Effect Of Space Charge Accumulation Research Articles

Aging Characteristics of the Insulation Layer of HVDC Cables and Effect of Space Charge Accumulation on Electric Field Distribution

Aging Characteristics of the Insulation Layer of HVDC Cables and Effect of Space Charge Accumulation on Electric Field Distribution

Effect of Space Charge Accumulation in Insulating Material Formed by DC Voltage Application Through Air Gap on Discharge Inception Voltage

In this paper, an accumulation of space charge in insulating materials and its effect on the discharge inception voltage were investigated by measuring the space charge distribution formed in the materials by applying a dc voltage to it through an air gap. In previous studies, the space charge accumulations in insulating materials were observed by applying the dc voltage to them through contacted electrodes. However, the voltage is applied to the material through the air gap in the actual usage of some insulating materials for motor windings. Therefore, we conducted the measurement of the space charge distribution in a sample with an air gap. The results showed that as space charge accumulates inside the insulating material, the voltage applied to the air gap increases, and the discharge inception voltage decreases.

A Contribution to Thermal Ageing Assessment of Glass Fibre Insulated Wire Based on Partial Discharges Activity

This paper aims to evaluate a Type-II insulated wire (i.e., Glass fibre insulated wire) as a function of thermal ageing time based on partial discharges (PD) activity. Partial discharge inception voltage (PDIV), partial discharge extinction voltage (PDEV), and repetitive partial discharge inception voltage (RPDIV) measurements have been performed on both unaged and thermally aged specimens. Each specimen modelled the turn-to-turn insulation; hence it was made by a pair of Glass fibre wires wrapped in PTFE tape for a mechanical purpose. The PD tests have been carried out under positive and negative unipolar square waveform excitations using different rise times: 80, 400 and 800 ns. The trend of PD quantities vs exposure time demonstrates that the effect of space charge accumulation under unipolar excitation must be taken into account when unaged and thermally aged specimens are compared. Results revealed that although sometimes thermally aged samples might show a temporary superiority in the short run, unaged ones always present a better performance after space charge accumulation, as expected. Following the statistic postprocessing of the collected data, shape/slope parameters of the Weibull distribution relevant to PDIV can be used as an ageing indicator for Glass fibre insulated wire. Finally, the permittivity evaluation vs thermal and electrical stresses have been performed, relying on the measured capacitance of each specimen just after every PD test. Such analysis revealed that thermal ageing increases permittivity in the long run. However, electrical stress has different impacts on permittivity depending on the rise time, polarity, and magnitude of the applied voltage.

Partial discharge characteristics of an air gap defect in the epoxy resin of a saturable reactor under an exponential decay pulse voltage

Saturable reactor insulation is currently stressed by an exponential decay pulse voltage under normal operating conditions. The partial discharge (PD) characteristics of epoxy resin under an exponential decay pulse voltage were studied here and were compared at 25 and 110°C. In addition, this study compares these PD characteristics with those under a sinusoidal voltage to better measure the insulation design margin of the saturable reactor under an exponential decay pulse voltage. Finally, this study explains the PD mechanism based on the three-capacitor circuit model and space charge accumulation. Compared with the sinusoidal voltage, a higher amplitude, a higher inception voltage and fewer PDs are obtained under the pulse voltage. The reason may be related to the accumulation of space charge. Due to the duality of the space charge effect, the promotion effect of space charge accumulation on the PD under the pulse voltage is dominant, and an increase in temperature will weaken the promotion effect. In contrast, the inhibitory effect of space charge accumulation on the PD under the sinusoidal voltage is dominant. The experimental results can provide a basis for the optimal design of saturable reactor insulation under an exponential decay pulse voltage.

Effect of deep level defects on space charge distribution in CdZnTe crystals

CdZnTe recently emerged as a leading semiconductor crystal for fabricating room-temperature x- and gamma-ray imaging detectors, due to its excellent energy resolution and sensitivity. However, its wide deployment is hampered by the low availability of high-quality CdZnTe crystals. As-grown CdZnTe crystals generally encounter the problems arising from the impurities and defects, especially deep level defects. The presence of impurities and defects leads to severe charge trapping, which significantly affects detector performance. Especially for high counting rate imaging detector used in medical imaging and tomography, the accumulation of space charge at deep levels significantly deforms the electric field distribution and subsequently reduces the charge collection efficiency. Therefore, a considerable interest is focused on the investigation of the space charge accumulation effect in CdZnTe crystal, which is the key factor to improve the performance of high counting rate imaging detector. Thus, the goal of this work is to investigate the effects of deep level defects on space charge distribution and internal electric field in CdZnTe detector. In order to reveal the major problem therein, Silvaco TCAD technique is used to simulate the space charge and electric field distribution profile in CdZnTe detector with considering the typical deep level defects <inline-formula><tex-math id="Z-20201111102325-1">\begin{document}$ \rm Te_{Cd}^{++} $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="22-20200553_Z-20201111102325-1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="22-20200553_Z-20201111102325-1.png"/></alternatives></inline-formula>in CdZnTe crystals with activation energy of <i>E</i><sub>v</sub> + 0.86 eV and concentration of 1 × 10<sup>12</sup> cm<sup>–3</sup> at room temperature. The simulation results demonstrate that the Au/ CdZnTe /Au energy band tilts intensively with the increase of applied bias, which makes the deep level ionization fraction increase. The space charge concentration also increases in the crystal. Meanwhile, the dead layer of electric field distribution decreases, which is of benefit to the carrier collection of CdZnTe detector. In addition, under the premiseof the high resistivity of CdZnTe crystal, the reduction of deep level defect concentration located at <i>E</i><sub>v</sub> + 0.86 eV can narrow the internal dead layer moderately. The deep level defect located at <i>E</i><sub>v</sub> + 0.8 eV can also reduce the space charge concentration near the cathode, which flattens the electric field distribution with narrower dead layer, thus significantly improving the carrier collection efficiency of CdZnTe detector. These simulation results will provide meaningful theoretical guidance for further optimizing the CdZnTe crystal growth, device design and fabrication.

Influence of extraction barrier on the loss process of photogenerated charge carrier in polymer bulk heterojunction solar cells

Based on a full device model adopting three-dimensional Pauli master equation approach, the charge carrier loss process due to poor extraction channels between electrode and active layer in polymer bulk heterojunction( BHJ) solar cells was studied. The influence of barrier height on device performance was simulated to reveal the importance of electrode improvement. It was found that relatively large extraction barrier height(over 0.40 eV) can lead to the significant diminishing of the overall charge collection efficiency, since bimolecular recombination rate would increase to a high level due to enhanced space charge accumulation effect near electrodes. In contrast, the percentage of charge carrier annihilated due to geminate recombination did not change significantly with barrier height variation. Our simulation results may provide the basis for a more accurate model and potential direction of polymer BHJ solar cells improvement.

エナメル線の被覆用絶縁材料中に蓄積する空間電荷の分布測定

Space charge distribution in a thin insulating layer of an enameled wire for motor windings was carried out using an improved PEA (pulsed electro-acoustic) measurement system under a dc and a square shape voltage. When a high voltage is applied to the windings of motor, a PD (partial discharge) sometimes occurs. Since the PD gives a physical damage to the insulating layer, many researchers have investigated the mechanism of PD generation. From their results, some researchers have pointed out the effect of space charge accumulation. Therefore, measurements of the space charge distribution in the insulating layer of the winding are required. The space charge accumulation in the insulating material is usually carried out using the PEA method. In this method, we observed the space charge distribution in film shape samples. However, the properties of specially-made film samples are different from those of the insulating layer with the actual configuration of the winding wire, and it is difficult to evaluate the actual influence of the space charge to the motor windings. In this research, we have improved the PEA system which is enable to measure the space charge distribution in the actual insulating layer of the winding wire.

Temporal evolution of atmosphere pressure plasma jets driven by microsecond pulses with positive and negative polarities

Current-voltage characteristics, discharge images, and optical spectra of atmospheric pressure plasma jets (APPJs) are studied using a microsecond pulse length generator producing repetitive output pulses with different polarities. The experimental results show that the APPJs excited by the pulses with positive polarity have longer plume, faster propagation speed, higher power, and more excited species, such as , O, He, , than that with the negatively excited APPJs. The images taken using an intensified charge-coupled device show that the APPJs excited by pulses with positive polarity are characterized by a bullet-like structure, while the APPJs excited by pulses with negative polarity are continuous. The propagation speed of the APPJs driven by a microsecond pulse length generator is about tens of km/s, which is similar to the APPJs driven by a kHz frequency sinusoidal voltage source. The analysis shows that the space charge accumulation effect plays an important role during the discharge. The transient enhanced electric field induced by the accumulated ions between the needle-like electrode and the nozzle in the APPJs excited by pulses with negative polarity enhances electron field emission from the cathode, which is illustrated by the bright line on the time-integrated images. This makes the shape of the APPJ excited using pulses with negative polarity different from the bullet-like shape of the APPJs excited by pulses with positive polarity.

Extrinsic effects on dielectric response of ultrafine grain BaTiO3 ceramics

The complex dielectric response of ultrafine grain barium titanate ceramics is investigated using broadband dielectric spectrometer. Extrinsic effects like conduction, space charge associating with grain boundaries are discussed. One dielectric relaxation ascribes to the interaction of defects with grain boundaries, for which the activation energy fitted by Arrhenius equation is equivalent to 0.26 eV and the value shifts to 0.41 eV after annealing treatment. Another relaxation phenomenon locating at elevated temperature can be attributed to interfacial polarization due to space charge accumulation effect. The study of complex impedance spectra suggests that grain boundary effects support extrinsic mechanism.

Charge accumulation and frequency characteristics of sequential tunneling.

This paper, as an addendum to Phys. Rev. B 46, 4714 (1992), provides a study of the finite frequency spectrum of noise current in sequential tunneling through double-barrier structures and the effect of space-charge accumulation.

Space charge effects in resonant tunnelling

The effect of space charge accumulation in resonant tunnelling devices is investigated. It is shown that the resonant current through a symmetric double-barrier device flows immediately after opening the resonant tunnelling channel and does not require an exponentially long time to reach its steady-state value. It is also shown that space charge effects increase the width of the resonant peak in the I-V characteristic of a double-barrier device which tends to reduce the magnitude of the negative differential resistance.

Building on the Gunn Effect

The solid-state scientists from industry, university and Government laboratories who gathered behind closed doors at the University of Colorado late in June weren't concerned with the leakage of industrial secrets. The competitors were all there; nobody without something to contribute was invited. The secrecy, in fact, was less to hinder the interchange of information than to permit such an interchange in a manner that would not be construed later as public disclosure. The secrecy was designed to guard property rights, not information, relating to what is called the Gunn effect, the electronic phenomenon discovered five years ago and now laying a base for what one Cornell University scientist believes to be the hottest new piece of industrial technology since the transistor. The Gunn effect and a successor, the limited space charge accumulation effect, were laboratory curiosities only a few years ago. They are dependent on oscillatory properties of the often-contrary semiconductor, gallium arsenide. The Gunn effect was discovered by Dr. Ian Gunn of IBM in 1963; the limited space charge effect was found by Dr. John Copeland of Bell Telephone Laboratories in October 1966. Now both are under intensive development by many organizations in the United States, Japan and several European nations. If development succeeds, the solidstate oscillators-little chips of gallium arsenide only a few times the diameter of a human hair-may do for microwave transmitters what transistors did for radio receivers: reduce them to pocket size. Oscillators now used in such circuitry are bulky and expensive vacuum tubes. Conventional microwave transmitters-frequencies in this range are in billions of cycles per second-can comprise rooms full of equipment. Miniaturization could accomplish such things as: * personalized radar, to be used by the blind, or by hunters, or as navigation aids on small craft and pleasure boats; * combined radio and television tieing home or office to all the world for the cost of a local phone call; * commercial radio-telephone links in remote areas where present heavy equipment can't be transported; * lightweight microwave transmitters for communications with spacecraft: an application already being tested by the National Aeronautics and Space Administration. All of this depends on the behavior of electrons in solids. The free electrons that are responsible for electrical conduction in solids occupy what are called energy bands: There are certain ranges of energy that the laws of quantum mechanics permit electrons to have, and these are separated by gaps, the energy values of which electrons may not have. When a voltage is applied across a piece of conductor, the electrons feel a force which causes them to move.