TBEA Energy (India) Pvt. Ltd.
Calculation
Grounding calculation (as per IEEE 80)
Project
Mehnakhera , REC‐221
Customer
HVPNL
Scenario
Date
Design &Engineering, EPC
23/11/2018
Checked
BMS
Rev
1
VSG
Approved
Input parameters
Calculation
40000
A
1
S
3
Symmetrical fault current in substation for conductor
sizing
Duration of shock for determining allowable body
current
Surface gravel layer resistivity
4
Surface gravel layer thickness
0.1
m
5
Soil resistivity
50
Ω‐m
6
Depth of burial of earth material
0.6
m
7
Number of rods in switchyard
219
8
Length of ground rod at each location
3
m
9
Maximum length in X – direction
289.737
m
10
Maximum length in Y – direction
187.158
m
11
40
12
13
Diameter of conductor / equivalent diameter in case
of flat conductor
Body weight
Enter value of k according to the weight of person
50
0.116
14
Enter resistance of the body of person
1000
1
2
3000
Ω‐m
mm
Ω
Ampacity calculation
1
Type of conductor
Steel‐1020
2
Reference temperature for material constants
20
°
3
0.0016
°
4
Thermal coefficient of resistivity at reference
temperature
Fusing temperature of conductor
1510
°
5
Ambient temperature
50
°
Page 1 of 6
∝
TBEA Energy (India) Pvt. Ltd.
Calculation
Grounding calculation (as per IEEE 80)
Project
Mehnakhera , REC‐221
Customer
HVPNL
Scenario
Date
Design &Engineering, EPC
6
23/11/2018
Checked
BMS
1
∝
Rev
1
VSG
Approved
605
°
7
Resistivity of conductor at reference temperature
15.9
µΩ ‐ m
8
Thermal capacity per unit volume
3.28
9
Time duration for sizing the earth mat conductor
1
S
10
Current for sizing of earth mat conductor
40
kA
11
Soil resistivity for corrosion allowance
50
Ohm ‐ m
∗ °
Grid configuration
1
Grid shape
Rectangle
2
Maximum length in X – direction
289.737
m
3
Maximum length in Y – direction
187.158
m
4
Spacing between parallel conductors
30
m
5
Number of conductor along the length wise
15
6
Number of conductor along the width wise
10
7
Number of electrodes
219
8
Length of individual electrode
3
m
9
Total length
6361.74
m
10
Total area of earth mat
54226.6
m
11
Total length of grid conductor
5704.74
m
12
Periphery length of the earthing equivalent area
953.79
m
13
Total ground rods length
657
m
Page 2 of 6
TBEA Energy (India) Pvt. Ltd.
Calculation
Grounding calculation (as per IEEE 80)
Project
Mehnakhera , REC‐221
Customer
HVPNL
Scenario
Date
Design &Engineering, EPC
Checked
23/11/2018
BMS
Rev
1
VSG
Approved
Output Symmetrical with rod ‐ Database
1
Ampacity calculation
1
∗
∗
∗ ∝ ∗
2
325.1200
ln
Check the size of the selected conductor whether it is sufficient or not
∗
4
20.35106006
mm
dmin with corrosion
dmin 2*corrosion allowance
24.99906006
mm
Minimum cross section required with corrosion allowance
490.588108
Cross section of selected conductor
1256

In case of conductor to be laid in soil having soil resistivity
from 25 to 100 Ω‐m – 91.5 mils 2.324 mm
Reference : Design of steel Earthing Grids in India, IEEE
transactions on Power Apparatus and Systems, Vol. PAS‐98
No. 6 Nov./Dec 1979, pp 2126‐2134
3
The reduction factor de – rating factor Cs
Page 3 of 6
Calculation
Grounding calculation (as per IEEE 80)
Project
Mehnakhera , REC‐221
Customer
HVPNL
Scenario
TBEA Energy (India) Pvt. Ltd.
Date
Design &Engineering, EPC
Checked
2 ∗
Rev
1
VSG
Approved
0.694828
0.09
Tolerable touch and step voltage
1.5 ∗
6 ∗
5
BMS
0.09 ∗ 1
1
4
23/11/2018
∗
∗
478.7
V
1566.8
V
0.103336
Ω
Grid configuration
∗
Split Factor
1
1
√20 ∗
∗
1
1
1
∗
Sf
0.6
Symmetrical grid current Ref. IEEE 80 clause no. 15.1.6
Ig
Sf * If
0.6 * 40000
24000
Decremental Factor Ref. IEEE 80 clause no. 15.1.4 & 15.10
Df
1
Corrective projection factor Cp
Cp
IG
1
Df * Cp * Ig
24000
Page 4 of 6
A
TBEA Energy (India) Pvt. Ltd.
Calculation
Grounding calculation (as per IEEE 80)
Project
Mehnakhera , REC‐221
Customer
HVPNL
Scenario
Date
Design &Engineering, EPC
23/11/2018
Checked
BMS
Rev
1
VSG
Approved
Maximum Ground Potential Rise
Ref. IEEE 80 clause no. 3.14 & 8.1.1
GPR
Ig * Rg
GPR
2480.072
Tolerable Touch Voltage
GPR for switchyard is exceeding tolerable touch voltage.
Hence, further check for attainable Touch/Mesh voltage and
Step voltage shall be carried out.
6 Calculation of attainable step and touch voltage
∗
∗
∗
12.10477
1
1
2 ∗
1
1
2 ∗
∗ ln
0.644
1.264911
0
16 ∗
∗
8 ∗
2 ∗
∗
ln
4 ∗
8
∗ 2 ∗
1.22 ∗
0.963963
2.435505
0.148 ∗
1.55
1
∗
6730.061
m
418.6119
V
Attainable Mesh/Touch Voltage
∗
∗
∗
Page 5 of 6
TBEA Energy (India) Pvt. Ltd.
Calculation
Grounding calculation (as per IEEE 80)
Project
Mehnakhera , REC‐221
Customer
HVPNL
Scenario
Date
Design &Engineering, EPC
1
∗
1
2 ∗
0.75 ∗
23/11/2018
Checked
1
BMS
1
∗ 1
Approved
0.5
Rev
1
VSG
0.307846
0.85 ∗
4837.005
m
186.0061
V
Attainable Step Voltage
∗
7
∗
∗
Safety check
Attainable voltage V
Tolerable voltage V
Touch voltage
418.6119
478.7
Step voltage
186.0061
1566.8
Conclusion
The attainable touch and step potentials are lower than tolerable values with considerable
amount of difference, hence the design is valid and the proposed Grid Configuration can be
used for Earthing in switchyard.
Page 6 of 6