AC Electrical Breakdown Strength Research Articles

Electrical Performance of Epoxy Resin Filled with Micro Particles and Nanoparticles

Abstract Composite insulators are widely used in the overhead transmission system. Compared with porcelain products, composite has many advantages such as light in weight, hydrophobicity characteristic and superior mechanical property. However, composite products are also suffering from issues such as low tracking resistance and early failures. The use of nano or micro fillers is considered to be one of the methods that can further improve the properties of the composite product. This study is aimed to study the electrical properties of nano and micro filled epoxy resin. SiO 2 and Al 2 O 3 nano and micro fillers are used in this research for comparison purposes. The host matrix, which is epoxy resin, is filled with nano particles, micro particles or both nano and micro particles. Micro particles and nano particles are dispersed into epoxy resin using planetary centrifugal mixing technique and degassed in vacuum. In total, seven types of materials are prepared in this study. These materials are (1) neat epoxy, (2) nanocomposite filled with 1 wt% nano SiO 2 fillers, (3) micro-composite filled with 20 wt% micro SiO 2 fillers, (4) micro-nano composite filled with 1 wt% nano SiO 2 and 20 wt% micro SiO 2 fillers, (5) nanocomposite filled with 1 wt% nano Al 2 O 3 fillers, (6) micro-composite filled with 20 wt% micro Al 2 O 3 fillers, (7) micro-nano composite filled with 1 wt% nano Al 2 O 3 and 20 wt% micro Al 2 O 3 fillers. In this study, AC electrical breakdown strength test are performed using a sphere-to-sphere setup. The thickness of all the samples is 1 mm ± 0.1 mm in accordance to the IEC standard. Surface partial discharge measurement is also performed to evaluate the surface property.

Space charge and AC electrical breakdown strength in polyethylene

Breakdown strength is an essential feature of dielectrics. Theoretically, the intrinsic strength is independent of the configuration of the dielectrics or electrodes and the category of applied electric fields. However, the measured breakdown strengths of a same material under direct high voltage (HVDC) and alternative high voltage (HVAC) are significantly different. This paper aims to give an explanation of this observed phenomenon based on constant intrinsic electrical breakdown strength and reveal the significant influence of charge transport on the breakdown process. The effect of space charge on dielectric performances is generally neglected under high voltage alternate current (HVAC) electric fields, due to the limited charge amount observed. The characteristics of space charge in polymeric under AC stresses and its importance to the breakdown strength of polyethylene are also presented in this paper. A numerical model based on space charge dynamics under high voltage electric fields has been used to explain the differences in the breakdown strength of polyethylene under AC and DC stresses. Bipolar charge transport theory is adopted to analyse the charge transportation processes. Space charge profiles at the time of breakdown occurrence under different electric fields (including DC voltage, 0.5, 5 and 50 Hz AC voltages) and in the samples with different thicknesses (from 50 to 200 μm) are simulated. The relationship between space charge and the breakdown strength is discussed. The simulated results agree well with the trend of experimental breakdown results: generally, breakdown occurs easier under AC stress than DC stress; the breakdown strength is increased with the decrease of the sample thickness. The results suggest the presence of space charge under AC stresses has a great impact on electric breakdown strength of the material.

Effects of Reactive Diluents on the Electrical Insulation Breakdown Strength and Mechanical Properties in an Epoxy System

In order to study the effect of reactive diluents on the electrical insulation breakdown strength and mechanical properties of, a polyglycol and an aliphatic epoxy were individually introduced to an epoxy system. Reactive diluents were used in order to decrease the viscosity of the epoxy system; polyglycol acted as a flexibilizer and 1,4-butanediol diglycidyl ether (BDGE) acted as an aliphatic epoxy, which then acted as a chain extender after curing reaction. The ac electrical breakdown strength was estimated in sphere-to-sphere electrodes and the electrical breakdown strength was estimated by Weibull statistical analysis. The scale parameters of the electrical breakdown strengths for the epoxy resin, epoxy-polyglycol, and epoxy-BDGE were 45.0, 46.2, and 45.1 kV/mm, respectively. The flexural and tensile strengths for epoxy-BDGE were lower than those of the epoxy resin and those for epoxy-polyglycol were lower than those of the epoxy resin.

실란처리된 Epoxy/MICA 콤포지트의 열적, 기계적 전기적 특성연구

In this study, epoxy/mica composite was prepared by mixing with mechanical stirrer together with homogenizer, and the effect of amino-type silane coupling agent was also studied. To reduce the viscosity without any decrement of other properties, 1,4-Butanediol diglycidyl ether (1,4-BDGE) as an aliphatic epoxy reactive diluent was introduced to the epoxy/mica composite in order to use as vanish for high voltage motor and generator stator winding. It was confirmed by scanning electron microscopy (SEM) observation that interfacial characteristics between organic epoxy and inorganic mica was modified by coupling agent treatment so that glass transition temperature increased, and tensile strength and electrical breakdown strength increased. The properties were estimated by Weibull statistical analysis and the ac electrical breakdown strength was 20.2% modified by treating silane coupling agent.

Effect of Nanosilica on the Mechanical Properties and AC Electrical Breakdown Strength of Epoxy/Microsilica/Nanosilica Composite

Epoxy/microsilica (65 phr)/nanosilica (0~5 phr) composites (EMNC) were prepared in order to develop a high-voltage insulation material, where phr means parts per hundred relative to the epoxy oligomer. Tensile and flexural tests of the composites were carried out, and the AC electrical breakdown strength was measured, after which all the data were estimated by Weibull statistical analysis. As the nanosilica content increased, the tensile strength increased, and the highest value was 117.7 MPa in the EMNC system with 3 phr nanosilica, which was ca. 10% higher than that of the system without nanosilica. The value then decreased after 3 phr. The flexural strength and AC electrical breakdown strength showed the same tendencies as the tensile strength. The highest value of the flexural strength was 184.6 MPa in the EMNC system with 3 phr of nanosilica, which was ca. 15% higher than that of the system without nanosilica. The strongest value of the AC electrical breakdown strength was 79.0 kV/0.5 mm in the EMNC system with 3 phr of nanosilica, which was ca. 34% higher than that of the system without nanosilica.

AC Electrical Breakdown Characteristics of an Epoxy/Mica Composite

Epoxy/mica composite was synthesized, in order to use it as an impregnation resin in a vacuum pressure impregnation (VPI) process, for manufacturing a high voltage rotary machine. The average particle size of the mica was 5~7 <TEX>${\mu}m$</TEX> and its content was 0, 20, 30 and 40 wt%. A plasticizer or a low molecular aliphatic epoxy was also used, to decrease the viscosity of the composite. The AC electrical breakdown strength was estimated in sphere-to-sphere electrodes, and the electrical breakdown data were estimated by Weibull statistical analysis. The electrical breakdown strength became higher with the addition of mica; and that of the system with 20 wt% mica was highest. The electrical breakdown strength of the system with an aliphatic epoxy was higher than that of the system with a, plasticizer.

AC breakdown characteristics of epoxy nanocomposites

Experiments were conducted to measure the ac breakdown strength of epoxy alumina nanocomposites with different filler loadings of 0.1, 1 and 5 wt%. The experiments were performed as per the ASTM D 149 standard on samples of thickness 0.5 mm, 1 mm and 3 mm in order to study the effect of thickness on the ac breakdown strength of epoxy nanocomposites. In the case of epoxy alumina nanocomposites it was observed that the ac breakdown strength was marginally lower for 0.1 wt% and 1 wt% filler loadings and then increased at 5 wt% filler loading as compared to the unfilled epoxy. The Weibull shape parameter (β) increased with the addition of nanoparticles to epoxy as well as with the increasing sample thickness for all the filler loadings considered. DSC analysis was done to study the material properties at the filler resin interface in order to understand the effect of the filler loading and thereby the influence of the interface on the ac breakdown strength of epoxy nanocomposites. It was also observed that the decrease in ac electric breakdown strength with an increase in sample thickness follows an inverse power-law dependence. In addition, the ac breakdown strength of epoxy silica nanocomposites have also been studied in order to understand the influence of the filler type on the breakdown strength.