Streamer Mode Detection under Lighting Impulse in Mineral Oil and Natural Ester Gap

The impulse breakdown tests are usually required for transformers and the breakdown strength is one of the essential properties of the insulating liquids in transformers. To understand the breakdown mechanism in insulating liquids, pre-breakdown phenomena have been intensively studied and it's found that the breakdown characteristics of transformer oil differ for different streamer modes. This paper constructs a streamer mode detection platform for breakdown characteristics of fast and slow streamer modes in mineral oil and natural ester. The standard lighting impulse breakdown tests are conducted and three kinds of signals including impulse voltage, discharge current and streamer optical signal are detected before breakdown. The average propagation velocity of the streamer during the breakdown is obtained according to the oil gap distance and time interval between the streamer initiation and breakdown. Then the slow and fast streamer mode are identified by the velocity. The standard lighting impulse breakdown tests are conducted in mineral oil and natural ester based on the detection platform and the breakdown characteristics under fast and slow streamer are obtained. The study in this paper is helpful to promote the development and perfection of the breakdown mechanism of dielectric liquids.