6.9 KV Fault 2

[dik]

I have a project supporting cable trays and I understand that it is possible for a fault to cause the cables to 'whip' around. Does anyone have an idea of the magnitude of the force generated by the 'whipping' motion?

thanks, Dik

 

[Marmite]

For single core cables you do get substantial magnetic forces between the cables under fault conditions. The force on the cables is proportional to the square of the fault current, and inversely proportional to the spacing. For single core cables laid in trefoil EN50368 gives the formula F= (0.17x Isqd)/S. F is the force in Nm, S is the cable diameter in m, I is the peak short circuit current in kA.
You could use this formula to specify the cable cleats and cleat spacing.
This formula gives the static load instantaneously created by the short circuit, however the phase changes
of the alternating current mean that the forces on the cable and their direction are changing continuously.
No simple formula and no static test can assess the effect of these dynamic forces. The ultimate proof of any
cable fixing system to withstand a short-circuit is to undertake a short-circuit test.
Regards
Marmite

 

[dpc]

http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/forwir2.html#c1

 

[dik]

Thanks, gentlemen... Dik