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Online Measurement of Voltage Gradient Distortion and Leakage Current of Heavily Contaminated Outdoor Insulation Using Thermal Imaging | IEEE Journals & Magazine | IEEE Xplore

Online Measurement of Voltage Gradient Distortion and Leakage Current of Heavily Contaminated Outdoor Insulation Using Thermal Imaging


Abstract:

A new thermal model of an insulator heat loss coefficient proves that evaporation power loss is more significant than thermal conduction to a moist environment. Consequen...Show More

Abstract:

A new thermal model of an insulator heat loss coefficient proves that evaporation power loss is more significant than thermal conduction to a moist environment. Consequently, the leakage current in a moist pollution layer may cause dry-band formation. Such bands are bridged and sustained by streamer discharges, which can initiate partial arcing. Clean-fog tests of contaminated insulators have been shown to provide infrared (IR) temperature data for the model, and the evaluation of voltage gradients in this dry-band regime. The same modeling also offers a unique method of online leakage current monitoring.
Page(s): 988 - 996
Date of Publication: 07 December 2023

ISSN Information:


I. Introduction

The wetted surface of a polluted insulator has a typical leakage conductance of a few microsiemens. This enables dry bands to divide the pollution layer because a leakage current of a few milliamperes in magnitude promotes evaporation from the thin moist layer [1]. The voltage difference across such bands, following their loss of conductivity, is sufficient to initiate electrical breakdowns that bridge the bands. These take the form of corona streamers [1, Fig. 1(a)] that are of low luminosity mainly in the ultraviolet (UV) spectral range. The streamer initiation across a dry band reduces the leakage current below that which was present prior to the band formation and causes negligible damage to the insulator. Nevertheless, the local energy dissipated by the streamers is shown by the infrared (IR) record to heat the insulator surface [Fig. 1(b)] which will prevent rewetting and so conserve the band. The temperature rise associated with dry-band formation is modest. In this case, where the insulator is in a clean fog environment at 14 °C, yet much of its surface is at 16 °C and the dry bands can reach 26 °C–27 °C.

Dry bands and partial arcs on the trunk section of a silicone rubber insulator. (a) Simultaneous visible and (b) IR images of dry band streamers. (c) Partial-arc inception and bridging of a dry band [1].

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