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Page 1: Earthing Calculations

"THE GATE" DOHA-QATAR ELECTROMECHANICAL WORKSSCHEMATIC DESIGN REPORT

EARTHING RESISTANCE ANALYSIS CALCULATIONS BASED ON BS 7430 : 1991

A.SELECTION OF AN EARTHING CONDUCTOR AND CONNECTION TO AN ELECTRODE

1. AVERAGE FAULT CURRENT, KA 302. FAULT CURRENT DURATION 1 or 3 SECONDS ( 1 or 3 ) 13. EARTH. CONDUCT. MATERIAL, COPPER or ALUM. or STEEL ( C or A or S ) C4. INITIAL TEMPERATURE, DEG.C 70 or5. FINAL TEMPERATURE, DEG.C 250

199.70

240FINAL TEMPERATURE, DEG.C

B.VERTICAL RODS (150,200,250,450,500 for copper)

(150,200,300,500 for aluminum)

1. RESISTIVITY OF THE SOIL, OHM.METER 1002. LENGTH OF ELECTRODE, METER 63. DIAMETER OF ELECTRODE , METER 0.01905 NO. OF ELECTRODES :4. ARRANGMENT OF ELECTRODES, LINE or SQUARE or RECTANGLE or TRIANGLE ( L or S or R or T) R (2,3,4,5,6,7,8,9,10 for L)

5. TOTAL NO. OF ELECTRODES IN LINE or IN SQUARE or IN RECTANGLE or IN TRIANGLE 36 (4, 8,12.16,20, 24, 28, 32, 36, 44, 52, 60, 68, 76 for S or R)

6. DISTANCE BETWEEN ADJACENT RODS, METER 6 (length / width <=2 for rectangle R)

7. TOTAL EARTHING RODS RESISTANCE, OHMS 3.91 (3 for triangle T)

C. HORIZONTAL ROUND ELECTRODES

1. LENGTH OF HORIZONTAL CONDUCTOR, METER 1602. DEPTH OF HORIZONTAL CONDUCTOR, METER 0.73. DIAMETER OF HORIZONTAL CONDUCTOR, METER 0.0199

1* MEANS THAT :1 = SINGLE LENGTH ( * )

2 =

3 =

4 = Minimum Maximum

5. SPACE BETWEEN STRAIGHT HORIZONTAL CONDUCTORS IN //, METER 48 3.2 48 Select space value bet. Max

6. NO. OF ONLY SINGLE HORIZONTAL CONDUCTOR IN //, one or two or three or four ( * ) 27. EARTHING RESISTANCE OF HORIZONTAL CONDUCTORS, OHMS 0.84

( * ) 0.02 <= ratio of spacing to length <= 0.3 shall be considered and applied only for conductors in //

D. CURRENT DENSITY

6. EARTHING CONDUCTOR CROSS SECTIONAL AREA, MM2

7. NEXT HIGHER STAND. EARTHING CONDUCTOR CROSS SEC. AREA, MM2

4. HORIZONTAL CONDUCTOR ARRANGEMENT, ( 1 or 2 or 3 or 4 )

TWO LENGTHS AT 900

THREE LENGTHS AT 1200

FOUR LENGTHS AT 900

CALCULATE - B

CALCULATE - C

CLEAR

CALCULATE - A

CALCULATE - A

CALCULATE - D

Page 2: Earthing Calculations

"THE GATE" DOHA-QATAR ELECTROMECHANICAL WORKSSCHEMATIC DESIGN REPORT

1. CURRENT DENSITY, AMPERES PER SQUARE METER2. SURFACE AREA OF VERTICAL RODS, SQUARE METER3. SURFACE AREA OF HORIZONTAL ELECTRODES, SQUARE METER4. SURFACE AREA OF VERTICLE AND HORIZONTAL ELECTRODES, SQUARE METER5. SHORT CIRCUIT GROUND (EARTH) GRID WITHSTAND, AMPERES

E. CONCLUSIONS1. Combination of the two values estimated under items (B) and (C) shall be less than any individual values of (B) or (C) because they are naturally conneted in parallel. So, the final total earthing resistance shall be less than the smallest value of 0.84

2. If Short Circuit Current Ground Grid withstand exceeds The fault current, the Grid will be safe otherwise it will not be safe, So the grid is

Page 3: Earthing Calculations

"THE GATE" DOHA-QATAR ELECTROMECHANICAL WORKSSCHEMATIC DESIGN REPORT

R =a =Rn =Rh =Rn2 =

###no. of electode

######

###

########################

(4, 8,12.16,20, 24, 28, 32, 36, 44, 52, 60, 68, 76 for S or R) ###Landa

#########

ELECTRODE ARRANGEMENT*##################

*

1 =

2 =

Select space value bet. Max 3 =

4 =

METALCAS

Page 4: Earthing Calculations

"THE GATE" DOHA-QATAR ELECTROMECHANICAL WORKSSCHEMATIC DESIGN REPORT

GROUNDING RESISTANCE ANALYSIS CALCULATIONS BASED ON IEEE Std.80

A.SELECTION OF GROUNDING CONDUCTOR AND CONNECTION TO AN ELECTRODE

1. FAULT CURRENT, KA rms 302. FAULT CURRENT DURATION 1 or 3 SECONDS ( 1 or 3 ) 13. GROUND MATERIALS ( 1, 2, 3, 4, 5, 6, 7, 8, 9 see definition below ) 1 Table (2)(1=copper annealed soft drawn, 2=copper commercial harddrawn, 3=copper commercial harddrawn, 4=copper clad steel wire,

5=copper clad steel wire, 6=copper clad steel rod, 7=steel 1020, 8=stainless clad rod, 9=stainless steel 304)

106.47

120 Equation (42)

B.VERTICAL GROUND RODS AND HORIZONTAL GROUND CONDUCTORS

1. RESISTIVITY OF THE SOIL, OHM.METER 1002. LENGTH OF ELECTRODE, METER 63. DIAMETER OF VERTICAL ELECTRODE , METER 0.019054. NO. OF RODS PLACED IN AREA 365. LENGTH OF GRID, METER 1606. WIDTH OF GRID, METER 607. TOTAL LENGTH OF ALL CONNECTED GRID CONDUCTORS, METER 5008. DEPTH OF HORIZONTAL CONDUCTOR, METER 0.7

960010. DIAMETER OF HORIZONTAL CONDUCTOR, METER 0.01411. FACTOR K1 1.0512. FACTOR K2 4.9513. GROUNDING RESISTANCE OF RODS , OHMS 0.74 Equation (55)14. GROUNDING RESISTANCE OF HORIZONTAL CONDUCTORS , OHMS 0.61 Equation (54)

C. MUTUAL GROUND RESISTANCE1. MUTUAL GROUND RESISTANCE, OHMS 0.42 Equation (56)

D. TOTAL GROUND RESISTANCE1. TOTAL GROUND RESISTANCE, OHMS 0.54 Equation (53)

6. GROUNDING CONDUCTOR CROSS SECTIONAL AREA, MM2

7. NEXT HIGHER STANDARD GROUNDING CONDUCTOR CROSS SEC. AREA, MM2

9. AREA OF GRID COVERED BY CONDUCTORS, M2

CALCULATE - A

CALCULATE - B,C,D

CLEAR

Page 5: Earthing Calculations

BS 7433 IEEE std.80

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