8)Table for value of as

Table for "as"



Note:Value "as" used as a input quantity in short ckt calculation

7)Calculation of forces generated because of short circuit

1) Peak electro-magnetic forces between phase conductors




Where, ip = peak value of 3 phase s/c current, in ka
l = distance between supports
a = centre to centre conductor distance


2) Peak electro-magnetic forces between sub-conductors



Where, ip = peak value of short circuit current, ka
ls = distance between supports/stiffeners
n = number of sub-conductors per phase
as = effective centre to centre distance


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6)Short circuit forces which act on Busbar

Short circuit forces which act on Busbar

Depending upon the direction of current carried by adjacent phases there are two kinds of forces produce
1) Attractive force
2) Repulsive force
Following fig. shows different current carrying combination by adjacent busbar conductor.

5)Std. size of Busbar & their current carrying capacities

Std. size of Busbar & there current carrying capacities

4)Derating factor for volume of enclosure & ventilation

Derating factor for volume of enclosure & ventilation





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3) Derating factors for proximity effect

3) Derating factors for proximity effect

Phase Spacing Derating Factors
3W 0.82
4W 0.89
5W 0.95
6W 0.99
>6W 1.00
What is w?

It is distance between busbar of same phases as shown in fig




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2) Derating Factors for Ambient Temp, altitudes

Derating Factors for Ambient Temp, altitudes.


1) Average ambient temperature




Where,

T1 = temp. Rise at the ambient temp. as referred by the BB manufacturer
T2 = temp. Rise at the ambient temp.where the panel will be installed


2) Derating factors for altitudes

Where busbars are intended for use at high altitudes & is tested near sea level, the limits of temperature rise should be reduced by 1% for each 1000 feet in excess of 3000 feet above sea level at which the busbar is to be installed



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1)Busbar Design Temperature rise considerations

Busbar Design Temperature rise considerations

Following are the points which need to be considered while designing the busbar system.

1) Material of busbar (e.g. For Aluminium final temperature is Limited to 85 °c
2) Shape of conductor
3) Arrangement of conductor(vertical or horizontal)
4) Volume of enclosure
5) Ventilation
6) Average ambient temperature
7) Material of insulating supports (e.g. SMC can safely withstand 150 °c).
8) Type of joint (e.g. plated joints can withstand higher temperature)
Kindly note that while claiming the ratings the manufacturer of the busbars made following assumptions

1) Ratings are for 50°c rise over 35 ° c ambient temperatures in still but unconfined air

2) For multiple bar arrangements, the space between bars is equal to the bar thickness

3) A.C. ratings are based on spacing at which proximity effect is negligible

A)Step by step busbar design

Now we will see how busbar system is designed?

1) Busbar Design Temperature rise considerations
2) Derating Factors for Ambient Temp, altitudes
3) Derating Factors for ventilation.
4) Derating factors for proximity effect
5) Std.Busbar size & their current carrying capacities
6) Short circuit forces which act on Busbar
7) Calculation of forces generated because of short circuit
8) Calculation stresses created by short circuit force
9) Stiffeners spacing
10) Insulating support design
11) One example for busbar calculation