Silicone rubber to extend life of power transformers

ERJ staff report (PR)

London - ABB is employing silicone rubber as part of a new technology to tackle the failure of bushings on power transformers at 132 kilovolt, and help extend the life of these critical units by at least 10 years.

Transformers are key components of high-voltage equipment for power generation plants, transmission systems and large industrial plant. The failure-risk development curves are steeper for industrial and power generation plants as the transformers in these installations tend to be used more intensively.

Transformers typically cost from £1 million upward and if they do fail, the financial impact can be much more significant. Unexpected failures can cause major disturbances to operating systems, resulting in unscheduled outages and power delivery problems.

The transformer bushings provide the insulated connection between the internal windings of the transformer and the substation’s overhead power lines or busbars. Historically, these bushings have been a solid porcelain or oil impregnated design, but after 20 years’ service their performance starts to degrade by partial discharge, and they can fail catastrophically by shattering.

As part of a new service, ABB can replace the brittle and easily damaged porcelain oil-impregnated bushings with epoxy resin-impregnated paper (RIP) bushing, protected by a silicone rubber insulator.

The bushings are produced by winding a crêped paper web onto a mandrel, with aluminium foil inserts for electrical field control. The body is vacuum impregnated and cured giving a partial discharge free bushing with low tan d (dissipation factor). After curing, the body is machined and the flange is attached.

The silicone rubber insulator is bonded to the RIP body in a patent-applied-for process, giving protection from the environment. The conductor is fixed to the top piece with a divided ring - patented by ABB - with a solid rod of copper or aluminium is used as conductor.