[btp-502-02-d15a]
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8/10/2019 [BTP-502-02-D15A]
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VALUE UNIT
50 KA1 sec
50 cm
= I X sqrt (t) / k 625 sqmm50 KA1 sec
80
1.1 x 625 687.5 sqmm
400 m
2 l w x t
20 -m
40000 cm7.5 cm50 cm
Ra = 0.13
2 dWhere,
300 cm6.5 cm
Rb = 5.54
6 0.92
1/ R ab 1/R a + 1/R bb
Rab Ra x R b / (R a + R bb)
Rab 0.11169388
VALUE UNIT
50 KA1 sec
50 cm
= I X sqrt (t) / k 625 sqmm50 KA1 sec
80t = Operating time in (secs) =k = 80 for steel as per IS-3043
I = Faulth Current (KA) =
TECHNICAL DATAa) Resistivity (avg.) of soil ( ) - m =
20 -m= (27.11+20.11+14.79+14.32+15.62)/5=18.39 say, 20(Reference Geotechnical report)b) Maximum fault current (I) - KA (rms) =c) Duration of shock (t) considered as sec.d) Depth of Burial of conductor (h) - cm
RESISTANCE OF EARTHING MAT:
Required Size of Earthing Grid (S)
Ground Resistance is less than 1.0 , hence the calculation is OK
Therefore 6 nos. of Earth Pits Provided are OK.
PRIMARY REQUIREMENTa) The impedence to ground (Over all resistance of the earthing system)should not exceed 1.0 as per IS:3043
EARTHING CALCULATION FOR PLANT AREA FOR BTP
Rab = Total earth resistance
Resistance of one electrode in isolation:(Refer IS-3043-1987)
Rb = 100 Ln 4l
L = Length of electrode in cmD = Diameter of electrode in cm
Since Over all resistance for 1 Electrode should be
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8/10/2019 [BTP-502-02-D15A]
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