Abstract
Nanoparticles enhance the positive and negative lightning breakdown voltages of vegetable insulating oils due to a reduced streamer velocity. Pre-breakdown streamers in vegetable oil based h-BN and Fe3O4 nanofluids were observed using the shadowgraph method under a lightning impulse voltage. The propagation of streamers until their stopping length is analyzed using shadowgraph images for the different nanofluids. The results suggest that these nanofluids present a higher breakdown voltage per unit length compared with pure oil. Secondary reverse streamers are observed to appear at the dissipation stage of the streamer. In particular, the secondary reverse streamer of the nanofluids appeared earlier and seemed to be shorter than that of pure oil under positive impulse voltages. The underlying mechanism was analyzed using space charge theory.
Highlights
Insulating oil, which serves as a cooling medium, is an important part of power transformer insulation system
The Fe3O4 nanoparticles are evenly distributed with an average size of aboutapproximately 20 nm
The results show that the positive secondary reverse streamer of the h-BN nanofluid was the fastest with an average time of approximately 172 μs, whereas, those for the Fe3O4 nanofluids and pure oil were 183 and 235 μs, respectively
Summary
Insulating oil, which serves as a cooling medium, is an important part of power transformer insulation system. Mineral insulating oil, the traditional oil used for transformer insulation, has a low fire point of approximately 170 ○C and possesses poor bio-degradability, allowing contaminating soil and water leakage to occur. vegetable insulating oil, which is an environmentally-friendly liquid dielectric, has drawn significant attention as a potential alternative to traditional mineral oils for power transformers. This would improve the insulating properties of oil to provide the long-term sustainable operation of power transformers.Nanofluids are formed from adding nanoscale particles to a base fluid and offer notable advantages to insulation enhancements. Research on the breakdown process of insulating oils has mainly focused on the streamer development at the pre-breakdown phase. The liquid dielectric produces a weak discharge channel under the action of a local high field strength and a “treelike”. Insulating oil, which serves as a cooling medium, is an important part of power transformer insulation system.. The traditional oil used for transformer insulation, has a low fire point of approximately 170 ○C and possesses poor bio-degradability, allowing contaminating soil and water leakage to occur.. Vegetable insulating oil, which is an environmentally-friendly liquid dielectric, has drawn significant attention as a potential alternative to traditional mineral oils for power transformers.. Vegetable insulating oil, which is an environmentally-friendly liquid dielectric, has drawn significant attention as a potential alternative to traditional mineral oils for power transformers.3,4 This would improve the insulating properties of oil to provide the long-term sustainable operation of power transformers. Research on the breakdown process of insulating oils has mainly focused on the streamer development at the pre-breakdown phase..
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