Calculation of Earthing Sys.

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