Alnahdah Earthing

LARSEN & TOUBRO LIMITEDECC Division - EDRC (Electrical)

PROJECT: Relocation of Riyam Substation and Transformer REF NO: PAGE 02 OF 06Repair Shop. PREPARED CHECKED APPROVED DATE

TITLE: EARTHING DESIGN CALCULATION FOR SSJ AKS DM 3-03-2016

THIS DESIGN IS GENERALLY BASED ON IEEE 80 - 2000AREA OF CROSS SECTION

S = I x SQRT(t) / k

S = AREA OF CONDUCTOR IN Sq.mm

I = EARTH FAULT CURRENT IN AMPS

t = EARTH FAULT CLEARING TIME IN secs.

k = SQRT(( Qc x (B+20)/delta20) x ln ( 1+ (Qf-Qi)/(B+Qi)))

I = 25000 amps

t = 3 sec

Qc = 0.00345 J / °C mm3 { Data for copper conductor }

B = 234.5 °C

delta20 = 0.000020 Ohm.mm

Qi = 40 °C

Qf = 700 °C

k = SQRT( (0.00345x (234.5 + 20) /0.00002) x ln ( 1+ ((700-40 ) / (235 +40) ) )= 231.909

S = 25000 x SQRT (3.0) / 231.909= 186.72 Sq.mm

Corrosion allowance considered for the conductor in percentage = 10 %

Minimum area of cross-section required = ### Sq.mmHence conductor size selected is, 300 Sq.mm (Which is the minimum size specified in the specification)

CONDUCTOR SIZE CHOSEN IS 50 x 6 Copper Flat

S/S - Riyam

Qc = Volumetric Heat capacity of conductor ( J / oC mm3 )

B = Reciprocal of Temp.Coefft. of Resistivity ( oC )

delta20 = Electrical Resistivity of conductor at 20 oC ( Ohm.mm )

Qi = Initial Temperature of Conductor ( oC )

Qf = Final Temperature of Conductor ( oC )

1 10.01.07 FOR APPROVAL AKS AKS

0 FOR APPROVAL AKS AKS

No. DATE REMARKS CHKD APPD

REVISION

PROJECT : MADINAT AL NAHDAH PRIMARY S/S 33/11.5kV SIGN DATE

DSND SSJ 10.01.07

PACKAGE : DRWN - -

CHKD AKS 10.01.07

TITLE : SCALE APPD AKS 10.01.07

EARTHING DESIGN CALCULATION - MAIN GRID DRG.No. REV.

CODE1

LARSEN & TOUBRO LIMITEDECC - Division EDRC

LARSEN & TOUBRO LIMITED

ECC Division - EDRC (Electrical)

PROJECT: MADINAT AL NAHDAH PRIMARY S/S 33/11.5kV REF NO: PAGE 01 OF 04PREPARED CHECKED APPROVED DATE

TITLE: EARTHING DESIGN CALCULATION - MAIN GRID SSJ AKS AKS 3-03-2016

CALCULATIONS ARE BASED ON IEEE 80 - 2000.DESIGN DATASystem Voltage = 33 kV

System Grounding = SOLID

Soil Resistivity p = 52.1 Ohm.m

Top Layer resistivity ps = 5000 Ohm.m

Max. Earth Fault Current (I) = 2000 AMPS

Conductor Size = 50 x 6 Copper Flat

Equivalent diameter d = 0.0195 m

Length of Substation L = 34.93 m

Breadth of Substation B = 34.93 m

No: of grids in X direction = 2

No: of grids in Y direction = 2

Equivalent Number of grids N=na*nb*nc*nd = 2

factor na = 2*Lc/Lp na = 2.000 factor nb= Sqrt(Lp/4/sqrt(A)) nb = 1.000 factor nc = (Lx*Ly/A)*e(0.7*A/Lx/Ly) nc = 1.000 factor nd = Dm / sqrt(Lx^2+Ly^2) nd = 1.000

Spacing of conductors D = 29 m

Total length of conductors Lc = 140 m

Peripheral length of the grid in mtr Lp = 139.72 m

Area of Grid Ag = ### sq.m

Depth of burial h = 0.6 m (As per specification)

Depth of Top Layer hs = 0.1 m

Total No of electrodes m = 14 Nos

Length of electrode Lr = 3 m

= 42 m

Maximum length of Lx = 34.93 mgrid conductor in X-Direction

Maximum length of Ly = 34.93 mgrid conductor in Y-Direction

Dm is the max distance bet any two points in = 49.40 i.e. Sqrt (34.93^2+34.93^2)the grid in mtr

Diameter of electrodes d1 = 15 mm

Duration of Fault Current ts = 1 sec

Total length of electrodes LR

LARSEN & TOUBRO LIMITED

ECC Division - EDRC (Electrical)

PROJECT: MADINAT AL NAHDAH PRIMARY S/S 33/11.5kV REF NO: LTO/193/SSSRM/0005 PAGE 01 OF 04PREPARED CHECKED APPROVED DATE


Tolerable Touch Potential (BASED ON IEEE 80 - 2000 CHAPTER 8)

Etouch = ( 1000 + 1.5 * Cs * ps ) * 0.116 / SQRT(ts) For body weight of 50 kg

Cs = 1 - a * { ( 1- p/ps) / ( 2 * hs + a) } Refer Equation-27 of page 23 of IEEE 80 - 2000a = 0.09 m

1 - 0.090*{( 1 - 52 / 5000 ) / ( 2 * 0.10 + 0.090 ) }Cs = 0.6929

Etouch = (1000 + 1.5 * 0.6929 * 5000 ) * 0.116 / SQRT( 1.0 )= 718.81 Volts

Tolerable Step Potential (BASED ON IEEE 80 - 2000 CHAPTER 8)

Estep = ( 1000 + 6.0 *Cs * ps ) * 0.116 / SQRT(ts) For body weight of 50 kgEstep = (1000 + 6.0 * 0.6929 * 5000 ) * 0.116 / SQRT( 1.0 ) = 2527.25 Volts

Mesh Potential Attainable (BASED ON IEEE 80 - 2000 CHAPTER 16)Refer Equation-91 of page 94 of IEEE 80 - 2000

Emesh = ( p * Km * Ki * I ) / (Lc + Lr)

Km =

Kii = 1.00 for grids with ground rods in perimeter

Kh = SQRT ( 1+ h/ho)ho = 1.00 m ( reference depth of grid)Kh = SQRT( 1 + 0.600 / 1.0 ) = 1.2649

Km = 1/ (2 * 22/7) * { ln [ 29.0^2/ (16 * 0.600 * 0.02 ) + (29.0 + 2 * 0.600 ) ^2 /( 8 * 29.0 * 0.02) - 0.600/ ( 4 * 0.02) ] + 1.00 / 1.2649 * ln [ 8 / (22/7 * (2 * 2.00 - 1 ) ) ] }

= 1.3237Ki = 0.644 + 0.148 * n = 0.644 + 0.148 *2

= 0.9400Emesh = 26*0.4421*2.5680*22500 / (800+56)

= 713.49 Volts

Step Potential Attainable (BASED ON IEEE 80 - 2000 CHAPTER 16)

Estep = ( p * Ks * Ki * I ) / ( 0.75*Lc + 0.85*m*Lr )

Ks =

n = 2 (Higher of the no.of grids in X & Y direction)Ks = ( 1 / 22/7 ) * { 1 / (2 * 0.600 ) + 1 / ( 29.0 + 0.600 ) + 1 / 29.0 * ( 1 - 0.5^(2 - 2 ) }

= 0.2759 Estep = ( 52 * 0.2759 * 0.9400 * 2000 ) / ( 0.75 * 139.7 + 0.85 * 14 *3 )

= 192.35 Volts

1/ (2 * ) * { ln[ D^2 /(16 * h * d)+ (D + 2h ) ^2 / (8* D * d) - h / (4 * d) ]

+ Kii / Kh ln[8 / ( * (2 * n-1) ) ] }

1 / * { 1 / (2 * h) + 1 / (D + h) + 1 / D * (1- 0.5^(n-2) ) }


PROJECT: MADINAT ALMADINAT AL NAHDAH PRIMARY S/S 33/11.5kV REF NO: LTO/193/SSSRM/0005 PAGE 01 OF 04PREPARED CHECKED APPROVED DATE


Comparison of Tolerable Etouch & Estep and Attainable Emesh & Estep

Tolerable Etouch = 718.81 Volts

Tolerable Estep = 2527.25 Volts

Attainable Emesh = 713.49 Volts

Attainable Estep = 192.35 Volts

Since Attainable Emesh is less than Tolerable Etouch andAttainable Estep is less than Tolerable Estep, the design is safe.

The minimum conductor to be buried in ground for meeting the Touch and Step potential can be calculated as follows:

Emesh(tolerable) = ( p * Km * Ki * Ig ) / ( Lc + Lr )

( Lc + Lr ) = ( p * Km * Ki * Ig ) / Emesh(tolerable)

= (52.1 * 1.3237 * 0.9400 * 2000.000 ) / 718.813= 180.37 Mtr

Estep(tolerable) = ( p * Ks * Ki * Ig ) / ( 0.75*Lc + 0.85*Lr )

(0.75 * Lc+0.85* Lr ) ( p * Ks * Ki * Ig ) / Estep(tolerable)

= (52.1 * 0.2759 * 0.9400 * 2000.000 ) / 2527.254

= 10.69 Mtr**

Actual conductor buried is 281m which greater than the minimum required length Hence the design is safe


PROJECT: MADINAT AL NAHDAH PRIMARY S/S 33/11.5kV REF NO: LTO/193/SSSRM/0005 PAGE 01 OF 04PREPARED CHECKED APPROVED DATE


CACULATION OF GROUNDING RESISTANCE

BASED ON IEEE 80-2000 CHAPTER 14

RESISTANCE OF GROUND RODS

Re =

K1 = 1.37 Refer Fig 25A page 67 IEEE 80 - 2000Re = 52 / (2 * 14 * 22/7 * 3 ) * [ ln (8 * 3 / 15 / 1000 )) - 1 + 2 * 1.37 *

(3 / sqrt(1220)) * (sqrt (14)-1)^2 ] = 2.6983 Ohms

RESISTANCE OF GROUND GRIDRs =

K1 = 1.37

K2 = 5.7 Refer Fig 25B page 67 IEEE 80 - 2000h' = SQRT(d * h)

= SQRT(0.02 * 0.60) = 0.1083 Rs = ( 52 / (22/7 * 139.72)) * [ ln ( 2 * 139.72 / 0.1083 ) + 1.37 *

( 139.72 / sqrt (1220.10 )) - 5.7 ] = 0.9119 Ohms

MUTUAL RESISTANCE BETWEEN GROUND GRID AND GROUND RODSRse =

K1 = 1.37

K2 = 5.7Rse = 52 / (22/7 * 139.72) * [ln (2 * 139.72 / 3 ) + 1.37 *

( 139.72 / sqrt (1220.10 )) - 5.7 + 1] = 0.63644 Ohms

COMBINED RESISTANCE OF GROUND GRID AND GROUND RODS

Rg = (Re * Rs - Rse^2 ) / ( Re + Rs - 2 * Rse)Rg = ( 2.6983 * 0.9119 - 0.6364^2 ) / ( ( 2.6983 * 0.9119 - 2 * 0.6364 )

= 0.8794 Ohms

CONCLUSIONHence the design adopted meets the specification requirement with respect to i) STEP & TOUCH POTENTIALii) COMBINED RESISTANCE OF GRID & GROUND RODS < 1.0 OHM

NOTEThe conductors shall be uniformly distributed in substation area leaving the space for Building.

Earth mat conductor as per above calculation shall be laid in s/s around the building adopting the calculated

spacing.

p / (2 * m * * l ) * [ln (8 * l / d) - 1 + 2 * K1 * l / SQRT(A) * (SQRT(m)-1)^2 ]

p / ( * Lc) * [ ln (2 * Lc / h') + K1 *( Lc / SQRT(A)) - K2 ]

p /( * Lc) * [ln (2 * Lc / l) + K1 * (Lc / SQRT(A)) - K2 + 1]


PROJECT: MADINAT AL NAHDAH PRIMARY S/S 33/11.5kV REF NO:PREPARED CHECKED APPROVED DATE

TITLE: SSJ AKS AKS 3-03-2016S/S -CONDUCTOR SIZING

THIS DESIGN IS GENERALLY BASED ON IEEE 80 - 2000AREA OF CROSS SECTION

S = I x SQRT(t) / k

S = AREA OF CONDUCTOR IN Sq.mm

I = EARTH FAULT CURRENT IN AMPS

t = EARTH FAULT CLEARING TIME IN secs.

k = SQRT(( Qc x (B+20)/delta20) x ln ( 1+ (Qf-Qi)/(B+Qi)))

I = 25000 amps

t = 3 sec

Qc = 0.00345 J / °C mm3 { Data for copper conductor }

B = 234.5 °C

delta20 = 0.000020 Ohm.mm

Qi = 40 °C

Qf = 700 °C

k = SQRT( (0.00345x (234.5 + 20) /0.00002) x ln ( 1+ ((700-40 ) / (235 +40) ) )= 231.909

S = 25000 x SQRT (3.0) / 231.909= 186.72 Sq.mm

Corrosion allowance considered for the conductor in percentage = 20 %

Minimum area of cross-section required = ### Sq.mmHence conductor size selected is, 300 Sq.mm (Which is the minimum size specified in the specification)

CONDUCTOR SIZE CHOSEN IS 50 x 6 Copper Flat

Qc = Volumetric Heat capacity of conductor ( J / oC mm3 )

B = Reciprocal of Temp.Coefft. of Resistivity ( oC )

delta20 = Electrical Resistivity of conductor at 20 oC ( Ohm.mm )

Qi = Initial Temperature of Conductor ( oC )

Qf = Final Temperature of Conductor ( oC )

307124533.xls Page No. 8 of 10

LARSEN & TOUBRO LIMITEDECC DIVISION-EDRC(ELECTRICAL)

CONSTRUCTION GROUP

PROJECT: Construction of 2x20 MVA, 33/11kV ALNAHDAH Primary S/S & 33kV LineCLIENT: Muscat Electricity Distribution CompanyCONSULTANT: Energoprojekt - Entel LLC

TITLE: PREPARED CHECKED APPROVED DATE

DOCUMENT NO: SSJ AKS AKS 22.12.06

Direction

East 68.90 N 46.83

. E 68.90

North 46.83 S ###

. W 42.31

West 42.31

.

South 105.98

.

Area of the polygon = 8497Radius of eqv. Circle 52.01

52.01 ohm-m

Remarks:

2. Calculations are based on IS:3043

3. Formula used is

where s - distance b/w spikesd - depth of the spiker - earth resistance

Avg. Resistivity (Ohm-

m)

Avg. Soil Resistivity =

The lowest resistivity outcome in all the samples is 35.18 ohm-meter in the West direction. Hence corrosion allowance of 15 % to be considered as Per CBAP guidelines.

1. Polygon drawn for the average Resistivity values available in N,E,W,S directions. Resultant Resistivity is calculated as the equivalent radius of the polygon area.

Re sistivity={2∗Π∗s∗r if ( d<s /20)

4∗Π∗s∗r

1+{(2∗s

√( s∗s )+(4∗d∗d ))−(s √(s∗s )+(d∗d ))} if (d≥s /20 )

0.00

100.00

200.00

46.83

68.90

105.98

42.31

307124533.xls Page No. 9 of 10


CONSTRUCTION GROUP



DOCUMENT NO: SSJ AKS AKS 22.12.06

0.00

100.00

200.00

46.83

68.90

105.98

42.31

307124533.xls Page No. 10 of 10


CONSTRUCTION GROUP



DOCUMENT NO. SSJ AKS AKS 22.12.06

Sl No. Direction Remarks

2 250 2.2 55.29 68.9 East5 250 0.97 60.95

10 250 0.72 90.48

2 250 2.14 53.78 46.83 North5 250 0.64 40.21

10 250 0.37 46.49

2 250 2 50.27 42.31 West5 250 0.66 41.47

10 250 0.28 35.18

2 250 3.7 92.99 105.98 South5 250 1.64 103.04

10 250 0.97 121.89

Distance between spikes

Depth of Spike (m)

Earth resistance

()

Earth resistivity

(-m)

Average Value (-m)

Alnahdah Earthing

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