Effects of magnetic field on electrical tree growth in silicone rubber under repetitive pulse voltage

Electric field, accompanying with the magnetic field produced by high current, can generate electro-magnetic force in HVDC system, which enormously affects the treeing process. Electrical tree behavior of silicone rubber (SiR) was investigated by application of magnetic field with repetitive pulse voltage. The samples were made of silicone rubber with a pin-plane electrode system. The inserted needle had a tip radius of 3 μm and the pin-plane distance was 2 mm. The rise time and fall time of the repetitive pulse voltage were 100 and 120 μs respectively. The pulse frequency was 200 Hz, while the pulse amplitude ranging from 6 to 12 kV was applied. The magnetic flux density (B) of the magnetic field was 100, 200 and 400 mT respectively. The results were presented from experimental investigations in order to characterize electrical tree as a function of amplitude and polarities of the applied pulse voltage. The patterns of electrical tree, tree length, accumulated damage and tree breakdown characteristics were studied. It is revealed that both the pulse amplitude and polarity have a significant impact on electrical tree growth characteristics of silicone rubber. Results show that the pulse amplitude plays the leading role in electrical tree initiation, propagation and breakdown processes. Compared with the positive pulse, it is suggested that the larger tree accumulated damage is more easily to occur with the negative pulse. It also has been found that tree structure is greatly dependent on the B of magnetic field. Results show that magnetic field promotes tree growth and accelerates the treeing process.

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