh = 1 + h / h 0 ( From eq.83 of IEEE Std 80-2013 )

Kh = 1.26

No. of Parallel Paths, n = n a nb nc nd

Where, From eq.85 to 88 of IEEE Std 80-2013 Lp

na = (2 Lc)/Lp nb =
4 A
0.7 A
L x Ly L x Ly
nc = nd = 1
A
Where,
Lp = Peripheral length of the grid = 310 m

Substituting the above values,

na = 18.19 nb = 1.111

nc = 1 nd = 1.00

n = 20.22

As per Eq.89 of IEEE 80-2013,

The corrective Factor, Ki = 0.644 + ( 0.148 x n )

Ki = 3.64
Substituting the values,
Km = 0.2345

Attainable Etouch Voltage = 13772.86 Volts

3.6 Calculation of Attainable Estep :

From Eq.92 of IEEE Std 80-2013,
Attainable Estep = [ r Ks Ki IG / L S ]

Page 45 of 91
 As per Eq.94 of IEEE Std 80-2013, the Spacing Factor for Step Voltage,

1 1 1 1
Ks = + + (1 - 0.5n-2)
p 2h D + h D

No. of Parallel paths, n = 20.22

As per Eq.89 of IEEE 80-2013,

The corrective Factor, Ki = 0.644 + ( 0.148 x n )
Ki = 3.64

Ks = 0.4598

As per Eq.93 of IEEE Std 80-2013,

Ls = 0.75 Lc + 0.85 LR

Ls = 16045.875 m

Substituting the values,

Attainable Estep Voltage = 36140.58 Volts

CONCLUSION :
Tolerable
Etouch = 3552.50 Volts

Attainable
Etouch = 13772.86 Volts 0.00

Tolerable
Estep = 13543.92 Volts

Attainable
Estep = 36140.58 Volts 0.00

Page 46 of 91
3. Touch and Step Voltage Criteria for Power House

3.1 Input Data :

(i) System Voltage, Vs = 13.8 kV

(ii.1) System fault Current, If = #REF! KA

(iii) Fault Duration, t = 1 sec

(iv.1) Length of Earth grid = #REF! meter

(iv.2) Width of Earth grid = #REF! meter

(iv.3) Area of Earth grid, A = #REF! sq.meter

(v) Conductor Size for main grid = 1256 sq.mm

(vi) Depth of burial w.r.t. ground level, h = 0.6 meter

(vii.1) Number of earth mat conductors in 'X' direction = #REF! No.

(vii.2) Length of earth mat conductors in 'X' direction = #REF! meter

(vii.3) Number of earth mat conductors in 'Y' direction = #REF! No.

(vii.4) Length of earth mat conductors in 'Y' direction = #REF! meter

(vii.5) Total Length of Buried conductor, Lc = #REF! meter

(viii.1) Total no. of ground rods = #REF!

(viii.2) Total ground rod length, LR = #REF! meter

(viii.3) Effective Buried Length for mesh voltage, LM = #REF! meter

(viii.4) Effective Buried Length for step voltage, LS = #REF! meter

(ix) Soil Resistivity, r = #REF! W-meter

(x) Surface Resistivity, rs = 10000 W-meter

(xi) Spacing for Earthing Mat below ,D = #REF! meter

(xii) Corrective weighting factor, Kii = 1

(xiii) Reference Depth of grid, h0 = 1 meter

(xvi) Thickness of tiles/Gravel/concrete etc, hs = 0.15 meter

Page 47 of 91
 3.2 Calculation of Tolerable Etouch & Estep Voltage :

a) Tolerable Etouch70 :
From Eq.33 of IEEE Std 80-2013
Tolerable Etouch70= [(1000 + 1.5CS rS) 0.157/ ÖtS ]
Where,
Cs = Reduction factor for derating the nominal value of surface layer

Cs = 1 - 0.09 [(1-r/rs)/(2hs + 0.09)] ( From eq.27 of IEEE Std 80-2013)

Cs = #REF!
tS = Duration of shock current in seconds , t = 0.5 sec
( from clause 16.2.2 of IEEE Std 80-2000 )
Substituting the above values,

Tolerable Etouch70 = #REF! Volts

b) Tolerable Estep70 = [(1000 + 6CS rS) 0.157/ ÖtS ] (from eq.30 of IEEE Std 80-2013)

Substituting the values,

Tolerable Estep70 = #REF! Volts

3.3 Calculation of Maximum Ground Potential Rise :

Max. Ground potential above remote earth, GPR = Ig x Rg Volts
Where,
Ig = grid current = If x Sf

Sf = Fault current division factor

Ig = #REF! KA at Sf = 0.5
Substituting the values,

Ground Potential Rise, GPR = #REF! Volts

Since, GPR > Estep70 (as per Figure 33 of IEEE Std 80-2000),calculate Emesh and Attainable
Estep voltages

3.4 Calculation of Attainable Etouch Voltage :

From Eq.80 of IEEE Std 80-2000, for Grid rods in the periphery,

Attainable Etouch Voltage = [ r Km Ki I g / L M ]

Lr
LM = Lc + 1.55+1.22 LR From eq.91 of IEEE Std 80-2000
Lx+L
2 2
y

Where,
Lr = Length of each ground rod = 1 m
Lx = Maximum length of grid conductor in x-direction = #REF! m
Ly = Maximum length of grid conductor in y-direction = #REF! m

Page 48 of 91
 LR = Total length of ground rods = #REF! m
Subtituting the above values,

= #REF! m
LM 50553.03

As per Eq.81 of IEEE Std 80-2000, the Spacing Factor for Mesh Voltage,

1 D2 (D + 2h)2 h Kii 8
Km = ln + - + ln
2p 16hd 8Dd 4d Kh p(2n-1)

Equ. Diameter of Earth conductor, d = 0.0400 meter

Kh = 1 + h / h 0 ( From eq.83 of IEEE Std 80-2000 )

Kh = 1.26

No. of Parallel Paths, n = n a nb nc nd

Where, From eq.85 to 88 of IEEE Std 80-2000 Lp

na = (2 Lc)/Lp nb =
4 A
0.7 A
L x Ly L x Ly
nc = nd = 1
A
Where,
Lp = Peripheral length of the grid = #REF! m
D = Maximum distance between any two points
on the grid = #REF! m
Substituting the above values,

na = #REF! nb = #REF!

nc = #REF! nd = 1.00

n = #REF!

As per Eq.89 of IEEE 80-2000,

The corrective Factor, Ki = 0.644 + ( 0.148 x n )

Ki = #REF!
Substituting the values,
Km = #REF!

Attainable Etouch Voltage = #REF! Volts

3.5 Calculation of Attainable Estep :

From Eq.92 of IEEE Std 80-2000,
Attainable Estep = [ r Ks Ki I g / L S ]

Page 49 of 91
 As per Eq.94 of IEEE Std 80-2000, the Spacing Factor for Step Voltage,

1 1 1 1
Ks = + + (1 - 0.5n-2)
p 2h D + h D

No. of Parallel paths, n = #REF!

As per Eq.89 of IEEE 80-2000,

The corrective Factor, Ki = 0.644 + ( 0.148 x n )
Ki = #REF!

Ks = #REF!

As per Eq.93 of IEEE Std 80-2000,

Ls = 0.75 Lc + 0.85 LR

Ls = #REF! m
37573.5

Substituting the values,

Attainable Estep Voltage = #REF! Volts

CONCLUSION :
Tolerable
Etouch = #REF! Volts

Attainable
Etouch = #REF! Volts SAFE

Tolerable
Estep = #REF! Volts

Attainable
Estep = #REF! Volts SAFE

Page 50 of 91
4. MAT
4.1 Input Data :

(i) System Voltage, Vs = 11 kV

(ii.1) System fault Current, If = 25 KA

(iii) Fault Duration, t = 1 sec

(iv.1) Length of Earth grid = 384 meter

(iv.2) Width of Earth grid = 8 meter

(iv.3) Area of Earth grid, A = 3072 sq.meter

(v) Conductor Size for main grid = 1256 sq.mm

(vi) Depth of burial w.r.t. ground level, h = 0.6 meter

(vii.1) Number of earth mat conductors in 'X' direction = 49 No.

(vii.2) Length of earth mat conductors in 'X' direction = 392 meter

(vii.3) Number of earth mat conductors in 'Y' direction = 2 No.

(vii.4) Length of earth mat conductors in 'Y' direction = 768 meter

Total Length of Buried conductor = 1160 meter

(vii.5) Effective Length of Buried conductor (Power

house,Transfomer yard,Potheadyard, Surge = 21197 meter
Chamber,TRT,Intake Structure,MAT,CVT) Lc,

(viii.1) Total no. of ground rods = 12 No.

(viii.2) Total ground rod length, LR = 36 meter

(viii.3) Effective Buried Length for mesh voltage, LM = 21253.4 meter

(viii.4) Effective Buried Length for step voltage, LS = 15928.57 meter

(ix) Soil Resistivity, r = 411.526 W-meter

(x) Surface Resistivity, rs = 10000 W-meter

(xi) Spacing for Earthing Mat below ,D = 8 meter

(xii) Corrective weighting factor, Kii = 1

(xiii) Reference Depth of grid, h0 = 1 meter

(xvi) Thickness of tiles/Gravel/concrete etc, hs = 0.3 meter

(xvii) Decrement factor for the entire duration of fault tf = 1.101

Page 51 of 91
4.2 Grid resistance of MAT

As per Eq.52 of IEEE Std 80-2013,

The total system resistance,

Where,
Rg = Ground resistance of grid conductors in W
Ground resistance of the grid, Rg

  
1 1  1 
Rg =
     1  
From eq.52 of IEEE Std 80-2013
L
 T 20 A  1  h  20  
 A 
Where,
r = Soil resistivity in W-m 411.53 ohm-m
Lt = Is the total buried length of conductors in m (Lc+Lr) 1196 m
A = Area covered by conductors in m2 3072 m2
h = is the depth of the grid in m 0.600

Rg = 3.5879 W

Grid resistance of MAT = 3.59 W

Page 52 of 91
 4.3 Calculation of Tolerable Etouch & Estep Voltage :

a) Tolerable Etouch70 :
From Eq.33 of IEEE Std 80-2013
Tolerable Etouch70= [(1000 + 1.5CS rS) 0.157/ ÖtS ]
Where,
Cs = Reduction factor for derating the nominal value of surface layer

Cs = 1 - 0.09 [(1-r/rs)/(2hs + 0.09)] ( From eq.27 of IEEE Std 80-2013 )

Cs = 0.875
tS = Duration of shock current in seconds, t = 0.5 sec
( from clause 16.2.2 of IEEE Std 80-2013 )
Substituting the above values,
Tolerable Etouch70 = 3135.97 Volts

b) Tolerable Estep70 = [(1000 + 6CS rS) 0.157/ ÖtS ] (from eq.30 of IEEE Std 80-2013)

Substituting the values,

Tolerable Estep70 = 11878 Volts

4.4 Calculation of Maximum Ground Potential Rise :

Max. Ground potential above remote earth, GPR = Ig x Rg Volts
Where,
Ig = grid current = If x Sf I G= Df X I g

Sf = Fault current division factor

IG = 13.7625 KA at Sf = 0.5
Substituting the values,

Ground Potential Rise, GPR = 49378.57 Volts

Since, GPR > Estep70 (as per Figure 33 of IEEE Std 80-2013),calculate Emesh and Attainable
Estep voltages

4.5 Calculation of Attainable Etouch Voltage :

From Eq.80 of IEEE Std 80-2013, for Grid rods in the periphery,

Attainable Etouch Voltage = [ r Km Ki I G / L M ]

Lr
LM = Lc + 1.55+1.22 LR From eq.91 of IEEE Std 80-2013
Lx+L
2 2
y

Where,
Lr = Length of each ground rod = 3 m
Lx = Maximum length of grid conductor in x-direction = 384 m
Ly = Maximum length of grid conductor in y-direction = 8 m

Page 53 of 91
 LR = Total length of ground rods = 36 m
Subtituting the above values,

LM = 21253.44 m

As per Eq.81 of IEEE Std 80-2013, the Spacing Factor for Mesh Voltage,

1 D2 (D + 2h)2 h Kii 8
Km = ln + - + ln
2p 16hd 8Dd 4d Kh p(2n-1)

Equ. Diameter of Earth conductor, d = 0.0400 meter

Kh = 1 + h / h 0 ( From eq.83 of IEEE Std 80-2013 )

Kh = 1.26

No. of Parallel Paths, n = n a nb nc nd

Where, From eq.85 to 88 of IEEE Std 80-2013 Lp

na = (2 Lc)/Lp nb =
4 A
0.7 A
L x Ly L x Ly
nc = nd = 1
A
Where,
Lp = Peripheral length of the grid = 784 m

Substituting the above values,

na = 2.96 nb = 1.880

nc = 1 nd = 1.00

n = 5.56

As per Eq.89 of IEEE 80-2013,

The corrective Factor, Ki = 0.644 + ( 0.148 x n )

Ki = 1.47
Substituting the values,
Km = 0.6663

Attainable Etouch Voltage = 260.59 Volts

4.6 Calculation of Attainable Estep :

From Eq.92 of IEEE Std 80-2013,
Attainable Estep = [ r Ks Ki IG / L S ]

Page 54 of 91
 As per Eq.94 of IEEE Std 80-2013, the Spacing Factor for Step Voltage,

1 1 1 1
Ks = + + (1 - 0.5n-2)
p 2h D + h D

No. of Parallel paths, n = 5.56

As per Eq.89 of IEEE 80-2013,

The corrective Factor, Ki = 0.644 + ( 0.148 x n )
Ki = 1.47

Ks = 0.3387

As per Eq.93 of IEEE Std 80-2013,

Ls = 0.75 Lc + 0.85 LR

Ls = 15928.575 m

Substituting the values,

Attainable Estep Voltage = 176.74 Volts

CONCLUSION :
Tolerable
Etouch = 3135.97 Volts

Attainable
Etouch = 260.59 Volts SAFE

Tolerable
Estep = 11877.79 Volts

Attainable
Estep = 176.74 Volts SAFE

Page 55 of 91
5. CVT
5.1 Input Data :

(i) System Voltage, Vs = 400 kV

(ii.1) System fault Current, If = 63 KA

(iii) Fault Duration, t = 1 sec

(iv.1) Length of Earth grid = 225 meter

(iv.2) Width of Earth grid = 9 meter

(iv.3) Area of Earth grid, A = 3141 sq.meter

(Area of CVT+ Cable tunnel (56x6)+ Surge
chamber -CVT(130x6))
(v) Conductor Size for main grid = 1256 sq.mm

(vi) Depth of burial w.r.t. ground level, h = 0.6 meter

(vii.1) Number of earth mat conductors in 'X' direction = 26 No.

(vii.2) Length of earth mat conductors in 'X' direction = 234 meter

(vii.3) Number of earth mat conductors in 'Y' direction = 2 No.

(vii.4) Length of earth mat conductors in 'Y' direction = 450 meter

Total Length of Buried conductor Lc

(vii.5) (Cable tunnel (56 x2 +7x6) & Audit to Surge 1194 meter
chamber ( 130 x 2 + 16x6 ))
=
Effective Length of Buried conductor (Power
(vii.6) house,Transfomer yard,Potheadyard, Surge = 21197 meter
Chamber,TRT,Intake Structure,MAT,CVT) Lc,

(viii.1) Total no. of ground rods = 8 No.

(viii.2) Total ground rod length, LR = 24 meter

(viii.3) Effective Buried Length for mesh voltage, LM = 21234.9 meter

(viii.4) Effective Buried Length for step voltage, LS = 15918.37 meter

(ix) Soil Resistivity, r = 693.657 W-meter

(x) Surface Resistivity, rs = 10000 W-meter

(xi) Spacing for Earthing Mat below ,D = 9 meter

(xii) Corrective weighting factor, Kii = 1

(xiii) Reference Depth of grid, h0 = 1 meter

(xvi) Thickness of tiles/Gravel/concrete etc, hs = 0.3 meter

(xvii) Decrement factor for the entire duration of fault tf = 1.101

Page 56 of 91
5.2 Grid resistance of CVT

As per Eq.52 of IEEE Std 80-2013,

The total system resistance,

Where,
Rg = Ground resistance of grid conductors in W
Ground resistance of the grid, Rg

  
1 1  1 
Rg =
     1  
From eq.52 of IEEE Std 80-2013
L
 T 20 A  1 h

20 
A  
Where,
r = Soil resistivity in W-m 693.66 ohm-m
Lt = Is the total buried length of conductors in m (Lc+Lr) 1218 m
A = Area covered by conductors in m2 3141 m2
h = is the depth of the grid in m 0.600

Rg = 5.9782 W

Grid resistance of CVT = 5.98 W

Page 57 of 91
 5.3 Calculation of Tolerable Etouch & Estep Voltage :

a) Tolerable Etouch70 :
From Eq.33 of IEEE Std 80-2013
Tolerable Etouch70= [(1000 + 1.5CS rS) 0.157/ ÖtS ]
Where,
Cs = Reduction factor for derating the nominal value of surface layer

Cs = 1 - 0.09 [(1-r/rs)/(2hs + 0.09)] ( From eq.27 of IEEE Std 80-2013 )

Cs = 0.879
tS = Duration of shock current in seconds, t = 0.5 sec
( from clause 16.2.2 of IEEE Std 80-2013 )
Substituting the above values,
Tolerable Etouch70 = 3148.23 Volts

b) Tolerable Estep70 = [(1000 + 6CS rS) 0.157/ ÖtS ] (from eq.30 of IEEE Std 80-2013)

Substituting the values,

Tolerable Estep70 = 11927 Volts

5.4 Calculation of Maximum Ground Potential Rise :

Max. Ground potential above remote earth, GPR = Ig x Rg Volts
Where,
Ig = grid current = If x Sf I G= Df X I g

Sf = Fault current division factor

IG = 34.6815 KA at Sf = 0.5
Substituting the values,

Ground Potential Rise, GPR = 207331.54 Volts

Since, GPR > Estep70 (as per Figure 33 of IEEE Std 80-2013),calculate Emesh and Attainable
Estep voltages

5.5 Calculation of Attainable Etouch Voltage :

From Eq.80 of IEEE Std 80-2013, for Grid rods in the periphery,

Attainable Etouch Voltage = [ r Km Ki I G / L M ]

Lr
LM = Lc + 1.55+1.22 LR From eq.91 of IEEE Std 80-2013
Lx+L
2 2
y

Where,
Lr = Length of each ground rod = 3 m
Lx = Maximum length of grid conductor in x-direction = 225 m
Ly = Maximum length of grid conductor in y-direction = 9 m

Page 58 of 91
 LR = Total length of ground rods = 24 m
Subtituting the above values,

LM = 21234.89 m

As per Eq.81 of IEEE Std 80-2013, the Spacing Factor for Mesh Voltage,

1 D2 (D + 2h)2 h Kii 8
Km = ln + - + ln
2p 16hd 8Dd 4d Kh p(2n-1)

Equ. Diameter of Earth conductor, d = 0.0400 meter

Kh = 1 + h / h 0 ( From eq.83 of IEEE Std 80-2013 )

Kh = 1.26

No. of Parallel Paths, n = n a nb nc nd

Where, From eq.85 to 88 of IEEE Std 80-2013 Lp

na = (2 Lc)/Lp nb =
4 A
0.7 A
L x Ly L x Ly
nc = nd = 1
A
Where,
Lp = Peripheral length of the grid = 468 m

Substituting the above values,

na = 5.10 nb = 1.445

nc = 0.6208749901 nd = 1.00

n = 4.58

As per Eq.89 of IEEE 80-2013,

The corrective Factor, Ki = 0.644 + ( 0.148 x n )

Ki = 1.32
Substituting the values,
Km = 0.7280

Attainable Etouch Voltage = 1089.95 Volts

5.6 Calculation of Attainable Estep :

From Eq.92 of IEEE Std 80-2013,
Attainable Estep = [ r Ks Ki IG / L S ]

Page 59 of 91
 As per Eq.94 of IEEE Std 80-2013, the Spacing Factor for Step Voltage,

1 1 1 1
Ks = + + (1 - 0.5n-2)
p 2h D + h D

No. of Parallel paths, n = 4.58

As per Eq.89 of IEEE 80-2013,

The corrective Factor, Ki = 0.644 + ( 0.148 x n )
Ki = 1.32

Ks = 0.3279

As per Eq.93 of IEEE Std 80-2013,

Ls = 0.75 Lc + 0.85 LR

Ls = 15918.375 m

Substituting the values,

Attainable Estep Voltage = 654.76 Volts

CONCLUSION :
Tolerable
Etouch = 3148.23 Volts

Attainable
Etouch = 1089.95 Volts SAFE

Tolerable
Estep = 11926.82 Volts

Attainable
Estep = 654.76 Volts SAFE

Page 60 of 91
6. Bus duct gallery
6.1 Input Data :

(i) System Voltage, Vs = 13.8 kV

(ii.1) System fault Current, If = 63 KA

(iii) Fault Duration, t = 1 sec

(iv.1) Length of Earth grid = 41 meter

(iv.2) Width of Earth grid = 5.6 meter

(iv.3) Area of Earth grid, A = 1148 sq.meter

4no of main unit (41 x 5.6m )and 1 no of Aux Unit
bus duct gallery (41 x 5.6 m)
(v) Conductor Size for main grid = 1256 sq.mm

(vi) Depth of burial w.r.t. ground level, h = 0.6 meter

(vii.1) Number of earth mat conductors in 'X' direction = 15 No.

(vii.2) Length of earth mat conductors in 'X' direction = 84 meter

(vii.3) Number of earth mat conductors in 'Y' direction = 3 No.

(vii.4) Length of earth mat conductors in 'Y' direction = 123 meter

Total Length of Buried conductor = 1035 meter

(vii.5) Effective Length of Buried conductor (Power

house,Transfomer yard,Potheadyard, Surge = 21197 meter
Chamber,TRT,Intake Structure,MAT,CVT) Lc,

(viii.1) Total no. of ground rods = 40 No.

(viii.2) Total ground rod length, LR = 120 meter

(viii.3) Effective Buried Length for mesh voltage, LM = 21393.9 meter

(viii.4) Effective Buried Length for step voltage, LS = 16000 meter

(ix) Soil Resistivity, r = 469.546 W-meter

(x) Surface Resistivity, rs = 10000 W-meter

(xi) Spacing for Earthing Mat below ,D = 3 meter

(xii) Corrective weighting factor, Kii = 1

(xiii) Reference Depth of grid, h0 = 1 meter

(xvi) Thickness of tiles/Gravel/concrete etc, hs = 0.3 meter

(xvii) Decrement factor for the entire duration of fault tf = 1.101

PAGE 61 OF 91
PAGE 62 OF 91
6.2 Grid resistance of Bus duct gallery

As per Eq.52 of IEEE Std 80-2013,

The total system resistance,

Where,
Rg = Ground resistance of grid conductors in W
Ground resistance of the grid, Rg

  
1 1  1 
Rg =
     1  
From eq.52 of IEEE Std 80-2013
L
 T 20 A  1  h  20  
 A 
Where,
r = Soil resistivity in W-m 469.55 ohm-m
Lt = Is the total buried length of conductors in m (Lc+Lr) 1155 m
A = Area covered by conductors in m2 1148 m2
h = is the depth of the grid in m 0.600

Rg = 6.3767 W

Grid resistance of Bus duct gallery = 6.38 W

PAGE 63 OF 91
 6.3 Calculation of Tolerable Etouch & Estep Voltage :

a) Tolerable Etouch70 :
From Eq.33 of IEEE Std 80-2013
Tolerable Etouch70= [(1000 + 1.5CS rS) 0.157/ ÖtS ]
Where,
Cs = Reduction factor for derating the nominal value of surface layer

Cs = 1 - 0.09 [(1-r/rs)/(2hs + 0.09)] ( From eq.27 of IEEE Std 80-2013 )

Cs = 0.876
tS = Duration of shock current in seconds, t = 0.5 sec
( from clause 16.2.2 of IEEE Std 80-2013 )
Substituting the above values,
Tolerable Etouch70 = 3138.49 Volts

b) Tolerable Estep70 = [(1000 + 6CS rS) 0.157/ ÖtS ] (from eq.30 of IEEE Std 80-2013)

Substituting the values,

Tolerable Estep70 = 11887.88 Volts

6.4 Calculation of Maximum Ground Potential Rise :

Max. Ground potential above remote earth, GPR = Ig x Rg Volts
Where,
Ig = grid current = If x Sf
I G= Df X I g
Sf = Fault current division factor
IG = 34.6815 KA at Sf = 0.5
Substituting the values,

Ground Potential Rise, GPR = 221153.83 Volts

Since, GPR > Estep70 (as per Figure 33 of IEEE Std 80-2013),calculate Emesh and Attainable
Estep voltages

6.5 Calculation of Attainable Etouch Voltage :

From Eq.80 of IEEE Std 80-2013, for Grid rods in the periphery,

Attainable Etouch Voltage = [ r Km Ki I G / L M ]

Lr
LM = Lc + 1.55+1.22 LR From eq.91 of IEEE Std 80-2013
Lx+L
2 2
y

Where,
Lr = Length of each ground rod = 3 m
Lx = Maximum length of grid conductor in x-direction = 41 m
Ly = Maximum length of grid conductor in y-direction = 5.6 m

PAGE 64 OF 91
 LR = Total length of ground rods = 120 m
Subtituting the above values,

LM = 21393.91 m

As per Eq.81 of IEEE Std 80-2013, the Spacing Factor for Mesh Voltage,

1 D2 (D + 2h)2 h Kii 8
Km = ln + - + ln
2p 16hd 8Dd 4d Kh p(2n-1)

Equ. Diameter of Earth conductor, d = 0.0400 meter

Kh = 1 + h / h 0 ( From eq.83 of IEEE Std 80-2013 )

Kh = 1.26

No. of Parallel Paths, n = n a nb nc nd

Where, From eq.85 to 88 of IEEE Std 80-2013 Lp

na = (2 Lc)/Lp nb =
4 A
0.7 A
L x Ly L x Ly
nc = nd = 1
A
Where,
Lp = Peripheral length of the grid = 93.2 m

Substituting the above values,

na = 22.21 nb = 0.829

nc = 1 nd = 1.00

n = 18.42

As per Eq.89 of IEEE 80-2013,

The corrective Factor, Ki = 0.644 + ( 0.148 x n )

Ki = 3.37
Substituting the values,
Km = 0.2465

Attainable Etouch Voltage = 632.38 Volts

6.6 Calculation of Attainable Estep :

From Eq.92 of IEEE Std 80-2013,
Attainable Estep = [ r Ks Ki I G / L S ]

PAGE 65 OF 91
PAGE 66 OF 91
 As per Eq.94 of IEEE Std 80-2013, the Spacing Factor for Step Voltage,

1 1 1 1
Ks = + + (1 - 0.5n-2)
p 2h D + h D

No. of Parallel paths, n = 18.42

As per Eq.89 of IEEE 80-2013,

The corrective Factor, Ki = 0.644 + ( 0.148 x n )
Ki = 3.37

Ks = 0.4598

As per Eq.93 of IEEE Std 80-2013,

Ls = 0.75 Lc + 0.85 LR

Ls = 15999.975 m

Substituting the values,

Attainable Estep Voltage = 1576.96 Volts

CONCLUSION :
Tolerable
Etouch = 3138.49 Volts

Attainable
Etouch = 632.38 Volts SAFE

Tolerable
Estep = 11887.88 Volts

Attainable
Estep = 1576.96 Volts SAFE

PAGE 67 OF 91
7. Surge Chamber
7.1 Input Data :

(i) System Voltage, Vs = 11 kV

(ii.1) System fault Current, If = 25 KA

(iii) Fault Duration, t = 1 sec

(iv.1) Length of Earth grid = 116 meter

(iv.2) Width of Earth grid = 13.25 meter

(iv.3) Area of Earth grid, A = 4001 sq.meter

Surge chamber to power house cavern( 77 x 8 m)
(v) Conductor Size for main grid = 1256 sq.mm

(vi) Depth of burial w.r.t. ground level, h = 0.6 meter

(vii.1) Number of earth mat conductors in 'X' direction = 16 No.

(vii.2) Length of earth mat conductors in 'X' direction = 212 meter

(vii.3) Number of earth mat conductors in 'Y' direction = 3 No.

(vii.4) Length of earth mat conductors in 'Y' direction = 348 meter

Total Length of Buried conductor = 1176 meter

(vii.5) Effective Length of Buried conductor (Power

house,Transfomer yard,Potheadyard, Surge = 21197 meter
Chamber,TRT,Intake Structure,MAT,CVT) Lc,

(viii.1) Total no. of ground rods = 14 No.

(viii.2) Total ground rod length, LR = 42 meter

(viii.3) Effective Buried Length for mesh voltage, LM = 21263.7 meter

(viii.4) Effective Buried Length for step voltage, LS = 15933.68 meter

(ix) Soil Resistivity, r = 693.657 W-meter

(x) Surface Resistivity, rs = 10000 W-meter

(xi) Spacing for Earthing Mat below ,D = 8 meter

(xii) Corrective weighting factor, Kii = 1

(xiii) Reference Depth of grid, h0 = 1 meter

(xvi) Thickness of tiles/Gravel/concrete etc, hs = 0.3 meter

(xvii) Decrement factor for the entire duration of fault tf = 1.101

PAGE 68 OF 91
7.2 Grid resistance of surge chamber

As per Eq.52 of IEEE Std 80-2013,

The total system resistance,

Where,
Rg = Ground resistance of grid conductors in W
Ground resistance of the grid, Rg

  
1 1  1 
Rg =
     1  
From eq.52 of IEEE Std 80-2013
L
 T 20 A  1  h  20  
 A 
Where,
r = Soil resistivity in W-m 693.66 ohm-m
Lt = Is the total buried length of conductors in m (Lc+Lr) 1218 m
A = Area covered by conductors in m2 4001 m2
h = is the depth of the grid in m 0.600

Rg = 5.3740 W

Grid resistance of surge chamber = 5.37 W

PAGE 69 OF 91
 7.3 Calculation of Tolerable Etouch & Estep Voltage :

a) Tolerable Etouch70 :
From Eq.33 of IEEE Std 80-2013
Tolerable Etouch70= [(1000 + 1.5CS rS) 0.157/ ÖtS ]
Where,
Cs = Reduction factor for derating the nominal value of surface layer

Cs = 1 - 0.09 [(1-r/rs)/(2hs + 0.09)] ( From eq.27 of IEEE Std 80-2013 )

Cs = 0.879
tS = Duration of shock current in seconds, t = 0.5 sec
( from clause 16.2.2 of IEEE Std 80-2013 )
Substituting the above values,
Tolerable Etouch70 = 3148.23 Volts

b) Tolerable Estep70 = [(1000 + 6CS rS) 0.157/ ÖtS ] (from eq.30 of IEEE Std 80-2013)

Substituting the values,

Tolerable Estep70 = 11927 Volts

7.4 Calculation of Maximum Ground Potential Rise :

Max. Ground potential above remote earth, GPR = Ig x Rg Volts
Where,
Ig = grid current = If x Sf I G= Df X I g

Sf = Fault current division factor

IG = 13.7625 KA at Sf = 0.5
Substituting the values,

Ground Potential Rise, GPR = 73959.65 Volts

Since, GPR > Estep70 (as per Figure 33 of IEEE Std 80-2013),calculate Emesh and Attainable
Estep voltages

7.5 Calculation of Attainable Etouch Voltage :

From Eq.80 of IEEE Std 80-2013, for Grid rods in the periphery,

Attainable Etouch Voltage = [ r Km Ki IG / L M ]

Lr
LM = Lc + 1.55+1.22 LR From eq.91 of IEEE Std 80-2013
L +L
2
x
2
y

Where,
Lr = Length of each ground rod = 3 m
Lx = Maximum length of grid conductor in x-direction = 116 m
Ly = Maximum length of grid conductor in y-direction = 13.25 m

PAGE 70 OF 91
 LR = Total length of ground rods = 42 m
Subtituting the above values,

LM = 21263.72 m

As per Eq.81 of IEEE Std 80-2013, the Spacing Factor for Mesh Voltage,

1 D2 (D + 2h)2 h Kii 8
Km = ln + - + ln
2p 16hd 8Dd 4d Kh p(2n-1)

Equ. Diameter of Earth conductor, d = 0.0400 meter

Kh = 1 + h / h 0 ( From eq.83 of IEEE Std 80-2013 )

Kh = 1.26

No. of Parallel Paths, n = n a nb nc nd

Where, From eq.85 to 88 of IEEE Std 80-2013 Lp

na = (2 Lc)/Lp nb =
4 A
0.7 A
L x Ly L x Ly
nc = nd = 1
A
Where,
Lp = Peripheral length of the grid = 258.5 m
Substituting the above values,

na = 9.10 nb = 1.011

nc = 1.000 nd = 1.00

n = 9.20

As per Eq.89 of IEEE 80-2013,

The corrective Factor, Ki = 0.644 + ( 0.148 x n )

Ki = 2.01
Substituting the values,
Km = 0.5983

Attainable Etouch Voltage = 538.60 Volts

7.6 Calculation of Attainable Estep :

From Eq.92 of IEEE Std 80-2013,
Attainable Estep = [ r Ks Ki I G / L S ]

PAGE 71 OF 91
 As per Eq.94 of IEEE Std 80-2013, the Spacing Factor for Step Voltage,

1 1 1 1
Ks = + + (1 - 0.5n-2)
p 2h D + h D

No. of Parallel paths, n = 9.20

As per Eq.89 of IEEE 80-2013,

The corrective Factor, Ki = 0.644 + ( 0.148 x n )
Ki = 2.01

Ks = 0.3418

As per Eq.93 of IEEE Std 80-2013,

Ls = 0.75 Lc + 0.85 LR

Ls = 15933.675 m

Substituting the values,

Attainable Estep Voltage = 410.60 Volts

CONCLUSION :
Tolerable
Etouch = 3148.23 Volts

Attainable
Etouch = 538.60 Volts SAFE

Tolerable
Estep = 11926.82 Volts

Attainable
Estep = 410.60 Volts SAFE

PAGE 72 OF 91
8. TRT
8.1 Input Data :

(i) System Voltage, Vs = 11 kV

(ii.1) System fault Current, If = 25 KA

(iii) Fault Duration, t = 1 sec

(iv.1) Length of Earth grid = 40 meter

(iv.2) Width of Earth grid = 10 meter

(iv.3) Area of Earth grid, A = 400 sq.meter

TRT- approx. 350x 4m and Aux.TRT 250 X 2m 6500 sq.meter
(v) Conductor Size for main grid = 1256 sq.mm

(vi) Depth of burial w.r.t. ground level, h = 0.6 meter

(vii.1) Number of earth mat conductors in 'X' direction = 5 No.

(vii.2) Length of earth mat conductors in 'X' direction = 50 meter

(vii.3) Number of earth mat conductors in 'Y' direction = 2 No.

(vii.4) Length of earth mat conductors in 'Y' direction = 80 meter

Total Length of Buried conductor = 3430 meter

(vii.5) Effective Length of Buried conductor (Power

house,Transfomer yard,Potheadyard, Surge
Chamber,TRT,Intake Structure,MAT,CVT) Lc, = 21197 meter

(viii.1) Total no. of ground rods = 24 No.

(viii.2) Total ground rod length, LR = 72 meter

(viii.3) Effective Buried Length for mesh voltage, LM = 21315.3 meter

(viii.4) Effective Buried Length for step voltage, LS = 15959.18 meter

(ix) Soil Resistivity, r = 245.434 W-meter

(x) Surface Resistivity, rs = 10000 W-meter

(xi) Spacing for Earthing Mat below ,D = 10 meter

(xii) Corrective weighting factor, Kii = 1

(xiii) Reference Depth of grid, h0 = 1 meter

(xvi) Thickness of tiles/Gravel/concrete etc, hs = 0.3 meter

(xvii) Decrement factor for the entire duration of fault tf = 1.101

Page 73 of 91
8.2 Grid resistance of surge chamber

As per Eq.52 of IEEE Std 80-2013,

The total system resistance,

Where,
Rg = Ground resistance of grid conductors in W
Ground resistance of the grid, Rg

  
1 1  1 
Rg =
    1  
From eq.52 of IEEE Std 80-2013
L
 T 20 A  1 h

20 
A  
Where,
r = Soil resistivity in W-m 245.43 ohm-m
Lt = Is the total buried length of conductors in m (Lc+Lr) 3502 m
A = Area covered by conductors in m2 6500 m2
h = is the depth of the grid in m 0.600

Rg = 1.4096 W

Grid resistance of surge chamber = 1.41 W

Page 74 of 91
 8.3 Calculation of Tolerable Etouch & Estep Voltage :

a) Tolerable Etouch70 :
From Eq.33 of IEEE Std 80-2013
Tolerable Etouch70= [(1000 + 1.5CS rS) 0.157/ ÖtS ]
Where,
Cs = Reduction factor for derating the nominal value of surface layer

Cs = 1 - 0.09 [(1-r/rs)/(2hs + 0.09)] ( From eq.27 of IEEE Std 80-2013 )

Cs = 0.873
tS = Duration of shock current in seconds, t = 0.5 sec
( from clause 16.2.2 of IEEE Std 80-2013 )
Substituting the above values,
Tolerable Etouch70 = 3128.76 Volts

b) Tolerable Estep70 = [(1000 + 6CS rS) 0.157/ ÖtS ] (from eq.30 of IEEE Std 80-2013)

Substituting the values,

Tolerable Estep70 = 11849 Volts

8.4 Calculation of Maximum Ground Potential Rise :

Max. Ground potential above remote earth, GPR = Ig x Rg Volts
Where,
Ig = grid current = If x Sf I G= Df X I g

Sf = Fault current division factor

IG = 13.7625 KA at Sf = 0.5
Substituting the values,

Ground Potential Rise, GPR = 19399.36 Volts

Since, GPR > Estep70 (as per Figure 33 of IEEE Std 80-2013),calculate Emesh and Attainable
Estep voltages

8.5 Calculation of Attainable Etouch Voltage :

From Eq.80 of IEEE Std 80-2013, for Grid rods in the periphery,

Attainable Etouch Voltage = [ r Km Ki I G / L M ]

Lr
LM = Lc + 1.55+1.22 LR From eq.91 of IEEE Std 80-2013
L2x + L2y
Where,
Lr = Length of each ground rod = 3 m
Lx = Maximum length of grid conductor in x-direction = 40 m
Ly = Maximum length of grid conductor in y-direction = 10 m

Page 75 of 91
 LR = Total length of ground rods = 72 m
Subtituting the above values,

LM = 21315.29 m

As per Eq.81 of IEEE Std 80-2013, the Spacing Factor for Mesh Voltage,

1 D2 (D + 2h)2 h Kii 8
Km = ln + - + ln
2p 16hd 8Dd 4d Kh p(2n-1)

Equ. Diameter of Earth conductor, d = 0.0400 meter

Kh = 1 + h / h 0 ( From eq.83 of IEEE Std 80-2013 )

Kh = 1.26

No. of Parallel Paths, n = n a nb nc nd

Where, From eq.85 to 88 of IEEE Std 80-2013 Lp

na = (2 Lc)/Lp nb =
4 A
0.7 A
L x Ly L x Ly
nc = nd = 1
A
Where,
Lp = Peripheral length of the grid = 100 m
D = Maximum distance between any two points
on the grid = 10 m
Substituting the above values,

na = 68.60 nb = 0.557

nc = 1 nd = 1.00

n = 38.20

As per Eq.89 of IEEE 80-2013,

The corrective Factor, Ki = 0.644 + ( 0.148 x n )

Ki = 6.30
Substituting the values,
Km = 0.4793

Attainable Etouch Voltage = 478.34 Volts

8.6 Calculation of Attainable Estep :

From Eq.92 of IEEE Std 80-2013,
Attainable Estep = [ r Ks Ki I G / L S ]

Page 76 of 91
 As per Eq.94 of IEEE Std 80-2013, the Spacing Factor for Step Voltage,

1 1 1 1
Ks = + + (1 - 0.5n-2)
p 2h D + h D

No. of Parallel paths, n = 38.20

As per Eq.89 of IEEE 80-2013,

The corrective Factor, Ki = 0.644 + ( 0.148 x n )
Ki = 6.30

Ks = 0.3271

As per Eq.93 of IEEE Std 80-2013,

Ls = 0.75 Lc + 0.85 LR

Ls = 15959.175 m

Substituting the values,

Attainable Estep Voltage = 436.02 Volts

CONCLUSION :
Tolerable
Etouch = 3128.76 Volts

Attainable
Etouch = 478.34 Volts SAFE

Tolerable
Estep = 11848.93 Volts

Attainable
Estep = 436.02 Volts SAFE

Page 77 of 91
9. Intake Structure
9.1 Input Data :

(i) System Voltage, Vs = 11 kV

(ii.1) System fault Current, If = 25 KA

(iii) Fault Duration, t = 1 sec

(iv.1) Length of Earth grid = 45 meter

(iv.2) Width of Earth grid = 10 meter

(iv.3) Area of Earth grid, A = 450 sq.meter

(v) Conductor Size for main grid = 1256 sq.mm

(vi) Depth of burial w.r.t. ground level, h = 0.6 meter

(vii.1) Number of earth mat conductors in 'X' direction = 10 No.

(vii.2) Length of earth mat conductors in 'X' direction = 100 meter

(vii.3) Number of earth mat conductors in 'Y' direction = 4 No.

(2 no. additional conductor for grid formation)
(vii.4) Length of earth mat conductors in 'Y' direction = 180 meter

Total Length of Buried conductor = 880 meter

Connecting grid from Intake strucure to Power house -

approx. 300 mtr 2 no of conductors = 600)
(vii.5)
Effective Length of Buried conductor (Power
house,Transfomer yard,Potheadyard, Surge = 21197 meter
Chamber,TRT,Intake Structure,MAT,CVT) Lc,

(viii.1) Total no. of ground rods = 4 No.

(viii.2) Total ground rod length, LR = 12 meter

(viii.3) Effective Buried Length for mesh voltage, LM = 21216.9 meter

(viii.4) Effective Buried Length for step voltage, LS = 15908.18 meter

(ix) Soil Resistivity, r = 245.434 W-meter

(x) Surface Resistivity, rs = 10000 W-meter

(xi) Spacing for Earthing Mat below ,D = 5 meter

(xii) Corrective weighting factor, Kii = 1

(xiii) Reference Depth of grid, h0 = 1 meter

(xvi) Thickness of tiles/Gravel/concrete etc, hs = 0.3 meter

(xvii) Decrement factor for the entire duration of fault tf = 1.101

Page 78 of 91
9.2 Grid resistance of Intake structure

As per Eq.52 of IEEE Std 80-2013,

The total system resistance,

Where,
Rg = Ground resistance of grid conductors in W
Ground resistance of the grid, Rg

  
1 1  1 
Rg =
    1  
From eq.52 of IEEE Std 80-2013
L
 T 20 A  1 h

20 
A  
Where,
r = Soil resistivity in W-m 245.43 ohm-m
Lt = Is the total buried length of conductors in m (Lc+Lr) 892 m
A = Area covered by conductors in m2 450 m2
h = is the depth of the grid in m 0.600

Rg = 5.1589 W

Grid resistance of Intake structure = 5.16 W

Page 79 of 91
 9.3 Calculation of Tolerable Etouch & Estep Voltage :

a) Tolerable Etouch70 :
From Eq.33 of IEEE Std 80-2013
Tolerable Etouch70= [(1000 + 1.5CS rS) 0.157/ ÖtS ]
Where,
Cs = Reduction factor for derating the nominal value of surface layer

Cs = 1 - 0.09 [(1-r/rs)/(2hs + 0.09)] ( From eq.27 of IEEE Std 80-2013 )

Cs = 0.873
tS = Duration of shock current in seconds, t = 0.5 sec
( from clause 16.2.2 of IEEE Std 80-2013 )
Substituting the above values,
Tolerable Etouch70 = 3128.76 Volts

b) Tolerable Estep70 = [(1000 + 6CS rS) 0.157/ ÖtS ] (from eq.30 of IEEE Std 80-2013)

Substituting the values,

Tolerable Estep70 = 11849 Volts

9.4 Calculation of Maximum Ground Potential Rise :

Max. Ground potential above remote earth, GPR = Ig x Rg Volts
Where,
Ig = grid current = If x Sf I G= Df X I g

Sf = Fault current division factor

IG = 13.7625 KA at Sf = 0.5
Substituting the values,

Ground Potential Rise, GPR = 70998.72 Volts

Since, GPR > Estep70 (as per Figure 33 of IEEE Std 80-2013),calculate Emesh and Attainable
Estep voltages

9.5 Calculation of Attainable Etouch Voltage :

From Eq.80 of IEEE Std 80-2013, for Grid rods in the periphery,

Attainable Etouch Voltage = [ r Km Ki I G / L M ]

Lr
LM = Lc + 1.55+1.22 LR From eq.91 of IEEE Std 80-2013
L2x + L2y
Where,
Lr = Length of each ground rod = 3 m
Lx = Maximum length of grid conductor in x-direction = 45 m
Ly = Maximum length of grid conductor in y-direction = 10 m

Page 80 of 91
 LR = Total length of ground rods = 12 m
Subtituting the above values,

LM = 21216.85 m

As per Eq.81 of IEEE Std 80-2013, the Spacing Factor for Mesh Voltage,

1 D2 (D + 2h)2 h Kii 8
Km = ln + - + ln
2p 16hd 8Dd 4d Kh p(2n-1)

Equ. Diameter of Earth conductor, d = 0.0400 meter

Kh = 1 + h / h 0 ( From eq.83 of IEEE Std 80-2013 )

Kh = 1.26

No. of Parallel Paths, n = n a nb nc nd

Where, From eq.85 to 88 of IEEE Std 80-2013 Lp

na = (2 Lc)/Lp nb =
4 A
0.7 A
L x Ly L x Ly
nc = nd = 1
A
Where,
Lp = Peripheral length of the grid = 110 m

Substituting the above values,

na = 16.00 nb = 1.1386

nc = 1 nd = 1.00

n = 18.22

As per Eq.89 of IEEE 80-2013,

The corrective Factor, Ki = 0.644 + ( 0.148 x n )

Ki = 3.34
Substituting the values,
Km = 0.3765

Attainable Etouch Voltage = 200.22 Volts

9.6 Calculation of Attainable Estep :

From Eq.92 of IEEE Std 80-2013,
Attainable Estep = [ r Ks Ki I G / L S ]

Page 81 of 91
 As per Eq.94 of IEEE Std 80-2013, the Spacing Factor for Step Voltage,

1 1 1 1
Ks = + + (1 - 0.5n-2)
p 2h D + h D

No. of Parallel paths, n = 18.22

As per Eq.89 of IEEE 80-2013,

The corrective Factor, Ki = 0.644 + ( 0.148 x n )
Ki = 3.34

Ks = 0.3858

As per Eq.93 of IEEE Std 80-2013,

Ls = 0.75 Lc + 0.85 LR

Ls = 15908.175 m

Substituting the values,

Attainable Estep Voltage = 273.59 Volts

CONCLUSION :
Tolerable
Etouch = 3128.76 Volts

Attainable
Etouch = 200.22 Volts SAFE

Tolerable
Estep = 11848.93 Volts

Attainable
Estep = 273.59 Volts SAFE

Page 82 of 91
4. Calculation of Earth Grid Resistance for Transformer cum GIS area
4.1 Input Data :

(i) System Voltage, Vs = 400 kV

(ii.1) System fault Current, If = 33.05 KA

(iii) Fault Duration, t = 1 sec

(iv.1) Length of Earth Mat = 20 meter

(iv.2) Width of Earth Mat = 9 meter

(iv.3) Area of Earth Mat, A = 182 sq.meter

(v) Conductor Size for main grid = 900 sq.mm

(vi) Depth of burial w.r.t. Raft level, h = 0.6 meter

(vii.1) Number of earth mat conductors in 'X' direction = 7 No.

(vii.2) Length of earth mat conductors in 'X' direction = 63 meter

(vii.3) Number of earth mat conductors in 'Y' direction = 3 No.

(vii.4) Length of earth mat conductors in 'Y' direction = 60.6 meter

(vii.5) Length of Buried conductor, Lc = 285 meter

(viii.1) Total no. of ground rods

For 1.0 m long = 5

(viii.2) Total ground rod length, LR = 15 meter

(ix) (Average) Soil Resistivity, r = 1632.00 W-meter

(x) Spacing for Earth Mat,D = 3 meter

4.2 Calculation of #REF!

As per Eq.53 of IEEE Std 80-2000,

R1 R2 - Rm2
The total system resistance, #REF! =
R1 + R2 - 2Rm
Where,
R1 = Ground resistance of grid conductors in W
Ground resistance of the grid, R1

r 2 Lc k1 Lc
R1 = ln + - k2 From eq.54 of
p Lc a '
A IEEE Std 80-2000

Where,
r = Soil resistivity in W-m 1632 ohm-m
Lc = Total length of all connected grid conductors in m 285 m
a' = a . 2h for conductors buried at depth h in m 0.1425 m
2a = Diameter of conductor in m 0.0339 m
A = Area covered by conductors in m2 181.8 m2
k1 = Coefficient from fig 25(a) of IEEE Std 80-2000 (curve-A) 1.320
k2 = Coefficient from fig 25(b) of IEEE Std 80-2000 (curve-A) 5.837

R1 = 55.3441 W

Ground resistance of the rod bed, R2

From eq.55 of IEEE Std 80-2000
r 4 Lr 2 k1 . Lr
R2 = ln -1 + ( n R - 1 )2
2p nRLr b A

Where,
Lr = length of each rod in m 3 m
2b = diameter of rod in m 0.036 m
nR = number of rods placed in area A 5

R2 = 110.821 W

Mutual ground resistance between the grid and the rod bed, R m
From eq.55 of IEEE Std 80-2000

r 2 Lc k1 Lc
Rm = ln + - k2 + 1
p Lc Lr A

Rm = 51.6131 W

Subtituting the above values,

#REF! = 55.123 W

4.3 #REF! = 55.123 W

Reference standard : IEEE Std 80-2000

5. Conductor Sizing for Surge Chamber, Tailrace, Intake Structure

Input data :- Properties of MS is as per Item 10 Table1 of IEEE Std 80-2000

(i) Conductor material = M.S.

(ii) System Voltage = 11 kV

(iii) Fault Current, If = 25 kA,

(iv) Fault Duration, tc = 1 sec

(v) Max. Allowable Temperature, Tm = 1510 *0

C see Note

(vi) Ambient Temperature, Ta = 50 C

0

(vii) Thermal Co-eff.of resistivity at reference

Temperature, ar = 0.0016 *

(viii) Resistivity of Ground Conductor at ref.

Temperature, rr = 15.9 * mW-cm

(ix) Thermal Capacity Factor, TCAP = 3.28 * J/(cm3.oC)

(x) K0 (=1/a0) = 605 *

Conductor Size :-
As per Eq.37 of IEEE Std 80-2000, conductor size is given by
If

A = TCAP x 10-4 X ln Ko + Tm
tc ar rr Ko + Ta

Conductor size, A = 203 sq.mm

Conductor size selected considering corrosion 50 X 6 MM MS Strip

allowance

Note:- 1) * marked values are taken as per IEEE.80

PAGE 85 OF 91
10. Touch and Step Voltage Criteria for Power House, Transformer cum GIS and Pothead Yard

10.1) Input Data :

(i) System Voltage, Vs = 13.8 kV

(ii.1) System fault Current, If = 63 KA

(iii) Fault Duration, t = 1 sec

(iv.1) Length of Earth grid = 556 metre

(iv.2) Width of Earth grid = 26 metre

(iv.3) Area of Earth grid, A = 14466 sq.metre

(v) Conductor Size for main grid = 1256 sq.mm

(vi) Depth of burial w.r.t. ground level, h = 0.6 metre

(vii.1) Number of earth mat conductors in 'X' direction = 130 No.

(vii.2) Length of earth mat conductors in 'X' direction = 3640 metre

(vii.3) Number of earth mat conductors in 'Y' direction = 7 No.

(vii.4) Length of earth mat conductors in 'Y' direction = 3909 metre

(vii.5) Total Length of Buried conductor, Lc = 10579 metre

(viii.1) Total no. of ground rods = 196

(viii.2) Total ground rod length, LR = 588 metre

(viii.3) Effective Buried Length for mesh voltage, LM = 11494.1 metre

(viii.4) Effective Buried Length for step voltage, LS = 8433.89 metre

(ix) Soil Resistivity, r = 426.42 W-metre

(x) Surface Resistivity, rs = 10000 W-metre

(xi) Spacing for Earthing Mat below ,D = 4.3 metre

(xii) Corrective weighting factor, Kii = 1

(xiii) Reference Depth of grid, h0 = 1 metre

(xvi) Thickness of tiles/Gravel/concrete etc, hs = 0.15 metre

Page 86 of 91
10.2) Calculation of Tolerable Etouch & Estep Voltage :

a) Tolerable Etouch70 :
From Eq.33 of IEEE Std 80-2000
Tolerable Etouch70= [(1000 + 1.5CS rS) 0.157/ ÖtS ]
Where,
Cs = Reduction factor for derating the nominal value of surface layer

Cs = 1 - 0.09 [(1-r/rs)/(2hs + 0.09)] ( From eq.27 of IEEE Std 80-2000 )

Cs = 0.779
tS = Duration of shock current in seconds , t = 0.5 sec
( from clause 16.2.2 of IEEE Std 80-2000 )
Substituting the above values,
Tolerable Etouch70 = 2816.71 Volts

b) Tolerable Estep70 = [(1000 + 6CS rS) 0.157/ ÖtS ] (from eq.29 of IEEE Std 80-2000)

Substituting the values,

Tolerable Estep70 = 10600.74 Volts

10.3) Calculation of Maximum Ground Potential Rise :

Max. Ground potential above remote earth, GPR = Ig x Rg Volts
Where,
Ig = grid current = If x Sf

Sf = Fault current division factor

Ig = 63 KA at Sf = 0.5
Substituting the values,

Ground Potential Rise, GPR = #REF! Volts

Since, GPR > Estep70 (as per Figure 33 of IEEE Std 80-2000),calculate Emesh and Attainable
Estep voltages

10.4) Calculation of Attainable Etouch Voltage :

From Eq.80 of IEEE Std 80-2000, for Grid rods in the periphery,

Attainable Etouch Voltage = [ r Km Ki I G / L M ]

Lr
LM = Lc + 1.55+1.22 LR From eq.91 of IEEE Std 80-2000
Lx+L
2 2
y

Where,
Lr = Length of each ground rod = 3 m
Lx = Maximum length of grid conductor in x-direction = 556 m
Ly = Maximum length of grid conductor in y-direction = 26 m

Page 87 of 91
 LR = Total length of ground rods = 588 m
Subtituting the above values,

LM = 11494.06 m

As per Eq.81 of IEEE Std 80-2000, the Spacing Factor for Mesh Voltage,

1 D2 (D + 2h) h Kii 8
Km = ln + - + ln
2p 16hd 8Dd 4d Kh p(2n-1)

Equ. Diameter of Earth conductor, d = 0.0400 metre

Kh = 1 + h / h 0 ( From eq.83 of IEEE Std 80-2000 )

Kh = 1.26

No. of Parallel Paths, n = n a nb nc nd

Where, From eq.85 to 88 of IEEE Std 80-2000 Lp

na = (2 Lc)/Lp nb =
4 A
0.7 A
L x Ly L x Ly
nc = nd = 1
A
Where,
Lp = Peripheral length of the grid = 1164.79804 m
D = Maximum distance between any two points
on the grid = 4.3 m
Substituting the above values,

na = 18.16 nb = 1.556

nc = 1 nd = 1.00

n = 28.26

As per Eq.89 of IEEE 80-2000,

The corrective Factor, Ki = 0.644 + ( 0.148 x n )

Ki = 4.83
Substituting the values,
Km = 0.2297

Attainable Etouch Voltage = 2591.11 Volts

10.5) Calculation of Attainable Estep :

From Eq.92 of IEEE Std 80-2000,
Attainable Estep = [ r Ks Ki IG / L S ]

Page 88 of 91
 As per Eq.94 of IEEE Std 80-2000, the Spacing Factor for Step Voltage,

1 1 1 1
Ks = + + (1 - 0.5n-2)
P 2h D + h D

No. of Parallel paths, n = 28.26

As per Eq.89 of IEEE 80-2000,

The corrective Factor, Ki = 0.644 + ( 0.148 x n )
Ki = 4.83

Ks = 0.4042

As per Eq.93 of IEEE Std 80-2000,

Ls = 0.75 Lc + 0.85 LR

Ls = 8433.894851 m

Substituting the values,

Attainable Estep Voltage = 6215.42 Volts

CONCLUSION :
Tolerable
Etouch = 2816.71 Volts

Attainable
Etouch = 2591.11 Volts SAFE

Tolerable
Estep = 10600.74 Volts

Attainable
Estep = 6215.42 Volts SAFE

From the above results,it can be seen that the Attainable E touch and Attainable Estep voltages are
less than the Tolerable Etouch and Tolerable Estep voltages and hence SAFE

10.6) Soil resistivity for Power house, Transformer cum GIS, Potheadyard

Soil resistivity for Power house = 245.43 W-meter

Soil resistivity for Transformer Cavern = 693.66 W-meter

Soil resistivity for Pothead yard = 883.15 W-meter

Soil resistivity for Tailrace = 245.43 W-meter

Soil resistivity for Surge Chamber = 245.43 W-meter

Soil resistivity for Intake structure = 245.43 W-meter

Average Soil resistivity = 426.42 W-meter

Page 89 of 91
Page 90 of 91
 Combined Grid Resistance
Calculation for additional Rod electrodes for Pump house Area

Average Soil resistivity = #REF! W /m

Grid Resistance (Rg) for the pump house Area = #REF! W

As per calculation grid resistance of pump house is 3.753 ohms. The earthng grid resistance should be
less than 3 ohm as per specification. To further reduce grid resistance, Rod earthing system will be
provided.
A Rod earthing system with proper dimensioning of the rod electrode is considered to be more effective
in reducing the earth resistance as compared to plat electrodes earthing. The number of rod electrodes
and their placement in adjoining of the earth mat is finalized depending upon the grounding system
resistance of the overall arrangement.

The resistance of the Rod electrode.

Rp = (100*р/2∏L) ln (4L/d)
where,
Rp = Resistance of rod electrode in ohms
р = soil resistivity in ohm-meter
L = Length of Rod
d = Diameter of Rod

=
Length of Rod 300 cm

=
Diameter of Rod (d) 4 cm

Rp = #REF!
= 93.03/8
Rpc = #REF!

So the 08 nos. of rod electrode are sufficient to reduce the ground resistance.

Combined ground resistance for pump house

1 1 1
+
RT = Rg Rpc

Rg X Rpc
RT = Rg + Rpc

RT = #REF! Ω

Page 91 of 91