Forces on single bus bar carrying fault current 1

[prc]

How to calculate the forces acting on a single rectangular,grounding bus bar (say 80x6mm ) 200 mm away from ground, running parallel to ground, carrying fault current. I could not find any formula in IEC 60865

 

[7anoter4]

In my opinion, you have to neglect the grounding return path through the Earth-if any-and to take into consideration the force between the main conductor and grounding bar.

 

[waross]

I agree with 7anoter4.
The magnetic field around a bus bar needs another field to interact with. Not only is the distance squared quite large for current returning through the ground, in the presence of earth of uniform resistivity, the magnetic forces will tend to divert the current through the earth, further increasing the distance squared.
for a very conservative result, consider the fault current to be returning through a bus bar or cable running on the surface of the ground. (Below the crushed gravel layer if this is a sub station.
The result will be quite conservative, however it will give you a safe design figure for the uplifting force on the bus bar supports.
You will be able to verify that the forces will be less than the safe working load on the supports.
Given the distances involved, the forces will be much, much less than the forces during a phase to phase fault.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[prc]

Thank you 7anoter4.My case is the bus bar from neutral bushing to ground supported over pin insulators on transformer tank. During LG fault, current of the order of a few kA can flow through bus bar. This can induce a current on transformer tank. It may not be as high as in a bus duct, but can be substantial,I believe. So this can result in repulsive forces on the bus bar?

 

[jghrist]

I don't know that is possible to calculate the forces on the bus bar. The current that it is interacting with is the winding current in the faulted phase and the current in the phase cable/conductor/bus to the fault. Calculation is complicated by the fact that there is a steel tank between the bus and the winding.