Short circuit withstanding of bus bars

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Rho_HV

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Anyone knows how to calculate short circuit withstand rating of bus bars? I suppose it is a function of bus bar cross sectional area, insulating material keeping bus bars separated, and distance between insulating points?
 
LMAO said:
Anyone knows how to calculate short circuit withstand rating of bus bars? I suppose it is a function of bus bar cross sectional area, insulating material keeping bus bars separated, and distance between insulating points?
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I would think the ability of mounting components to withstand the magnetic forces applied to them would come into play and to some extent may even be a bigger factor then cross sectional area itself.
 
kwired said:
I would think the ability of mounting components to withstand the magnetic forces applied to them would come into play and to some extent may even be a bigger factor then cross sectional area itself.
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That's correct; that's what I meant by "insulating material". We use insulating material (usually fiberglass) to mount and reinforce the bus bars and keep them separated.
 
It's not calculated, it's tested and measured under standard testing specifications according to the type of equipment. There are too many variables involving structure rigidity, insulation material, bolting patterns, etc. etc. etc. to generically calculate it. It might help to know why you are asking if you want to know which standards would apply.
 
LMAO...

While calculable, there are some fifty factors to consider... the greatest being the peak value of the current carried! To give you an idea of the complication, one must even know the MOI (Moment-of-Inertia) of various components!

Jraef is right! Leave it to those with experience!

Regards, Phil Corso
 
151001-1154 EDT

LMAO:

I believe you are asking how to determine the force between two parallel conductors with equal currents, but in opposite directions.

Study a book such as "Electric and Magnetic Fields", Attwood, John Wiley, 1949, 3rd Edition. In that book on page 273 is an equation for two parallel wires where R<<D. You could start with this equation as very rough estimate, For a more accurate result you need to develop your own equation for your geometry. You can probably find computer programs today that will sole the problem for you. Look for field analysis program ads in Spectrum.

In the end you need to do real world testing, but a calculation before testing might save time and money.

.
 
I agree with Jraef and Phil Corso. However, before testing one has to design it and check [calculate] the possible damages.
In my opinion, here are 2 issues:
1)The rated steady state maximum carrying capacity [withstand] current.
2) Short-circuit thermal and electromagnetic [dynamic] effect.
The steady state current could be calculated according some manufactures' method like ABB -See ABB_Electrical_Swithgear_Manual ed.11 Part 4 Dimensioning Switchgear Installations.
The short-circuit withstand current could be calculated according to IEC 60865-1 and 2 [Short-circuit currents –Calculation of effects]
It has to be an ANSI or NEMA replica of this standard, I think.
 
Alright. What I am understanding from reading responses is: there is really no straightforward way to "calculate" short circuit withstanding (rating) of bus bars; they have to be "tested". I agree; there are just way too may variables and factors.
 
UL has some standards I think you could use from their switch board and panel board program that could be adapted to other uses. mostly it seems to be about spacing to grounded surfaces and distance between supports.

You could also just buy bus bars that are already listed with a SCCR.
 
What short circuit current are we talking about?

Magnetic repulsion can be calculated. The tricky bit is knowing the mechanical strength of the support insulators for each location in the panel and the rigidity of the bars.

Busbar size can be calculated with some basic information but it’s mainly temperature related. Temperature that can affect the support insulator integrity.
The rapid rise in temperature under fault can be calculated using the adiabatic equation.
 
qcroanoke said:
Or you could calculate it the way Calvin's dad does......
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Not so far from the truth...


I was part of the team building this test fixture at Boeing for the 777 wing attachment and was there when this video was shot. The wings are essentially "glued" to the fuselage with epoxy, which had never been done before. So the FAA required that they build it to withstand 150% of the worst possible forces it could see in nature. They did, but they had to test it to be sure; calculations were only good to a point...
 
Jraef said:
Not so far from the truth...


I was part of the team building this test fixture at Boeing for the 777 wing attachment and was there when this video was shot. The wings are essentially "glued" to the fuselage with epoxy, which had never been done before. So the FAA required that they build it to withstand 150% of the worst possible forces it could see in nature. They did, but they had to test it to be sure; calculations were only good to a point...
Click to expand...

Interesting!
Bad news is if you're ever on a 777 and the wings are deflecting 24 feet you're probably not gonna make it......
 
Tony S said:
What short circuit current are we talking about?

Magnetic repulsion can be calculated. The tricky bit is knowing the mechanical strength of the support insulators for each location in the panel and the rigidity of the bars.

Busbar size can be calculated with some basic information but it’s mainly temperature related. Temperature that can affect the support insulator integrity.
The rapid rise in temperature under fault can be calculated using the adiabatic equation.
Click to expand...

Tony,
I think it will be easier doing a cost/benefits comparison between estimating the hassles in calculating versus just buying from reputable vendors all switchgear/ switchboard with a withstand rating stamped on them. I can spare more time with my kids doing that.:)
 
Jraef said:
Not so far from the truth...


I was part of the team building this test fixture at Boeing for the 777 wing attachment and was there when this video was shot. The wings are essentially "glued" to the fuselage with epoxy, which had never been done before. So the FAA required that they build it to withstand 150% of the worst possible forces it could see in nature. They did, but they had to test it to be sure; calculations were only good to a point...
Click to expand...

Awesome, thanks!

BTW, what kind of epoxy was used? That would be some handy stuff to have around the house!
 
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