Cavity Discharge Research Articles

Partial discharge in a cylindrical cavity in XLPE under DC voltage: Simulation and experiment

A simulation model is established to investigate the influence of applied voltage and temperature on DC partial discharge characteristics of a XLPE sandwich internal cavity sample. The field and temperature dependent conductivity of XLPE is considered, and its influence on the electrical field distribution is computed. The calculation results show that the voltage across the cavity changes with time under constant DC, and the steady cavity voltage is 32.7% higher than that just after voltage application. When calculating the cavity voltage at 70 °C, the error is over 500%, if the characteristics of the conductivity of XLPE is not considered. Residual cavity voltage with the opposite polarity after decreasing voltage is discovered by computation, and discharges with the polarity opposite to the applied voltage are detected by experiment. By simulation, the partial discharge repetition rate increases by two orders of magnitude when the temperature increases from 23 to 70 °C. The repetition rate measured by experiment increased by over one order of magnitude. The change of repetition rate is attributed to the reduction of cavity voltage recovery time influenced by the temperature dependence of the XLPE conductivity.

Foreign Inclusions, Enclosed Cavities, Partial Discharge Models and Discharge Energy: A Short Review Regarding Solid Dielectrics and Composite Insulating Systems

Partial discharges in cavities are one of the main reasons of breakdown of insulating materials and insulating systems in general. The present paper aims at commenting some aspects of the relation between partial discharges and insulation damage. Some basic models explaining the workings and impacts of discharges in cavities are discussed. Discussions about the possibility of damage in the presence of multiple cavities as well as of the risks of minute discharges and/or charging phenomena below the so-called inception voltage are conducted. It is remarked that the question of the relationship between discharge parameters and insulation damage is still an important one, especially for composite insulating systems.

Influence of dielectric constant on dielectric strength by defect discharge and molecular polarization in solid insulation materials

Dielectric constant and dielectric strength are two intrinsic electrical parameters of solid insulating materials. In order to finally understand the relationship between them, the one-sided influence of dielectric constant on dielectric strength is investigated. For theoretical analysis, we propose that the influence is realized indirectly by two mechanisms: defect discharge in the micro level and molecular polarization in the nanoscale. The transition phase is composed of the field enhancement related to permittivity and the breakdown of defect molecular bond. While the local field around the bond is always higher than the cavity interior field, the breakdown field is a competition between the two mechanisms. According to the simulation model of electrostatic field, the electric field around the cavity is significantly enhanced with a larger dielectric constant. In view of the simulation result of partial discharge, the discharge intensity of dielectric and gas breakdown in the cavity is promoted by the increase of material permittivity. To confirm the defect distribution and quantity, several prepared samples are scanned with the ultrasonic microscope and the cavities are measured via image software. Based on the published experiment data from oxide films and polymer bulks, a revised relationship is plotted and fitted for the dielectric strength and the dielectric constant. As molecular polarization is applicable to oxide films with few defects and high permittivities, defect discharge is more effective for polymer bulks with generous cavities and low permittivities. Since molecular polarization leads to breakdown by enhancing the local electric field, cavity discharge is mainly due to the lower breakdown threshold of defect.

DIAGNOSIS AND PHYLOGENETIC ANALYSIS OF THE CIRCULATING PESTE DES PETITS RUMINANTS VIRUS IN Al-SHARQIA GOVERNATE

Peste des petits ruminants (PPR) is a Morbillivirus within the Paramyxoviridae family which characterized by highly contagious nature with high morbidity and mortality rates in domestic small ruminants. The aim of this study was to investigate an outbreak of PPRV in a flock of sheep and goats in Belbes city, AL-Sharkia governorate in 2018 by virus isolation and conventional RT-PCR. Phylogenetic analysis of N gene sequence of PPRV isolate. Also, compare it with other isolate from previous outbreak in Zagazig city, Al-Sharkia governorate in 2017 as a measurement of the infection status in Egypt. The current study applied on a flock of 55 small ruminants (42 goats and 13 sheep) in Belbes city which suspected to be infected by PPRV. All infected animals were not vaccinated against PPRV and randomly move from place to place. The morbidity rate was 100% and mortality rate was (23.8% in goats and 7.69% in sheep). Diseased animals suffered from fever, mucopurulent ocular discharge, nasal discharge, dyspnea, diarrhea, necrotic tissue and diphtheritic membrane in oral cavity. The ten samples (6 tissue scraping from oral lesions and 4 oculo-nasal swabs) were tested by conventional reverse transcription PCR which revealed 100% sensitivity compared to VI (virus isolation) 70%. Comparative of N gene sequence of both PPRV isolates revealed that homogenous population of PPR virus isolates up to 99%. Also, the PPRV isolate of the current study is related to Ethiopian strain and the previous Egyptian strains (Ismailia 3/Egy/2010 isolate, El-Kalubeya isolate and Ismailia 1-2014 isolate). The PPRV isolate of present study and all previous Egyptian isolates belong to lineage IV in phylogenetic analysis. The results emphasize the importance of molecular methods for a broader understanding of the epidemiology and development of the virus in the country.Key words: PPRV; Conventional RT- PCR; phylogenetic analysis; Al-Sharqia

Effect of magnetic field on partial discharge parameters in power cables and on the breakdown characteristics of impregnated paper insulation

This article demonstrates that parameters of partial discharges in power cables and impregnated paper insulation breakdown characteristics vary in presence of grid-frequency alternating magnetic field. Experimental and theoretical demonstrations confirm that magnetic field affects the probability of partial discharges in air cavities inside inhomogeneous insulation. Based on the developed method, the impact of magnetic field on breakdown probability and on Weibull distribution parameters that approximate experimental breakdown voltage data is estimated. The differences in chemical and structural properties of the breakdown area in electrical and electromagnetic fields are determined using scanning electron microscopy and energy dispersive spectroscopy.

Formation of a Plasma Ring by a Microwave Discharge in a Narrow Coaxial Cavity beyond the ECR Region

Results are presented from the experimental study of conditions for the formation of a plasma ring by a microwave discharge in a narrow coaxial cavity in an axisymmetric magnetic field the magnitude of which is below the electron-cyclotron resonance value. It is established that the necessary condition for this process is the presence of an electrostatic wave propagating in the azimuthal direction, the circumference of the plasma ring being a multiple of the wave half-length.

Self-Excitation of Low-Frequency Oscillations in the Plasma Ring Formed by an ECR Discharge in a Narrow Coaxial Cavity

The conditions for the excitation of low-frequency oscillations in a plasma ring formed by an ECR discharge in a narrow coaxial cavity filled with argon were studied experimentally. The domain of the discharge parameters where these oscillations are stable is determined. It is supposed that the oscillations recorded are excited due to the appearance of an electrostatic wave propagating in the azimuthal direction.

Electrostatic field theoretic approach to analyze the partial discharge phenomenon pertaining to insulation degradation

This paper elucidates the application of electrostatic field theory to analyze partial discharge due to the void formation inside the insulating material. Formation of voids leads to accumulation of static charges leading to capacitance build-up. The most probable cause of insulation failure is due to the subjection of high voltage. Prolonged high voltage poses a threat and leads to insulation failure. Failures occur in the tip gap between the conductor and insulating material’s inner periphery. Probable causes of such failures are corona discharge, surface discharge and treeing, leading to formation of Lichtenberger figures in the material and cavity discharge. This paper presents a way of fabricating the inner lining of the insulator with a semiconductor layer obeying avalanche breakdown at breakdown voltage or voltages at which partial discharge is likely to occur. With the onset of high voltage which can cause a discharge, the semiconductor experiences avalanche breakdown giving out a single photon ejection by Geiger mode (principle). A superior prevention method of using Teflon for insulation instead of XLPE/PILC has been suggested and simulated using COMSOL. Detection using Avalanche photo-detector(LiDAR) may enable us to track the probable location of the occurrence of partial discharge and isolate the system.

High-Speed Imaging of Forced Ignition Kernels in Nonuniform Jet Fuel/Air Mixtures

This paper describes experimental measurements of forced ignition of prevaporized liquid fuels in a well-controlled facility that incorporates nonuniform flow conditions similar to those of gas turbine engine combustors. The goal here is to elucidate the processes by which the initially unfueled kernel evolves into a self-sustained flame. Three fuels are examined: a conventional Jet-A and two synthesized fuels that are used to explore fuel composition effects. A commercial, high-energy recessed cavity discharge igniter located at the test section wall ejects kernels at 15 Hz into a preheated, striated crossflow. Next to the igniter wall is an unfueled air flow; above this is a premixed, prevaporized, fuel–air flow, with a matched velocity and an equivalence ratio near 0.75. The fuels are prevaporized in order to isolate chemical effects. Differences in early ignition kernel development are explored using three synchronized, high-speed imaging diagnostics: schlieren, emission/chemiluminescence, and OH planar laser-induced fluorescence (PLIF). The schlieren images reveal rapid entrainment of crossflow fluid into the kernel. The PLIF and emission images suggest chemical reactions between the hot kernel and the entrained fuel–air mixture start within tens of microseconds after the kernel begins entraining fuel, with some heat release possibly occurring. Initially, dilution cooling of the kernel appears to outweigh whatever heat release occurs; so whether the kernel leads to successful ignition or not, the reaction rate and the spatial extent of the reacting region decrease significantly with time. During a successful ignition event, small regions of the reacting kernel survive this dilution and are able to transition into a self-sustained flame after ∼1–2 ms. The low-aromatic/low-cetane-number fuel, which also has the lowest ignition probability, takes much longer for the reaction zone to grow after the initial decay. The high-aromatic, more easily ignited fuel, shows the largest reaction region at early times.

Imaging findings associated with nasopharyngeal amyloidosis in an Arabian stallion

SummaryA 3‐year‐old Arabian stallion presented for imaging and further work‐up of nasal discharge and respiratory stridor secondary to nasal amyloidosis. Thickening of the nasal mucosa with heterogeneous attenuation of the affected tissues was identified on CT images. The nasal mucosa, mucosa of the arytenoid cartilages, and regional lymph nodes were hypointense on T2 and T1 MRI images with moderate, patchy contrast enhancement. Biopsy and histopathology of the nasal mucosa, mucosa of the arytenoid cartilages and regional lymph nodes confirmed the original diagnosis of amyloidosis. Six fractions of helical tomotherapy did not provide significant improvement in respiratory effort, and permanent tracheostomy was performed. Haemorrhagic nasal discharge and mucosal plaques in the nasal cavity, pharynx, larynx, and trachea worsened over a 19‐month interim. This paper offers the first description of the CT and MRI findings of nasopharyngeal amyloidosis in a horse, and the first description of the use of helical tomotherapy in an equine patient.

A stochastic model for contact surfaces at polymer interfaces subjected to an electrical field

Abstract Morphology of the contact area between solid insulation materials ultimately determines the short- and long-term electrical properties of the complete insulation system. The main purpose of this paper is to propose a statistical model to examine the real area of contact between solid dielectric surfaces and secondly to verify and correlate the model outputs with experiments. The model computes real area of contact, number of contact spots and average cavity size at the interface as a function of elasticity, contact force and surface roughness. Then, using the average cavity size and the Paschen's law, the discharge inception field of the cavity (CDIE) is estimated. AC breakdown strength (BDS) testing of solid-solid interfaces was carried out, where cross-linked polyethylene (XLPE) samples with four different surface roughnesses were tested at various contact pressures. Following the increased contact force, the calculated average cavity size decreased by a factor of 4.08−4.82 from the roughest to the smoothest surface, corresponding to increased CDIEs by a factor of 2.01−2.56. Likewise, the experimentally obtained BDS values augmented by a factor of 1.4−1.7 when the contact pressure was elevated from 0.5 MPa to 1.16 MPa. A linear correlation between the CDIE and BDS was assumed, yielding a correlation coefficient varying within 0.8−1.3. When the 90% confidence intervals were considered, the range reduced to 0.86−1.05. This correlation suggests that interfacial breakdown phenomenon is strongly related to the interfacial cavity discharge. Hence, the proposed model is verified with experiments.

Influence of secondary electron yield of material on two-sided multipactor discharge in cavity

The influences of secondary electron yield (SEY) of material on the transient and saturation characteristics of two-sided multipactor discharge in cavity are numerically investigated by using particle-in-cell and Monte-Carlo methods. The numerical results indicate that as the SEY increases, the rate of electron number increases and the average value and magnitude of steady electron number also increase. The oscillation start-time of discharge current is shortened, and the steady value of discharge current increases and tends to be saturated. Both the average value and magnitude of steady discharge power increase and tend to be saturated. Both the time-delay and pulse width of deposited power waveform increase and also tend to be saturated. Under the circumstances of higher and lower value of SEY, the physical images of electron phase space, charge density, average impact energy, average SEY, electron number and discharge current are in detail shown in particle-in-cell simulation. The results can be concluded as follows. Under the circumstances of lower value of SEY, the saturation characteristics is determined by both debunching and reverse field of space charge effects. But under the circumstances of higher value of SEY, the multipactor mechanism tends to be one-sided mode in the steady stage which can be obviously determined by reverse-field of space charge effect.

Influence of multipactor discharge on field-buildup process in radio-frequency plate cavity

In this paper, the hybrid physical model is established based on the equivalent circuit for describing dynamic radio-frequency (RF) field buildup and the particle-in-cell (PIC) method for describing two-sided multipactor discharge in plate cavity. By using our built 1D3V-PIC code for multipactor discharge and fully equivalent circuit code for RF field buildup, the influence of multipactor discharge on the dynamic process of RF field buildup is numerically investigated and analyzed in detail under the condition of cavity with different Q-values. The numerical results could be concluded as follows. Under the condition of no multipactor discharge in dynamic process of RF field buildup, the higher the Q-value, the longer the buildup-time is. The input energy is equal to the sum of stored energy and consumed energy in cavity, the speed of energy storing is higher than the speed of energy consuming at the beginning stage of RF field buildup and then the speed of energy storing becomes lower than the speed of energy consuming. When the process of RF field buildup is finished, the average power of input is equal to the average power of consumed power in cavity. Under the condition of multipactor discharge loading in dynamic process of RF field buildup, the higher the Q-value, the later the start-time is and the longer the interaction time-interval of multipactor discharge is. The bigger the area of secondary electron emission, the higher the peak-value of secondary electron current is. The failure of RF field-buildup is caused by the continuous loading of multipactor discharge. The higher the Q-value or the bigger the area of secondary electron emission, the lower the probability of RF field buildup success is. The simulated results could partly provide a reference for engineering design.

Nasal Foreign Body: A Retrospective Study

Background: Nasal foreign bodies are a frequent accident to otolaryngologist especially in young children. They are generally harmless and can be managed easily in outpatient department but may become life threatening if it is overlooked or attempt at removal by unskilled hand. Objective: To evaluate the nature, location, mode of presentation, technique of removal and outcome of foreign body in the nose.Setting: A retrospective study of 110 cases of nasal foreign body was done in Comilla medical college and two upazilla health complexes (Nangalkot and Chowddagram) of Bangladeesh within the period of July 2015 to December 2015.Result: The most frequent foreign body were seeds of various vegetables (27.27%), mostly found in right nasal cavity (57.27%) and unilateral foul smelling nasal discharge (36.36%) was the common presenting complaint. We found high incidence in 2-5 year age group (79%) with male predominance. Most of the foreign bodies (94.55%) were removed under direct vision with various instruments with or without local anesthesia. Conclusion: Nasal foreign body is a one of the most common ENT emergencies in our country. Prompt and appropriate management can reduce morbidity.Keywords: Nasal foreign body, otolaryngologist, seed, anesthesia, ENT emergency.

Effect of a transverse plasma jet on a shock wave induced by a ramp

We conducted experiments in a wind tunnel with Mach number 2 to explore the evolution of a transverse plasma jet and its modification effect on a shock wave induced by a ramp with an angle of 24°. The transverse plasma jet was created by arc discharge in a small cylindrical cavity with a 2 mm diameter orifice. Three group tests with different actuator arrangements in the spanwise or streamwise direction upstream from the ramp were respectively studied to compare their disturbances to the shock wave. As shown by a time-resolved schlieren system, an unsteady motion of the shock wave by actuation was found: the shock wave was significantly modified by the plasma jet with an upstream motion and a reduced angle. Compared to spanwise actuation, a more intensive impact was obtained with two or three streamwise actuators working together. From shock wave structures, the control effect of the plasma jet on the shock motion based on a thermal effect, a potential cause of shock modification, was discussed. Furthermore, we performed a numerical simulation by using the Improved Delayed Detached Eddy Simulation (IDDES) method to simulate the evolution of the transverse plasma jet plume produced by two streamwise actuators. The results show that flow structures are similar to those identified in schlieren images. Two streamwise vortices were recognized, which indicates that the higher jet plume is the result of the overlap of two streamwise jets.

Measurement of corner separation zone response on a compression ramp to plasma actuation within the hypersonic boundary layer

This study was performed to characterize the dominant frequencies present in the boundary layer uptsream of and in the corner separation zone of a compression surface in Mach 4.5 flow and to determine a control effect of transient plasma actuation on the boundary layer. Schlieren imaging was used to distinguish the corner separation zone for 20°, 25°, and 30° compression ramps mounted on flat plates. Spectra of the natural disturbances present in the boundary layer and separation zone were gathered using a high-speed Shack-Hartmann wavefront sensor and surface mounted PCBTM pressure sensors while varying flow parameters by adjusting total pressure, temperature, and ramp angle. Shallow cavity discharge plasma actuators were used as a high-frequency localized thermal forcing mechanism of the boundary layer. The plasma effect was negligible for forcing frequencies (50 kHz) below the natural dominant frequency (~55-80 kHz). High frequency perturbations that can promote the transition to turbulence were amplified when the plasma forcing frequency (100 kHz) was higher than the natural dominant frequency (~55-80 kHz). This technique can potentially be used for active control of hypersonic boundary layer transition and the supersonic flow structure on the compression surface.

Simulation of partial discharges in cavities and streamers with high spatial resolution

The electrical characteristics of partial discharges in cavities and streamer channels were simulated with the high spatial and temporal resolution. The parallel computations on graphic processing units were applied for the numerical solution of this system of equation. The current in an external circuit as well as the true charge during partial discharge were calculated for different positions of a single void and for two voids in electrode gap. The parallel algorithm for the stochastic growth of streamer in a dielectric was developed. The electric characteristics of the partial discharges due to the streamer growth were studied.

Comparison between the 1st and 3rd order mode temporal characteristics of two-sided multipactor discharge in cavity

For investigating the influence of high order two-sided multipactor discharge on the accelerator field-building process, the temporal characteristics of the 3rd order two-sided multipactor discharge in oxygenfree copper cavity are studied numerically. The particle-in-cell and Monte-Carlo methods are used in the simulation and the characteristics of the 1st order mode are also studied for comparison. The numerical results can be concluded as follows. In the multipactor discharge evolution, the electron number, discharge current, deposited and discharge power increase exponentially and tend to be saturated. At the saturation stage of the 3rd order mode, the values of electron number, discharge current, deposited and discharge power are lower than at the saturation stage of the 1st order mode. Meanwhile, the rising time of waveform in the 3rd order mode is longer than in the 1st order mode. There is a time-delay phenomenon in the waveform of discharge current, which results in a partial charging process in multipactor discharge. The average value of the discharge power is equal to the average deposited power. The value of discharge power in the 3rd order mode is about 1% of that in the 1st order mode. Therefore, the 3rd order mode is not significant in accelerator field-building process compared with the 1st order mode. The characteristic of the 1st order two-sided multipactor discharge is the accelerated motion of single electron beam, while that of the 3rd order is the complex accelerated-decelerated-accelerated motion of multi-electron beams. When the multipactor discharge enters into the saturation stage, the space charge effect of the 3rd order mode is not stronger than that of 1st order mode.

Internal partial discharge in cavity of polyurethane

Parameters and time development of internal partial discharges in insulation material - polyurethane were studied. The internal defect was created by a needle, which was moved back by 1mm in order to create an air filled cavity in addition to the micro-cavity at the tip of the needle. In the experiment polyurethane pattern was stressed by high AC voltage and parameters of the partial discharges until breakdown of insulation material were recorded. The discharge activity generated in the air cavity, the point of the greatest stress degrades gradually the insulation. This degradation is connected with growth of an electrical tree, which parameters are described. The apparent charge magnitude, voltage and the time of occurrence of each PD event were recorded by LDS- 6.

Needle electrode-based microplasma formed in a cavity chamber for optical emission spectrometric detection of volatile organic compounds through a filter paper sampling

A novel microplasma device, which generates discharge in a Poly (dimethylsiloxane) (PDMS) cavity chamber with two normal syringe needles, serving as both gas channels and electrodes, was prepared by an innovative casting technology. This microplasma device maintains a stable discharge even after working under large periods of time (4h) and even if impurity deposition is produced on the needle electrode tips. The cavity discharge chamber of this device can also be used as a sampling compartment. 14 kinds of volatile organic compound (VOC) samples, with 6 series depending on carbon chain structures and boiling points (from 34.6 to 232.9°C), can directly diffuse into the plasma by using a filter paper. The filter paper was placed right under the microplasma zone in the chamber. Most VOC samples could be well detected (<20min for each) and discriminated in this microplasma system through a portable spectrometer. Combined with the peak ratio (300–900nm spectrometric range available) analysis, discharge parameters, specific characteristics of each sample and comparison of each homologous group could be systematically made by this device. The present work proposes a new approach for fast screening of volatile organics in water bodies or other solvents. The utility of this device was demonstrated by that BTEX-containing aqueous samples, as an example, could be detected at 50mg/L level with detection limits of 2.5μg/L.