Positive DC Bias Voltage Research Articles

Effect of Harmonic Superimposed DC Voltage on Electrical Tree Characteristics in XLPE

As the insulation material of HTS DC cable, cross-linked polyethylene (XLPE) will meet the dual effects of low temperature and the harmonic superimposed DC voltage during its operation, which will change the aging process of XLPE. To solve this problem and to provide the theoretical basis for the design of HTS cable, electrical treeing process under harmonic superimposed DC voltage at 30 and -196 °C were investigated in this study. Results revealed that the treeing process under harmonic superimposed DC voltage has polarity effects, that positive DC bias voltage is easier to initial electrical tree than negative DC bias voltage. Although low temperature slows down the electrical treeing process, we still should pay more attention to the third harmonic in the daily operation of HTS cables.

Effects of Temperature Gradient on Electrical Tree Initiation and Breakdown Phenomenon in XLPE Under Harmonic Superimposed DC Voltage

In this article, the temperature of the needle tip and the ground electrode were changed to obtain different temperature gradients. The harmonic superimposed DC voltage was also simultaneously applied to study the electrical tree initiation, growth and breakdown characteristics in cross-linked polyethylene (XLPE) under the temperature gradient. The tree inception voltage, tree structure, tree length, accumulated damage (AD) and breakdown time were used to analyze the electrical tree degradation process. It was found that the greater the temperature gradient, the easier it is for electrical trees to be initialed which is related to the different charge behaviors affected by the trap distribution indicated by surface potential decay (SPD) results at different temperatures. With the temperature gradient increasing, the electrical tree length increases firstly but then decreases slightly when the temperature of the ground electrode is fixed, but the electrical tree length and AD increase linearly with the temperature gradient increasing when the temperature of the needle tip is fixed. The temperature rise of the ground electrode has a more serious impact on the safety of the insulation compared with the temperature rise of the needle tip. Positive DC bias voltage is more likely to cause damage and breakdown than negative DC bias voltage under the temperature gradient. These results indicate that the temperature gradient and harmonic superimposed DC voltage will promote the electrical growth in cable insulation, so special attention should be paid to the safety of electrical equipment under such special conditions.

Simulation study of a pulsed DBD with an electrode containing charge injector parts

By using a multispecies fluid model, the tunability and controllability of plasma parameters such as distributions of electron density, electron energy, ion density, and electric field in a microdielectric barrier discharge (DBD) with a charge injector electrode and driven by negatively polarized nanosecond pulsed voltage superimposed on a positive DC bias voltage are investigated. To this end, the effects of changing features of pulsed voltage like pulse rise time (10–20 ns), pulse peak width (10–15 ns), and pulse fall time (20–30 ns) on characteristics of argon plasma formed inside the reactor are studied. The results show that with the increase in pulse width and pulse rise time, the density of electron and ion increases, while fall time change does not significantly affect the plasma parameters. Generally, the results of this study explicitly prove the possibility of controlling plasma formed inside DBD reactors driven by negative pulse voltage combined with a positive DC voltage, which is very important in waste gas conversion applications.

The synergism of peak to peak value, frequency and superimposed DC bias voltage on electric-field-induced strain of PZT based-macro fiber composites

The macro fiber composites (MFCs) with uniform and repeatable electromechanical performance have been a popular choice in various applications like structural actuation, vibration control, structural health monitoring, and energy harvesting. Herein, the strains of lead zirconate titanate based MFCs subjected to various driving signals were conducted via the strain-electrometry method. The formation mechanism of the strains was profoundly expounded, and the variation of the strains as a function of peak to peak value, frequency and superimposed DC bias voltage was further explored. The results demonstrate that both longitudinal and transverse strain-voltage curves with the voltage cyclic loading are closed “ellipse-like” hysteresis loops, in which the strain of ascending branch is smaller than that of the descending branch. Both strains increase with increasing the peak to peak value of driving signal and the increase is more remarkable at smaller bias voltage and lower frequency, while decrease with increasing the positive DC bias voltage and the decrease is specially obvious at larger peak to peak value and lower frequency. Besides, the dispersive effect of the strains induced by larger peak to peak value, particularly with smaller superimposed bias voltage, is more apparent than that induced by smaller peak to peak value. The longitudinal and transverse strains of MFCs with an active area of 40 mm × 30 mm range from 74.8 με to 1688.3 με, and 20.3 με to 488 με, respectively. This research indicates that through properly and carefully synthetical modulation of electrical parameters of driving signal, a notably enhanced strain can be achieved in MFCs for the specific applications such as actuation and high frequency structural control.

Growth and partial discharge characteristics of electrical tree in XLPE under AC-DC composite voltage

The growth characteristics of electrical trees under DC and AC voltages are quite different. In order to investigate the influences of AC component in HVDC cable system on the electrical tree properties, the growth and discharge characteristics of electrical trees under AC-DC composite voltages were studied in this paper. The results showed that the AC component greatly accelerated the developing process of the electrical trees. The influences of the positive and negative DC bias voltages on the electrical tree growth properties were quite different. The growth rate under negative DC bias voltage was similar to that under pure AC voltage and pine-branch type electrical trees were more likely to form. In contrast, the growth rate of the electrical tree increased with the increase of the positive DC bias voltage and it was much faster than the negative DC biased one. More branch-like electrical trees would form under positive DC bias voltage. When the AC component decreased, the developing process of the electrical tree was fairly tough and it was easy to form bush-like electrical trees, which were the typical conducive electrical trees with fairly small discharges. Under the positive DC bias voltage, there was a fast re-growth process of electrical tree after the bush tree formed, and the positive DC bias voltage could promote the coming of the re-growth process. However, the detected partial discharge during this process was quite small. The test results indicated that it may pose a great threat to the safety of the cable insulation if there is a large AC component in the HVDC cable system.

Hybrid simulation of a dc-enhanced radio-frequency capacitive discharge in hydrogen

A PIC-MCC/fluid hybrid model was employed to study a parallel-plate capacitively coupled radio-frequency discharge in hydrogen, under the application of a dc bias voltage. When a negative dc voltage was applied to one of the electrodes of a continuous wave (cw) plasma, a ‘beam’ of secondary electrons was formed that struck the substrate counter-electrode at nearly normal incidence. The energy distribution of the electrons striking the substrate extended all the way to VRF + |Vdc|, the sum of the peak RF voltage and the absolute value of the applied dc bias. Such directional, energetic electrons may be useful for ameliorating charging damage in etching of high aspect ratio nano-features. The vibrational distribution function of molecular hydrogen was calculated self-consistently, and was found to have a characteristic plateau for intermediate values of the vibrational quantum number, v. When a positive dc bias voltage was applied synchronously during a specified time window in the afterglow of a pulsed plasma, the ion energy distributions (IEDs) of positive ions acquired an extra peak at an energy equivalent of the applied dc voltage. The electron energy distribution function was slightly and temporarily heated during the application of the dc bias pulse. The calculated IEDs of and ions in a cw plasma without dc bias were found to be in good agreement with published experimental data.

Control of ion energy distributions using a pulsed plasma with synchronous bias on a boundary electrode

Ion energy distributions (IEDs) on a grounded substrate in a Faraday-shielded argon inductively coupled plasma were measured with a retarding field energy analyzer. A Langmuir probe was also used to measure space- and time-resolved plasma parameters. IEDs and plasma parameters were studied with continuous or pulsed positive dc bias voltage on a ‘boundary electrode’ in contact with the plasma. For continuous wave plasmas without applied bias, the IED exhibited a single broad peak at the plasma potential. Applying a continuous positive dc bias on the boundary electrode shifted the peak of the IED to higher energy. Application of a synchronous dc bias on the boundary electrode during the afterglow of a pulsed plasma resulted in a double-peaked IED. The mean energies of the two peaks, as well as the peak separation, were controlled by adjusting the applied dc bias and the discharge pressure. The full width at half maximum (FWHM) of the peak corresponding to the synchronous dc bias diminished with decreasing electron temperature. The FWHM was controlled by varying the time window in the afterglow during which dc bias was applied.

Electrical and Thermal Interface Conductance of Carbon Nanotubes Grown under Direct Current Bias Voltage

The electrical resistance of individual multiwalled carbon nanotubes and the thermal interface resistance of nanotube arrays are investigated as functions of dc bias voltage used during growth. Nanotubes were grown from Fe2O3 nanoparticles supported on Ti/SiO2/Si substrates by microwave plasma chemical vapor deposition (MPCVD) under dc bias voltages of −200, −100, 0, +100, and +200 V. Electrical resistances of individual nanotubes were obtained from I−V measurements of randomly selected nanotubes, while thermal interface resistances of nanotube arrays were measured using a photoacoustic technique. The study reveals that individual nanotubes and nanotube arrays grown under positive dc bias voltage (+200 V) show significant increases in their electrical and thermal interface conductance, respectively. The nanotubes have been further characterized by X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and electron microscopy in order to account for the marked differences in electrical and thermal int...

Characterization of (100)-orientated diamond film grown by HFCVD method with a positive DC bias voltage

The (100)-orientated diamond film was deposited by hot-filament chemical vapor deposition (HFCVD) technology with a positive DC bias voltage. The morphology, X-ray diffraction (XRD), RAMAN spectrum and dark current versus applied voltage characteristics analysis show that the positive dc bias can increase the nucleation density and (100)-orientated growth, making the growth of the high quality diamond film easier and cheaper than using other methods.

Dendrimer-Templated Fe Nanoparticles for the Growth of Single-Wall Carbon Nanotubes by Plasma-Enhanced CVD

A fourth-generation (G4) poly(amidoamine) (PAMAM) dendrimer (G4-NH2) has been used as a template to deliver nearly monodispersed catalyst nanoparticles to SiO2/Si, Ti/Si, sapphire, and porous anodic alumina (PAA) substrates. Fe2O3 nanoparticles obtained after calcination of the immobilized Fe3+/G4-NH2 composite served as catalytic "seeds" for the growth of single-wall carbon nanotubes (SWNTs) by microwave plasma-enhanced CVD (PECVD). To surmount the difficulty associated with SWNT growth via PECVD, reaction conditions that promote the stabilization of Fe nanoparticles, resulting in enhanced SWNT selectivity and quality, have been identified. In particular, in situ annealing of Fe catalyst in an N2 atmosphere was found to improve SWNT selectivity and quality. H2 prereduction at 900 degrees C for 5 min was also found to enhance SWNT selectivity and quality for SiO2/Si supported catalyst, albeit of lower quality for sapphire supported catalyst. The application of positive dc bias voltage (+200 V) during SWNT growth was shown to be very effective in removing amorphous carbon impurities while enhancing graphitization, SWNT selectivity, and vertical alignment. The results of this study should promote the use of exposed Fe nanoparticles supported on different substrates for the growth of high-quality SWNTs by PECVD.

Stable and erasable patterning of vanadium pentoxide thin films by atomic force microscope nanolithography

Long lasting colored pattern formation on sol–gel deposited vanadium pentoxide (V2O5) thin films is demonstrated by atomic force microscope (AFM) nanolithography. The films can be locally colorized by application of a positive dc bias voltage on the conductive AFM tip. The patterns can be erased, or “bleached,” by application of a negative bias voltage. The changes in optical reflectivity, topography, and conductivity measurements made on as-deposited, colored, and bleached areas were consistent with a model in which the incorporation of hydrogen ions into V2O5 thin films is responsible for the coloration process.

Effects of Ions on Properties of a-Si:H Films Prepared by ECR Plasma CVD Method

A study has been made on the effect of ions on the structural and electrical properties of a-Si:H films prepared by ECR plasma CVD method using H2, He and Ar as a plasma generation gas and SiH4. Deposition rates of over 10 µm/h can be achieved with H2 and He plasma, while Ar plasma generation attains half the deposition rates of H2 and He plasma. The increase of (SiH2)n chains in films is related to the reduced microwave power, increased pressure and positive DC bias voltage being applied to the substrates. The concentration of (SiH2)n chains dominates the photoconductivities. Films having the low concentration of (SiH2)n have ηµτ of 6×10-7 cm2/V after the depositions without substrate heating and 6×10-6 cm2/V after annealing at 280degC for 30 min. The energy transfer of incident ions to the film surface plays the most important role in obtaining highly photoconductive films.