Doubled underground cable life

 

Underground cable over 25 years old are near catastrophic failure

Through the 1980’s, underground cable insulation was manufactured using cross-linked polyethylene (XLPE) insulation were manufactured using a steam-curing process to cure the insulation.

This method introduced water and ionic impurities into the insulation resulting in electrochemical degradation of its insulation properties over the cable’s service life. This degradation is known as a water tree formation.

If not treated, the cable will ultimately fail

Failure can be prevented and cable life extended

Injection technology, otherwise known as cable insulation rejuvenation, is a well-established option to cable replacement. Cable injection technology involves the injection of a diffusive, water-reactive material into the conductor core of a buried power cable insulated with solid dielectric materials.

Once inside the cable, the fluid diffuses into the cable’s insulation and chemically combines with the water content inevitably contained within. This process retards the growth of water trees, the primary cause of cable failure in aged solid dielectric cable, simultaneously increasing overall insulation breakdown strength .

The silicon-based fluid is injected under pressure through the interstitial spaces of the conductor strands. The properties of the injection fluid causes oligomerisation with water molecules in the water tree. The resulting larger molecules fill the void, repairing the dielectric properties.

Treated cables demonstrate long term survival rates on par with new cables. With application costs in the order of one third to half of the cost of cable replacement it is not surprising that injection technology has experienced remarkable market success. Most of this market growth, however, has been limited to medium voltage distribution cables.

For over three decades cable rejuvenation using dialkoxysilane fluids has been the most capital efficient method to prevent cable failure due to aging resulting from all manner of defects including but not limited to water treeing, electrical treeing, and manufacturing defects. Over the last decade rejuvenation has surpassed replacement as the most utilised method of rehabilitation 

The process

The process works by injecting the fluid into the strands of aged cable which migrates into the cable insulation to repair the damage caused by aging. The fluid repairs, upgrades, and extends the life of medium-voltage cables and is non-flammable, nontoxic, and environmentally friendly. SPR cable injection seals the ends of the cable against water intrusion and is claimed to be capable of extending cable life by 40 years or more, offering better-than-new reliability.

Thousands of km of cable have been successfully injected with the process. Injection is possible with energised and de-energised cables. Tests on a section of rejuvenated cable recovered after the cable was scrapped for other reasons have shown that the rejuvenated cable had properties comparable with new cable.

The fluid:

1 – repairs the water trees and prevents further water tree formation

2 – restores the cable insulation properties

3 – effectively extends the cable life 30+ years.

Cost comparison

Experience with numerous projects has shown that the cost of rejuvenation ranges could be less than 50% of the cost of cable replacement. Rejuvenation takes considerably less time than replacement and involves less disruption of infrastructure