UV Corona Research Articles

Possible Evidence for Shear-driven Kelvin–Helmholtz Instability along the Boundary of Fast and Slow Solar Wind in the Corona

This paper reports the first possible evidence for the development of the Kelvin–Helmholtz (KH) instability at the border of coronal holes separating the associated fast wind from the slower wind originating from adjacent streamer regions. Based on a statistical data set of spectroscopic measurements of the UV corona acquired with the UltraViolet Coronagraph Spectrometer on board the SOlar and Heliospheric Observatory during the minimum activity of solar cycle 22, high temperature–velocity correlations are found along the fast/slow solar wind interface region and interpreted as manifestations of KH vortices formed by the roll-up of the shear flow, whose dissipation could lead to higher heating and, because of that, higher velocities. These observational results are supported by solving coupled solar wind and turbulence transport equations including a KH-driven source of turbulence along the tangential velocity discontinuity between faster and slower coronal flows: numerical analysis indicates that the correlation between the solar wind speed and temperature is large in the presence of the shear source of turbulence. These findings suggest that the KH instability may play an important role both in the plasma dynamics and in the energy deposition at the boundaries of coronal holes and equatorial streamers.

DC corona characteristics derived from corona cage tests and simulations

This study presents experimental and simulation studies on DC corona characteristics to investigate the behavior of high voltage direct current transmission (HVDC) lines. Experimental studies are performed using an indoor corona cage and various conductor configurations, which are the scaled models of the prospective HVDC line in Turkey. Following the preliminary tests with single line models of aluminum rods and stranded conductors, DC corona inception voltages (CIVs) of prospective bundled conductor configurations are measured by using a daylight UV corona camera and a high-sensitive micro ammeter. Measurements include three different sub-conductor spacing both for the positive and for the negative DC voltages. Corona currents are measured for the voltages above the CIV levels. Experimental studies are varied by complementary simulations using a FEM based software, COMSOL Multyphysics. Following the development of 3D models of the corona cage and the prospective conductor configurations, electric field distribution along the conductor surfaces are determined. CIV measurements and simulation results are used to compute the corona inception electric field strengths of the aforementioned configurations. Radio interference voltages and audible noise levels of the configurations are finally calculated at a constant test voltage using the empirical formulations and the field simulation results. The results are discussed at the end to guide the design of intended HVDC line in Turkey.

Effects of view angle and measurement distance on electrical equipment UV corona discharge detection

A UV radiation detecting platform is set up to evaluate the influence of view angle and measurement distance in UV detection technology, then a coordinate conversion equation is proposed to compensate the influencing factors. Since the photon number of dischargeable power equipment changes with the varied external factors including distance, angle, humidity, and wind force, the research studies the effects of both view angle and distance while others are invariant. Results show that the variation of view angle and distance has an impact on UV detection. Given that different observation points have different view angle and observation distance, photon numbers at different points could be calibrated to the optimal position in accordance with the proposed equation. In addition, the 3-D simulation and conversion curves also verify the validity of proposed theory. Accordingly, the results of this study can provide a reference to improve the effectiveness and application of UV imager in fault diagnosis.

Research on Fault Detection System of Power Equipment Based on UV and Infrared Image

UV corona on power system can reflect the location of the fault and the severity of the fault, the traditional UV and infrared detection equipment can only use the band and the visible light band image of the power system fault detection. In this paper, a power system fault detection system based on ultraviolet and infrared dual-band images is designed. The principle of UV imaging detection and image fusion are introduced respectively. The software of the host computer is written by MFC. The software can acquire both ultraviolet and infrared, the two images are fused using the image fusion algorithm based on edge detection and cross correlation and the highest point temperature is plotted. Experiments show that the system can detect the failure of power equipment in time, and has a certain practical value, which puts forward a new idea for fault detection of power equipment.

Air Modification Apparatus by Using a UV Lamp and Corona Discharge

An air modification apparatus was developed by using a UV lamp and two sets of corona discharge electrode pairs (UV2C). This apparatus works with no fan, and decomposes volatile organic compounds in air where the concentration of exhausted ozone is very low. The apparatus generates nitrogen oxide and collects dust in the air. The modification of air increases the quality of human daily life. The decontamination to the air was performed by using a simple atmospheric discharge system.

UV 투과율 향상 필터 기술을 이용한 전력설비 방전 검출용 자외선 코로나 카메라 개발

UV inspection technology is being used for predictive maintenance of power facility together with IR-thermography and ultrasonic devices. In this paper, the UV corona camera design, fabrication, and perform a simple test to be take advantage of the diagnostic equipment. The UV corona camera developed a 6.4 °×4.8 ° of the field of view as a conventional camera to diagnose a wide range of slightly enlarged, and power equipment to measure the distance between the camera and the distance meter has been attached. The transmission between 250 to 280㎚ was 11% (12.5% x 88% x 98%) by combing the transmission on absorption film, window and other filter(UG 5, nickel sulphate and so on). In a distance of 5m with the UV corona camera it is possible to detect partial discharge with a PD level of 2.5pC and a RIV level of 3.6㏈㎶.

Influence of projection effects on the observed differential rotation rate in the UV corona

Following previous investigations by Giordano and Mancuso [1] and Mancuso and Giordano [2,3] on the differential rotation of the solar corona as obtained through the analysis of the intensity time series of the O VI 1032Å spectral line observed by the UVCS/SOHO telescope during solar cycle 23, we analysed the possible influence of projection effects of extended coronal structures on the observed differential rotation rate in the ultraviolet corona. Through a simple geometrical model, we found that, especially at higher latitudes, the differential rotation may be less rigid than observed, since features at higher latitudes could be actually linked to much lower coronal structures due to projection effects. At solar maximum, the latitudinal rigidity of the UV corona, with respect to the differential rotating photosphere, has thus to be considered as an upper limit of the possible rigidity. At solar minimum and near the equatorial region throughout the solar cycle, projection effects are negligible.

고전압 방전 검출용 자외선 코로나 카메라 개발 및 방전 이미지 분석

In this paper, the UV corona camera was developed using the solar blind and Multi Channel Plate(MCP) technology for the target localization of UV image. UV camera developed a of the field of view as a conventional camera to diagnose a wide range of slightly enlarged, and power equipment to measure the distance between the camera and the distance meter has been attached. UV camera to measure the discharge count and the UV image was developed, compared with a commercial camera, there was no significant difference. In salt spray environments breakdown voltage was lower than the normal state, thereby discharging the image was rapidly growing phenomenon.

자외선 카메라 개발을 위한 직류 연면방전 특성

Recently, UV(ultra-violet rays) camera has attracted a great deal of interest from the view point of easy judgement in inspections and diagnoses of the safety of power equipment. Especilly, UV camera is applied the inspection of UV with corona discharge. One of the most important and difficult problems is the basic research of filter design, materials and corona discharge. In this paper, we will report on the UV generation, corona pulse count and the polarity effect of positive and negative DC surface discharge in air. Also, corona discharge characteristics are analyzed using prototype UV camera of Korea. UV generation and corona pulse count due to surface discharge in positive needle is higher than that of negative needle.

Coronal Rotation at Solar Minimum from UV Observations

UVCS/SOHO observations have been analyzed to reconstruct intensity time series of the O VI 1032 A and H 11216 A spectral lines at different coronal heliolatitudes from 1.5 to 3.0 solar radii from Sun center. Evidence was found for coronal differential rotation that differs significantly from that of the photospheric plasma. The study of the latitudinal variation shows that the UV corona decelerates toward the photospheric rates from the equator up to the poleward boundary 2 of the midlatitude streamers, reaching a peak of 28.16+/-0.20 days around +30 from the equator at 1.5 solar radii, while a less evident peak is observed in the northern hemisphere. This result suggests a real north-south rotational asymmetry as a consequence of different activity and weak coupling between the magnetic fields of the two hemispheres. The study of the radial rotation profiles shows that the corona is rotating almost rigidly with height.

Ultraviolet Corona Discharge Detection Based on Photomultiplier

High voltage equipments, especially polymer insulators may be getting into aging conditions due to the existence of corona discharge on the surface after a long term of running, which would accelerate the deterioration of the surface insulation performance, and even make equipments step into calamity ultimately. So it is significant to detect corona discharge on surface to ensure insulators' stable running. This paper presents the development of a novel corona discharge detection system based on photomultiplier tube (PMT), which has good functions of distance detection for corona discharge in determined region from surface of high voltage equipment and corona characteristics data analysis. In the verification experiments, it was shown that UV corona light can be also taken as characteristic for detecting corona discharge, other than corona leakage current detection, and a linear relationship was shown between the light magnitude and the current magnitude. Furthermore, mean peak value and number of pulses whose peak value is above threshold are extracted from the basic data, which can be used to quantify the development of corona discharge. The results of investigation on polymer insulators suggested that detection of the region between metal end fitting and first shed should be emphasized. The measurements of corona discharge distribution along insulators can be used to learn about the degradation conditions. Detection of polymer insulators in lab and field inspection experience are both soundly verifying the usefulness of the corona detection system.

Effect of ATH content on electrical and aging properties of EVA and silicone rubber blends for high voltage insulator compound

AbstractThe effect of trihydrated alumina (Al2O3, 3H2O) (ATH) filler in ethylene‐vinyl acetate copolymer (EVA) and silicone rubber blends was investigated by performing a series of laboratory experiments to simulate different natural aging conditions. Samples with varying ATH content in a 50‐50 blend of EVA and polydimethylsiloxane (PDMS) (silicone rubber, MQ) were tested to investigate the tracking resistance, resistance to UV radiation, corona, heat, and water immersion. Changes in surface resistivity, volume resistivity, and hydrophobic characteristics were evaluated for different compounds having ATH content. These exercises were mainly carried out to optimize the filler level. In immersed condition the water absorption increases with ATH content. The recovery of hydrophobicity, after aging by heat, is appreciable at higher ATH levels, than at lower ATH levels. The tracking and erosion resistance decrease as ATH content increases. When compounds containing different ATH content were subjected to corona treatment, the samples with higher ATH levels exhibited better results. All samples changed their color to a darker shade and there was an increase in the hydrophobicity, when subjected to UV radiation. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 3505–3516, 2007

Electrical and environmental stress and the hydrophobic stability of SIR, EVA and their blends

This paper treats the effects of electrical and environmental stresses on the hydrophobicity of polymers intended for use in nonceramic insulators. We investigated the effect of UV radiation, corona discharges, dry-band arcing, acid rain and water absorption on hydrophobic transfers in, and the aging of, room temperature vulcanized (RTV)-silicone rubber (SIR), high temperature vulcanized (HTV)-silicone rubber (SIR), ethylene vinyl acetate (EVA) rubber and the blends made from HTV-SIR and EVA. Acid rain had little influence on hydrophobicity in any of the samples. EVA and the blends with low silicone ratios to EVA allowed much larger reduction in hydrophobicity after or while subjected to the above stresses (except for acid rain) than did the silicone rubbers and a blend with a high silicone ratio to EVA. Salt-fog tests were conducted to correlate the hydrophobic stabilities of materials with leakage current levels thereon. The hydrophobic stability of the silicone rubbers was attributed to low-molecular-weight silicone components that were able to migrate and finally cover the aged surface layers. Because EVA possessed less fluid components and less chemical stability under electrical and environmental stresses, its hydrophobicity was readily reduced and hardly recovered, which led to higher current leakage and early material aging. For each material, the critical hydrophobic level permitting leakage current to develop was determined by adding a non-ionic wetting agent to saline water.

Long term variations in the Extreme UV corona: the EIT/SoHO perspective

Since the start of the SoHO mission, EIT -the Extreme ultraviolet Imaging Telescope- offers a global view of the solar corona over the whole rising phase of the current activity cycle. Such a dataset is unprecedented. We give here the current results of an on-going investigation over the entire EIT archive. In the Fe XV images (2 MK), the on-disk and off-disk intensity distributions have been evaluated, and their evolution is described. Additionally, we developed an image processing technique that extracts the smallest detectable features. The cosmic ray hits are statistically disentangled from the solar point-like phenomena, and the trends in both rates are assessed.

Ultraviolet Radiation Curing Treatments for Shrink-Resistant Wool Fabric

The application of uv curing and corona discharge technology to textiles is intro duced and discussed, The influence of uv photoreactive monomer on the shrinkage and mechanical properties of corona and nonpretreated 100% wool gabardine fabric is detailed. Machine washability can be achieved at low add-on by incorporating a uv curable silicone into the formulation and a post-cure steam treatment.

ＰＥラミネート系加工紙の接着性評価 ＰＥと紙との熱圧接着

In order to improve adhesion properties of polyethylene to paper sheets, UV radiation treatment and corona discharge treatment were examined as surface treatments methods for three types of paper boards.Acidic paper board, neutral paper board and coated paper board were used as sample sheets. The following results were obtained : (1) It was shown by the contact angle and the wetting index that the wettabilities of coated paper board, of acidic paper board and of neutral paper board were in the order of magnitude. Corona discharge treatment and UV radiation treatment were effective in the increase in their wettabilities for these sample sheets. (2) Corona discharge treatment for both the acid paper and the neutral one was effective on improvement in the adhesion properties. The coated paper showed a better adhesion property than other two kinds of paper boards even without a treatment. The adhesion properties with the coated paper were furthermore improved by the above treatment.(3) Chemical states of paper surface with and without the treatment were assessed by X-ray photoelectron spectroscopy (ESCA). It was found by using ESCA that these treatments promoted the increase in oxygen amount upon the paper surface, and carbonyl and carboxyl groups increased especially with corona discharge treatment.

Surface modification of poly(methyl methacrylate) by graft copolymerization

AbstractGraft copolymerization was carried out onto a poly(methyl methacrylate) (PMMA) plate for surface modification. The following treatments were conducted to introduce peroxides into the PMMA surface prior to graft copolymerization: UV irradation, corona discharge, glow discharge, and ozone exposure. The static contact angle of the PMMA plate toward water decreased from 66° to 45 and 38° by the pre‐treatment with corona and glow discharge for 5 min, respectively, whereas the pre‐treatment with UV irradiation and ozone exposure caused no appreciable decrease in contact angle. When graft copolymerization of acrylamide (AAm) was carried out onto the pre‐treated PMMA plates by near‐UV light irradiation to decompose the peroxides in the presence of riboflavin, the contact angle further decreased to approximately 20° and the amount of AAm polymer grafted was 20–25 μg · cm−2 for the pre‐treatments with corona discharge, glow discharge and UV irradiation. However, graft copolymerization was practically not achieved onto the PMMA plate pre‐treated with ozone exposure. On the other hand, when graft copolymerization was performed at 50°C after degassing without UV irradiation, the amount of AAm polymer grafted was always less than 10 μg · cm‐2, independent of the pre‐treatment methods.