Measured and Simulated PD Characteristics of Closely Coupled Air Cavities in Polymeric Insulation

Electrical equipment such as generators and cables have insulation between current-carrying conductors and the grounded parts. Insulation is regarded as the weakest link where various problems can occur. Among these problems are partial discharges (PD). The present work is on comparatively characterizing PD of single and closely coupled cavities in polymeric insulation material. Artificial cavities were created in the laboratory to study PD characteristics. Single artificial cavities of 1.5 mm and two closely coupled cavities were studied. The separation distance between the two cavities varied from 0.4 mm to 3.5 mm. The findings are that the double cavity partial discharge magnitude is greater when the distance between the two cavities is minimal compared to an independent single cavity. The pulse repetition rate is higher in double cavities than in a single cavity. However, the PD repetition rate in closely coupled double cavities is not necessarily double that of an isolated single cavity under the same voltage conditions. The findings can be explained using the widely accepted theory of PD mechanisms. These results can be a useful basis in electrical equipment for improved interpretation of PD measurements.