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Moisture accelerates degradation of electric insulators, claims new study

Moisture in the atmosphere can expedite degradation of insulators that protect the long conductor or wires which transmit electricity from place to place, a study has found. The study was conducted by researchers from the Indian Institute of Science, Bangalore.

Current carrying conductors, like the wires that supply electricity to our homes, experience partial arcs or corona discharges near the vicinity of high voltage conductors. Corona discharges, as they are called, appear as blue light in the air surrounding the medium, and may also produce some sound.

“Corona is the ionization of the air due to a localized highly intensified electric field. Since any irregularities (sharp/rough projections from the objects) in high voltage systems give rise to a high electric field, this phenomenon is normally observed in high voltage systems as an audible or a visible corona”, explains Dr. Subba Reddy, who led the study. Such discharges are undesirable in electrical systems because they cause power losses, electromagnetic interference, produce audible noise and also damage insulation of electrical systems.

“The systems that experience corona effect are all around our electricity distribution systems - high voltage transmission line insulators, high voltage transformers, hardware or power connectors used in high voltage substations etc.”. Since electricity is a prized commodity, any wastage is undesirable. To minimize such loses, it becomes necessary to understand additive effects of other elements involved in the ecosystem.

This is the first study to experimentally analyze the corona effect with moisture on the insulating surfaces. “A study of this kind simulates the practical situation which a polymeric insulator undergoes in its service condition”, adds Mr Shakthi Prasad, research scholar working with Dr. Reddy.

The researchers conducted a series of experiments and observed the effects of corona on three types of insulators commonly used in electric systems. They applied the voltages and current needed to produce a corona discharge, and artificially created fog to mimic atmospheric moisture. The experiments were conducted with both AC and DC voltages. They went down till molecular level to understand the effects of fog on the insulator.

Their studies revealed that the degradation of the insulator, and hence the power loss, accelerated in the presence of moisture. Also, AC voltage resulted in higher degradation. Surface rupture too was observed for the corona treated sample in the presence of moisture.

The insulators studied in these experiments are used to make high voltage insulators, large high voltage bushings, insulating cables used in aircrafts, telecommunication systems etc. The researchers hope that their results may spur much more activities in understanding of how high voltage and the atmospheric conditions team up to degrade the insulators used.

Author information: Dr Subba Reddy is a Principal Research Scientist at the Department of Electrical Engineering, Indian Institute of Science, Bangalore. Shakthi Prasad is a PhD student.

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