Short circuit forces/loads on powerline structures 2

[MEG1122]

Hello everyone.... Can someone tell me why powerline structures are not designed for the forces due to short circuit currents whereas substation buses design take these forces into account? I have seen some substation gantry designs taking into account the wire loads due to short circuit currents aswell.

 

[RRaghunath]

Transmission towers in places where wind loads to be considered are large.
When compared the wind load, the dynamic forces due to short circuit are not much and hence are not to be separately considered, I guess. Experts on the forum may confirm.

 

[jraef]

That, and the fact that at high voltages, the current is typically low (which is why you use high voltages). Substation bus structures are usually at MV levels so carrying more base current, ergo short circuit current is going to be higher.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[KillBill7]

Substation structures (buses , jumpers) don't see longitudinal loads similar to what a typical full tension span see, so the governing loads are usually short circuit forces for these structures including the gantry structures which are most of the time are slack spanned. Typical powerlines , depending on line location, are designed for both deterministic loads and reliability based loads where you would apply large overload factors and use return-period based wind and ice loads. These weather loads are normally higher than the short circuit loads.

 

[jghrist]

Also consider that there are no net short circuit forces on the three phase structure. Forces are between phases.

 

[cuky2000]

Transmission lines have much longer spans, much larger sags, and larger phase spacings than those in substations. Therefore, the following effect has to be considered:
1)The longer spans increase the tower force reactions due to the wind and dead load on the phase conductors and shield wire and minimize the effect due to the flexibility effect of the string line.
2)Larger phase spacing reduces the short circuit forces dramatically on the phase conductors.

Therefore, the extreme wind or combinations of ice and wind are the dominant factor that diminishes the short circuit load effect on the transmission line structures.

 

[Finch24]

Jraef has explained very well!