DOI : 10.17577/IJERTV5IS040847
- Open Access
- Total Downloads : 279
- Authors : Keyur B. Jyotishi, Deep P. Patel, Dhruv J. Patel, Gaurang Patel
- Paper ID : IJERTV5IS040847
- Volume & Issue : Volume 05, Issue 04 (April 2016)
- DOI : http://dx.doi.org/10.17577/IJERTV5IS040847
- Published (First Online): 25-04-2016
- ISSN (Online) : 2278-0181
- Publisher Name : IJERT
- License:
This work is licensed under a Creative Commons Attribution 4.0 International License
A Comparison of Different Cases for Calculation of Earth Grid Design on the bases of Ieee 80-2000
Keyur Jyotishi
Department of Electrical Engineering
Shroff S. R. Rotary Institute of Chemical Technology Ankleshwar(393002), India
Dhruv Patel
Department of Electrical Engineering
Shroff S. R. Rotary Institute of Chemical Technology Ankleshwar(393002), India
Deep Patel
Department of Electrical Engineering
Shroff S. R. Rotary Institute of Chemical Technology Ankleshwar(393002), India
Gaurang Patel
Sr. Engineer-Elect.& MARKETING Takalkar Power Engineers & Consultants Pvt. Ltd.
Vadodara, India
Abstract: This paper provides stepwise calculation of earth grid with different cases which are affected in calculation of earth grid calculation like for different soil resistivity, different material and different human weight. Also this paper consists of comparison and appropriate graph for those different cases which are provided.
It should provide low impedance path to ground the fault current.
-
STEPS FOR DESIGNING EARTHING SYSTEM
Keywords: Soil resistivity, Step voltage, Touch voltage, Mesh Voltage, Permissible Body current, Body resistance, etc.
-
INTRODUCTION
Field data A,?
Conductor size 3I,
Step 1
Step 2
A conducting connection, whether accidental or intentional, by which an electric circuit or equipment is
Touch and step criteria
Etouch 50 Estep 50
Step 3
connection to the earth or to some conducting body relatively large extent that serves in place of the earth is called Earthing. [1]
Since the early days of the electric power industry, safety of personnel in and around electric power installations has been
Step 11 Modify Data
D,n,Lc,Lt
Initial Design D,L,Lc,A
Grid Resistance Rg, Lc, Lr
Grid Design Ig, tf
Step 4
Step 5
Step 6
a prime concern. A mechanism by which Safety of personnel is affected is the ground potential rise of grounded structures during electric power faults and the possibility of humans touching grounded structures and, therefore, subjecting themselves to voltages. [2]
Purpose of substation Earthing system:
The objective of an earthing system in substation is to provide under and around the substation a surface which shall be at a uniform potential and zero or absolute earth potential. The provision of this surface of injury potential under and around the substation ensure that no human being in the substation is subject to shock or injury on the occurrence of a short circuit or development of other abnormal condition in equipment installed in the yard. The
Step 7 Ig*Rg<Etouch
Mesh Voltage
Em,Es,Ks,Km,Ki
Mesh Voltage
Em,Es,Ks,Km,Ki
Yes Step 8
Step 9 No Em<Etouch
Yes
Step 10
No Es<Etouch
Yes
primary requirements of good earthing system in a sun- station are:
-
It should balance the circuit potentials with respect to ground and limit the overall potential rise.
Mesh Voltage Em,Es,Ks,Km,Ki
Step 12
-
It should protect human and equipment from over- voltage.
FIG 1 Steps For Designing Earthing System
Touch Voltage:
The potential difference between the ground potential rise and the surface potential at the point where a person is standing while at the same time having a hand in contact with a grounded structure.
E = (10000+ 1.5(c )( ) 0.116
touch s s t
Ground mat: Earth mat is a solid metallic plate or a system of closely spaced bare conductors that are connected to and often placed in shallow depths above a ground grid or elsewhere at the earths surface, in order to obtain an extra protective measure minimizing the danger of the exposure to high step or touch voltages in a critical operating area or places that are frequently used by people. Grounded metal gratings placed on or above the soil surface, or wire mesh placed directly under the surface material, are common forms of a ground mat. [1]
STEP 1 FIELD DATA
TABLE 1 FIELD DATA
Step voltage:
FIG 2 TOUCH VOLTAGE
The difference in surface potential experienced by a person bridging a distance of 1 m with the feet without contacting any grounded object
Estep = (10000+ 6(cs )(s ) o.116
. t
FIG 3 Step VOLTAGE]
Ground potential rise (GPR): The maximum electrical potential that a substation grounding grid may attain relative to a distant grounding point assumed to be at the potential of remote earth. This voltage, GPR, is equal to the maximum grid current times the grid resistance
GPR = IG X Rg
Ground current: A current flowing into or out of the earth or its equivalent serving as a ground is called as the ground current.
System earthing: Intentional earthing of neutral conductor for controlling circuit voltage to earthing and detection of unwanted connection between live conductors and earth is called system earthing.
Sr no
Description
Unit
Value
1
Symmetrical fault current in substation
A
40000
2
Duration shock for determining allowable body current
sec
0.5
3
Duration of fault current sizing ground conductor
sec
1
4
Surface layer resistivity
-m
3000
5
Surface layer thickness
m
0.1
6
Grid reference depth
m
1
7
Soil resistivity
-m
59.67
8
Depth of ground grid conductor
m
0.6
9
Length of grid conductor in x direction
m
158.1
10
Length of grid conductor in y direction
m
102.5
11
Spacing between parallel conductor
m
9
12
Length of ground rod/pipe at each location
m
3
13
No of pipe/rod placed in area
nos
30
14
Decrement factor for determining IG
–
1
15
No of grid conductor in x direction
nos
13
16
No of grid conductor in y direction
nos
19
17
Equivalent earthing mat area
m2
16205.3
18
Total length of buried conductor
m
4272.8
19
Total length of ground rod/pipe
m
90
Sr no
Description
Unit
Value
/td>
1
Symmetrical fault current in substation
A
40000
2
Duration shock for determining allowable body current
sec
0.5
3
Duration of fault current sizing ground conductor
sec
1
4
Surface layer resistivity
-m
3000
5
Surface layer thickness
m
0.1
6
Grid reference depth
m
1
7
Soil resistivity
-m
59.67
8
Depth of ground grid conductor
m
0.6
9
Length of grid conductor in x direction
m
158.1
10
Length of grid conductor in y direction
m
102.5
11
Spacing between parallel conductor
m
9
12
Length of ground rod/pipe at each location
m
3
13
No of pipe/rod placed in area
nos
30
14
Decrement factor for determining IG
–
1
15
No of grid conductor in x direction
nos
13
16
No of grid conductor in y direction
nos
19
17
Equivalent earthing mat area
m2
16205.3
18
Total length of buried conductor
m
4272.8
19
Total length of ground rod/pipe
m
90
For all the different cases for same material like steel the entire field will remain same but there is a change in Soil resistivity (i.e. 60 -m, 70 -m, 80 -m, 100 -m,120 -m,
14 -m, 150 -m, 160 -m, 180 -m, 200 -m) and due to that there will be change in Spacing between Parallel conductors and due to that there will be change in no of conductors on X-direction and Y direction and Total change in length of buried conductors and calculated mesh and touch voltage for economical and safe design of Earth grid for sub-station.
STEP 2: DETERMINATION OF SIZE FOR CONDUCTOR
The size of conductor is depends on the type of material. Hear we take Four Different Material (i.e. Steel, Copper, and Copper with clad, Stainless steel) The size of conductor is depends on the factor like r, Ko at 00c, Tm, r, Tcap which is different for different material.
Mate-rial
r factor at R.t
Ko at 00c
Tm
r
Tcap
Steel
0.0016
605
1510
15.9
3.28
Copper
0.0039
234
1083
1.72
3.42
Copper clad
0.0037
245
1084
4.4
3.85
Stainless steel
0.0013
749
1400
72
4.03
Mate-rial
r factor at R.t
Ko at 00c
Tm
r
Tcap
Steel
0.0016
605
1510
15.9
3.28
Copper
0.0039
234
1083
1.72
3.42
Copper clad
0.0037
245
1084
4.4
3.85
Stainless steel
0.0013
749
1400
72
4.03
TABLE 2 MATERIAL CONSTANT
Now for calculation of size of conductor For Steel
Material vs Required Area
1400
1200
1000
800
600
400
200
0
Material vs Required Area
1400
1200
1000
800
600
400
200
0
Steel Copper Copper Stainless
Steel Copper Copper Stainless
Marerial cald
steel
Marerial cald
steel
Requuired Area
Requuired Area
FIG 4 Graph Material Vs Required Area
STEP 3 TOUCH AND STEP CRITERIA
The Tolerable Touch and Step Voltage is mostly depends on the human weight. There is no effect of type of material and soil resistivity. The tolerable touch and step voltage is
TCAPX10-4
K + T
Estep = (10000+ 6(cs )(s ) o.116
I = Amm 2 X (
tc.r.r
)Xln( 0 m )
Ko + Ta
[3]t [1]
1
Amm 2 = -4
Etouch = (10000+1.5(cs )(s ) 0.116
t
( TCAPX10
tc.r.r
)Xln( K0 + Tm )
Ko + Ta
E.g. for 50 kg human tolerable touch and step voltage using above data is
2 = 520.5348 mm2
In case of conductors to be laid in soils having resistivity from 25 to 100 -metre -15 percent allowance.
2 = 1.15 520.5348
=598.6151 mm2
0.09× (1 – )
Cs = 1- s
2hs + 0.09
Cs = 0.695827
So,
[4] [5]Similarly
E = (10000+1.5(c )( ) 0.116
TABLE 3 REQUIRED AREA
touch s s t
Etouch = 677.722 V
Material
2
Steel
598.6151
Copper
230.888
Copper clad
347.9078
Stainless steel
1227.25
Material
2
Steel
598.6151
Copper
230.888
Copper clad
347.9078
Stainless steel
1227.25
And
Estep = (10000+ 6(cs )(s ) 0.116
t
[1]Estep = 2218.7437 V
Similarly
For 70 kg human
Etouch = (10000+1.5(cs )(s ) 0.157 [1]
t
Etouch = 931.766V
And
Estep = (10000+ 6(cs )(s ) 0.157
t
Estep = 3060.91V
Material Vs Step Voltage
-
Steel
-
steel 70
-
Copper
-
Copper 70
-
Copper clad
-
Copper clad 70
-
Stainless steel
Material Vs Step Voltage
-
Steel
-
steel 70
-
Copper
-
Copper 70
-
Copper clad
-
Copper clad 70
-
Stainless steel
For different material the value of tolerable step and touch voltage is
TABLE 4 EFFECT OF RSISTIVITY ON GRID RESISTANCE
1 2 3 4 5 6 7
Material
8 8 Stainless steel
1 2 3 4 5 6 7
Material
8 8 Stainless steel
1000
800
600
400
200
0
1000
800
600
400
200
0
4000Material Vs Touch voltage
1 Steel
4000Material Vs Touch voltage
1 Steel
Step
Step
FIG 5 Graph Material Vs Step Voltage
0.8
0.6
0.4
0.2
0
Resistivity (-m)
Length of buried conductors (mtr)
Grid Resistance ()
60
4272.8
0.2214
70
4635.9
0.2584
80
4645.9
0.2954
100
5259.6
0.3666
120
6143.9
0.4367
140
6143.9
0.5095
150
6143.9
0.5459
180
7130.7
0.6510
200
7130.7
0.7234
Resistivity (-m)
Length of buried conductors (mtr)
Grid Resistance ()
60
4272.8
0.2214
70
4635.9
0.2584
80
4645.9
0.2954
100
5259.6
0.3666
120
6143.9
0.4367
140
6143.9
0.5095
150
6143.9
0.5459
180
7130.7
0.6510
200
7130.7
0.7234
Resestivity vs Resistance
0 50 100 150 200 250
-m
Touch
Touch
FIG 7 Graph Of Resistivity Vs Resistance
3000
2000
1000
0
1 2 3 4 5 6 7 8
Material
-
steel 70
-
Copper
-
Copper 70
-
Copper clad wir 6 Copper clad wri 7 Stainless steel
8 Stainless steel 7
3000
2000
1000
0
1 2 3 4 5 6 7 8
Material
-
steel 70
-
Copper
-
Copper 70
-
Copper clad wir 6 Copper clad wri 7 Stainless steel
8 Stainless steel 7
FIG 6 Graph Material Vs Touch Voltage
Conclusion: Tolerable Step voltage and Touch Voltage is not depends on the material it is depends on the weight of human body.
STEP 4 DETERMINE THE GRID RESISTANCE
For = 60-m the grid resistance is
STEP 5
GROUND POTENTIAL RISE
For = 60-m the Ground Potential Rise is GPR = IG X Rg [1]
GPR = 5407.23 V
Resistivity m
GPR
60
5407.234
70
5909.804
80
6348.771
100
7056.66
120
7616.903
140
8095.579
Resistivity m
GPR
150
8302.598
180
8807.663
200
9094.702
Resistivity m
GPR
60
5407.234
70
5909.804
80
6348.771
100
7056.66
120
7616.903
140
8095.579
Resistivity m
GPR
150
8302.598
180
8807.663
200
9094.702
TABLE 5 EFFECT OF RESISTIVITY ON GPR
Rg = ×{ 1 +
L
1
20A0.5
(1 +
1
1+ ( 20)0.5
A
)} [6]
Rg = 0.2214 ohm
For Different cases like for different resistivity there will be change in distance between parallel conductors and there will be change in length of buried conductor.
So the resistivity will be change
Resistivity VS GPR
10000
8000
6000
4000
2000
0
60 70 80 100 120 140 150 180 200
RESISTIVITY
Resistivity VS GPR
10000
8000
6000
4000
2000
0
60 70 80 100 120 140 150 180 200
RESISTIVITY
So,
Es =
xI0 Ks Kii
GPR
GPR
((0.75× Lc ) + (0.85× LR ))
FIG 8 Graph Of Resistivity Vs Gpr
STEP 6 CALCULATE THE MESH VOLTAGE
= 465.32
For different resistivity
Resistivity(-m)
60
465.32
631.37
70
466.82
633.40
80
515.30
631.60
100
553.58
678.52
120
624.18
669.47
140
688.20
620.48
160
731.45
659.47
180
750.16
676.33
200
810.38
585.05
Resistivity(-m)
60
465.32
631.37
70
466.82
633.40
80
515.30
631.60
100
553.58
678.52
120
624.18
669.47
140
688.20
620.48
160
731.45
659.47
180
750.16
676.33
200
810.38
585.05
TABLE 6 EFFECT OF RESISTIVITY ON SYSTEM VOLTAGES
m 2
m 2
1 D2
(D + 2h)2 h
Kii 8
K = {ln( 16hd
Where
+
8Dh
+ ) +
4d Kh
(ln )
(2n¬1)
[6]n = (na X nb X nc X nd)
Where na, nb, nc and nd is depends on the Total length of buried conductors (Lc) and Peripheral length of buried conductor (Lp).
So for resistivity ()=60 -m, The Spacing between parallel conductors =9 m so
Lc = {(Lx X Nx) + (Ny X Ly)} Lc = 4002.8 m
Lp = {(2XLx) + (2XLy)} Lp = 521.2 m
So
n = 15.5398
So
= 0.6099
And
= 0.644 + (0.148 X n) = 2.943902
So Mesh Voltage is
m
m
E = xIG Km Kii [6]
So From the equation of Step and Mesh Voltage, System or Calculated Mesh and Step Voltage is depends on the Soil Resistivity it is not depends on the type of material.
-
-
-
ACKNOWLEDGMENT
We gratefully acknowledge Mr. Gaurang Patel, Takalkar Power Engineers and Consultants Pvt. Ltd, Vadodara and Ankur Gheewala, Department of Electrical Engg., Shroff S.
R. Rotary Institute of Chemical Technology for their comments and contribution, many of which have helped us to improve knowledge and paper.
-
REFERENCES
-
IEEE 80-2000., IEEE Guide for Safety in AC Substation Grounding, (Revision of IEEE 80-1986) approved 30 January 2000.
-
Central Board of Irrigation & Power (CBIP) Publication no.223
-
Sverak, J. G., Sizing of ground conductors against fusing, IEEE Transactions on Power Apparatus and Systems, vol. PAS- 100, no. 1, pp. 5159, Jan. 1981.
-
Dawalibi, F. P., Xiong, W., and Ma, J., Effects of deteriorated and contaminated substation surface covering layers on foot resistanc calculations, IEEE Transactions on Power Delivery, vol. 8, no. 1, pp. 104113, Jan. 1993.
-
Meliopoulos, A.P., Patel, S., and Cokkonides, G. J., A new method and instrument for touch and step voltage measurements, IEEE
Lc + (1.55+{1.22[
(L
Lr x 2 + L
y 2 )0.5
]}LR
Transactions on Power Delivery, vol. 9., no. 4, pp. 18501860, Oct. 1994.
-
Sverak, J. G., Simplified analysis of electrical gradients above a
= 498.044
For Calculated Step Voltage
ground grid; Part IHow good is the present IEEE method? IEEE Transactions on Power Apparatus and Systems, vol. PAS-103, no. 1, pp. 725, Jan. 1984.
Ks = 1 ( 1 + 1 + 1 (1¬0.5(n¬2)))
[6]2h D + h D
= 0.33394