57352002 earthing calculation

7/30/2019 57352002 Earthing Calculation

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Earthing Calculation

ROW1 Ohm meter 39.29

1.1 Soil resistivity(taken for calculation) ROW Ohm meter

1.2 Soil resistivity due to concrete ROWS Ohm meter 500

1.3 Fault current(for conductor size design) I KA 50.00

1.4 Fault duration for sizing TF1 sec 1.00

1.5 Fault duration for step and touch potentials TF2 sec 0.70

1.6 Depth of burial of grid conductors h metres 0.80

1.7 Thickness of concrete hs metres 0.20

1.8 N umber of ground rod/pipe electrodes,3m long N nos 150

1.9 Area of the earth mat AG sq.metres 640,000

1.10 Effective earth fault current I kA 22.245

(Refer enclosed annexure for this calculation)

2.1 Factor K0 (1/ALPHAR)-TR

216.412.2 TCAP is defined by

TCAP = 4.184*SW*SH

3.75

2.3 Minimum area of cross section A = I*(SQRT(X1/X2))

where

2.4 X1 = (TF1*ALPHAR*ROWE*10000)/TCAP

169.24

2.5 X2 = LN(1+(TM-TA)/(K0-TA))

1.31

2.6 Minimum area of cross section A sq.mm 568.432.7 Diameter of conductor mm 26.91

2.8 Temperature co-efficient of material ALPHAR 0.00423

2.9 R esistivity of earthing material ROWE micro-ohm/ 15.00

2.10 Specific heat of material SH cal/gram/C 0.114

2.11 Density of material SW gram/cc 7.86

2.12 Reference temperature of material constant TR C 20

2.13 Max.allowable temperature for welded joints TM C 500

2.14 Ambient temperature TA C 50

2.15

Average rate of corrosion is 0.12 mm per annum is considered for a period of 40 years.

Total Corrosion expected =0.12*40 4.8 mm

Calculations are based on IEEE Vol 80,1986 version.

North Chennai Thermal Power ProjectStage II(2x525 MW)


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CS = 1-a*((1-s)/u) where

a=0.106 metre;s=(ROW/ROW S);U=(2hs+a)

s = 0.1000

u = 0.506

a = 0.11

CS = 0.811

3.5 Permissible Estep volts

3.6 Permissible Etouch volts

4

4.1 Length of the earth mat L metres 800.00

4.2 Breadth of the earth mat B metres 800.00

4.3 Assumed spacing for the conductors D metres

4.4 Total no of conductors parallel to length N1 nos (B/D)+1

17

4.5 Total no of conductors arallel to breadth N2 nos L/D)+117

4.6 Total quantity of conductors laid LC metres (N1*L)+(N2*B)

27,200

4.7

Interconnections to the grid(30% of calculated

quantity) LINT metres 8,160

4.7 Total ground rods length LR metres 450

4.8 Effective grid conductor length L metres

5.1 Emesh = (ROW*KM*KI*I *1000)/L5.2 E step = (ROW*KS*KI*I *1000)/L

5.3 KM = (1/(2*3.14))*(LN(A+B-C)+D*LN(E))

5.4 where A = D^2/(16*h*d)

4,882.813

5.5 B = (D+2*h)^2/(8*D*d)

166.4100

5.6 C = (h/4*d)

5.000

5.7 D = (Kii/Kh)

0.745

5.8 E = 8/(3.14*(2n-1))

= 0.077


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5.15 KI,the irregularity factor = 0.656+0.172*n

3.580

5.16 KS = (1/3.14)*(A+B+C(1-E))

WHERE

5.17 A = 1/ 2*h)

0.625

5.18 B = (1/(D+h))

0.0205.19 C = 1/D

0.020

5.20 E = 0.5^(n-2)

0.0000305

5.21 KS = 0.2117

5.22 Hence E step KS*KI*ROW*I *1000/L

Volts

Volts

To achieve the above conditions,the following condition has to be satisfied.

6.1 L = (KM*KI*ROW*I *1000)/Permissible Emesh

metres

7.1 RG ohm ROW*(F+G*(1+(1/J)))

where

7.2 F = (1/L)

0.00003

7.3 G = 1/(SQRT (20*A))

0.000287.4 J = 1+(h*(SQRT (20/A)))

1.004

7.5 Hence RG = ohm

8

Total grid potential rise IR Volts I*RG

volts

Hence from the above calculation the conductors

provided meet the Step and touch potential criter ia

and also the other re uirement.

The mat will be made to suit the above requirement.

As shown in the enclosed diagram.


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1 Parameters for design purposes:1.1 Soil resistivity ROW Ohm meter 45.0


1.3 Fault current I KA 50.00





1.8 Number of ground rod/pipe electrodes,3m long N nos 10

1.9 Area of the earth mat AG sq.metres 10,0001.10 Effective earth fault current Ia kA 23.40

2 Evaluation of conductor sizing


216.41

2.2 TCAP is defined by

TCAP = 4.184*SW*SH

3.75


where

2.4 X1 = (TF1*ALPHAR*ROWE*100

169.24

2.5 X2 = LN(1+(TM-TA)/(K0-TA))

1.31

2.6 Minimum area of cross section A sq.mm 568.43

2.7 Diameter of conductor mm 26.91


2.9 Resistivity of earthing material ROWE micro-ohm/ 15.00






2.15 Corrosion allowanceAverage rate of corrosion of steel is 61 mils for the f irst 12 years and 50% of that value

30.5 mils for the next 12 years.After this period,it is assumed that no corrosion takes place.

(Reference IEEE Transactions of PAS-Volume 98.


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-0.835

CS =1 for no gravel/ concrete.

ALTERNATIVELY,


a=0.106 metre;s=(ROW/ROWS);U=(2hs+a)

s = 0.0900

u = 0.506

a = 0.11

CS = 0.809

Choose a lower value of CS from the above.Hence CS=0.82

3.5 Permissible Estep volts 479.723.6 Permissible Etouch volts 223.91

4 Preliminary layout



4.3 Assumed spacing for the conductors D metres 10.00


11

4.5 Total no of conductors parallel to breadth N2 nos (L/D)+1

11


2,200

4.7 Interconnections to the grid LINT metres 660

4.7 Total ground rods length LR metres 30.00

4.8 Effective grid conductor length L metres 2,895

5 Estimation of actual mesh and step voltages

5.1 Emesh = (ROW*KM*KI*I*1000)/L

5.2 E step = (ROW*KS*KI*I*1000)/L

5.3 KM = (1/(2*3.14))*(LN(A+B-C)+D*

5.4 where A = D^2/(16*h*d)

195.313

5.5 B = (D+2*h)^2/(8*D*d)

42.05005.6 C = (h/4*d)

5.000

5.7 D = (Kii/Kh)


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5.12 Number of parallel conductors n = SQRT(N1*N2)

11

5.13 KI,the irregularity factor = 0.656+0.172*n2.548

5.14 Hence E mesh = KM*KI*ROW*I*1000/L

1,222.491 volts

PERMISSIBLE VALUE 223.91


2.548

5.16 KS = (1/3.14)*(A+B+C(1-E))

WHERE

5.17 A = 1/(2*h)0.625

5.18 B = (1/(D+h))

0.093

5.19 C = 1/D

0.100

5.20 E = 0.5^(n-2)

0.0019531

5.21 KS = 0.2603

5.22 Hence E step KS*KI*ROW*I*1000/L

515.599


6 Minimum conductor length requirement


6.1 L = (KM*KI*ROW*I*1000)/Permi

7,395.77 metres

7 Evaluation of grid resistance

7.1 RG ohm ROW*(F+G*(1+(1/J)))

where

7.2 F = (1/L)

0.00035

7.3 G = 1/(SQRT (20*A))

0.00224

7.4 J = 1+(h*(SQRT (20/A)))

1.0367.5 Hence RG = 0.213 ohm

8 Grid potential rise


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0)/TCAP


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LN(E))


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issible Emesh


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1 Parameters for design purposes:

1.1 Soil resistivity ROW Ohm meter 73.0











216.41


TCAP = 4.184*SW*SH

3.75

2.3 Minimum area of cross section A = I*(SQRT(X1/X2))where

2.4 X1 = (TF1*ALPHAR*ROWE*100

169.24

2.5 X2 = LN(1+(TM-TA)/(K0-TA))

1.31










2.15 Corrosion allowanceAverage rate of corrosion of steel is 61 mils for the f irst 12 years and 50% of that value




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-0.745


ALTERNATIVELY,


a=0.106 metre;s=(ROW/ROWS);U=(2hs+a)

s = 0.1460

u = 0.506

a = 0.11

CS = 0.821


3.5 Permissible Estep volts 479.723.6 Permissible Etouch volts 223.91

4 Preliminary layout





20



19,948

4.7 Interconnections to the grid LINT metres 5,984

4.7 Total ground rods length LR metres 30.00





5.3 KM = (1/(2*3.14))*(LN(A+B-C)+D*

5.4 where A = D^2/(16*h*d)

861.328

5.5 B = (D+2*h)^2/(8*D*d)

76.00605.6 C = (h/4*d)

5.000

5.7 D = (Kii/Kh)


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22


4.492

5.14 Hence E mesh = KM*KI*ROW*I*1000/L

474.659 volts



4.492

5.16 KS = (1/3.14)*(A+B+C(1-E))

WHERE

5.17 A = 1/(2*h)0.625

5.18 B = (1/(D+h))

0.046

5.19 C = 1/D

0.048

5.20 E = 0.5^(n-2)

0.0000008

5.21 KS = 0.2288

5.22 Hence E step KS*KI*ROW*I*1000/L144.479




6.1 L = (KM*KI*ROW*I*1000)/Permi

25,760.69 metres


7.1 RG ohm ROW*(F+G*(1+(1/J)))

where

7.2 F = (1/L)

0.00004

7.3 G = 1/(SQRT (20*A))

0.00050

7.4 J = 1+(h*(SQRT (20/A)))

1.0087.5 Hence RG = 0.076 ohm



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0)/TCAP


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LN(E))


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issible Emesh


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ABB-PE EARTHING DESIGN FOR NEYVELI IN POWER BLOCK AREA 121757677.xls.ms_office


1 Parameters for design purposes:

1.1 Soil resistivity ROW Ohm meter 73











216.41


TCAP = 4.184*SW*SH

3.75


where2.4 X1 = (TF1*ALPHAR*ROWE*10000)/TCAP

169.24

2.5 X2 = LN(1+(TM-TA)/(K0-TA))

1.31





2.10 Specific heat of material SH cal/gram/C 0.1142.11 Density of material SW gram/cc 7.86




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2.15 Corrosion allowanceAverage rate of corrosion of steel is 61 mils fo r the first 12 years and 50% of that value



Total corrosion=(61+30.5)2 =183 mils ie 4.64mm.

2.16 Diameter of the conductor after corrosion= 31.55 mm.

2.17 Diameter of the conductor chosen d 0.04 M

3 Permissible step and touch voltages

3.1 E step = (1000+(6*CS(hs,K)*ROWS))*0.116/(SQRT TF2)3.2 E touch = (1000+(1.5*CS(hs,K)*ROWS))*0.116/(SQRT TF2)

3.3 CS is a reduction factor depending upon the depth of gravel /concrete and reflection factor K.

CS is obtained from Figure 8 of IEEE. = 0.82

3.4 K = (ROW-ROWS)/(ROW+ROWS)

-0.745


ALTERNATIVELY,


a=0.106 metre;s=(ROW/ROWS);U=(2hs+a)s = 0.1460

u = 0.506

a = 0.11

CS = 0.821


3.5 Permissible Estep volts 479.72

3.6 Permissible Etouch volts 223.91

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4 Preliminary layout4.1 Length of the earth mat L metres 400.00




24


32


19,162

4.7 Interconnections to the grid LINT metres 5,7484.7 Total ground rods length LR metres 150.00





5.3 KM = (1/(2*3.14))*(LN(A+B-C)+D*LN(E))

5.4 where A = D^2/(16*h*d)330.078

5.5 B = (D+2*h)^2/(8*D*d)

51.2404

5.6 C = (h/4*d)

5.000

5.7 D = (Kii/Kh)

0.745

5.8 E = 8/(3.14*(2n-1))

= 0.047

5.9 KM = (1/(2*3.14))*(LN(A+B-C)+D*LN(E))

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= 0.581

5.10 Kii=1 for grids with ground rods along the perimeterKii=1 for grids with ground rods at the grid corners

Kii=1 for grids with ground rods along the perimeter and throughout the grid area

5.11 Kh = SQRT(1+h/ha) where ha=1 metre.

= 1.342


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5.413

5.14 Hence E mesh = KM*KI*ROW *I*1000/L457.814 volts



5.413

5.16 KS = (1/3.14)*(A+B+C(1-E))

WHERE

5.17 A = 1/(2*h)

0.625

5.18 B = (1/(D+h))

0.0725.19 C = 1/D

0.077

5.20 E = 0.5^(n-2)

0.0000000

5.21 KS = 0.2466

5.22 Hence E step KS*KI*ROW*I*1000/L

194.262


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6.1 L = (KM*KI*ROW*Ia*1000)/Permissible Emesh

24,000.74 metres


7.1 RG ohm ROW*(F+G*(1+(1/J)))

where

7.2 F = (1/L)

0.00004

7.3 G = 1/(SQRT (20*A))0.00065

7.4 J = 1+(h*(SQRT (20/A)))

1.010

7.5 Hence RG = 0.097 ohm


Total grid potential rise IR Volts I*RG

4,833.56 volts

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57352002 earthing calculation

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