On the dielectric performance of modified epoxy networks

Epoxy resins represent a commonly used basis for insulation materials and have been used in many different electrical applications. The formation of these systems involves reactions between a hardener, such as an amine-curing system, and an epoxy terminated resin. Recent studies have reported that epoxy resin systems can exhibit enhanced physical properties when the stoichiometry of the resin is varied using reactive diluent. This has been attributed to the increased free volume within the molecular structures within the epoxy resin network. The work described here set out to investigate this hypothesis concerning the potential benefits of varying the network structure of epoxy resin through the inclusion of monofunctional reactive diluents within the epoxy formulation. This research is of potential significance because any modification of the epoxy resin network results in modified thermal, mechanical and electrical properties and, consequently, represents a potential mean of tailoring overall performance to suit particular applications

The effect of material processing on the dielectric properties of polystyrene boron nitride nanocomposites

Extensive experimental work in the area of polymer nanocomposites has been done over the past two decades to explore their potential. In this study, a range of related polymer nanocomposite materials was prepared using a solvent blending method, using dichloromethane (DCM), toluene (TOL) and chlorobenzene (CB) to dissolve the polymer, atactic polystyrene (a-PS), and disperse the filler, hexagonal boron nitride (hBN). Where TOL and CB were used, heat was used in material processing, whereas the material was processed at room temperature with DCM. The largest increase in breakdown strength is observed in the materials processed with TOL and CB. The hBN appears to be well dispersed in these systems and more agglomerated in the DCM system as shown from SEM

The effect of resin/hardener stoichiometry on the electrical properties of silicon nitride/epoxy nanocomposites

The effect of resin/hardener stoichiometry was investigated for both unfilled epoxy and nanocomposite samples. The results indicate that incorporating silicon nitride nanofiller, which contains amine groups on its surface, has a significant influence on the resin/hardener reaction. At 2 wt.% of nanofiller, it was estimated that the powder contains amine groups equivalent to around 5 wt.% of the hardener mass, which results in the displacement of the optimum resin/hardener mass ratio by the same amount (~5 wt.%). The dielectric spectra showed that the B relaxation is directly related to the hydroxyether groups that are generated by the reaction between the epoxy and the amine groups. Therefore, the relaxation strength is proportional to the crosslinking density and consequently related to the glass transition temperature. The DC conductivity increases considerably as a result of incorporating silicon nitride nanofiller when not compensating for its impact on the resin/hardener stoichiometry. This might be related to the increase in the amine content of the material caused by the amine groups existing on the surface of the nanoparticles. When the stoichiometry effect is taken into account, the DC conductivity decreased to a value that is comparable to that of the unfilled polymer

Electrical breakdown strength of boron nitride polyethylene nanocomposites

There is a growing demand for the design of high-performance insulators for high voltage applications. It was proposed that the addition of nanofillers to a polymer could potentially enhance the electrical properties of insulators when compared to the conventional unfilled or microfilled polymers [1]. These materials have captured the interest of many researchers worldwide since then, as present dielectric materials could benefit from improvements in properties such as dielectric strength, dielectric loss, electrical and thermal conductivity, and permittivity that nanodielectrics offer. However, many of the underlying principles remain uncertain, such as the polymer/nanofiller interface, and researchers are still exploring solutions to common challenges faced by nanodielectrics such as nanoparticle agglomeration [2].The work presented in this paper is based on a hexagonal boron nitride nanocomposite in a polyethylene blend host polymer. A polyethylene blend composed of 80% low density polyethylene (LDPE) and 20% high density polyethylene (HDPE) is chosen as the polymer matrix since it has a higher electrical breakdown strength than pure LDPE. Hexagonal boron nitride was chosen as a nanofiller because of its attractive properties for high voltage applications such as high dielectric strength, high thermal conductivity, and mechanical robustness [3]. A solution blending method is used to mix the nanoparticles in the polymer as better quality materials and nanoparticle dispersion are achieved.This paper will investigate the AC electrical breakdown behaviour of the prepared polymer nanocomposite materials. The electrical breakdown strength of the unfilled polymer will be compared to the untreated hexagonal boron nitride filled polymer at different loading levels. The addition of this nanofiller is expected to alter the dielectric strength due to changes in the material’s structure. The chemical structure of hexagonal boron nitride is illustrated in Figure 1, where there is an equal number boron and nitrogen atoms firmly bound together. The breakdown results will then be analysed using a two-parameter Weibull distributio

The Electrical Breakdown of Thin Dielectric Elastomers:Thermal Effects

Dielectric elastomers are being developed for use in actuators, sensors and generators to be used in various applications, such as artificial eye lids, pressure sensors and human motion energy generators. In order to obtain maximum efficiency, the devices are operated at high electrical fields. This increases the likelihood for electrical breakdown significantly. Hence, for many applications the performance of the dielectric elastomers is limited by this risk of failure, which is triggered by several factors. Amongst others thermal effects may strongly influence the electrical breakdown strength. In this study, we model the electrothermal breakdown in thin PDMS based dielectric elastomers in order to evaluate the thermal mechanisms behind the electrical failures. The objective is to predict the operation range of PDMS based dielectric elastomers with respect to the temperature at given electric field. We performed numerical analysis with a quasi-steady state approximation to predict thermal runaway of dielectric elastomer films. We also studied experimentally the effect of temperature on dielectric properties of different PDMS dielectric elastomers. Different films with different percentages of silica and permittivity enhancing filler were selected for the measurements. From the modeling based on the fitting of experimental data, it is found that the electrothermal breakdown of the materials is strongly influenced by the increase in both dielectric permittivity and conductivity

Modified Implicit Discretization of the Super-Twisting Controller

In this paper a novel discrete-time realization of the super-twisting controller is proposed. The closed-loop system is proven to be globally asymptotically stable in the absence of a disturbance by means of Lyapunov theory. Furthermore, the steady-state error in the disturbed case is computed analytically and shown to be independent of the parameters. The steady-state error only depends on the sampling time and the unknown disturbance. The proposed discrete-time controller is compared to previously published discrete-time super-twisting controllers by means of the controller structure. In extensive simulation studies the proposed controller is evaluated comparative to known controllers. The continuous-time super-twisting controller is capable of rejecting any unknown Lipschitz-continuous perturbation. Furthermore, the convergence time decreases, if any of the gains is increased. The simulations demonstrate that the systems closed in the loop with each of the known controllers lose one of these properties, introduce discretization-chattering effects, or do not yield the same accuracy level as with the proposed controller. The proposed controller, in contrast, is beneficial in terms of the above described properties of the continuous-time super-twisting controller