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Design and qualification tests of HVAC and HVDC cables include accelerated life testing on models that can have different length and insulation thickness. Breakdown strength, voltage breakdown and accelerated life tests could be performed using different rising voltage procedures, from continuous ramp to step tests, with rise rate, step width and length of various extent. Comparing then the experimental data is not straightforward. This paper has the aim of deriving expressions which can be used to achieve homogeneous test data sets, including dielectric strength values and life times, from test procedures and models which may differ for voltage rise rate, initial step voltage, step length and width, as well as cable length and thickness. The fitting of the proposed model to experimental data is made referring to test objects consisting of polymeric cable models for HVDC applications.

The expression of the dimensional effect proposed by Enrico Occhini in the 70's is still commonly used to transform cable insulation breakdown and life data, obtained through laboratory accelerated testing on cable models to those relevant to full-size cables. However, the Occhini model does not take into account the dependence of dielectric strength on insulation thickness. Indeed, the balance between the insulation losses generated in the volume and the dissipated energy which occurs through cable insulation surface affect dielectric strength and this can have an impact in cable characterization and testing. This paper presents a modification of the statistical expression of dimensional effect, through the introduction of the dependence of dielectric strength on insulation thickness due to thermal instability. The modelling study carried out in the paper, and the preliminary validation of the revised model, show that the derived correction terms can influence both the design field and the life line estimation for cables having different insulation thickness and lengths. Eventually, it is highlighted how much and in which way the dimensional effect issues can impact on the results of prequalification and type tests made according to the present IEC and CIGRE specifications.

Increasing specific power in emerging assets, as those for electrification transport, is a must that is substantiated through the use of power electronic drives, having increasingly higher voltage, switch slew rate and frequency. This paper proposes time-domain based algorithms able to separate and identify PD pulses occurring during voltage impulse rise time, thus very hardly detectable. The paper investigates the validity of such algorithms as a function of voltage amplitude and modulation frequency. The proposed method is effective in extreme conditions where PD pulses and switching noise overlap integrally in the frequency domain, and they are not easily recognizable in the time domain even by an expert eye.

Pole-to-ground faults in HVDC transmission systems with Voltage Source Converters may cause Long Temporary Over-Voltages on the healthy pole of the configuration. This work aims at a preliminary experimental evaluation of the effect caused by the repetitive application of such Long TOVs on the XLPE insulation for HVDC cables. This paper also studies the changes in the dielectric relaxation properties, with their proposed mechanism, of 0.15 mm-thick XLPE sheets after being subjected to different levels of electrical aging due to TOVs.

The growth of DC supply in distribution and electrical transport raises the issue of assessing the long-term behavior of electrical insulation. Type and prequalification tests are specified for cables, but ensuring a life at low failure probability may be not as obvious as under AC. Besides caring of reliable operation under DC steady-state, design must take into account that DC insulation systems are subjected, during operation, to numerous energizations and, sometimes, voltage polarity inversions, during which the electric field distribution is as under AC. This may favor partial discharge occurrence and, thus, increase degradation rate, because, in general, the partial discharge inception voltage in AC is lower than that in DC. The potential sources of accelerated degradation of DC insulation, and how they can affect reliability and life, are discussed in this paper, focusing on partial discharges. Issues related to partial discharge measurements under DC power supply and diagnostic tools are also examined, highlighting a worrisome lack of focus on DC electrical insulation.

Going towards efficient speed control of rotating machines, transport electrification, renewables and hybrid grids, power electronics is becoming a major player in generation, transmission distribution and utilization of electrical energy. This paper focuses on electrified transport, including aerospace, where the trend to higher voltage and specific power is leading to the investigation of new designs and materials for electrical insulation. Since insulating organic materials are the most likely candidate, measuring partial discharges, which is the most harmful electrical degradation process, is a must. A new technique for separation of partial discharge pulses from commutation noise is presented, which would work even when switch slew rate is so fast that partial discharge pulses, which occur mostly during voltage commutation transients, are almost totally overlapped, in time and frequency, with switching voltage impulses. Separation of partial discharge pulses from noise allows also identification of the type of defects generating PD to be carried out, which is the basis for condition maintenance. It is shown that the proposed technique can work successfully also to measure partial discharges on-line, during operation of rotating machines, thus constituting a promising tool for condition monitoring of motors and drives developed to fit to advanced electrified traction needs.

This study presents a critical evaluation of the effect of two different sample manufacturing techniques on the morphological and dielectric properties of polypropylene (PP)-based nanocomposites, namely mini-scale injection molding (IM) vs. pilot-scale cast film extrusion. Polarized light microscopy revealed that the IM specimen morphology exhibited a layered "skin-core" type morphology, largely differing from the spherulitic morphology of the corresponding extruded cast films. Higher degree of crystallinity in the IM specimens was evidenced by calorimetric and X-ray diffraction methods. The processing-dependent morphological differences were found to affect the isothermal charging current (ICC) and thermally stimulated depolarization current (TSDC) characteristics due to differences in charge mobility and trapping, thus making direct comparison of IM and cast film specimens non-straightforward. Nevertheless, mini-scale injection molding can be seen as a resource-efficient sample manufacturing method for facilitating early-stage screening of the best-performing material candidates, given that the morphological features are carefully taken into account. I. INTRODUCTION The engineering dielectric properties of semi-crystalline polymers are known to be closely related with their crystalline structure and bulk morphological features. For instance, the processing-dependent morphology evolution at different scales of structures ranging from small (lamellar) to large (e.g. spherulitic) scale dictates the formation and dielectric properties of the crystalline-amorphous interface [1], thus making processing and specimen preparation non-trivial factors when evaluating and comparing dielectric performance of new materials [2]-[4]. PP based nanocomposite materials are currently being developed for high voltage direct current (HVDC) cable insulation applications in the EU project GRIDABLE, involving material optimization, compounding and sample manufacturing at several different batch sizes at VTT. Recently, mini-scale compounding and injection molding have been identified as a potential resource-efficient alternative for pilot-scale compounding and cast film extrusion to facilitate early-stage screening of the best-performing material candidates. This paper presents a critical comparison of the morphological and dielectric features of PP-based mini-injection molded and extruded cast film specimens, and evaluates the feasibility of the mini-injection molding technique for assessing the effect of nanosilica on the charge trapping and transport properties of PP based nanocomposites. acceptedVersion

This paper has the purpose to derive an analytical model ("continuum" model) able to describe the behavior of partial discharge (PD) repetition rate and amplitude, occurring in a cavity embedded in polymeric insulation, as a function of the frequency of the supply voltage, going from AC power supply frequency, 50–60 Hz, to DC. In the range between DC and 50–60 Hz focus is made on data coming from tests under AC sinewave with very low frequency (VLF) such as 0.1 Hz and 0.01 Hz, which are commonly used for cable testing. It is shown that the proposed "continuum" model can provide reasonably good fit to the experimental results obtained in the range DC to 60 Hz, regarding PD repetition rate and amplitude. To reach such result, the equivalent circuit is modified from that commonly used and made by fully-capacitive or resistive components, in order to take into account the change of polarization mechanisms which, depending on dielectric material, may play a non-negligible role to establish the repetition rate from low frequency to DC power supply. In addition, the residual voltage after a PD event has to vary with frequency to reach good fitting. Also, it is shown that PD amplitude under DC and VLF can be lower than under AC 50–60 Hz due to the delay time of the firing electron, thus experimental PD amplitude varies with frequency depending on material and defect typology and location.

New nanostructured insulating materials are investigated, within the European project GRIDABLE, to be used for DC cable and capacitors. Besides electrical, thermal and mechanical properties, and life behavior, work is being done to evaluate their capability to endure highly stressing conditions as those cause by the inception of partial discharges, PD. This paper, in particular, analyzes what happens during energization of a DC cable or capacitors, when voltage goes from zero to the nominal value in a few seconds, while the internal electrical field takes longer time to reach the DC steady state configuration. During an energization transient, indeed, electrical field in insulation, and insulation defects (as cavities), is driven by permittivity, not conductivity as in steady state. Hence, PD might occur with high repetition rate, which would not occur, or at much lower repetition rate, in steady state. The way to evaluate the time constant of the transient, that is, through charging current measurement, is described and successfully fitted to the results of PD measurements performed on two types of polypropylene, PP: neat and nanostructured, and a cross-linked polyethylene, XLPE, having significantly different electrical characteristics.

With increased voltage and faster switch rise time, the major issues faced while designing insulation systems for inverter-fed rotating machines is how to measure PD correctly and evaluate PDIV-RPDIV in type and qualification tests for Type I insulation. The current PD measurement techniques as per IEC 60034-27-5 involve the use of high pass filters to suppress the switching disturbance and retain the PD. This approach, however, may be not effective for fast risetime and high-Amplitude voltages, where the disturbance spectrum spreads out in the higher frequency range and can overlap with the PD spectrum, rendering any frequency domain approach poorly effective. Therefore, new techniques for separation of PD from voltage switching disturbance must be investigated. This paper presents a time-domain approach for PD measurement under fast impulses and high voltage values. Results show that this approach has several advantages over the conventional one, and it can be used alone or in combination with filtering techniques.

The presence of harsh electromagnetic environments, as those caused by the use of power electronics in industrial assets and renewables, as well as DC in T&D and transport vehicles, will require new approaches to the design and maintenance of electrical insulations. Stresses that were not experienced under conventional, sinusoidal, power supply will most likely affect significantly life and reliability of electrical equipment. This paper looks at type of stresses, life and aging models, diagnostic properties and fast degradations processes which must be considered at the time of insulation design and diagnosed during operating life. A new algorithm for the estimation of a Dynamic Health Index is proposed, and it is shown how much effective it can be when fast-degradation phenomena, as partial discharges, incept in insulation, requiring immediate maintenance action.

It is well known that partial discharge (PD) is a threat to electrical insulation in all electrical apparatus, but we also know that PD harmfulness, and thus damage, depends on the type of defect generating the PD. As an example, having corona PD in switchgear boxes, rather than surface PD on bushings or internal PD on cable terminations, will trigger completely different actions from maintenance managers, even if the amplitude of the first (corona PD) is much larger than those of the last (internal PD). Indeed, corona PD may not need any medium- to short-term action, surface PD can just require some careful periodic checking, and internal PD in cable joints/terminations will have to be addressed promptly.

This paper reports on the effects of a series of fluid-dynamic dielectric barrier discharge plasma actuators on a NACA0015 airfoil at high angle of attack. A set of jet actuators able to produce plasma jets with different directions (vectoring effect) and operated at different on/off duty cycle frequencies are used. The experiments are performed in a wind tunnel facility. The vectorized jet and the transient of the flow induced by unsteady duty cycle operation of each actuator are examined and the effectiveness of the actuator to recover stall condition in the range of Reynolds numbers between 1.0 × 105 and 5.0 × 105 (based on airfoil chord), is investigated. The actuator placed on the leading edge of the airfoil presents the most effective stall recovery. No significant effects can be observed for different orientations of the jet. An increase of the stall recovery is detected when the actuator is operated in unsteady operation mode. Moreover, the frequency of the on/off duty cycle that maximizes the stall recovery is found to be a function of the free stream velocity. This frequency seems to scale with the boundary layer thickness at the position of the actuator. A lift coefficient increase at low free stream velocities appears to linearly depend on the supply voltage.

Many researchers are investigating the feasibility of using polypropylene in HVDC cables. To understand the basic electrical properties of nanocomposite polypropylene, this work investigates the influence of nanostructuring on DC breakdown strength, life under periodic voltage polarity reversals and space charge accumulation properties. Preliminary results show that unfilled samples feature higher charge accumulation, lower breakdown strength, and shorter life than the nanocomposite counterpart. Based on these results, nanostructured dielectrics can give an important improvement in electrical insulation properties.

The main purpose of this work is to evaluate the charge stored in the surface of a volumetric Dielectric Barrier Discharge (DBD) when supplied by a variable voltage waveform. DBD reactors are used in a wide range of industrial applications and can be considered as a model for partial discharges occurring in insulating materials. The knowledge of the amount of charge stored onto the dielectric surface is a key-role parameter to better understand discharge evolution mechanism.

In this paper the AC and DC partial discharge inception voltages, PDIV, are modeled and validated through measurements performed on multi-layer flat specimens with artificial defects. The results highlight that, depending on temperature and material conductivity, there can be a large difference between PDIV under DC and AC, which depends on insulation temperature, thus, e.g., cable loading. Indeed PDIV-DC can be much larger than PDIV-AC at room temperature, but the two values can be very close (with PDIV -DC being even smaller than PDIV-AC) at maximum operating temperature, i.e. full load.

Distributed generation, dc transmission and distribution, and power electronics for ac/dc/ac conversion bring the advantages of increased control and flexibility in electric power management. These advantages also introduce challenges that must be managed. An electrical environment where voltage is not anymore strictly sinusoidal implies that a new approach for the design and maintenance of electrical insulation systems has to be devised. Non-sinusoidal voltage supply often causes increased failure probability and, thus, reduced reliability and life of an electrical asset. This research addresses the implications of the transient and steady waveform distortion introduced by power electronic systems and dc supply, for which the electrical insulation was designed and tested through consolidated criteria based on sinusoidal voltage supply. Based on condition monitoring, a health index definition is proposed, which allows the condition of the insulation of an electrical apparatus to be assessed as a function of operation time, and, based on the aging and life models, the evaluation of maintenance actions and of the feasibility and extent of life extension plans to be carried out.

In this study we examine both the effect of changing the applied voltage waveform shape and the modulation on-time on the amount of ozone dissolved within a liquid in a dielectric barrier discharges (DBD) bubble reactor. In this device, the discharge forms at the gas–liquid interface allowing for effective transfer of the plasma effluent into the liquid. To produce different voltage waveforms, a multilevel inverter power supply capable of generating arbitrary waveforms without switching-on and switching-off transients has been used. Of the four waveforms used in the study (sinusoidal, sawtooth, square and short-pulse), the square waveform was found to be the most efficient at producing the highest ozone concentration for a fixed peak voltage and average power. To determine the effect of the modulation on-time, the number of cycles during the on-time were increased from 1 up to 1000, adjusting the off-time accordingly to maintain the same duty cycle. Shorter on-time periods were found to be more efficient. Experimental and computational results indicate that the time between subsequent discharges is critical for increased ozone generation efficacy, as this needs to be long enough for ozone produced in one discharge event to diffuse away from the discharge region before the next discharge event occurs, thereby avoiding its partial destruction in the plasma. This insight provides a valuable criterion for the optimization of DBD reactors used in novel biomedical, agricultural and environmental applications.

The problem to recognize the noise and identify the type of source generating discharges detected during campaigns of partial discharge measurements in an electrical apparatus is of utmost importance in the quality control, diagnostic, after laying testing and condition monitoring of DC insulation systems. This paper has the purpose to provide potential tools that are able to give considerable contribution into noise and partial discharge identification. In particular, the use of the T-F classification map, well assessed in AC, is able to cluster separately noise and discharges under DC supply as well. Then, simple algorithms involving the probability distribution of the amplitude values of the detected signals, as well as the recorded signal structure, could allow noise and PD identification, thus enabling noise rejection, and recognition and identification of the type of sources generating discharges.

Partial discharge (PD) detection is a fundamental test for the design and diagnosis of insulation systems, particularly organic materials which must operate throughout their whole life without PD. The measurement of Partial Discharge Inception Voltage (PDIV) and Repetitive Partial Discharge Inception Voltage (RPDIV), the latter defined for power electronic-type supply, is therefore a key issue for the design and qualification tests of Type I insulation system of rotating machines fed by power converters. While experience and technology for PD inception measurements under sinusoidal voltage supply is well established, the same does not hold under repetitive-pulse voltage waveforms, such as those provided by inverters. In addition, electromagnetic noise generated by electronic switch commutation can overlap with PD pulses signals and this is even more cumbersome when fast rise-time components are employed, such as GaN or SiC semiconductors. Moreover, this is also the condition which is the most stressful for stator wire insulation. This work investigates methods to detect PD pulses on enameled wires, rejecting noise efficiently, under repetitive impulsive voltages with different rise times, from 60 ns to 1000 ns. The proposed techniques can be implemented to achieve un-supervised noise rejection, which would be an important goal for both off-line and on-line PD testing.

This paper presents a preliminary feasibility investigation, in the framework of a recent European project, GRIDABLE, aiming at the development of nanostructured Polypropylene, PP, materials as insulation for DC LV-MV capacitors and MV-HV cables. Results of electrical property characterization of various types of PP-SiO 2 materials for DC capacitors are presented in this paper, focusing on breakdown strength and space charge measurements. They indicate that the nanofiller may influence the degradation rate of materials, modifying the space charge accumulation dynamics and extent, as well as the threshold field value for space charge accumulation. Statistical analysis of breakdown voltage shows that the presence of nanoparticles may also improve noticeably the breakdown behavior.

This paper has the purpose to point at the weaknesses implicit in nanostructuration of insulating polymers for cable insulation, with reference to polypropylene and nanosilica. It also tries to single out which types of properties would be more or less affected by nanofiller introduction, and if in a positive or negative way, depending on nanofiller functionalization process. It is shown, for example, that nanofiller might increase, rather than decrease, space charge and conduction current, as an effect of functionalization, and that a decrease of space charge is not necessarily correlated to an increase of life.

Feasibility of HVDC and UHVDC insulated cables should not be considered as obvious when planning and designing transmission DC lines. Proper cable insulation design criteria and development of new materials able to withstand higher electro-thermal stresses could be needed to reach the feasibility of the insulated cable component of an UHVDC link.

This paper introduces techniques for partial discharge, PD, recognition under DC, both in steady state and in transient condition, during which the field in insulation varies slowly from a permittivity-driven to a conductivity-driven profile. This transient can be significantly long, depending on insulating material characteristics, and condition PD phenomenology and impact of PD on insulation life. Focusing mainly on the behavior of PD repetition rate as a function of time, after insulation energization by a DC voltage step, PD triggered by transient field can be separated from those relevant to steady state, which may indicate a criterion to estimate the partial discharge inception voltage, PDIV, under DC supply.

This paper presents an investigation on the effect of the number of levels and voltage magnitude of a multilevel power electronic supply on reliability of insulation systems. Particular attention is given to partial discharge, PD, behavior, referring to organic (Type I) insulating materials used for rotating machines fed by variable source inverters, VSI. As described in standard IEC 60034-18-41 and 42, repetitive voltage impulses, as those generated by pulse-width modulation, PWM, supply, can incept PD due to uneven voltage distribution in windings and transient overvoltage, which would not occur with an AC power supply. The presence of PD will affect drastically reliability, and thus life, of electrical insulation, to an extent which depends on their amplitude and repetition rate. The effect of number of inverter levels and peak voltage on PD repetition rate and amplitude is modelled, validated by experimental data, and correlated to insulation aging rate, showing that increasing the number of levels is beneficial for insulation reliability and providing an analytical support to PD measurements under PWM.

This study presents preliminary results on the morphology, structure and dielectric properties of laboratory scale cast and biaxially oriented silica-PP films, currently being developed in the European project GRIDABLE. Space charge measurements on the thick cast films indicated a reduction of positive space charge and faster depolarization characteristics upon inclusion of nano-silica, being indicative of reduction of trap depth and density distribution in comparison to neat PP. Likewise, for the biaxially oriented silica-PP thin films, increased amount of shallow traps and a reduction of concentration of traps in the deep trap range (∼ eV) were observed. Nano-silica was also found to reduce the dielectric loss at high temperatures in the frequency range appropriate to use. Such dielectric property modifications can potentially lead to benefits for insulation reliability and lifetime, especially at higher temperatures. A two-step compounding via a master batch approach was also found to be a viable option for the up-scaling of nanocomposite production.

This paper presents space charge accumulation characteristics of cable grade and capacitor grade nanostructured polypropylene (PP) materials, providing initial results regarding the electrical properties of nanofilled PP materials belonging to the European project GRIDABLE. This project has the aim to develop DC cable extruded insulation and MV and LV DC capacitor films having enhanced performance with respect to presently used materials. The paper shows that nanostructuration may be beneficial, especially at higher temperature, to improve the capacitor-grade material performance. On the other hand, this work validates the importance of surface functionalization of nanofillers, leading to lower space charge accumulation on DC cable-grade materials. acceptedVersion

This paper shows results of a preliminary study about electric strength and electrical endurance properties of various types of polyimide tapes, including the corona-resistant ones, in the presence and absence of partial discharges. Feasibility of insulation design for applications, such as automotive, where the rated voltage is increasing significantly, and the presence of partial discharges during operating life is likely, in investigated, with apparently positive indications.

This paper highlights the effects voltage supply waveform can have on partial discharge, PD, characteristics in insulation systems of rotating machines fed by power electronics drives. While standards allow both sinusoidal and repetitive voltage impulse waveforms to be used for insulation design and type tests, the dependence of PD on the voltage waveform implies that the machine design and performance can be affected significantly by the waveform. Partial discharge inception voltage, partial discharge patterns and insulation life are, in fact, dependent on the type of test waveform. This can affect significantly the design of machine insulation system.

The partial discharge inception voltage (PDIV) and the repetitive partial discharge inception voltage (RPDIV) are key parameters for the characterization of the insulation system of rotating machines fed by power converters. In particular, these quantities have a fundamental role in the design and qualification of Type I insulation which has to last all life without partial discharges (PD). This paper analyzes the two definitions, taken from the IEC 60034-18-41 and IEC 60034-18-42 standards, and shows potential discrepancies which can affect significantly insulation system design, especially going from two-level inverter to sinusoidal waveforms.

This paper has the aim of providing possible solutions for PD measurements, noise rejection and PD source identification focusing mainly on extruded cables. PD tests performed on defective cables under DC and AC indicate how PD DC measurements can be done effectively, and show that noise rejection and PD source identification approaches used nowadays for AC might be extended with good potentiality also to DC.

In this work space charge accumulation characteristics of nanostructured polypropylene films are investigated, providing preliminary results for the basis of the new materials formulations to be developed in the European project GRIDABLE, where novel MV and LV DC capacitor films having enhanced performance with respect to present polypropylene films are being developed. This paper shows that nanostructuration may be beneficial, especially at higher temperature, to improve material performance. Better space charge performance will help in optimizing the dielectric strength, design field and reliability of the insulation system for DC use. acceptedVersion

There are two thought trends concerning partial discharge, PD, measurements and diagnostics in electrical insulation systems. One is make it simple and refer to PD amplitude and repetition rate. The other is try to identify the typologies of discharges and focus on each type of source generating PD for diagnostic and maintenance decisions. In this paper, an approach towards the determination of a health index for rotating machines is presented. It is based on the harmfulness of typical defects able to generate PD and, hence, on the capability of the detection system (sensor, filters, PD detector, software) to provide efficient noise rejection and/or noise and PD source identification. The output, that is, the global health index, is thought to be helpful to support maintenance manager decisions about the actions which may be needed to keep reliability of a rotating machine at the desired level, and also to evaluate in terms of cost/effectiveness the potential maintenance actions.

This paper discusses challenges to the adoption of long distance HV and UHVDC power transmission cables of 800 kV and higher. Specifically, this paper first discusses current HVDC cable technologies and then presents a procedure to find out what the key parameters are determining the feasibility of a polymeric cable system for ultra-high voltage direct current (UHVDC) applications. An electrical-statistical design process is combined with a thermal design process to determine whether the cable ratings can be achieved in design having long service design. Based on the results of the simulations, material performance gaps are identified and suggestions are made for prioritizing materials research and development.

CIGRE documents, IEEE and IEC standards permit alternate power supply frequencies to reduce the size of the power supply for offline tests, such as those using resonant systems, Very Low Frequency (VLF) and Damped Alternating Current (DAC). To provide insight into the risks of adopting these alternatives, partial discharge (PD) measurements are reported herein for medium voltage (MV) cables with artificial defects, in a range of supply frequencies from 0.01 Hz to 60 Hz and at different temperatures. The results show that varying temperature and frequency changes the PD repetition rate, amplitude and energy, raising questions about the interpretation of diagnostic measurements made at VLF and any other alternate method allowed by the standard.

This paper reports the characterization of a low-power, atmospheric pressure plasma source developed for and successfully tested in applications of plasma medicine. The source produces plasma by ionizing a helium flow containing traces of air. The effluent gas is thus enriched in reactive oxygen and nitrogen species as well as helium metastable excited states. Electrical measurements, Schlieren imaging, OES and various chemical analyses and probes enabled us to fully characterize the plasma source and to determine some fundamental parameters for treating living samples such as the power feeding the discharge, the optimal source to target distance, the maximum exposure time, and to identify the major chemical species responsible for the biological action on exposed living matter.

The attention given to high voltage direct current (HVDC) cables appears to be at an all-time high. In the July/August 2017 issue of IEEE Electrical Insulation Magazine, the focus was on different aspects of the design and testing of HVDC cable systems. There are several reasons for this, one of the most important probably being the worldwide attention on harvesting renewable energy at a scale never seen before. The prices of building large offshore windfarms in Europe as reflected in a recent normalized cost of electricity have unexpectedly dropped in the last year, as illustrated in Figure 1, which will further accelerate the development of HVDC cables to link offshore and onshore substations. The winning bid in 2016 for the Borssele II, 700-MW windfarm in the Netherlands was as low as 54.5€ ($61)/MWh [1].

Defining a methodology providing an objective assessment of the health conditions of electrical apparatus is a must for an effective asset management approach, which can provide the most appropriate Return of Investment (ROI) keeping the asset at the desired reliability level. At present, diagnostic and monitoring techniques are available to evaluate electrical apparatus conditions, but too often the output is made by patterns, values and subjective indications which are not able to provide a real clue to help asset and maintenance manager decisions. This paper proposes an algorithm for the estimation of a health index, HI, for polymeric cable systems based on off-line and on-line measurement of diagnostic markers. The health index is a number ranging between 0 (worst condition, indicating imminent failure) and 1 (unaged cable, potentially able to provide the design life), which can allow a functional estimation of residual life to be obtained. An example of HI and residual life calculation for a cable system is provided, which shows feasibility and potentiality of the algorithm.

It has been demonstrated already that adjustable speed drives, and, in general, power electronics waveforms, can harm insulation systems of rotating machines, causing significant reduction of reliability and life. Indeed, the type of supply voltage made by repetitive impulses alters significantly the electric field distribution in the turn-to-turn and phase-to-ground insulation, and also the machine terminal peak voltage can be increased significantly, with respect to the expected value at the inverter output [1]–[11].

This paper deals with investigation of Partial Discharge (PD) and surface erosion endurance on Type I (organic) insulation. Considering two types of reference materials of the Kapton family, one having enhance resistance to PD (CR, corona resistant), a short-term PD test procedure using needle-plane electrodes was devised in order to get fast characterization of the capability of an insulating material to endure PD. Partial Discharge data and surface erosion were acquired and measured hourly, in order to obtain both a life line plot and a time behaviour of the erosion depth. Life lines were also obtained through accelerated electrothermal life tests, using cylindrical-shape electrodes. The results show significantly different PD endurance and erosion rate between the two tested materials, thus indicating that the investigated short-term procedures may be useful for the selection of insulating materials and for the estimation of the design field.

A new generation of nanostructured polymeric insulating material is being developed under the GRIDABLE European project framework. One of the main objectives of this project is the improvement of the dielectric properties and the life performance of High Voltage DC cables insulating materials. The dielectric performance of pre-production grade PP/SiO2 with different formulations are evaluated in this work by means of space charge accumulation measurements, electrical conductivity tests and statistical analysis of breakdown voltage. Results are compared with state of the art XLPE and PP.

Despite a long series of initiatives, projects and political statements, an objective measure of the actual impact of investments in eGovernment in the Italian regions, and particularly in the Marche Region, is not easy to carry out and appreciate. This contribution makes a first original effort toward this direction, providing an empirical analysis of the progresses obtained in the process of digitalization of the PA and eGovernment in the Marche Region

The electrohydrodynamic (EHD) interaction induced in atmospheric air pressure by a surface dielectric barrier discharge (DBD) actuator has been experimentally investigated. Plasma synthetic jet actuators (PSJAs) are DBD actuators able to induce an air stream perpendicular to the actuator surface. These devices can be used in the field of aerodynamics to prevent or induce flow separation, modify the laminar to turbulent transition inside the boundary layer, and stabilize or mix air flows. They can also be used to enhance indirect plasma treatment effects, increasing the reactive species delivery rate onto surfaces and liquids. This can play a major role in plasma processing and chemical kinetics modelling, where often only diffusive mechanisms are considered. This paper reports on the importance that different electrode geometries can have on the performance of different PSJAs. A series of DBD aerodynamic actuators designed to produce perpendicular jets has been fabricated on two-layer printed circuit boards (PCBs). Both linear and annular geometries were considered, testing different upper electrode distances in the linear case and different diameters in the annular one. An AC voltage supplied at a peak of 11.5 kV and a frequency of 5 kHz was used. Lower electrodes were connected to the ground and buried in epoxy resin to avoid undesired plasma generation on the lower actuator surface. Voltage and current measurements were carried out to evaluate the active power delivered to the discharges. Schlieren imaging allowed the induced jets to be visualized and gave an estimate of their evolution and geometry. Pitot tube measurements were performed to obtain the velocity profiles of the PSJAs and to estimate the mechanical power delivered to the fluid. The optimal values of the inter-electrode distance and diameter were found in order to maximize jet velocity, mechanical power or efficiency. Annular geometries were found to achieve the best performance.

We analyze the state of the art of indicators on eGovernment, eHealth, eProcurement and ePartecipation. We survey the main methodological properties of these indicators, and uncover the principal stylized facts and trends; at the same time, we highlight their heuristic limits and potential inconsistencies. Finally, we address empirically the issue of the explanation of the indexes scores – i.e. how the supply of the various eServices in each country is affected by political, institutional and socio-economic differences, and is followed by actual usage. The econometric analysis uncovers the importance of broadband penetration and higher education as drivers for most of the types of eServices and users (citizens and businesses). Moreover, a corruption-free and agile public sector shows up to be an important pre-condition for more effective supply and usage. Despite severe data limits and the complexity of the underlying diffusion phenomena, our study of eServices availability and usage across European countries is a first empirical contribution aimed at disentangling broad empirical trends – with their correlates - from unresolved methodological issues. As such, this work appears useful to inform the policy debate and practice, in a phase characterized by a prospective reorientation of public eServices provision.

La durezza della crisi economica e la velocita di sfaldamento della base manifatturiera del paese, cosi come emergono dai dati sul reddito pro-capite e la produttivita, travalicano ormai il portato euristico acquisito da categorie analitiche quali "crisi strutturale", "ristrutturazione industriale" o "delocalizzazione produttiva". Allo stesso tempo, il termine di "declino" richiede una disambiguazione. Per la prima volta dal secondo dopoguerra, i fattori di globalizzazione economica e le dinamiche geopolitiche, impattando sugli irrisolti elementi di fragilita del sistema produttivo nazionale, possono innescare esiti di declino industriali auto-cumulativi e non reversibili. Inoltre, l’esame di alcuni dei caratteri del modello di specializzazione italiano e delle dinamiche di generazione e diffusione tecnologica (RS questa pericolosa stasi e poi rafforzata dal protratto impasse del quadro socio-politico e dall’assenza di politiche industriali coraggiose. Il presente contributo, nel riflettere su questi fenomeni "epocali", ripercorre alcune questioni irrisolte sul modello di sviluppo italiano, con l’ambizione di rimettere il tema del declino socio-economico e culturale del paese al centro dell’agenda di ricerca e della politica industriale.

The research on nanofluids has shown important improvements of the electrical performance, but so far the attention has only been focused on their use in transformers. The target of this work is to understand if nanofluids can be applied as insulators for power electronics modules, where the major stresses are caused by square waves or PWM voltages. Breakdown events in non-uniform field conditions and different voltage configurations have been deeply investigated revealing the effects of space charge mechanisms. While for DC fields the nanofluids contribution is positive, a completely different conclusion can be evinced from sinusoidal and square waves, where the situation even worsens at higher frequencies. Schlieren images of breakdown events seem to confirm the postulated hypotheses.

Surface dielectric barrier discharges (S-DBDs) have received renewed attention in recent years for their potential application in emerging biomedical, environmental and agricultural applications. In most of these applications, the plasma is not in direct contact with the substrate being treated and the transport of reactive species from the plasma to the substrate is typically assumed to be controlled by diffusion. Here, we demonstrate that generally this is not the case and that electrohydrodynamic (EHD) forces can produce jets that enhance the delivery of these species, thereby influencing the efficacy of the S-DBD device. In particular, we have studied the degradation of potassium indigotrisulfonate solutions exposed to S-DBDs generated in devices with annular electrodes of diameters varying between 10 mm and 50 mm. All the devices were driven at constant linear power density (watts per cm of plasma length) and although local plasma properties remained the same in all the devices, a three-fold efficacy enhancement was observed for devices of diameter ∼30 mm due to EHD effects.

none 13 si In this contribution, a poly(butylene succinate)-based copolymer containing thioether linkages (P(BS85BTDG15)) has been synthesized and characterized from the molecular, thermal and mechanical point of view. The results have been compared to the parent homopolymer. Films obtained both by PBS and P(BS85BTDG15) have been subjected to surface modification by means of non-thermal plasma surface treatment and the effect on physic/mechanical properties has been considered. Hydrolytic degradation rate under physiological conditions and in vitro biocompatibility of treated and non-treated polymeric films have been also investigated. The introduction of thioether linkages and the plasma etching enhanced the polymer surface wettability, thus resulting in an increased hydrolytic degradation rate. On the other hand, bulk properties were not significantly affected. Biocompatibility assays highlighted the absence of potentially cytotoxic products into the culture medium and proved that the investigated polymeric films can support cell adhesion and proliferation. mixed Fabbri, Martina; Gigli, Matteo; Costa, Michela; Govoni, Marco; Seri, Paolo; Lotti, Nadia; Giordano, Emanuele; Munari, Andrea; Gamberini, Rita; Rimini, Bianca; Neretti, Gabriele; Cristofolini, Andrea; Borghi, Carlo A Fabbri, Martina; Gigli, Matteo; Costa, Michela; Govoni, Marco; Seri, Paolo; Lotti, Nadia; Giordano, Emanuele; Munari, Andrea; Gamberini, Rita; Rimini, Bianca; Neretti, Gabriele; Cristofolini, Andrea; Borghi, Carlo A