Effect of DC Voltage Ramp Rate on Breakdown in Ferrofluid Based on Transformer Oil

P. Bartkoa, M. Rajňáka, b, R. Cimbalaa, I. Kolcunováa, K. Paulovičováb, M. Timkob, P. Kopčanskýb, J. Kurimskýa aFaculty of Electrical Engineering and Informatics, Technical University of Košice, Letná 9, 041 54 Košice, Slovakia bInstitute of Experimental Physics, SAS, Watsonova 47, 040 01 Košice, Slovakia

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In the presented experimental study, the transformer oil based magnetic nanofluids with iron oxide nanoparticles are tested for DC breakdown as a variable depended on voltage ramp rate at ambient conditions. The breakdown tests were performed on four samples of various concentrations of nanoparticles with 0, 0.05, 0.15, and 0.35 vol.%. The measurements were conducted in accordance with IEC 60897 by using needle to sphere electrode geometry. Carrier oil and ferrofluids were tested at negative needle polarity of electric potential towards grounded sphere and then vice versa. By utilizing the particular breakdown measurement method with a variable DC voltage ramp rate, a statistically large set of breakdown data was obtained. The data-sets were collected as a function of negative DC voltage ramp rates 470, 750, and 1100 V/s, respectively. The test results show that the higher is the ramp-rate of DC voltage, the higher is the dielectric breakdown strength. It has been found that with the negative needle - grounded sphere geometry, there was dielectric breakdown at higher voltage than the other way around. Also, the effect of nanoparticle concentration in the oil on the increasing dielectric breakdown strength was observed.

DOI:10.12693/APhysPolA.137.970 topics: ferrofluid, dielectric strength, DC breakdown voltage