35KVAC Load Break in a below grade manhole system

[larrym]

We are working on a project installing a submarine power cable. It has been suggested that we install load breaks in the manhole where the cable transitions from submarine cable to terrestrial cable to allow isolating the two segments for troubleshooting in the future.

My first inclination was to make this transition inside a separate watertight splice case for each conductor (total of three) or similar with hot/cold shrink splice methods. The concern raised is reterminating the cable whenever the splice is opened with require cutback of the conductors and eventually consume whatever slack is placed in the manhole at installation.

My concern is using a load break in an environment that could potentially be sea water flooded long term. Reading thru the spec sheets I see the term submersible but don't see any specs on how deep or how long.

Thoughts, suggestions, ideas welcomed

Regards
Larry

Larry Mackey

 

[7anoter4]

In my experience in the underground duct bank systems in power stations it is impossible to create a sealed manhole even a mile from the sea shore. The manhole will be eventually filled of water. The duct bank is like a beam supported on the manhole window and the open space of the window around the duct bank it cannot be well sealed due to duct bank and manhole movements.
In my opinion you have to search an other possibility above the ground.

 

[JJ_Roy]

Based on my underground and submarine cable experience, very seldom do you need to sectionalize a cable segment for fault finding unless you have a cable system that has bifurcated segments (multiple cables per phase), the cable splits to different locations somewhere along the segment, or the cable is extremely long beyond the capabilities of the locating equipment. The long cable scenario is very unlikely with AC systems. A person experienced in cable fault finding should be able to locate faults using common fault locating methods (TDR, Resistance Bridge, etc.) even in systems that include submarine cables.

If, for some reason, you do need to sectionalize the submarine cable from the land cable for fault finding, an experienced cable jointer typically can “break” the joint and then re-joint without too much issue. There are still a couple of options if you still want to have the ability to sectionalize the cable.

Google search: Prysmian CLICK-FIT joints and
Trayer.com (submersible switchgear)

I also recommend getting an experienced submarine cable consultant on-board as there are a lot of traps with submarine cable installations that even experienced underground engineers get caught in.