Dry-band and discharge activity characterization using visual and IR data analysis

The role of dry bands on a wet pollution layer in insulator flashover has been well described in the literature. Silicone rubber insulators are now widely used because of their superior performance in high voltage power systems under polluted environments. However, the discharge activity is not totally eliminated under pollution and it may initiate tracking and erosion on the insulator surface. For this reason, effective laboratory tests of formulations of polymeric materials and insulator designs are a key point for long term performance. Research at Cardiff University established new test procedures in order to achieve controlled, reproducible evaluation of contaminated 11 kV silicone rubber composite insulators. Electrical parameters of voltage and leakage current are recorded during flashover tests of polluted insulators in a clean-fog chamber; in addition a high-definition camera and an IR camera are used to capture video records of the discharge activity. Computer procedures have been developed to post-process visual and IR records. Since the quantity of data is great, this is not a trivial task. In particular it is possible to evaluate the number of dry bands present at any selected instant, their location and temperature; the number of pixels belonging to each spark is calculated since it can give a good indication of spark extension and position. With the adoption of the new test technique and the post-processing procedure of electrical, visual and IR data, it is possible to evaluate not only the flashover condition but also to determine accurately variations of the dry bands and the discharge activity during the test.