Silicon Injections in Cable, bang for your buck?

[havocnova]

Hi everyone,

I work at an electric utility and are considering silicon injection in some existing crosslinked polyethylene (XLPE)cables. The companies guarantee the silicon to last for 20 years after injection. Here are the questions we came up with:

1) Let's say you have a cable with a life expectancy of 40 years, it has developed water trees at the 30 year mark and is injected with silicon. Does that mean the cable will now have a life of 50 years (30 + 20)? or will that injection just ensure the cable lasts another 10 years to it's 40 year mark? This can determine a big difference in replacement costs (now vs later).

2) Is there a probability of water tree development after a cable has been injected? Is the cable technically still XLPE and is prone to water tree development?

3) Are there any research papers that challenge the economic viablity of choosing cable injection versus direct replacement over the life of the replacemnt cable? A cable with life expectancy 50 years for example, and is there a break even point?

Thanks in advance for your responses!

 

[BJC]

Puget Sound Energy had ( may still have ) an extensive program of replacing and repairing 12 Residential distrubtion system cable. At the time of the cable replacement it was Puget Sound Powerr and Light. They have since reorganized so I don't know who's left there.

They had a very precise program for identifying cables to be replaced or repaired based on installed life and the original production run.
IMO it would be worth a dime to call them and if you can arrange it go see them or have one of them come to your place.

 

[apowerengr]

1. 50 years
2. no, the fluid retards water much like strand-filling
3. not that I've seen.

Cost/Benefit analysis is based on cable capacity expectancy vs. replacement cost. If you need to upgrade the capacity within 20 years don't inject it but replace it. If not, inject it and move on.

There are other threads asking similar questions. I've done many such projects and the economics are best evaluated on a case by case basis in my opinion.

 

[jraef]

Discussed previously, you may want to peruse this thread.

thread238-156645

 

[magoo2]

There's a couple of "got-yah's" that you should be aware of.

If you're dealing with 30-year old cable, chances are that it has been repaired a time or two. Each of the splices need to be located and the splices replaced so that the liquid will flow around the splice. This adds to the basic cost of the service. You can do an economic analysis based on the length of cable, cable replacement cost, splice replacement cost, etc. to give you a feel of whether the project is worthwhile or not. Or this will give you a feel for when the economics generally won't work in favor of injection. They generally rely on TDR sets to locate splices.

30-year old cable was largely unjacketed. Concentric wires were often damaged during installation, dragged along the ground, etc. Also certain areas are subject to severe corrosion problems. The point is to make sure the concentric neutral is intact before you spend money on injection.

Injection seems to work best with small cables, that is, they can get the fluid to flow easier and it can permeate the insulation easier with smaller diameter cables.

Obviously an injected cable is not and will never be as good as new cable. I think the injected insulation system is still XLPE and will degrade much like the original XLPE. All you've done is dried out the insulation and partially permeated some of the water trees in that insulation. So you've effectively raised the bar on effective insulation breakdown level by drying out the cable but it's still XLPE and will continue to lose insulation strength like XLPE and not TR-XLPE. I generally assume that you may get 5 to 10 additional years of life out of injected cable and base our economic analysis on that time period. At 10 years, I find that injection is cost-effective; at 5, it is not.

 

[havocnova]

From what I gather from all the responses and other threads, the cable injection can be an option, but not THE ultimate solution as it's never as good as a direct replacement. So an economic evaluation will have to be done on a case by case analysis.

Thanks to everyone for sharing their comments and experiences!