insulators failure modes
Failure modes of insulators
Author:orient insulator   time:5/16/2011 5:03:10 PM  read:1226times

Flashovers, caused by air breakdown or pollution, generally do not cause physical damage to the insulators and the system can often be restored by means of autoclosing. Some other events, however, cause irreparable damage to the insulators.
Puncture
As previously mentioned, prcelain pin-type and cap and pin insulators may suffer
punctures between the pin and the either the pin or the high voltage conductor. These occurrences are usually caused bu very steep impulse voltage, where the time delay for air flashover exceeds that of puncture of porcelain.Punctures caused by severe stress over dry bands also occor on composite insulators on sheds and through the sheath. A puncture of the sheath is particularly serious as this exposes the glass fibre rod to the environment.
Shattering
Glass insulators shatter when exposed to severe arcing or puncturing due to
vandalism. One advantage is that they retain their mechanical integrity.
Erosion
Prolonged arcing of glass insulators leads to erosion of the surface layer of the
glass. This may lead to shattering of the glass discs a result of the tempering process used during manufactyre. Arcing and corona over long periods may cause removal of shed or sheath material in the case of polymeric insulators. Severe erosion may lead to the exposure of the glass fibre core.
Tracking
Tracking occurs when carbonised tracks form because of arcing. These tracks are
conductive. This phenomenon only occors in carbon-based polymers.
Brittle fracture
Water entry into the glass fibre core of composite insulators, coupled with the
influence of weak acids, has been shown to lead to brittle fracture of the rod. The by-products of partial discharges in the presence of water can lead to the formation of weak acids. The integrity of the metal/polymer and glass/polymer interfaces is therefore extremely important especially if acid-resistant glass is not used.
Corrosion
The corrosion of metal fittings clearly affects the mechanical performance and
lifetime of insulators. The corrosion products, running onto the insulator sheds can also initiate deterioration.

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