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AGEING OF OUTDOOR INSULATION UNDER LOW LEAKAGE CURRENTS
[Thesis]. Manchester, UK: The University of Manchester; 2010.
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Abstract
Ageing of outdoor insulation under low leakage currents are concerns for safety and reliability in transmission line operations. Overhead line elements such as insulators and ADSS (All Dielectric, Self-Supporting) cables are subject to electric fields, resultant leakage currents, and resulting surface discharges such as coronas and dry-band arcs. Under certain conditions, the normally benign long-term low current ageing effect may transform to more severe ageing forms, having a detrimental impact on the insulation materials and creating high rates of unexpected failures.In this thesis, a series of experimental studies are reported which have created low current discharges under variable electrical and environmental conditions. The electrical properties of resulting arcs are investigated and their impact on the insulation materials is analyzed. Based on the test results, new modelling approaches have been developed for the simulation of dry-band arcing activity. The respective ‘Double Sinusoidal Model’ and ‘PSCAD simulation’ are able to simulate the voltage and current traces of low current arcs, while the ‘Triple Cylinder Model’ is used to analyze the heat flow around the arcing region. Based on both experiment and simulation, the phenomenon of ‘dry-band arc compression’ is reproduced. Research confirms previous suggestions that such a compression process may lead to more aggressive damage on insulation surfaces, and could possibly accelerate the long-term ageing effect into a short-term hazard. As a result, this thesis supports the argument that processes controlling insulation lifetime may not be continual and gradual, but are determined by extreme events such as the occurrence of dry-band arc compression.