Cable Joints 1

[safy2004]

We have under ground cables with rated voltage 11kV, and maximum highest voltage is 12 kV buried with sand, the earth in this area has very high humidity.
If I want to make joint for this cable, what should be the specifications of this joint, should I ask for higher insulation voltage(more than 12 kV) to make sure the joint will not fail in future, or the same specifications of the cable 11 – 12 kV is sufficient.
I will appreciate any help.
Thanks in advanced.

 

[Marmite]

You should use the appropriate joint for the voltage of the cable. Joints for 11kV tend to be 15kV rated anyway. If water gets into the joint it will probably fail eventually regardless of the rating of the joint. These days your choices are really between heatshrink and coldshrink technology. If it's a paper lead cable then go for the heatshrink as you can get a more reliable seal in the crutch. If it's polymeric then you could use either. Heatshrink has been around longer and is tried and tested. The humidity shouldn't be a problem. It is normal for joints to be in wet ground. A standing head of water above 2m or so would potentially be a problem though. You should look at joints from the likes of 3M, Tyco Raychem and Prysmian. These are the main players who have spent the money on development. Although cable jointing has been deskilled to some extent by the advent of new technology, the correct preparation of the cables has become increasingly important to get the reliability, so use a skilled jointer.
Regards
Marmite

 

[apowerengr]

Cable joints should be based on the insulation level of the cable, the neutral/sheid construction type and the installation conditions. Heat or cold shrink or pre-moulded are all viable options provide the installers can prepare and install the product per the instructions. Some joints handle different ambient conditions better than others fo for high heat applications be wary.

 

[safy2004]

Thanks Marmite,apowerengr;
What I want to know is that what is the relation between the insulation voltage of the cable and the insulation voltage of the joint, where I can find the standard which identify this relation.
Regards,

 

[Marmite]

Unless you are running the cables at a voltage in excess of their design rating, you just need to buy the joint to suit the cable. Go on any of the manufacturers websites and look for 11kV cable joints. As long as they are rated at 11kV or above and suitable for the type of cable you have, they will do the job. If you have size 11 feet you buy size 11 shoes. It's as simple as that. If you buy joints rated way in excess of 11kV, eg designed for 22kV or 33KV you are wasting your money. You'll just end up with a bag of bits left over.
Regards
Marmite

 

[lovink]

Although the mentioned brands of 3M, Tyco Raychem and Prysmian are certainly well known, you might also look at Lovink in Holland with the LoviSil 11kV cable joints. These have been designed specifically for wet soil conditions because of the high water table in Holland (below sealevel!). These joints are based on fluid silicone technology and are used today in many parts of the UK, Europe and South East Asia.