High Voltage Underground Cable Installation

[timm333]

Just need some information about XLPE underground cables in industrial location. Up to 132 kV, the cables can be direct-buried with the splicing done in dehumidified environment (using cable jointing tents).

Can the cables of voltages above 132 kV (for example 380 kV cables) also be direct-buried, or should these be installed in tunnels with the splicing done in manholes? Thanks for help.

 

[NewtonLaw]

230 kV cables direct buried

230 kV cables direct buried

We have installed very short runs of 230kV EPR cable but only where it was the best economic alternative. Usually using a manhole and duct system is a better economic alternative to direct burying cables above about 35 kV. Consider the size of the hole necessary to repair/splice a failed 380 kV cable. Also the amount of possible damage to local homes, etc. due to ground potential rise.

 

[timm333]

At PDF page 6 of the link: http://www.landsnet.is/uploads/1068.pdf, it says that direct-buried cables are acceptable up to 132 kV. Will the ground potential rise resulting from a faulted 132 kV cable be acceptable in industrial locations?

 

[Julius Right]

British National Grid, in my opinion, describes here the U.K. today practice. It is not forbidden for the future installation up to 400 kV. See XLPE cables chapter:
"At voltages of 132 kV and below XLPE cable are buried directly in the ground. At present National Grid only installs 275 kV and 400 kV XLPE in tunnels but this is subject to ongoing review and future installations may, in some cases, be buried directly in the ground."
However, in U.S.A -or else where- it is a usual practice. See-for instance:
http://www.nexans.com/Corporate/2013/60-500_kV_High_Voltage_full_BD2.pdf
Type of installation. Direct burial.

 

[timm333]

Thanks. If the cable is installed in trench/manhole system, then the cable splicing would be done in the jointing-chambers. If it is desired to avoid these jointing-chambers, is it possible to do the splicing in the direct-buried pits (while the cable is still installed in the trench/manhole system)?

 

[Tony S]

It’s possible but far from ideal. As with any HV cable jointing/splicing cleanliness is paramount. I’ve had my fair share of cable repairs in muddy holes in the ground, it doesn’t make things easy.

What is your objection to installing chambers? It’s a new installation, how much will they add to the overall price?

 

[timm333]

This is new installation. Another problem of splicing the cable in direct-buried would be that the whole cable would have to be sized for direct-buried. We were thinking that the installation could be easier if the jointing chambers are avoided, but it looks that jointing chambers should be used for splicing.

 

[timm333]

Direct-buried high voltage cables should be avoided in residential and commercial areas due to the risk of ground potential rise. Will direct-buried cables (132 KV - 380 kV) be Ok in the industrial areas? If step and touch voltage calculations are required for direct-buried cables (132 kV - 380 kV) in industrial areas, then the calculations of which section of IEEE-80 would apply here? Thanks for help.

 

[timm333]

The IEEE-80 standard applies to the substation grounding. Is there also some standard which addresses the ground potential rise calculations for direct-buried cables?