1,721,139 research outputs found
Piezolelectric Nanocomposite Materials for Mechanical Sensing and Energy Harvesting
Full text linkThis paper explores the design, fabrication, and application of piezoelectric nanocomposite materials, focusing on their utilization in mechanical sensing and energy harvesting. By embedding piezoelectric nanofibers within polymeric matrices, we have developed multifunctional materials with enhanced mechanical properties and significant piezoelectric responses. Two specific applications are highlighted: the integration of piezoelectric composites into prosthetic devices for self-sensing capabilities and the use of PZT (Lead Zirconate Titanate) nanofibers for energy harvesting. The results demonstrate that these materials are promising candidates for next-generation biomedical devices and energy-efficient systems
Editorial
No full textIn my new role as DEIS president for
2024, it is a pleasure to introduce myself
to the entire community. I am a profes
sor of Innovative Electrical Technologies
and Insulation System Design and
Diagnostics at the University of Bologna.
Previously, I served as DEIS Meetings
Committee chair from 2016 to 2019, VP
technical in 2020 to 2021, and VP admin
in 2022 to 2023. I am eager to continue
contributing to the growth and success of
DEIS in the coming year
Evaluation of dc insulation performance based on space-charge measurements and accelerated life tests
No full textSpace charge observation is becoming the most widely used technique to evaluate polymeric materials for dc insulation applications, particularly HV cables. However, quantities are still lacking that can help to summarize and interpret the huge amount of data resulting from space charge measurements, and that also are associated with the electrical performance of the insulation. The purpose of this paper is to propose test methods and parameters, based on the pulsed electroacoustic technique, which can be used for the evaluation of the electrical performance of polymeric insulation under dc fields. These parameters are related to the space charge magnitude and mobility, as well as to the internal electric field amplification, the rate of charge accumulation, and the threshold field above which charge is stored in the insulation. In order to investigate the meaning of the parameters proposed for the assessment of insulation performance, the correlation between these parameters associated with space charge and insulation life is discussed. Examples are reported with reference to five different candidate materials for dc cable insulation
The effect of non-sinusoidal voltage on intrinsic aging of cable and capacitor insulating materials
No full textThis paper investigates the effect of non-sinusoidal voltage, i.e. voltage affected by the presence of harmonics, on intrinsic aging of cable and capacitor insulating materials, i.e. crosslinked polyethylene (XLPE) and polypropylene (PP). The results of life tests under sinusoidal and distorted voltage, the latter obtained superimposing one or more harmonics on the 50 Hz component, are processed by statistical techniques derived from design-of-experiment procedures. It is shown that the factor predominant on aging acceleration due to the voltage distortion is voltage-peak increase, but also waveform slope and voltage rms value have statistical significance. Life models are obtained for XLPE and PP insulating materials, which show the endurance of the two materials to aging under non-sinusoidal conditions. © 1999 IEEE
Searching for the factors which affect self-healing capacitor degradation under non-sinusoidal voltage
No full textThe purpose of this paper is to show how voltage distortion may cause accelerated aging of insulation systems, particularly of self-healing capacitors. Distortion is due to the presence, in the supply voltage waveform, of harmonics which are typically detected in distribution ac networks. These harmonics sum up to the fundamental component giving rise to voltage waveforms which can considerably differ, for peak value and shape, from the sinusoidal waveform. The results of life tests carried out on capacitors subjected to non-sinusoidal voltage allow an investigation on the most significant factors which affect endurance to be performed, resorting to appropriate statistical techniques. Voltage peak seems to be the most significant factor for aging acceleration, but also waveshape and rms voltage play a significant role. A life model is thus derived, which provides a relationship between failure time, defined as the time required to reach a given decrease of capacitance, and appropriate figures derived from the voltage waveform. These figures take into account, in fact, voltage peak, waveshape and rms
The effect of voltage distortion on ageing acceleration of insulation systems under partial discharge activity
Full text linkThe features of harmonic distortion which may affect significantly the reliability of typical ac-power network equipment, such as low-voltage self-healing capacitors used for reactive power and harmonic compensation are investigated. Moreover, the effect of high-frequency pulse-like voltage generated by adjustable speed drives (ASD) on electrical machine insulation is also investigated, resorting to life tests carried out on different insulating materials of the standard and "corona resistant" type, at electrical field levels able to incept partial discharges (PD)
Multiscale properties of polymeric insulating materials: from microscale polarizability to macroscale permittivity
Full text linkThis article presents an innovative and easy way for the calculation of the real part of permittivity for some of the most common insulating materials used for electrical applications, namely: polyethylene (PE), polypropylene (PP), polytetrafluorethylene (PTFE), ethylene-propylene diene monomer (EPDM), polyamide-imide (PAI), and epoxy resin (EP). This is achieved by the implementation and validation of the additivity approach for polarizability, along with the derivation of molecular volumes by means of chemical calculations involving real density of the considered materials. The proposed approach significantly reduces the computational time and effort for the calculation of macroscopic permittivity. Simulated values show good accordance with experimental results, thus validating the approach
Radiation-Induced Degradation in Polymeric Materials: Alterations in Physical–Chemical Properties and Their Effects on Electrical Performance of Insulation Systems
No full textThis paper investigates the effects of radiation on polymeric materials used as insulation systems in electrical equipment such as cables for nuclear and particle accelerator applications. After a detailed description of the physics of radiation-induced damage in the polymeric matrix, a comprehensive analysis of the physical–chemical and electrical properties of aged materials is carried out, ranging from the microscopical ones (e.g., variation in crystallinity) to macroscopical ones (e.g., mechanical and electrical properties). In particular, significant attention is given to the electrical tests aiming at investigating the impact of free charges and radicals, induced by radiation, on conductivity and permittivity variations of the studied insulation system. The results show that electrical properties may successfully be correlated with state-of-the-art condition monitoring techniques, for example, oxidation level and mechanical resistance, suggesting the possibility to use electrical quantities as a diagnostic method for the nondestructive evaluation of the electrical equipment ageing state
Aging acceleration of insulating materials for electrical machine windings supplied by PWM in the presence and in the absence of partial discharges
No full textThe aging behavior of three kinds of insulating materails for electrical machine windings supplied by pulse width modulation (PWM) inverters in the presence and absence of partial discharges were investigated. Life tests were carried out on twisted pairs subjected to sinusoidal voltage, as well as unipolar and bipolar square pulses. The aging acceleration under high frequency pulses were found to occur in the absence of partial discharges. The failure times were proportional to the ratio of test to supply frequency. The beakdown was much more accelerated under partial discharge regime and the failure times were observed to follow a superlinear law as function of frequency
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