Earthing strip size for
transformer. 
Cross Section Area of Earthing Conductor As per IS
3043
A = (If x√t) / K
Where:
t
= Fault current Time (Second)., 1 sec or 3 sec
K
= Material Constant, Material Constant, For GI=80, copper K=206, Aluminium
K=126).
Part-A:
Typical Protective conductor size required for Transformer Ratings
(100-500KVA)
|
|
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|
|
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||
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Sr.
|
A
|
B
|
C
|
D
|
E
|
F
|
|
1
|
Transformer Rating ( KVA)
|
100
|
160
|
250
|
315
|
500
|
|
2
|
Secondary Voltage (V)
|
433
|
433
|
433
|
433
|
433
|
|
3
|
Full Load current
|
133
|
213
|
333
|
420
|
667
|
|
4
|
Percentage Impedance Z%
|
5
|
5
|
5
|
5
|
5
|
|
5
|
Short Circuit Current (SC) in A =FLC*(100/Impedance)
|
2660
|
4260
|
6600
|
8400
|
13340
|
|
6
|
Area of Protective conductor Reqd in sq.mm = SC *√t/k
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|
|
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|
|
7
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t = 1 Sec
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|
8
|
Copper k = 206
|
12.9
|
20.7
|
32.0
|
40.8
|
64.8
|
|
9
|
Recommended strip size
|
25 x 3 mm
|
25 x 3 mm
|
25 x 3 mm
|
25 x 3 mm
|
25 x 3 mm
|
|
10
|
Alluminium k = 126
|
21.1
|
33.8
|
52.4
|
66.67
|
105.9
|
|
11
|
Recommended strip size
|
25 x 3 mm
|
25 x 3 mm
|
25 x 3 mm
|
25 x 3 mm
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25 x 6 mm
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|
12
|
Steel, k= 80
|
33.3
|
53.3
|
82.5
|
105
|
166.8
|
|
13
|
Recommended strip size
|
25 x 3 mm
|
25 x 3 mm
|
25 x 6 mm
|
25 x 6 mm
|
40 x 6 mm
|
|
14
|
t =3 Sec
|
|
|
|
|
|
|
15
|
Copper k = 206
|
22.34
|
35.85
|
56.42
|
70.67
|
112.23
|
|
16
|
Recommended strip size
|
25 x 3 mm
|
25 x 3 mm
|
25 x 3 mm
|
25 x 3 mm
|
25 x 6 mm
|
|
17
|
Alluminium k = 126
|
36.55
|
58.54
|
90.76
|
115.47
|
183.42
|
|
18
|
Recommended strip size
|
25 x 3 mm
|
25 x 3 mm
|
25 x 6 mm
|
25 x 6 mm
|
40 x 6 mm
|
|
19
|
Steel , k= 80
|
57.68
|
92.32
|
142.89
|
181.86
|
288.9
|
|
20
|
Recommended strip size
|
25 x 3 mm
|
25 x 6 mm
|
25 x 6 mm
|
40 x 6 mm
|
50 x 6 mm
|
PART-B:
Typical Protective conductor size required for Transformer Ratings
(630-2000KVA)
|
Sr.
|
A
|
G
|
H
|
I
|
J
|
K
|
L
|
|
1
|
Transformer Rating ( KVA)
|
630
|
750
|
1000
|
1250
|
1600
|
2000
|
|
2
|
Secondary Voltage (V)
|
433
|
433
|
433
|
433
|
433
|
433
|
|
3
|
Full Load current
|
840
|
1000
|
1333
|
1667
|
2133
|
2667
|
|
4
|
Percentage Impedance Z%
|
5
|
5
|
5
|
6
|
6
|
6
|
|
5
|
Short Circuit Current (SC) in A
|
16801
|
20001
|
26668
|
27779
|
35558
|
44447
|
|
6
|
Area of Protective conductor Reqd in sq.mm = SC *√t/k
|
|
|
|
|
|
|
|
7
|
t = 1Sec
|
|
|
|
|
|
|
|
8
|
Copper k = 206
|
81.96
|
97.57
|
130.09
|
135.51
|
173.45
|
216.81
|
|
9
|
Recommended strip size
|
25 x 6 mm
|
25 x 6 mm
|
25 x 6 mm
|
25 x 6 mm
|
40 x 6 mm
|
40 x 6 mm
|
|
10
|
Alluminium k = 126
|
133.34
|
158.74
|
211.65
|
220.47
|
282.2
|
352.75
|
|
11
|
Recommended strip size
|
25 x 6 mm
|
40 x 6 mm
|
40 x 6 mm
|
40 x 6 mm
|
50 x 6 mm
|
75 x 6 mm
|
|
12
|
Steel, k= 80
|
210.01
|
250.01
|
333.35
|
347.24
|
444.47
|
555.59
|
|
13
|
Recommended strip size
|
40 x 6 mm
|
50 x 6 mm
|
75 x 6 mm
|
75 x 6 mm
|
75 x 6 mm
|
75 x10 mm
|
|
14
|
t =3 Sec
|
|
|
|
|
|
|
|
15
|
Copper k = 206
|
141.26
|
168.17
|
224.22
|
233.56
|
298.96
|
373.7
|
|
16
|
Recommended strip size
|
25 x 6 mm
|
40 x 6 mm
|
40 x 6 mm
|
40 x 6 mm
|
50 x 6 mm
|
75 x 6 mm
|
|
17
|
Alluminium k = 126
|
230.95
|
274.94
|
366.58
|
381.86
|
488.78
|
610.97
|
|
18
|
Recommended strip size
|
40 x 6 mm
|
50 x 6 mm
|
75 x 6 mm
|
75 x 6 mm
|
75 x 10 mm
|
75 x 10 mm
|
|
19
|
Steel , k= 80
|
363.74
|
433.03
|
577.37
|
601.42
|
769.82
|
962.28
|
|
20
|
Recommended strip size
|
75 x 6 mm
|
75 x 6 mm
|
75 x10 mm
|
75 x10 mm
|
100 x 10 mm
|
100 x 10 mm
|
Reader
can choose safely factor as 1.5.
Suppose
calculated strip size is 40x6 sqmm = 240sqmm
Considering
safety factor , strip size = 240x1.5 = 360 sqmm.
Electrode
always should be installed in 2 and opposte side of equipment. The distance
between electrode is not less than height of one electrode.
