Flashover Characteristics on the Gap of Rod to Plane Applied Bipolar Impulse Voltage

This paper describes the fifty percent flashover voltage and the V-t curve for a rod-plane gap applied bipolar impulse voltage, and the behaviour of the space charge in the gap. In the distribution line, the bipolar impulse voltage had been observed frequently when lightning hit near it. Then, the bipolar impulse wave used in the experiment was decided as the composite voltage wave made from the preceding wave of positive (or negative) polarity, 20/500 μsec. and the following wave of negative (or positive) polarity, 2/60 μsec. The connecting time of the abovementioned two pulses was decided as 20±5 μsec.. The test gap was the rod-plane gap with a gap length of 6.0cm, and the rod diameter of 1.0cm as a non-uniform field, mainly. As for the experimental results, when the applied preceding impulse voltage was positive polarity and a corona occurred, the fifty percent flashover voltage was up by 15%. And, when the preceding impulse voltage was negative polarity and with a corona, the fifty percent flashover voltage was down by 10%. The space charge phenomena as the cause given by the abovementioned results were observed by using an image converter camera

Discharge Phenomena of the Insulator Assembly and Occurrence of Critical Cascading Flashover Phenomena

This paper describes conditions for an occurrence of cascading flashover phenomena on the insulator assembly with the use of a high voltage transmission line by experiments in a laboratory room. The 154 kV suspension insulator assembly is employed as testing apparatus which consists of a chain of 9 standard suspension insulators equipped with an arcing horn. In the experiments, the apparatus is separated into two parts consisting of a bare insulator chain and a pair of arcing horns. The lightning impulse with positive polarity or negative are applied to the test pieces, and the over-voltage is used in those tests. Thus, the creeping flashover occurred with short lag time. The V-t curves and the 50% cascading flashover voltage were obtained and the prebreakdown phenomena were observed from the tests, then, it is concluded that the critical cascading flashovers occur with short time lag (T₀＝1.8 μ sec. or less) and a high steepness (1833 kV/μ sec. or more), and corona on the insulator surface starts from negative side electrode

Experimental Study of Critical Cascading Flashove on Insulator Assembly Using Model Arrangements (Part 1) : The Influence of a floating Electrode, Placed in the Air at Mid-Gap, on the Formation of a Flashover Path

This paper describes the phenomena of cascading flashovers in model arrangements for experimental analysis of critical cascading flashovers in an insulator assembly used on high voltage transmission lines. The testing model used consisted of a 15 cm gap length of rod-rod electrode which was 1.0 cm in diameter with a hemispherical end, with a potentially floating electrode which was a copper wire of 0.16 cm diameter. The applied lightning impulse voltage of positive or negative polarity was much higher than the breakdown voltage when the flashover occurred for only a short time lag. The experimental results included V-t curve and 50% flashover voltage characteristics for a gap on the testing model, flashover path, pre-breakdown corona distributions, and cascading flashover rates. The flashover phenomena in the air gap with a floating electrode clarified that the cascading flashover rate remained at a constant value whether the floating electrode existed or not. The coronas from the floating electrode were generated only when the coronas from the rod electrode reached the floating electrode. In order to form a cascading flashover, it was necessary that the bright leader coronas from the rod electrode grow toward the floating electrode, causing the coronas from the floating electrode to generate and meet the other coronas growing from the rod electrode

Experimental Approach to Shielding and Reducing Effects on Ion Currents and Electric Fields at Earth Level under a DC Transmission Line

Use of a d. c. transmission line to find a way to reduce ion currents and electric fields at earth level is a most important matter for environmental safety. This paper discusses the relation between the ion currents and the electric fields at earth level, measured by using a unipolar d. c. transmission line scale model and a bipolar d. c. transmission line. Electric fields at earth level were calculated by means of the image charge method without taking into consideration the space charge caused by the d. c. line. The middle scale models for the unipolar and the bipolar d. c. lines were set at the height of the d. c. lines at 2m. Both types of scale models were set up in a sufficiently spacious room. Two small scales for the unipolar and the bipolar d. c. lines, with the height of the d. c. lines set at 20cm above the earth and the separating distance between the two d. c. lines set at 35 to 75cm, were placed in a suitable roomo. Both the experimental results are discussed here in comparison with the calculated fields. As a conclusion, in using the model unipolar d. c. line with a shielding wire, the shielding effects for both the electric fields and the ion currents at earth level nearly coincided with the calculated fields. However, in using the model bipolar d. c. lines, the reducing effect for the ion currents dind't coincide with the ealculated fields, actually not quite half of the calculated fields. In particular, the ion currents, at earth level on the positive voltage side were reduced very well, relative to those on the negative voltage side. They were measured in relation to the ratio of the separating distance of the bipolar d. c. lines to the the height of the d.c. line from earth level

Behavior of The Space Charge Produced by The Positive Impulse Corona in Air

This paper describes the behavior of the space charge produced by the corona by applying the positive lightning impulse voltage to the rod-plane air gap. The relation between the amount of space charge and the injected charge from the rod electrode is discussed here. It was found that the amount of space charge became smaller than the injected charge for the corona highly developed so as to bridge the gap between the electrodes

Space Charge Measurement Using a Small Sphere as a Probe

A method for measuring the space charge produced by impulse corona in an air gap has been developed, using a small sphere as a probe. The probe is located far from the corona volume, and is connected to earth through resistance or capacitance. The probe induces a current or charge by electrostatic induction from the space charge. Since the induced charge on the probe is proportional to the space charge, it is possible to analyze the magnitude and polarity of the space charge from the probe signal. It is also possible to analyze the temporal variation caused by corona growth or movement of the space charge

Experimental Study of Critical Cascading Flashover on Insulator Assembly Using Model Arrangements (Part II) : The Influence of a Floating Electrode, Placed on a Porcelain Board, on the Formaiton of a Flashover Path

This paper describes the phenomena of cascading flashovers in model arrangements for experimental analysis of critical cascading flashovers occuring in an insulator assembly used on high voltage transmission lines. The testing model used consisted of a pair of rod-rod electrodes, a potentially floating copper wire and a porcelain board. The applied lightning impulse voltage of positive or negative polarity was much higher than the breakdown voltage, when the flashover occurred for only a short time lag. The experimental results included flashover paths and pre-breakdown corona distributions, and cascading flashover rates. The flashover phenomena on the testing model clarified that the cascading flashover rate was related to the position of the porcelain board with the floating wire and that the corona from the floating wire was generated just before the corona from the rod electrode reached the floating wire. In the summary, the influence of the floating electrode on the formation of flashover paths discussed in comparison with previous reports. As a result of this series of experiments, it was clarified that a cascading flashover occurred only through coexistence with the porcelain surface and floating metal

HCHL expression in hairy roots of Beta vulgaris yields a high accumulation of p-hydroxybenzoic acid (pHBA) glucose ester, and linkage of pHBA into cell walls.

As part of a study to explore the potential for new or modified bio-product formation, Beta vulgaris (sugar beet) has been genetically modified to express in root-organ culture a bacterial gene of phenylpropanoid catabolism. The HCHL gene, encoding p-hydroxycinnamoyl-CoA hydratase/lyase, was introduced into B. vulgaris under the control of a CaMV 35S promoter, using Agrobacterium rhizogenes LBA 9402. Hairy root clones expressing the HCHL gene, together with non-expressing clones, were analysed and revealed that one expression-positive clone accumulated the glucose ester of p-hydroxybenzoic acid (pHBA) at about 14% on a dry weight basis. This is the best yield achieved in plant systems so far. Determination of cell-wall components liberated by alkaline hydrolysis confirmed that the ratio of pHBA to ferulic acid was considerably higher in the HCHL-expressing clones, whereas only ferulic acid was detected in a non-expressing clone. The change in cell-wall components also resulted in a decrease in tensile strength in the HCHL-expressing clones

National trends in the outcomes of subarachnoid haemorrhage and the prognostic influence of stroke centre capability in Japan: retrospective cohort study

Objectives To examine the national, 6-year trends in in-hospital clinical outcomes of patients with subarachnoid haemorrhage (SAH) who underwent clipping or coiling and the prognostic influence of temporal trends in the Comprehensive Stroke Center (CSC) capabilities on patient outcomes in Japan.Design Retrospective study.Setting Six hundred and thirty-one primary care institutions in Japan.Participants Forty-five thousand and eleven patients with SAH who were urgently hospitalised, identified using the J-ASPECT Diagnosis Procedure Combination database.Primary and secondary outcome measures Annual number of patients with SAH who remained untreated, or who received clipping or coiling, in-hospital mortality and poor functional outcomes (modified Rankin Scale: 3–6) at discharge. Each CSC was assessed using a validated scoring system (CSC score: 1–25 points).Results In the overall cohort, in-hospital mortality decreased (year for trend, OR (95% CI): 0.97 (0.96 to 0.99)), while the proportion of poor functional outcomes remained unchanged (1.00 (0.98 to 1.02)). The proportion of patients who underwent clipping gradually decreased from 46.6% to 38.5%, while that of those who received coiling and those left untreated gradually increased from 16.9% to 22.6% and 35.4% to 38%, respectively. In-hospital mortality of coiled (0.94 (0.89 to 0.98)) and untreated (0.93 (0.90 to 0.96)) patients decreased, whereas that of clipped patients remained stable. CSC score improvement was associated with increased use of coiling (per 1-point increase, 1.14 (1.08 to 1.20)) but not with short-term patient outcomes regardless of treatment modality.Conclusions The 6-year trends indicated lower in-hospital mortality for patients with SAH (attributable to better outcomes), increased use of coiling and multidisciplinary care for untreated patients. Further increasing CSC capabilities may improve overall outcomes, mainly by increasing the use of coiling. Additional studies are necessary to determine the effect of confounders such as aneurysm complexity on outcomes of clipped patients in the modern endovascular era