Measurement Of The Insulating Properties And Internal Space Charge Of Nano-modified Liquid Dielectric

Dielectric breakdown of liquid characteristics is an important factor affecting andrestricting the development of electrical equipment and power systems. In the processof electrical equipment operation, internal electric field of liquid has a great impact onits dielectric insulation performance. The emergence and distribution of space chargeplay a significant role on changing the electric field.In order to improve the insulationperformance of transformer oil, this paper studied the effect of different conductiveproperties of nanoparticles modified transformer oil on its breakdown characteristics.In this paper, three kinds of nanoparticles with different conductivity: conductivemagnetic Fe3O4nanoparticles, semiconductive TiO2nanoparticles and non-conductiveAl2O3nanoparticles are chosen and added into transformer oils to form nanofluids withdifferent surface modifications. By AC and switching impulse breakdown test, macrobreakdown characteristics of transformer oil-based nanofluids with differentconcentration were compared, and optimal concentration of three kinds of nanofluidswas obtained，that are0.03g/L,0.01g/L and0.02g/L. Then AC and impulsebreakdown strength of three nanofluids with optimal consentration was measured. Theobserved results indicated that the addition of any kind of nanoparticles to transformeroil can enhance its insulation strength, except that under the condition of negativelightning impulse breakdown voltage. At the optimal concentrations of nanofluids, thebreakdown voltages under positive polarity have greater enhancements, that are,44.1%、33.3%and35.5%respectively. The results show improvement of differentlevels in comprehensive impulse breakdown properties of transformer oil modified bythree kinds of nanoparticles. This paper analyzes the high insulating properties oftransformer oil-based nanofluids under impulse voltage from the perspective of spacecharge distribution, and explains the differences in breakdown characteristics of threenanofluids by combining polarization theory.Considering the significance of space charge to breakdown process and in order tofurther study the mechanism of nanoparticles on the improvement of breakdowncharacteristic of dielectric liquid, this paper built and optimized the measurementplatform of electric field and space charge for dielectric liquids with high-Kerr constant.On this basis, with considering the characteristics of low-Kerr constant transformer oil,photodetectors with higher sensitivity was utilized to replace high-speed CCD. Also, spatial filter was added for the optimization and improvements of the measurementplatform of electric field and space charge for dielectric liquids, which laid thefoundation for subsequent experiments. In order to better observe the effect ofnanoparticles on space charge in dielectrics liquid, measurement platform of electricfield and space charge for high-Kerr constant dielectric liquids with high measuringaccuracy was utilized in this paper to measure and analyze the electric field and spacecharge of both pure and nano-modified propylene carbonate under the same voltage atthe same time. The results indicates that the space charges in nanofluids tend toaggregate in the vicinity of the electrodes compared to those in pure liquids due to thebarrier effect of nanoparticles on space charges after the modification of varying typesof nanoparticles, which leads to more uniform electric field distribution betweenparallel electrodes and thus contributes to improve the breakdown voltage.