How Calculate Cable Short Circuit Current from Short Circuit Current from Table?
You
may find the short circuit current for a particular type of cable for a
specified period of time from your cable manufacturer’s provided catalogue. For
example the below table is showing different sizes from 16 square mili-meter to
2500 square mili-meter of cable in first left column and time duration from 0.1
second to 5 second in next 10 columns.
Table:
Typical short circuit current (kA)
CSA (sqmm)
|
Duration in Second
|
|||||||||
0.1
|
0.2
|
0.3
|
0.4
|
0.5
|
1.0
|
2.0
|
3.0
|
4.0
|
5.0
|
|
16
|
7.2
|
5.1
|
4.2
|
3.6
|
3.2
|
2.3
|
1.6
|
1.3
|
1.1
|
1.02
|
25
|
11.3
|
8
|
6.5
|
5.7
|
5.1
|
3.6
|
2.5
|
2.1
|
1.8
|
1.6
|
35
|
15.8
|
11.2
|
9.1
|
7.9
|
7.1
|
5
|
3.5
|
2.9
|
2.5
|
2.24
|
50
|
22.6
|
16
|
13.1
|
11.3
|
10.1
|
7.2
|
5.1
|
4.1
|
3.6
|
3.2
|
70
|
31.7
|
22.4
|
18.3
|
15.8
|
14.2
|
10
|
7.1
|
5.8
|
5
|
4.5
|
95
|
43
|
30.4
|
24.8
|
21.5
|
19.2
|
13.6
|
9.6
|
7.8
|
6.8
|
6.1
|
120
|
54.3
|
38.4
|
31.3
|
27.1
|
24.3
|
17.2
|
12.1
|
9.9
|
8.6
|
7.7
|
150
|
67.8
|
48
|
39.2
|
33.9
|
30.3
|
21.5
|
15.2
|
12.4
|
10.7
|
9.6
|
185
|
83.7
|
59.2
|
48.3
|
41.8
|
37.4
|
26.5
|
18.7
|
15.3
|
13.2
|
11.8
|
240
|
108.5
|
76.7
|
62.7
|
54.3
|
48.5
|
34.3
|
24.3
|
19.8
|
17.2
|
15.3
|
300
|
135.7
|
95.9
|
78.3
|
67.8
|
60.7
|
42.9
|
30.3
|
24.8
|
21.5
|
19.2
|
400
|
180.9
|
127.9
|
104.4
|
90.4
|
80.9
|
57.2
|
40.4
|
33
|
28.6
|
25.6
|
500
|
226.1
|
159.9
|
130.5
|
113.1
|
101.1
|
71.5
|
50.6
|
41.3
|
35.8
|
32
|
630
|
284.9
|
201.4
|
164.5
|
142.4
|
127.4
|
90.1
|
63.7
|
52.0
|
45.0
|
40.3
|
800
|
361.8
|
255.8
|
208.9
|
180.9
|
161.8
|
114.4
|
80.9
|
66
|
57.2
|
51.2
|
1000
|
452.2
|
319.8
|
261.1
|
226.1
|
202.2
|
143
|
101.1
|
82.6
|
71.5
|
64
|
1200
|
542.6
|
383.7
|
313.3
|
271.3
|
242.7
|
171.6
|
121.3
|
99.1
|
85.8
|
76.7
|
1600
|
723.5
|
511.6
|
417.7
|
361.8
|
323.6
|
228.8
|
161.8
|
132.1
|
114.4
|
102.3
|
2000
|
904.4
|
639.5
|
522.2
|
452.2
|
404.5
|
286
|
202.2
|
165.1
|
143
|
127.9
|
2500
|
1130.5
|
799.4
|
652.7
|
565.3
|
505.6
|
357
|
252.8
|
206.4
|
178.8
|
159.9
|
Here
is some limitation is that only some particular times are mentioned; say 1
second then 2 second. But if you need short circuit current for 1.5 second or
1.75 second for a particular size of cable that you cannot find from your short
circuit current table. In this situation as a cable engineer you must calculate
the short circuit current for desired period of time.
Before
going to calculate the short circuit current we need to keep in mind some basic
point about short circuit current. Short circuit current table give the value for
particular type of cable conductor and screen based on some conditions, like-
- Short circuit starts from the maximum operating
- Maximum temperature during short circuit;
- Maximum short circuit current duration is 5 seconds.
Now,
come to the main point: if the short circuit current is required at duration
not mentioned in the catalogue what we asked before. Then we need to obtain by
dividing the short circuit current for 1 second by the square root of the
required duration.
How Calculate Cable Short Circuit Current
First
of all we need to know the short circuit current for 1 second and the duration
of time. Then we can calculate short circuit current for that time duration.
Let
follow the formula for cable short circuit current calculation:
Where
Isct=
Short circuit current for t second in kA
Isc1=
Short circuit current for 1 second in kA
t
= Duration of time in second.
kA-
Kilo-Ampere.
For example:
What is the short
circuit current for 3.5 second for 2500 sqmm cable?
Solution:
Given time duration is
3.5 second,
Short circuit current
for 1 second is 357 kA;
So, Isct =
357/(P3.5)= 190.83 kA
Hope,
it will help you to calculate the short circuit current for your cable. To know
more about your cable, please keep in touch.
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