Abstract
The insulating performance of oil is vulnerable to particles especially the conductive particles. This paper investigated the influence of copper particles of micrometer size on the breakdown strength and frequency-dependent properties of vegetable oil. The AC breakdown voltage of contaminated vegetable oil with copper particles of different numbers (ranging from 103 to 106) was measured. The frequency-dependent dielectric properties including volume resistivity, relative permittivity and dissipation factor of the contaminated vegetable oil with copper particles of various volumetric concentrations (0.011%, 0.056% and 0.112%) were measured. Identical experiments were conducted with mineral oil for comparison. Results show that the AC breakdown voltage of vegetable oil decreases with the increase of copper particle concentration. The mineral oil exhibits a similar trend, but the influence of copper particles on the AC breakdown voltage of vegetable oil is less significant than that on mineral oil because of its greater viscosity. The relative permittivity and dissipation factor increase with increasing copper volumetric concentration while the volume resistivity decreases. The influence of copper particles on them is significant at low frequencies and this influence becomes inconspicuous as the frequency increases. Similar results were observed for mineral oil.
Highlights
Power transformers are the key components of the power system and insulating oil plays a major role in power transformers, acting as insulation and coolant [1]
Breakdown Voltage of Vegetable Insulating Oil Contaminated with Copper Particle
The AC breakdown voltage and the frequency-dependent dielectric properties of vegetable and mineral insulating oil contaminated with copper particles were measured and analyzed in this work
Summary
Power transformers are the key components of the power system and insulating oil plays a major role in power transformers, acting as insulation and coolant [1]. Vegetable insulating oil has been used successfully in distribution transformers in certain countries and regions, and they are under research and development for application in large power transformers [2,3,4]. Its high permittivity is conducive to improving electric field distribution in oil-paper insulation structure. Vegetable insulating oil has greater hydrophilicity than mineral insulating oil as hydrogen bonds exist in molecules of natural esters, which contributes to extending the remaining life of paper insulation in transformer [5]. Particles are typical pollutants that affect insulating performance of insulating oil. The particles in insulating oil are mainly metallic particles including copper, iron and Energies 2017, 10, 938; doi:10.3390/en10070938 www.mdpi.com/journal/energies
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