Andrej Krivda

Dielectric properties of epoxy based nanocomposites for high voltage insulation

Epoxy polymer with micro, nano and micro + nano silica fillers have been evaluated for their electrical performance in high voltage insulation applications. The dielectric strength of these samples was measured in accordance with the ASTM D-149 standard. Dielectric spectroscopy was used to understand the role of space charge and interfaces in these materials. The results of dielectric spectroscopy suggest that significant improvement in the electrical performance can be expected by using samples containing nanofillers and micro + nanofillers when compared to materials containing only microfillers. However, the dielectric strength measurement showed no statistically significant improvement for the nanofilled samples. Techniques other than dielectric breakdown may be required to adequately characterize differences in the electrical performance of the dielectrics. For example, a partial discharge test using a highly non-uniform field may be more useful as it would correspond to simulate actual service conditions.

Characterization of epoxy microcomposite and nanocomposite materials for power engineering applications

This article presents the results from round-robin tests performed on epoxy composite materials. These results show the potential of these materials for use as electrical insulation in some specific applications. A small section of the article addresses the health and safety issues related to the use of nanoparticles in the electrical power engineering industry. We define epoxy nanocomposites as epoxy-based materials containing exclusively nanosized filler particles. Epoxy microcomposites are defined as epoxy materials containing exclusively microsized filler particles, and epoxy micro+nano composites are materials containing both microsized and nanosized particles.

Electrical properties analysis of micro and nano composite epoxy resin materials

This work deals with the study of micro and nanosilica filled epoxy resin samples carried out in the framework of CIGRE WG D1.24 cooperative test program. This program focused on chemical, electrical and electrostatic properties of epoxy based nanodielectrics for electrical engineering applications. Epoxy based samples filled with micro and/or nanoparticles of silica were characterized by transmission electron microscopy, dielectric spectroscopy, conduction current and space charge measurements. These mutually complementary techniques were used to examine the effect of the size and quantity of silica particles on the electrical properties of the analyzed materials. The analysis of charge injection, polarization, trapping and conduction phenomena has allowed the modeling of dielectric behavior of the studied materials under multiple stresses. The Schottky Injection and Space Charge Limited Current models were studied to explain conduction phenomena. A composition of micro and nano-sized silica particles accumulating the smallest amount of space charge is also proposed.

Tracking and erosion resistance of high temperature vulcanizing ATH-free silicone rubber

Traditionally aluminum trihydrate (ATH) is added to high-temperature vulcanized (HTV) silicone rubber for outdoor insulation applications to improve flame retardancy and the electrical tracking and erosion performance. In this work, the flammability of ATH-free HTV silicone rubber formulations were evaluated by the UL94 vertical burning test. The most promising candidates, as well as reference formulations filled with silica or silica/ATH only, were then evaluated by the inclined plane tracking and erosion test at 4.5 kV. The best result was obtained by silicone rubber containing 100 phr silica and 15 phr melamine cyanurate. It was suggested that this was a result of the arc quenching ability of the melamine hence extinguishing the electrical arc. If the filler level was too high, resulting in poor dispersion, the resistance to tracking and erosion was significantly reduced. Thus formulating a HTV silicone rubber with good tracking and erosion resistance is a balance between having a high enough filler content, while still maintaining a good dispersion of the particles in the polymer matrix, as well as good bonding between the particles and the matrix.

Corona resistance of epoxy nanocomposites: experimental results and modeling

Epoxy composites with micro, nano and micro + nano silica fillers have been evaluated for their resistance to corona using point plane electrodes. The experiments were conducted for 500 h and the surface erosion was measured after every 100 h using a surface profilometer. The results show significant improvement in corona resistance of micro+nanofilled samples and nanofilled samples when compared with the microfilled samples and unfilled materials respectively. The results emphasize the importance of good filler dispersion. A model to map the degradation path in the filled and unfilled samples was developed using Dijkstras shortest path algorithm. Reasonable agreement between the length of degradation path and the corona resistance in samples containing both micro + nanofillers has been demonstrated.

Epoxy based materials containing micro and nano sized fillers for improved electrical characteristics

In this paper the effect on dc and ac electrical properties of silica nano and micro particles dispersed in epoxy resins is discussed. In particular, space charge, conductivity, dielectric strength and partial discharge resistance is analyzed. The results show that nanostructured materials exhibit smaller space charge accumulation with respect to both base and microfilled materials. Regarding PD resistance, micro + nano filled materials display longer lifetimes with respect to base epoxy resin and materials including nanofillers or microfillers alone.

Inclined-Plane Tracking and Erosion Test according to the IEC 60587 Standard

The main goal of the paper is to summarise experiments using the tracking and erosion test according to the IEC 60587 standard. Various polymeric materials, e.g., high temperature vulcanised silicone rubber, liquid silicone rubber, epoxy resin and fibre reinforced materials were tested and differences in performance noted. A leakage current monitoring system has also been developed and the results of leakage current analysis are presented. Possible improvements of the present standard are also discussed.

Polymer composites with a large nanofiller content: a case study involving epoxy

A situation involving a polymer nanocomposite containing a large amount of inorganic filler was studied. An epoxy nanocomposite with a content of 20% wt of nanosilica was used. Emphasis was put on imaging at the nanoscale and some dielectric responses were measured using dielectric spectroscopy. Using Transmission Electron Microscopy (TEM) in a High-Angle Annular Dark Field (HAADF) scanning mode, an area of less than 4 nm around an isolated particle was imaged and found to have a very low atomic number. With Atomic Force Microscopy (AFM) in peak-force mode agglomerates were clearly imaged. With respect to the dielectric response, no interfacial relaxation peak was observed. In presence of some agglomeration, the real part of the permittivity was found to be decreased by the addition of the nanofiller. Higher-field measurements unravelled nonlinear variations of the conduction versus an applied field. It was shown that the use of a large filler concentration resulted in greater interphase overlapping between the nanoparticles.

Inclined-plane tracking and erosion test according to the IEC 60587 Standard

The present IEC 60587 IEC standard needs several improvements which would help manufacturers of power equipment and material suppliers to assess outdoor polymeric materials in a more reliable way.

Dielectric study with epoxy-based nanostructured microcomposites containing silica

Material samples were prepared consisting of silica particles in an epoxy matrix. The generic compound contained a large amount of micrometric silica (e.g. 60% wt.) and a few % of nanosilica. Investigation of the microstructure of the samples showed that indeed the microcomposites exhibited a nanostructured morphology. Dielectric spectroscopy was used to compare the behavior of materials differing in composition. Posttreatment using heat was necessary to obtain a reproducible dielectric response. Dielectric features linked to the material compositions were annotated. For the case of 65-% total wt. silica, it was found that when the nanophase varies from 0 to 5%, the increase in the dielectric constant could fluctuate by as much as 10% in the low-frequency range.