AS BUILT 2
12.Mar.2007
1 0 Rev
K.WATANABE
K.WATANABE
AS BUILT
18 Apr 2005
H.ISHIZUKA
Released for Construction as per Approval of OE – DRCS No. C-MMH/MTH/0047 dated 23rd Sep 2003. status “1”
27th Aug 2003
H.ISHIZUKA
First Issue (For Review)
Date
Drawn
th
Description
M.FUKUI
K.WATANABE
M.FUKUI
T.FUJISAWA
T.FUJISAWA
Ch’k’d
App’d
Certifies that it has examined the present document and it complies with the requirem ents of the EPC Contract Client PO Box 45810 Sas Al Nakhl Island Abu Dhabi UAE
Project
UMM AL NAR INDEPENDENT WATER AND POWER PROJECT Consultant
Victory House Trafalgar Place Brighton BN1 4FY United Kingdom Tel+44(0) 1273 365000 Fax+44(0) 1273 365100 Web www.mottmac.com
Contractor
Sub-Contractor
MITSUI & CO,. (MIDDLE EAST)E.C Sub-Contractor/Contractor Dwg No.
ACXUN1851 Title
CALCULATION FOR EARTHING SYSTEM Job Number
Size
M222001
Scale
A4
document No
Rev
N.A.
2 Sheet
000-1400-BZB01-GV002-0001
1 of 12
The information in this material is confidential and contains Toshiba’s intellectual property including know-how. It shall not be disclosed to any third party, copied, reproduced, used for unauthorized purposes nor modified without prior written consent of Toshiba. Toshiba Corporation
1
Document number (Owner)
: 000-1400-BZB01-GV002-0001
Document number (TOSHIBA)
: ACXUN1851
CALCULATION OF EARTHING SYSTEM
APPROVED BY SCAL
FUJISAWA AUG.27.2003 DESIGNED BY
UNIT
CHECKED BY
DRAWING NO.
H.ISHIZUKA AUG.27.2003 DRAWN BY
H.ISHIZUKA
REGISTER
2
ACXUN1851
REV.
1
CONTENTS 1.
INTRODUCTION····························································································································· 3
2.
REFERENCE ·································································································································· 4
3.
EXPLANATION OF EARTHING SYSTEM ····················································································· 4
4.
SOIL RESISTIVITY ························································································································· 4
5.
EARTHING SYSTEM CALCULATION (FOR POWER BLOCK) 5.1 ELECTRICAL PARAMETER··································································································· 5 5.2 EARTHING CHARACTERISTICS··························································································· 5 5.3 SAFETY CHARACTERISTICS OF NETWORK DESIGN
ANNEX-A
CALCULATION OF EARTHING MESH ·········································································· 7
ANNEX-B
SOIL RESISTIVITY DATA ····························································································· 12
REFERENCE DOCCUMENTS 000-4000-BZB01-GV001-001
EARTHING GRID LAYOUT
(OVERALL)
EARTHING GRID LAYOUT
(POWER BLOCK AREA)
(WCXUN1101) 000-4000-BZB01-GV001-002 (WCXUN1102)
3
1. INTRODUCTION Earthing mesh in the Plant area will be provided to protect the human being from the step and touch potentials and provide free path for earth fault current for equipment protection. Each mesh design, sizing of the conductor required for forming the earth mesh are done in accordance with IEEE Std.80. The results of this study will be used for forming the earthing mesh, depth of burial, driving depth of the electrode and total number of electrodes required. 2. REFERENCE IEEE Std.80-2000 : Guide for safety in AC Substation Grounding 3. EXPLANATION OF EARTHING SYSTEM 3.1 Composition of Earthing system 3.1.1
The earthing system shall be composed of a earthing distribution grid system (meshed network) constructed by sub-grade earthing conductors and earthing electrodes.
3.1.2
The main earthing distribution grid system consisting of bare copper conductor with a cross-section of 300 mm 2 is to be provided.
3.1.3
The earthing system being of an inter-connected mesh system with a maximum distance between two meshes not exceeding 30m.
3.1.4 All connections are carried out by means of exothermic welding process. 3.1.5 Adjacent to the transformer neutral grounding, earthing electrodes are to be driven into the soil and connected to earthing mesh. 3.1.6
In order to achieve an overall earth resistance of 1 ohm, earth electrodes are to be driven at certain points into the soil and connected to earthing mesh.
3.1.7 Earthing electrodes are 3 meter length with a diameter of 17.5 mm. 3.1.6 Earthing resistance is required less than 1 ohm. 4. SOIL RESISTIVITY Resistance (R ) of the soil was measured using Wenner’s method. Summary DATA are shown on Annex-B. Soil resistivity was computed by using the formula: ρ = 2π aR separation.)
(“a” is electrode
From the value measured in the Plant area, the average value of top layer resistivity is
less than 12.33 Ω-m and lower layer is less than 11.85 Ω-m. However, top layer resistivity is considered as 15 Ω-m and bottom layer resistivity as 15 Ω-m for calculation.
4
5.
EARTHING SYSTEM CALCULATION (FOR POWER BLOCK)
5-1 ELECTRICAL PARAMETERS 3I0
Symmetrical fault current in for conductor sizing
40
(kA)
tf
Duration of fault current
3
(s)
f
Frequency
50
(HZ)
tc
Duration fault current for sizing ground conductor
3
(s)
ts
Duration of shock for body current
3
(s)
X/R
Ratio X/R
0.3
*2)
Df
Decrement factor for Ig
1.0
*1)
5-2 EARTHING CHARACTERISTICS A
Total area enclosed by grounding grid
54,400
(m2)
Lc
Length of grid system conductor
4,120
(m)
Rectangular grid’s length (longer side)
340
(m)
Rectangular grid’s width (shorter side)
160
(m)
Nos of parallel conductor of longer side
6
(pcs)
Nos of parallel conductor of shorter side
13
(pcs)
ρ
Soil resistivity
15
(ohm-m)
ρs
Surface layer resistivity
3000
(ohm-m)
hs
Surface layer thickness
0.2
(m)
h
Dipth of grounding grid conductor
1.5
(m)
Dm
Maximum distance between any two parallel conductor
30
(m)
Tm
Maximum allowable temperature
1083
(degC)
TA
Ambient temperature
46
(degC)
αr
Thermal coefficient of resistivity
0.00393
K
1/ar at 0 deg C
234
ρr
Resist. Ground cond. At refer temp. Tr
1.72
(Ohm/cm3 )
TCAP
Thermal capacity factor for table
3.42
(J/cm3 C)
Ac
Minimum conductor section area
--
(mm2)
S
Conductor section area
300
(mm2)
d1
Diameter of grid conductor
20
(mm)
Nr
Nunber of Rods
0
(pcs)
*3)
Lr
Length of rods
3.0
(m)
*3)
Dr
Rod diameter
17.2
(mm)
*3)
5
5-3 OUTPUT DATA Rg
Resistance of grounding system
(Ohm)
GPR
Ground potential rise
(V)
Em
Mesh voltage
(V)
Es
Step voltage
(V)
Estep50
Tolerable step voltage for human with 50 kG body weight
(V)
Etouch50
Tolerable touch voltage for human with 50 kG body weight
(V)
Notes: *1) Most conservative value is considered. *2) Assumed value *3) This calculation is applied for without electrode mesh system 5-4 SAFETY CHARACTERISTICS OF NETWORK DESIGN Sf
Current division factor
1.0
Ig
Maximum grid current
40,000
(A)
Max allowable value
Computed Value
Safety condition
Etouch50
313 (V)
311 (V)
Yes
Estep50
1,052 (V)
47 (V)
Yes
Rg
less than 1.0 (Ω)
0.032 (ohm)
Good
GPR
Ground potential rise
1,280 (V)
--
GENERAL NOTE 1) The calculation is made considering an average mesh grid of 30x30m, but in some areas the mesh grid is more close. This means that the actual values shall be lower than the calculated ones.
6
ANNEX-A Calculation of Earthing mesh Step1:
(For Power Block)
Earthing Grid conductor sizing calculation
To determine the minimum cross sectional area of the main earthing conductor, followings are considered: -
Maximum fault current.
-
Material for the earth conductor is annealed copper stranded wire.
-
Following formula is used for to calculate the earthing conductor size, as per IEEE Std.80.
Section 11 (Eq-37), Table 1.
TCAP × 10 -4 K 0 + Tm I = A´ ( ) × ln( ) tc × ar × pr K 0 + Ta This equation is can be arranged to give required conductor size as a function of conductor current.
A=I´
t c ´ a r ´ r r ´ 10 4 TCPA æ Tm - Ta ö Inç1 + ÷ Ko + Ta ø è
I
= rms current in KA
Tc
= time of current flow in s
A
= conductor cross section in min
2
(mm )
2
Tm = max. allowable temperature in deg C Ta αo
= ambient temperature in deg C = thermal coefficient of resistivity at 0 dec C
αr = thermal coefficient of resistivity at reference temperature T, ρr
= the resistivity of the ground conductor at reference temperature T,in μΩ/cm
Ko = 1/α0,or (1/αr)-Tr TCAP = thermal capacity factor from Table 1,in j/cm3/deg C
7
3
1-1 For main mesh where: I
= 40
kA
Design requirement
Tm
= 1083
deg C
IEEE 80-2000 Section 11, Table1
Ta
= 46
deg C
Design requirement
αr
= 0.00393
IEEE 80-2000 Section 11, Table1
ρr
= 1.72
IEEE 80-2000 Section 11, Table1
Ko
= 234
IEEE 80-2000 Section 11, Table1
Tc
= 3.0
Design requirement
TCAP = 3.42
A = 40 ´
IEEE 80-2000 Section 11, Table1
3 ´ 0.00393 ´ 1.72 ´ 10 4 3.42 æ 1083 - 46 ö Inç1 + ÷ 242 + 46 ø è
=248 (mm2) According to the above calculation, 300 mm2 main earthing conductor is acceptable. 1-2
For earthing ring
where: I
= 31.5
kA
Design requirement
Tm
= 1083
deg C
IEEE 80-2000 Section 11, Table1
Ta
= 46
deg C
Design requirement
αr
= 0.00393
IEEE 80-2000 Section 11, Table1
ρr
= 1.72
IEEE 80-2000 Section 11, Table1
Ko
= 234
IEEE 80-2000 Section 11, Table1
Tc
= 3.0
Design requirement
TCAP = 3.42
A = 31.5 ´
IEEE 80-2000 Section 11, Table1
3 ´ 0.00393 ´ 1.72 ´ 10 4 3.42 æ 1083 - 46 ö Inç1 + ÷ 242 + 46 ø è
=196 (mm2) According to the above calculation, 240 mm2 earthing ring conductor is acceptable.
8
Step2:
Calculation of earthing resistance
As per IEEE80-2000 section14 (eq52)
é 1 1 1 æ öù Rg =ρê + çç1 + ÷÷ú 20 A è 1 + h × 20 / A øû ë LT where Rg
ground resistance
:
--
(ohm)
ρ
soil resistivity
:
15
(ohm-m)
A
area occupied by the ground grid
:
54,400
(m2)
LT
total buried length of conductors
:
4,120
(m)
h
depth of the grid
:
1.5
(m)
Rg=
0.032 (Ohm)
Step3: Maximum grid current IG
I G = D f × If = 1.0 x 40 =
40 (kA)
where Sf
fault current division factor
:
1.0
Ig
rms symmetrical grid current
:
40
(kA)
If
rms value of symmetrical ground fault current
:
40
(kA)
IG
maximum grid current
:
40
(kA)
Df
decrement factor for the entire duration of fault tf
:
1.0
Step4: GPR
GPR = I G × R g GPR = 40000 x 0.032 = 1280 (V)
9
Step5: Mesh voltage 5-1 The geometrical factor (Km)
Km =
1 2p
é æ D2 (D + 2h)2 - h ö÷ + K ii ln 8 ù ç ln + ê ç 8 Dd1 4d 1 ÷ø K h p (2n - 1) úû êë è 16hD
where: Km
Spacing factor for mesh voltage 2/n
:
--
:
--
Kii
Corrective factor K ii = 1
Kh
K h = 1 + h / ho
:
1.5811
ho
1m
:
1.0
(m)
(2 × n)
(reference depth of grid)
h
Depth of burial
:
1.5
(m)
d1
Diameter of conductor(m)
:
0.02
(m)
D
Distance of conductor(m)
:
30
(m)
n
Effective number of parallel conductor in a given grid
:
8.53
(pcs)
:
1.9066
n = n a × nb × nc × n d
na = Ki
2 × LC , nb = LP
LP 4× A
,
nc = n d = 1
Ki = 0.644 + 0.148 x n
Km =
5-2
1.1215
Mesh Voltage (Em)
ρ× Km × Ki × I G Em = LM
= 15 x 1.1215 x 1.9066 x 40000 / 4120 = 311 (V) where LM
The effective buried length , LM = LC + LR
:
--
(m)
LC
The total length of the conductor in the horizontal grid
:
4120
(m)
LR
The total length of all ground rods
:
0
(m)
10
Step 6: Check of touch voltage 6-1 The maximum driving voltage for touch voltage is :
Etouch so = (1000 + 1.5C s × r s )
0.116 tS
= (1000+1.5x 0.817 x 3000)x 0.116 / SQRT(3) = 313 (V) where:
æ r ö ÷ 0.09 × çç1 r S ÷ø è CS = 1 2 × hS + 0.09 6-2 Actual touch voltage
E touch = E m = 311 (V) 6-3 Decision
Em E touch 50 Actual touch voltage is well below the tolerable touch voltage, so it is ACCEPTABLE.
Step7: Check of step voltage 7-1 Tolerable of step voltage The maximum driving voltage for step voltage is :
E step50 = (1000 + 6C S ×ρS )
0.116 tS
= (1000+6x0.817x3000)x 0.116/sqrt(3) = 1,052 (V) 7-2 Actual step voltage
E S = K S ´ K i ´ r ´ I G / LS = 0.127x 1.9066x 15x 40000/ 3090 = 47
(V)
where:
LS = 0.75 ´ LC + 0.85 ´ LR
7-3 Decision
E S E step50 Actual step voltage is well below the tolerable step voltage. So it is ACCEPTABLE
11
ANNEX-B SOIL RESISTIVITY DATA Point Axis
A
B
PPE1
at GT AREA
Point
PPE2
at ELECT BLDG
Location
X=2100.000
Y=1100.000
a (meter)
R (Ω)
ρ（Ωｍ）
1
0.1685
1
1
2.09
13
1.5
0.54
5
1.5
1.9
18
2
0.62
8
2
3.28
41
3
0.71
13
3
0.98
18
4
0.80
20
4
0.66
17
5
0.437
14
Axis
A
Location
X=1841.500
Y=1045.000
a (meter)
R (Ω)
ρ（Ωｍ）
5
0.65
20
6
0.22
8
6
0.342
13
7
0.20
9
7
0.655
29
8
0.18
9
8
0.236
12
9
0.21
12
9
0.132
7
10
0.095
6
10
0.1
6
15
0.05
5
15
0.088
8
20
0.025
3
20
0.065
8
25
0.015
2
25
0.05
8
30
0.0055
1
30
0.0145
3
1
1.15
7
1
1.739
11
1.5
1.101
10
1.5
1.105
10
2
0.98
12
2
0.958
12
3
0.86
16
3
0.88
17
4
0.58
15
4
1.037
26
5
0.528
17
B
5
0.49
15
6
0.445
17
6
0.46
17
7
0.38
17
7
0.385
17
8
0.21
11
8
0.355
18
9
0.195
11
9
0.32
18
10
0.15
9
10
0.138
9
15
0.105
10
15
0.105
10
20
0.082
10
20
0.095
12
25
0.04
6
25
0.0625
10
30
0.0332
6
30
0.022
4
Average of the top layer resistivity (1 to 2 meters depth)
is
12.3
ohm-m.
Average of the lower layer resistivity
is
11.9
ohm-m.
Note) Measurement test of soil resistivity has be carried out in April 2003 and reported by TSB. Please refer to Test report of soil investigation document. 12
