AS BUILT2 12.Mar.2007 18 Apr 2005 27th Aug 2003 Date th K.WATANABE AS BUILT Released for Construction as per Approval of OE – DRCS No. C-MMH/MTH/0047 dated 23rd Sep 2003. status “1” K.WATANABE K.WATANABE T.FUJISAWA Ch’k’d M.FUKUI M.FUKUI T.FUJISAWA App’d 1 0 Rev H.ISHIZUKA H.ISHIZUKA Drawn First Issue (For Review) Description 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 Scale Rev M222001 document No A4 N.A. Sheet 2 1 of 12 000-1400-BZB01-GV002-0001 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 2003 DRAWN BY DRAWING NO.2003 DESIGNED BY H. ACXUN1851 1 REGISTER 2 .27.27.ISHIZUKA AUG. REV.ISHIZUKA CHECKED BY H.Document number (Owner) Document number (TOSHIBA) : 000-1400-BZB01-GV002-0001 : ACXUN1851 CALCULATION OF EARTHING SYSTEM APPROVED BY SCAL UNIT FUJISAWA AUG. 3 SAFETY CHARACTERISTICS OF NETWORK DESIGN ANNEX-A ANNEX-B CALCULATION OF EARTHING MESH ·········································································· 7 SOIL RESISTIVITY DATA ····························································································· 12 REFERENCE DOCCUMENTS 000-4000-BZB01-GV001-001 (WCXUN1101) 000-4000-BZB01-GV001-002 (WCXUN1102) EARTHING GRID LAYOUT (POWER BLOCK AREA) EARTHING GRID LAYOUT (OVERALL) 3 .2 EARTHING CHARACTERISTICS··························································································· 5 5. 2. INTRODUCTION····························································································································· 3 REFERENCE ·································································································································· 4 EXPLANATION OF EARTHING SYSTEM ····················································································· 4 SOIL RESISTIVITY ························································································································· 4 EARTHING SYSTEM CALCULATION (FOR POWER BLOCK) 5.CONTENTS 1. 3. 4.1 ELECTRICAL PARAMETER··································································································· 5 5. 5. 1. Summary DATA are shown on Annex-B.1. 3.3 The earthing system being of an inter-connected mesh system with a maximum distance between two meshes not exceeding 30m. Each mesh design. sizing of the conductor required for forming the earth mesh are done in accordance with IEEE Std.7 Earthing electrodes are 3 meter length with a diameter of 17.5 mm.4 All connections are carried out by means of exothermic welding process. the average value of top layer resistivity is less than 12. 4.80. The results of this study will be used for forming the earthing mesh. 2.1.1 The earthing system shall be composed of a earthing distribution grid system (meshed network) constructed by sub-grade earthing conductors and earthing electrodes. 3.5 Adjacent to the transformer neutral grounding.1. earth electrodes are to be driven at certain points into the soil and connected to earthing mesh. 3. depth of burial.1. 3. 4 .1. 3. top layer resistivity is considered as 15 Ω-m and bottom layer resistivity as 15 Ω-m for calculation. However. 3.6 Earthing resistance is required less than 1 ohm. REFERENCE IEEE Std.1.6 In order to achieve an overall earth resistance of 1 ohm.85 Ω-m.1.33 Ω-m and lower layer is less than 11.2 The main earthing distribution grid system consisting of bare copper conductor with a cross-section of 300 mm 2 is to be provided.80-2000 : Guide for safety in AC Substation Grounding 3. EXPLANATION OF EARTHING SYSTEM 3. SOIL RESISTIVITY Resistance (R ) of the soil was measured using Wenner’s method.) (“a” is electrode From the value measured in the Plant area.1. 3. 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. Soil resistivity was computed by using the formula: ρ = 2π aR separation.1 Composition of Earthing system 3. earthing electrodes are to be driven into the soil and connected to earthing mesh. driving depth of the electrode and total number of electrodes required. 3 1.0 (kA) (s) (HZ) (s) (s) *2) *1) 5-1 ELECTRICAL PARAMETERS 5-2 EARTHING CHARACTERISTICS A Lc Total area enclosed by grounding grid Length of grid system conductor Rectangular grid’s length (longer side) Rectangular grid’s width (shorter side) Nos of parallel conductor of longer side Nos of parallel conductor of shorter side ρ ρs hs h Dm Tm TA αr K ρr TCAP Ac S d1 Nr Lr Dr Soil resistivity Surface layer resistivity Surface layer thickness Dipth of grounding grid conductor Maximum distance between any two parallel conductor Maximum allowable temperature Ambient temperature Thermal coefficient of resistivity 1/ar at 0 deg C Resist.72 3. Tr Thermal capacity factor for table Minimum conductor section area Conductor section area Diameter of grid conductor Nunber of Rods Length of rods Rod diameter 54.5.0 17. Ground cond. 3I0 tf f tc ts X/R Df EARTHING SYSTEM CALCULATION (FOR POWER BLOCK) Symmetrical fault current in for conductor sizing Duration of fault current Frequency Duration fault current for sizing ground conductor Duration of shock for body current Ratio X/R Decrement factor for Ig 40 3 50 3 3 0.5 30 1083 46 0.42 -300 20 0 3.00393 234 1.400 4. At refer temp.2 1.120 340 160 6 13 15 3000 0.2 (Ohm/cm3 ) (J/cm3 C) (mm2) (mm2) (mm) (pcs) (m) (mm) *3) *3) *3) (m2) (m) (m) (m) (pcs) (pcs) (ohm-m) (ohm-m) (m) (m) (m) (degC) (degC) 5 . 280 (V) 1.0 40. 6 .032 (ohm) 1. but in some areas the mesh grid is more close.0 (Ω) Ground potential rise Computed Value 311 (V) 47 (V) 0.000 (A) Resistance of grounding system Ground potential rise Mesh voltage Step voltage Tolerable step voltage for human with 50 kG body weight Tolerable touch voltage for human with 50 kG body weight (Ohm) (V) (V) (V) (V) (V) Safety condition Yes Yes Good -- GENERAL NOTE 1) The calculation is made considering an average mesh grid of 30x30m. *2) Assumed value *3) This calculation is applied for without electrode mesh system 5-4 SAFETY CHARACTERISTICS OF NETWORK DESIGN Sf Ig Current division factor Maximum grid current Max allowable value Etouch50 Estep50 Rg GPR 313 (V) 1.5-3 OUTPUT DATA Rg GPR Em Es Estep50 Etouch50 Notes: *1) Most conservative value is considered. This means that the actual values shall be lower than the calculated ones.052 (V) less than 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 .in j/cm3/deg C 7 . 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.80. ρr = the resistivity of the ground conductor at reference temperature T. Section 11 (Eq-37). as per IEEE Std.in μΩ/cm 3 Ko = 1/α0. Material for the earth conductor is annealed copper stranded wire. Following formula is used for to calculate the earthing conductor size. followings are considered: Maximum fault current.Ta ö Inç1 + ÷ Ko + Ta ø è (mm ) 2 I Tc A = rms current in KA = time of current flow in s = conductor cross section in min 2 Tm = max. Table 1.or (1/αr)-Tr TCAP = thermal capacity factor from Table 1.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. 72 = 234 = 3. 300 mm2 main earthing conductor is acceptable.72 ´ 10 4 3.00393 = 1. Table1 where: TCAP = 3. Table1 Design requirement IEEE 80-2000 Section 11. Table1 IEEE 80-2000 Section 11.00393 = 1.42 A = 40 ´ 3 ´ 0. 1-2 For earthing ring I Tm Ta αr ρr Ko Tc = 31. Table1 IEEE 80-2000 Section 11. Table1 IEEE 80-2000 Section 11. Table1 TCAP = 3.5 ´ 3 ´ 0.42 æ 1083 . Table1 IEEE 80-2000 Section 11.46 ö Inç1 + ÷ 242 + 46 ø è =248 (mm2) According to the above calculation. 240 mm2 earthing ring conductor is acceptable.5 = 1083 = 46 = 0.00393 ´ 1.0 kA deg C deg C Design requirement IEEE 80-2000 Section 11.00393 ´ 1.42 æ 1083 .72 ´ 10 4 3. Table1 Design requirement IEEE 80-2000 Section 11. 8 .0 kA deg C deg C Design requirement IEEE 80-2000 Section 11.42 A = 31.46 ö Inç1 + ÷ 242 + 46 ø è =196 (mm2) According to the above calculation. Table1 Design requirement IEEE 80-2000 Section 11.72 = 234 = 3.1-1 For main mesh where: I Tm Ta αr ρr Ko Tc = 40 = 1083 = 46 = 0. Table1 Design requirement IEEE 80-2000 Section 11. 0 x 40 = where Sf Ig If IG Df fault current division factor rms symmetrical grid current rms value of symmetrical ground fault current maximum grid current decrement factor for the entire duration of fault tf : : : : : 1.120 1.5 (ohm) (ohm-m) (m2) (m) (m) Rg= 0.Step2: Calculation of earthing resistance As per IEEE80-2000 section14 (eq52) é 1 1 1 æ öù Rg =ρ ç1 + ÷ú ê + ç ÷ 20 A è 1 + h × 20 / A øû ë LT where Rg ρ A LT h ground resistance soil resistivity area occupied by the ground grid total buried length of conductors depth of the grid : : : : : -15 54.400 4.032 = 1280 (V) 9 .0 (kA) (kA) (kA) 40 (kA) Step4: GPR GPR = I G × R g GPR = 40000 x 0.0 40 40 40 1.032 (Ohm) Step3: Maximum grid current IG I G = D f × If = 1. 53 (m) (m) (m) (m) (pcs) (2 × n) : : : : : : : K h = 1 + h / ho 1m (reference depth of grid) Depth of burial Diameter of conductor(m) Distance of conductor(m) Effective number of parallel conductor in a given grid n = n a × nb × nc × n d 2 × LC .h ö + K ii ln 8 ù ÷ ln ç + ê ç 8 Dd1 4d 1 ÷ K h p (2n . nb = LP na = Ki LP 4× A .148 x n Km = 1.5811 1.5 0.9066 x 40000 / 4120 where LM LC LR The effective buried length .644 + 0.0 1. nc = n d = 1 : 1.9066 Ki = 0. LM = LC + LR The total length of the conductor in the horizontal grid The total length of all ground rods : : : -4120 0 (m) (m) (m) 10 .02 30 8.1) ú û ê è 16hD ø ë where: Km Kii Kh ho h d1 D n Spacing factor for mesh voltage Corrective factor K ii = 1 : 2/n --1.1215 5-2 ρ× Km × Ki × I G Em = LM = 311 (V) Mesh Voltage (Em) = 15 x 1.1215 x 1.Step5: Mesh voltage 5-1 The geometrical factor (Km) Km = 1 2p é æ D2 (D + 2h)2 . 052 (V) 7-2 Actual step voltage E S = K S ´ K i ´ r ´ I G / LS = 0.85 ´ LR 7-3 Decision E S E step50 Actual step voltage is well below the tolerable step voltage. 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 ) 0.75 ´ LC + 0.116 tS = (1000+6x0.127x 1.Step 6: Check of touch voltage 6-1 The maximum driving voltage for touch voltage is : Etouch so = (1000 + 1.116 / SQRT(3) = 313 (V) where: æ r ö 0.09 × ç1 ÷ ç r ÷ è S ø CS = 1 2 × hS + 0.116 tS = (1000+1.5C s × r s ) 0.817 x 3000)x 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.116/sqrt(3) = 1. So it is ACCEPTABLE 11 .9066x 15x 40000/ 3090 = 47 (V) where: LS = 0.817x3000)x 0.5x 0. 138 0.46 0.1 0.65 0.082 0.958 0.28 0.05 0.09 1.15 1.98 0. Y=1045.66 0.04 0.105 0.5 2 3 4 A 5 6 7 8 9 10 15 20 25 30 1 1.000 ρ（Ωｍ） 1 5 8 13 20 20 8 9 9 12 6 5 3 2 1 7 10 12 16 15 15 17 17 11 11 9 10 10 6 6 B A Axis Point PPE2 Location a (meter) 1 1.18 0.015 0.355 0. .195 0.5 2 3 4 5 6 7 8 9 10 15 20 25 30 is is at ELECT BLDG X=1841. ohm-m.98 0.088 0.62 0.000 ρ（Ωｍ） 13 18 41 18 17 14 13 29 12 7 6 8 8 8 3 11 10 12 17 26 17 17 17 18 18 9 10 12 10 4 Average of the top layer resistivity (1 to 2 meters depth) Average of the lower layer resistivity Please refer to Test report of soil investigation document.095 0.132 0.5 2 3 4 5 6 7 8 9 10 15 20 25 30 1 1.1685 0.20 0.095 0.88 1.54 0.ANNEX-B SOIL RESISTIVITY DATA Point Axis PPE1 Location a (meter) 1 1.05 0.739 1.000 R (Ω) 0.037 0.15 0. 12 Note) Measurement test of soil resistivity has be carried out in April 2003 and reported by TSB.3 11.445 0.21 0.9 ohm-m.342 0.21 0.49 0.9 3.022 12.80 0.22 0.655 0.105 0.025 0.528 0.065 0.38 0.236 0.0055 1.0625 0.500 R (Ω) 2.0332 Y=1100.0145 1.5 2 3 4 B 5 6 7 8 9 10 15 20 25 30 at GT AREA X=2100.105 0.32 0.437 0.385 0.58 0.101 0.71 0.86 0.