BUSBAR CALULATION CALULATION FOR 2000A COPPER COPPER BUSBARS BUSBARS
DATA AVAILABLE / ASSUMED
1. 2. 3. 4. 5.
Fault level Ambient Temp. Temp. Rise Max. busbar temp. while carrying full load current Permissible final temp. of busbar after short circuit for 1 Sec.
: : : :
50KA for 1 Sec. 45oC 40oC 85oC (45oC + 40oC)
:
200oC
6.
Busbar Material
:
Electrolytic grade Copper
7.
Required Current Rating
:
2000A
8.
Size of Busbars (Selected)
:
(3.5 X 3 X 100 X 6) Sq.mm Cu.
9.
Enclosure sizes (Provided)
:
900 x 345 Sq.mm
A.
CALCULATIONS FOR SHORT CIRCUIT :
Minimum Cross Sectional area of Copper Busbar required for 50KA fault level for 1 Sec. can be calculated by by the formula formula given below: I --------- A OR
A
t
=
=
I ----------0.122
If fault current is 50KA then A =
Where :
0.122
t
50 . 0.122
1
=
I A
= =
t
=
Fault Current Current (KA) Cross Sectional Sectional area of Busbar in Sq.mm. Time in Sec.
409.8 Sq. mm
Where as we are are using 1800 Sq. mm mm Cross Sectional Sectional of Copper Busbar Busbar Which is more more than the the required. Therefore selected Bus bar bar are quite suitable for 50KA 50KA Fault level for 1 Sec.
[Contd…2..]
-:2:-
B.
CALCULATION FOR THERMAL RATING :
1.
De-Rating factor due to material of Busbar
2.
De-Rating Factor due to ambient temperature. Derating factor
=
=
1
.
1/1.7 T2 . T1
T1
=
Temp. rise over the ambient temperature as referred by the Bus bar manufacturer
T2
=
Temp. rise over the ambient temperature where the Panel Is installed.
The Derating factor to be applied on the ratings given in for 45Degree C ambient is 1/ 1.7 0.588 . 40 . = (0.88) = 0.93 45 3.
De-Rating Factor due to enclosure : The % ratio of Cross Sectional area of Bus bar & Cross sectional area of enclosure.
=
Total Cross Sectional area of bus bar Total Cross Sectional area of enclosure
=
3.5 x 3 X 100 x 6 900 x 345
=
0.02028
=
2.029%
Now Derating factor for this percentage ratio
=
0.80
So, Total derating factor for 2000A
=
1 x 0.93 x 0.80 = 0.744
Current carrying capacity of 100x6 mm Cu Busbar
=
1480A
Multiplying factor for 3 Busbar
=
2.09
6300 310500
[Contd…3..]
-:3:-
Now Total Current carrying of 3x100x6 mm Cu Busbar
=
1480 x 2.09
=
3093.2A
Effective current carrying capacity Of Busbars after considering de-rating factor
=
3093.2x0.744 = 2301A
From the above calculation we note that the current carrying capacity of selected cross section of Busbar 1800 Sq.mm, is 2301A.
