At M.V. (10.5KV), what is the difference in material between 1250A, 40KA busbar & 1250A, 50KA?
hi and welcome to PF
your question is extremely vague
What material ?
outline more clearly what you are referring to with as much relevant info as possible
I'm sorry, I'm talking about busbar material (the conductor, insulation, supports and etc......).
Here's some busbar information. This seems to be for more typical busbars and may not be as useful for high power applications. Still, most of the same problems will still need to be solved.
For high power AC systems, lots of engineering work will need to be done. The electrical characteristics will depend on geometry. Typically these will be large hollow roundish metal structures. Aluminum alloys are a popular choice, but has some concerns about mechanical/electrical connections.
After the electrical characteristics are determined, structural problems need to be solved.
This is a specialized field and you may need to hire a power engineer with experience with station/substation design if you need specifics.
One of the design considerations is rigidity.
Under high current faults the conductors are attracted to one another,
so it is required they be stout enough that a downstream fault will not make them bend and touch between supports which would cause another fault.
So i'll assume your 40 and 50 ka numbers are fault current ratings,beyond the 1.25 ka.
Presumably the busbar is supported as necessary and made more rigid considering the forces produced by fault current. Those forces are in proportion to the product of the currents as indicated in that Hyperphysics image above, http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/wirfor.html
502/402 = 1.56+,
ie 56% more bracing required.
That of course raises the cost of busbar and breakers.
Sometimes you'll see a current limiting inductor in switchgear.
It limits fault current allowing use of less expensive busbar and breakers downstream . My plant had them in the 4kv switchgear , located between the breakers supplying multi-thousand horsepower motors and those feeding only multi-hundred horsepower motors.
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