Underground cable installaltion 1

[KillBill7]

Hi Guys........ We have site contractor installing the 35kV cable underground from the riser pole to the substation yard. Does anyone know about the guidelines for any slack allowance in cable on each side of the dip to account for earth freeze and thaw? I assume we would need to allow for cable contraction and expansion?

 

[RRaghunath]

We used to leave 5m loop (hope my memory is serving me well) at each termination.
This is more to be able to cut the damaged termination (while in service) and redo using the loop already available.
The loop length in your case could be longer depending on the site requirement.

 

[7anoter4]

Since the copper wire from a cable presents the maximum expansion factor of about 17 mm per 1km and 1 grade C, and if the installation temperature is -20oC and the coldest ambient temperature is -40oC then the retraction of the cable will be 340 mm and if the installation temperature was +40oC the retraction length will be 1360 mm per 1 km.
The same in dilatation case if the installation temperature was -20oC and the normal temperature of the conductor will be 90oC then the cable will expand 1870 mm per 1 km. In short circuit case if the copper conductor temperature reach 250 oC the expansion length will be then 4.6 m.
The insulation and jacket expansion factor is 10-15 times higher but the expansion force is not enough to overcome the copper wire resistance and to produce another significant expansion.
.

 

[KillBill7]

Thanks for the input. This is helpful information.