Self-healing dielectric liquids to enable self-repair in fluid filled power cables

Fluid filled cables (FFCs) are insulated with a layer consisting of tightly lapped insulation paper, impregnated with a low viscosity mineral oil. Although improvements in polymer insulation have led to many being replaced, roughly 8,500km of FFC circuits still remain as legacy circuits, typically in heavily urbanized areas where replacement is either prohibitively expensive or impossible. If the sheath of an FFC is breached, oil will leak from the insulation layer, representing a risk to both cable integrity and the surrounding environment. Within the UK 400,000L of insulation oil is lost annually[1], and the severity of the problem is expected to increase; many circuits are now operating substantially beyond their operational lifetime, and the increasing fragility of lead cable sheaths (through crystallization and embrittlement) is becoming a significant concern. Here, we present a potential solution through the replacement of the insulation oil with a self-healing fluid (SHF). In the event of a breach (be it on the sheath or within a plumb joint) the SHF will crosslink in the presence of oxygen present in the surrounding backfill, resulting in the formation of a solid mass that prevents further oil leakage. In cases where direct sheath healing cannot be achieved (with particularly large or rapid leaks) the SHF will subsequently cure within the backfill, resulting in the formation of an oil-proof barrier that can effectively contain the oil, thereby limiting further environmental pollution.