0000000000082125
AUTHOR
L. Testa
showing 13 related works from this author
The role of micro-structural and mechanical properties in the framework of the model for damage inception and growth from air-filled voids in Polyeth…
2007
An innovative, physical, aging and life model for polymeric insulation systems, founded on damage inception and growth at the level of microscopic cavities, was developed previously by the authors. This paper is focused on the role played by micro-structural and mechanical properties (such as crystallinity and Young's modulus) in the framework of such model. These concepts are applied to the case of LDPE, HDPE and XLPE matrixes. The relevant estimates of damage growth rate and time-to-failure as a function of void size and applied electric field in typical working conditions for HVDC power cables are performed. The results show that, under the assumptions made, the crystallinity level itsel…
Effect of Aspect ratio and water contamination on the electric properties of nanostructured insulating materials
2010
Organically-modified nanofiller clays can have significantly different aspect ratios as well as accumulate a relatively large amount of water in the composite bulk due to the contribution of the filler itself and the interaction between filler and polymer matrix. This paper investigates the effect of water absorption in a nanostructured thermoplastic polymer, namely ethylene-vinyl-acetate (EVA), on electrical property modifications considering the contribution of aspect ratio. The change of electrical properties (particularly space charge accumulation, electric strength, bulk conductivity and permittivity/losses) is studied as a function of water content absorbed by nanofillers having diffe…
Magnetic Stochastic Resonance in systems described by Dynamic Preisach Model
2008
Stochastic resonance (SR) is generally considered as an enhancement of the system response for certain finite values of the noise strength. In particular the signal to noise ratio (SNR) and the signal amplification show a maximum as a function of the noise intensity. This effect has been experimentally observed in many physical systems and also in magnetic systems. However, as far as magnetic systems are concerned, the dynamic features of the systems have been neglected and it has been assumed that the typical relaxation time is negligible. However this is clearly a rough approximation. In order to clarify this relation, in this paper we numerically study magnetic stochastic resonance in se…
Partial Discharge Tests Using CIGRE Method II Upon Nanocomposite Epoxy Resins
2007
Nanocomposite polymers are becoming a new family of dielectric materials with promising insulating properties. In order to apply this technology to insulation systems, a study about the material longterm endurance (life) is needed. In this paper results from comparative life tests performed upon base and nanostructured epoxy resin samples are presented. The nanofiller is a organophillic-modified ultra-clean montmorillonite. Specimens were subjected to ageing under surface discharge phenomena using a standard electrode configuration, that is the CIGRE method II. Life data and partial discharge phase resolved patterns, acquired during time under stress, are presented and commented, in order t…
Space Charge Dynamics in Nanostructured Epoxy Resin
2008
The results of a comparative analysis performed on specimens of nanostructured epoxy resins obtained by different filler concentrations are reported in this paper. The specimens were prepared by dispersion of bohemite nanoparticles into a cycloaliphatic epoxy resin cross linked under UV. Dielectric properties, in particular space charge accumulation, are measured as a function of nanofiller content. Results indicate that space charge build up and charge mobility are affected largely by filler content. Concentrations of nanofiller of 5-7 wt% show a significant decrease of the space charge with respect to the base epoxy-resin and an increased mobility of negative carriers .
Stochastic resonance in magnetic systems described by Preisach hysteresis model
2005
We present a numerical study of stochastic resonance in magnetic systems described by Preisach hysteresis model. It is shown that stochastic resonance occurs in these systems. Specifically, the signal-to-noise ratio sSNRd and the signal amplification sSAd present a maximum as a function of noise intensity. We also found that the hysteresis loops, dynamically described by the system, are strongly modified near the maxima of SNR and of SA.
Electrical tree growth in EVA-layered silicate nanocomposites
2006
This work deals with the growth of electrical treeing in different EVA-layered silicate nanostructured compounds. The experimental activity evidenced that the intercalated nanocomposites have longer lifetimes than pure EVA under the same constant AC stress conditions. A monitoring of the tree growth morphology allowed to evidence very interesting features of the intercalated nano-compounds showing a barrier effect to the treeing path. A preliminary investigation on the possible arrangement of the filler particles inside the matrix was also carried out.
On the dependence of magnetic stochastic resonance features on the features of magnetic hysteresis
2005
Numerical study of magnetic stochastic resonance (SR) in several magnetic systems having different hysteresis loops was performed. The various hysteresis loops were modeled by using Preisach model in which several identification functions were used. The results showed the dependence of SR on the parameters of Preisach function. The results also showed how the field H/sub 0/ shifted the onset of SR and how a large dispersion of the distribution of hysterons degraded the SR.
Model of ageing inception and growth from microvoids in polyethylene-based materials under AC voltage
2008
Several degradation mechanisms may affect polymeric insulation system reliability. Some authors postulate that, even in a perfect dielectric, nanoscale cavities can enlarge due to various mechanisms (from mechanical fatigue to lowering of the degradation reaction energy barrier) up to a point where highly energetic phenomena, which bring about breakdown, can be incepted. Other authors are more focused on the inherent limits of manufacturing processes, which leave cavities within the insulation system whose size is large enough to cause electron avalanches, thus a measurable partial discharge (PD) activity, from the time the system is put in service or as a function of external factors (e.g.…
Electric strength, space charge and surface discharge characterization of nanostructured epoxy-silicate insulating materials
2005
A set of surface discharge ageing procedures, space charge observations and dielectric strength measurements has been implemented on a type of insulating nanofilled epoxy-resin (nanostructured by compatibilised synthetic layered silicates) and on its non-filled base resin. Promising improvements in the electrical behaviour of the nanofilled epoxy, particularly as concerns surface discharge endurance, were detected. Regarding space charge, it was found that its accumulation rate as a function of ageing time is lower for the nanostructured resin. Finally, the nanofilled material evidenced a highly homogeneous behaviour of the dielectric strength data distribution.
Electrical treeing in EVA-bohemite and EVA-montmorillonite nanocomposites
2009
The present experimental work focuses on the growth of electrical treeing inside different Ethylene-vinyl acetate (EVA) nanocomposites containing Bohemite (an aluminum oxide hydroxide) and Montmorillonite (a phyllosilicate clay mineral) nanoparticles. Bohemite and Montmorillonite particles have different aspect ratios: the first one has a nanometric cube-like symmetry, while the latter has a typical layered structure. The results evidence that the growth of the electrical treeing inside the original polymer can be altered significantly by the dispersion of inorganic nanoparticles.
Dielectric spectroscopy analysis of EVA-silicate nanocomposite insulating materials
2005
Nanocomposite materials show promising results for applications as electrical insulation. Among several materials presently under investigation, previous works indicate that polypropylene and ethylene-vinilacetate filled by nanosilicates present lower content of space charge and higher electric strength. However, efforts are needed to explain nanocomposite behaviour and characterize their electrical, thermal and mechanical properties. In this paper, the results of broad-band dielectric spectroscopy performed on ethylene-vinylacetate copolymer filled by layered micro and nanosized silicates are reported. The nanofillers consist of montmorillonite and fluorohectorite, that is, natural and syn…
An improved MSD-based method for PD defects classification
2006
The new proposed method of pattern recognition is based on the application of Multi-resolution Signal Decomposition (MSD) technique of wavelet transform. This technique has showed off interesting properties in capturing the embedded horizontal, vertical and diagonal variations within an image obtained from the PD pattern in a separable form. This feature was exploited to identify in the PD pattern's MSD, relative at various family of partial discharge sources, some detail images typical of a single discharge phenomenon. The classification of a generic PD phenomenon is feasible through a comparison between its detail images and the detail images typical of a single discharge phenomenon. Test…