Electrical Discharge Activity Research Articles

Detecting and Locating Corona Discharges in Low-Pressure Aircraft Environments Using Optical Sensors

Today, there is a clear trend toward electrification of transportation systems, including aircraft. Due to the enormous power requirements, they must operate at high voltages. However, the combined effect of higher voltage levels and low pressure environments is conducive to the occurrence of electrical discharges in electrical systems. Therefore, there is an urgent need to develop cost-effective systems to detect the discharges in the early stages before major failures can occur. This paper compares two optical sensors for early discharge detection in a simulated aircraft environment. The experimental study is performed in a low pressure chamber using a needle plane electrode. The pressure is changed from that corresponding to ground level to that corresponding to flight altitude, i.e., from 100 kPa to 20 kPa. The effect of the supply frequency is also studied, since modern aircraft operate in a wide range of frequencies up to about 800 Hz. Both variables, especially pressure, have shown significant effects on the CIV value. The results have also shown a similar sensitivity of both sensors for all the experimental conditions analysed, allowing a fast and sensitive detection and localization of incipient electrical discharge activity.

Experience in treating children with ocular dyskinesia and hemifacial spasm secondary to pontine tumours adjacent to the fourth ventricle and systematic review.

To investigate the treatment plan and prognosis of children with ocular dyskinesia and hemifacial spasm secondary to pontine tumours adjacent to the fourth ventricle. In this retrospective study, the clinical information of 10 consecutively collected children with ocular dyskinesia and hemifacial spasm secondary to pontine tumours adjacent to the fourth ventricle was analyzed. All 10 children underwent pontine tumour resection through a trans-cerebellomedullary fissure approach; 4 children underwent preoperative diffusion tensor imaging scans to determine the relationship between the tumour and facial nerve nucleus, and the other 6 children underwent intraoperative deep electroencephalography (EEG) tumour monitoring, in which the tumour electrical discharge activity of the tumour was recorded. A voxel distribution map was established to describe the distribution of the tumour location, and patient prognosis was evaluated through clinical and imaging follow-up. All 10 children achieved total tumour resection; 9 tumours were pathologically suggested to be ganglioglioma (WHO grade I), and 1 was a hamartoma. The symptoms of the original ocular dyskinesia and hemifacial spasm disappeared immediately after the operation. The children were followed up for 4-75months, and none of the symptoms recurred; four cases with preoperative diffusion tensor imaging showed that the tumour was close to the facial nerve. Four in six intraoperative electrophysiological monitoring showed that the tumour had electrical discharge behaviour, and the tumour distribution map indicates a high density of tumour presence in the facial nerve nucleus and the nucleus of the abducens nerve. In paediatric patients, the facial symptoms are related to the location and abnormal electrical discharge of the tumour. There is no significant correlation between ocular dyskinesia and the location of the tumour. Conventional antiepileptic therapy for this disease is ineffective, and early surgical intervention for total tumour resection can achieve a clinical curative effect.

Ultraviolet pulse pattern for different types of insulator material during surface discharge activities

In the past, there were several different types of discharge detection methods that have been employed for the detection and monitoring of surface discharge activities at transmission line insulators. However, the existing detection system does not work well when the discharge activity is weak and sensitive to surrounding temperature and environmental conditions. The recent development of surface discharge detection devices that have been employed currently are ultraviolet (UV) imaging and UV pulse devices but the former is known to be expensive. In this paper, a UV pulse sensor which is known as the R2868 UVTRON Flame Sensor has been employed to assess the effectiveness of the sensor for detecting the electrical discharge activity of the insulator surface. The samples used for the electrical discharge generation testing and measurement are the 11 kV glass and porcelain pin-type insulators. The tests have been conducted by exposing both the insulations to dry and wet conditions with each of them subjected to a variety of applied voltages across the samples. It was concluded that the experimental works had been successfully conducted and the sensor was sensitive and effective in detecting the electrical discharge activities on both two samples.

Low-Pressure Optical Detection, Location, and Quantification of Electrical Discharges in Aircraft Wiring Systems

Strict regulations issued by international administrative bodies limit the CO2 equivalent emissions for new aircraft, while increasing efficiency requirements. To reach this goal, next generations of aircraft will use more electrical power than their predecessors, so distribution voltage levels will inevitably increase to limit the weight of the electrical wiring interconnect system (EWIS). However, such increased voltage levels generate higher electric stresses in insulation materials as well as in electric and electronic components; thus new failure modes triggered by electrical discharges will appear, their effects being aggravated by harsh environments typical of aircraft systems. The combined effect of higher electrical stresses, compact designs, and low-pressure operating conditions greatly intensifies the risks of premature insulation failure due to electrical discharge activity. This paper shows that by using image sensors, it is possible to detect, localize, and quantify the intensity of electrical discharges occurring in aircraft environments. Through experiments carried out in a low-pressure chamber using an image sensor, this work detects and determines the intensity of electrical discharges generated in electrical wires in their initial stage, long before major faults develop. This paper also shows that the intensity of the discharges calculated from the digital images obtained with the image sensor is directly proportional to the electrical energy involved in the discharge process and increases linearly with the applied voltage. Due to the difficulty of detecting these failure modes at a very early stage, this strategy could potentially facilitate predictive maintenance tasks while contributing to increased levels of aircraft safety.

Surface Discharges Performance of ETFE- and PTFE-Insulated Wires for Aircraft Applications

Compared to their predecessors, the next generations of aircrafts will be more electrified, require more electrical power and operate at higher voltage levels to meet strict weight and volume constraints. The combined effect of low-pressure environments, increased voltage levels and compact designs intensifies the risks of premature insulation degradation due to electrical discharge activity. This paper studies the resistance to surface discharges of PTFE (polytetrafluoroethylene) and ETFE (ethylene tetrafluoroethylene), two insulation materials widely used in today’s aircraft wiring systems due to their outstanding properties, such as a wide temperature operation range and a high dielectric strength. The study is carried out in a low-pressure chamber, which was pressurized within the pressure range of 10–100 kPa that includes most aircraft applications. There is a compelling need for experimental data to assess the resistance of insulation materials to surface discharges at a very early stage as a function of the environmental pressure. Data on resistance to surface discharges in low-pressure environments for aeronautical applications are lacking, while most standards for insulation systems are based on tests under standard pressure conditions. The results provided in this work can be useful to design wiring systems for future more electric aircrafts, as well as to design fault detection systems for an early detection and identification of faults related to surface discharges. Therefore, the data and analysis included in this paper could be of great interest to design and develop insulation systems for wiring systems and standard assessment methods, as well as to design fault detection strategies for the early detection and identification of surface discharges for future generations of more electric aircrafts.

Thunderstorm High‐Frequency Radio Bursts With Weak Low‐Frequency Radiation

AbstractBrief bursts of high‐frequency (HF) and very high frequency (VHF) radio emissions unaccompanied by strong low‐frequency radiation have been observed during initiation and propagation of lightning or thunderstorm electrical breakdown without leading to fully fledged lightning. This paper investigates a physical mechanism to generate such radio bursts by electrical discharge activity inside a thundercloud. When a discharge consists of many high‐frequency emission sources, such as streamers, that generate currents in random directions, its radiation spectrum peaks in the HF and VHF bands, and the spectral magnitudes in low frequencies are much smaller or even negligible. Combined with recent observational findings, the present study suggests that lightning initiation may begin with a short burst of many randomly occurring small‐scale discharges in a localized thundercloud region.

Fabrication of high-aspect-ratio microgrooves using an electrochemical discharge micromilling process

In this study, we created high-aspect-ratio microgrooves in hard, brittle materials using an electrochemical discharge machining (ECDM) process by introducing microtextured machining tool. To enhance the electrical discharge activity, the morphology of the tool side surface was treated via micro-electrical discharge machining to produce fine microprotrusive patterns. The resulting microtextured surface morphology enhanced the electric field and played a key role in improving the step milling depth in the ECDM process. Using the FEM analysis, the evaluation of the field enhancement factor is also addressed. Our experimental investigation revealed microgrooves having an aspect ratio of 1:4, with high geometric accuracy and crack-free surfaces, using one-step ECDM.

Laboratory investigation of corona initiation by ice crystals and its importance to lightning

This article reports on a new laboratory investigation of the initiation of corona discharges by small vapour‐grown ice crystals. This study was motivated by questions regarding the initiation of lightning and the possible role played by corona discharges on ice hydrometeors. Ice crystals were grown in a static diffusion chamber on a horizontally suspended glass fibre, with environmental conditions selected to mirror those of the thunderstorm environment where initiation of lightning is believed to occur. An in situ parallel plate electrode assembly was then rotated into position, so that the crystals were at the centre. The crystals were then subjected to slowly increasing electric fields until they underwent corona discharge. The discharges were observed and recorded under dark ambient conditions using an image‐intensified video microscope, along with a synchronous record of the applied voltage. The threshold electric fields for corona discharge were determined as a function of air pressure, temperature and ice crystal length in the direction of the applied electric field. The new results are relevant to a better understanding of hydrometeor‐mediated electrical discharge activity in thunderstorms.

Comparison of laser ablation and inclined plane tracking tests as a means to rank materials for outdoor HV insulators

As the popularity of polymeric composites for outdoor high voltage (HV) use continues to increase, surface degradation through electrical discharge activity is becoming a more serious issue. In order to design composites offering improved resistance to degradation, and hence improved component lifetimes, tests need to be performed under controlled conditions in order to rank different materials. Inclined plane tracking tests are often used to determine the relative performance of various material formulations used in their construction. An alternative approach is to employ a high power laser to deposit known amounts of energy at a known rate to the sample surface. In this paper a variety of material formulations were subjected to inclined plane tracking tests as well as to laser ablation testing. The results indicate that the two test methods compare favorably and that laser ablation offers a quick and cost effective way of screening candidate material formulations, prior to more detailed study.

Raised Activity of L-Type Calcium Channels Renders Neurons Prone to Form Paroxysmal Depolarization Shifts

Neuronal L-type voltage-gated calcium channels (LTCCs) are involved in several physiological functions, but increased activity of LTCCs has been linked to pathology. Due to the coupling of LTCC-mediated Ca2+ influx to Ca2+-dependent conductances, such as KCa or non-specific cation channels, LTCCs act as important regulators of neuronal excitability. Augmentation of after-hyperpolarizations may be one mechanism that shows how elevated LTCC activity can lead to neurological malfunctions. However, little is known about other impacts on electrical discharge activity. We used pharmacological up-regulation of LTCCs to address this issue on primary rat hippocampal neurons. Potentiation of LTCCs with Bay K8644 enhanced excitatory postsynaptic potentials to various degrees and eventually resulted in paroxysmal depolarization shifts (PDS). Under conditions of disturbed Ca2+ homeostasis, PDS were evoked frequently upon LTCC potentiation. Exposing the neurons to oxidative stress using hydrogen peroxide also induced LTCC-dependent PDS. Hence, raising LTCC activity had unidirectional effects on brief electrical signals and increased the likeliness of epileptiform events. However, long-lasting seizure-like activity induced by various pharmacological means was affected by Bay K8644 in a bimodal manner, with increases in one group of neurons and decreases in another group. In each group, isradipine exerted the opposite effect. This suggests that therapeutic reduction in LTCC activity may have little beneficial or even adverse effects on long-lasting abnormal discharge activities. However, our data identify enhanced activity of LTCCs as one precipitating cause of PDS. Because evidence is continuously accumulating that PDS represent important elements in neuropathogenesis, LTCCs may provide valuable targets for neuroprophylactic therapy.Electronic supplementary materialThe online version of this article (doi:10.1007/s12017-013-8234-1) contains supplementary material, which is available to authorized users.

S100 calcium binding proteins and ion channels.

S100 Ca2+-binding proteins have been associated with a multitude of intracellular Ca2+-dependent functions including regulation of the cell cycle, cell differentiation, cell motility and apoptosis, modulation of membrane–cytoskeletal interactions, transduction of intracellular Ca2+ signals, and in mediating learning and memory. S100 proteins are fine tuned to read the intracellular free Ca2+ concentration and affect protein phosphorylation, which makes them candidates to modulate certain ion channels and neuronal electrical behavior. Certain S100s are secreted from cells and are found in extracellular fluids where they exert unique extracellular functions. In addition to their neurotrophic activity, some S100 proteins modulate neuronal electrical discharge activity and appear to act directly on ion channels. The first reports regarding these effects suggested S100-mediated alterations in Ca2+ fluxes, K+ currents, and neuronal discharge activity. Recent reports revealed direct and indirect interactions with Ca2+, K+, Cl−, and ligand activated channels. This review focuses on studies of the physical and functional interactions of S100 proteins and ion channels.

Reproduction and feeding habits of the highly seasonal Brachyhypopomus bombilla (Gymnotiformes: Hypopomidae) from southern Brazil with evidence for a dormancy period

The reproductive biology and feeding habits of the hypopomid Brachyhypopomus bombilla were studied. The species has seasonal behavior, with breeding and feeding activity occurring mostly during the Southern Hemisphere spring and summer. We defined fractional spawning for the species and a relative fecundity similar to those previously reported for other gymnotiform species. According to the analysis of the food items, B. bombilla was included in the trophic category invertivorous, feeding mainly on autochthonous insects. The reproductive periods of males and females as well as female feeding activity were significantly related to the photoperiod. During a period of 5 months, when the lowest water temperatures and shortest photoperiod were recorded, all the specimens of B. bombilla were found buried in the muddy bottom of the creek, with lower electric organ discharge activity, empty stomachs, and gonads in early stages of the maturation process. This period, herein defined as a dormancy period, is reported here for the first time for a species of the Gymnotiformes order.

On the structure and chemistry of electrical trees in polyethylene

The structure and chemistry of two electrical trees (designated Tree A and Tree B) grown in low density polyethylene have been studied by a combination of confocal Raman microprobe spectroscopy, optical microscopy and scanning electron microscopy. Despite being grown under similar conditions (A, 30 °C and 13.5 kV; B, 20 °C and 13.5 kV), these two trees exhibit very different structures. Tree A exhibits a branched structure while Tree B is more bush-like. In Tree A, the very tips of the structure are made up of hollow tubules, which exhibit just the Raman signature of polyethylene. On moving towards the high voltage needle electrode, fluorescent decomposition products are first detected which, subsequently, are replaced by disordered graphitic carbon. From the relative intensity of the graphitic sp2 G and D Raman bands, the constituent graphitic domains are estimated to be ∼4 nm in size, which leads to a local tree channel resistance per unit length of 1–10 Ω µm−1. These structures are therefore sufficiently conducting to prevent local electrical discharge activity. In Tree B, the observed fluorescence increases continuously from the growth tips to the needle. Here, the tree channels are not sufficiently conducting to prevent electrical discharge activity within the body of the tree. These results are discussed in terms of mechanisms of tree growth and, in particular, the chemical processes involved.

The BOLD response: a new look at an old riddle.

Functional imaging has struggled for two decades to establish a quantitative link between the neuronal activity and the change in signal obtained. This review proposes a division of neuronal activity into a component relating to the electrical discharge activity and a component relating to the size of the activated neuronal population. These two components are argued to have opposing influences on the BOLD signal. The influence of these two components on the BOLD signal, are summarised in the standard model.

When more means less: a paradox BOLD response in human visual cortex

The predictions of the 'Linear Transfer Model' (LTM) have been tested only by modulating the frequency of the action potentials while keeping the size of the activated neuronal population constant. The LTM states that the blood oxygenation level-dependent contrast (BOLD) signal is directly proportional to the neuronal activity averaged over milliseconds or seconds. We examined the influence on the BOLD response, of manipulating the size of the activated neuronal population while maintaining the electrical discharge activity constant. We performed functional MR measurements on 30 awake, healthy adult volunteers (15 male and 15 female) using a flashed and reversing checkerboard. These stimuli induced the same vascular response and the same increase in the electrical discharge activity but varied in the size of the neuronal population being activated. The BOLD response measured by the extent of activation and the BOLD signal amplitude, was larger for the flashed than to the reversing checkerboard. An assessment of the local deoxyhemoglobin (HbR) concentration indicated that the neuronal activity was lower during the flashed checkerboard than the reversing checkerboard. Because the checkerboard associated with the lower neuronal activity yielded the larger number of activated voxels and the larger BOLD signal, our results run contrary to the predictions of the 'Linear Transfer Model' and for this reason we refer to them as paradoxical. Stimuli defined by luminance contrast or a chromatic contrast yielded identical results. We conclude that the 'LTM' may apply to stimuli that modulate the electrical discharge activity but not to stimuli that modulate the size of the activated neuronal population.

ESTIMATION OF PARTIAL DISCHARGE PARAMETERS IN GIS USING ACOUSTIC EMISSION TECHNIQUES

Conventional electrical techniques for the monitoring of partial discharge (p.d.) activity in enclosed systems like gas insulated substations (GIS) have certain inherent limitations, which has prompted the exploration of non-electrical techniques. Acoustic detection of p.d. in a GIS is based on the retrieval and analysis of mechanical signals produced on the walls of the metallic enclosure due to electrical discharge activity within. A theoretical modelling of the process by which a discharge produced within the GIS sets up detectable signals on the walls of the enclosure seems to be lacking. The present work consists of the development of a model for the propagation of electrically induced acoustic waves through gaseous medium, and their effect on the walls of the GIS, giving adequate representation to fluid–structure coupling. A numerical simulation of the process is shown to yield important information about the proper type of instrumentation required for such non-invasive tests, and aid in designing robust strategies for locating the source of the discharge.

EVIDENCE OF CIRCADIAN RHYTHM OF ELECTRIC DISCHARGE IN EIGENMANNIA VIRESCENS SYSTEM

The gymnotid electric fish, Eigenmannia virescens, exhibits electric discharge rhythmicity both in alternate light-dark (LD; 12h light, 12h dark [LD 12:12]) and in constant dark (DD) conditions. It suggests that the electric discharge rhythm is under control of the circadian clock. The free-running periods (FRPs) of electric discharge rhythms at 21°C in DD are greater than, but close to, 24h. The maximum of the electric discharge in the Eigenmannia system peaks approximately at circadian time 6 (CT6) in the middle of the subjective day. The circadian oscillator in the system is temperature compensated. This original report reveals the relationship between electric discharge activity and the circadian pacemaker in Eigenmannia and provides an alternative system to investigate circadian rhythms in vertebrates. (Chronobiology International, 17(1), 43–48, 2000)

S100 calcium binding protein affects neuronal electrical discharge activity by modulation of potassium currents

S100 calcium binding protein has been associated with a variety of intra- and extracellular calcium-mediated functions, including learning and memory. We have previously localized S100-immunoreactive neurons correlated with spontaneous discharge activity in the central nervous system of the mollusc, Helix pomatia. In this study, we further investigated the effects of S100 (S100B and S100A1) on electrical discharge activity and membrane currents of Helix neurons, using current- and voltage-clamp techniques. Extracellular application of disulphide-linked S100B (S100B-s-s) in pico- to nanogram/ml concentrations was found to hyperpolarize the membrane resting potential, to inhibit spontaneous discharge activity of action potentials, to alter the stimulus response behaviour from tonic to phasic, to decrease the duration and increase the afterhyperpolarization of action potentials, and to reduce the cell input resistance. Measurement of membrane currents revealed that the total outward current was increased by S100B-s-s. Separation of outward currents showed that three types of potassium currents were altered: (i) an inward rectifying current, (ii) a calcium-activated potassium outward current, both increased by S100B-s-s, and (iii) a delayed, voltage-dependent potassium outward current which was decreased by the protein. The transient potassium outward and the calcium inward currents were not affected by S100B-s-s. Immunocytochemistry showed intracellular labelling of the cytoplasm after extracellular application of the protein, indicating internalization and suggesting an internal site of action. Injection of S100A1 mimicked the effects of S100B-s-s on discharge activity and action potentials. We conclude from our experiments that S100 calcium binding protein, by modulation of potassium currents, may play a role as a neuromodulator in nervous functions.

Estimation of Partial Discharge Parameters in GIS Using Acoustic Emission Techniques

Electrical discharge activity within an electrical power apparatus has detrimental effects on the insulating components of the system, and thus its prognosis and diagnosis are of utmost importance. Traditional electrical methods have been replaced by newer techniques such as acoustic detection. Among these, acoustic methods possess certain inherent advantages, especially where complex electrical systems like GIS are involved. The major concerns therein are the estimation of the magnitude of the discharge level as well as location of the source of discharge. The present work addresses, on a theoretical basis, problems connected with identification, measurement and location of electrical discharges, in particular in GIS. Models for the inception and propagation of p.d. within GIS have been proposed. This study, based essentially on a numerical simulation model, corroborates many of the experimental findings reported in the existing literature, and in addition attempts to suggest newer directions in magnitude estimation and location of p.d.

Electric field computation on an insulating surface with discrete water droplets

Knowledge of the electric field along the external surface is a fundamental requirement for reliable assessment of electric discharge produced surface changes, degradation and flashover of outdoor insulation. Presented in this paper is a method of electric field computation on an insulating surface in the presence of discrete water droplets. The computational method is based on the charge simulation technique. The electric field intensification produced by water droplets is calculated and correlated with electric discharge activity that occurs on outdoor insulators under contaminated conditions. The results are useful for analyzing the performance of outdoor insulating devices, especially non-ceramic insulators, under contaminated conditions.