Surface Discharge In Air Research Articles

Use of Data-Driven Approaches for Defect Classification in Stator Winding Insulation

Partial discharges (PD) in the high voltage insulation systems are both a symptom and cause of terminal and impending failures. The use of data-driven methods based on PD measurements will enable predictive strategies to replace traditional maintenance strategies. This paper employs machine learningbased classification models to identify and characterizePD signals originating from lab-made artificial defects in epoxy-mica material samples. Three different PD sources were studied: surface discharges in air, corona discharges, and discharges caused by internal cavities/delaminations. To generate high-quality datasets for the training, validation, and testing of classification models, Phase-Resolved PD (PRPD) data for each test object was obtained at room temperature under 50 Hz AC excitation at 10 % above the PD inception voltage (PDIV) of each sample. Relevant statistical and deterministic features were extracted for each observation and were labeled based on the defect type (supervised learning). Finally, the trained and validated ML models were used to identify PD sources in the service-aged stator winding insulation. Support vector machines (SVM), ensemble, and k-nearest neighbor (kNN) algorithms achieved significantly high accuracy (≥ 95 %) of defect identification.

A computational study of negative surface discharges: Characteristics of surface streamers and surface charges

We investigate the dynamics of negative surface discharges in air through numerical simulations with a 2D fluid model. A geometry consisting of a flat dielectric embedded between parallel-plate electrodes is used. Compared to negative streamers in bulk gas, negative surface streamers are observed to have a higher electron density, a higher electric field and higher propagation velocity. On the other hand, their maximum electric field and velocity are lower than for positive surface streamers. In our simulations, negative surface streamers are slower for larger relative permittivity. Negative charge accumulates on a dielectric surface when a negative streamer propagates along it, which can lead to a high electric field inside the dielectric. If we initially put negative surface charge on the dielectric, the growth of negative surface discharges is delayed or inhibited. Positive surface charge has the opposite effect.

Stability of Steel X03Cr23Ni6Mo4Cu3NbN (after ESR) Against the Impact of Products of the Atmospheric Pressure Surface Discharge Plasma

Under the effect of the surface discharge in air at atmospheric pressure, the edge of the electrode exposed in the plasma undergoes significant changes (oxidation, erosion, local melting, redeposition of oxides from the gas phase, etc.). The degradation of the working electrode, in the cases, e.g., aluminum or copper electrodes, can cause a continuous change in the electrical characteristics of the device, the executive part of which is the surface discharge system. This work presents the results of an experimental study of the effect of surface discharge plasma products excited by a sinusoidal voltage of 20 and 110 kHz in ambient air on steel X03Cr23Ni6Mo4Cu3NbN (after ESR) acting as an exposed electrode. It is shown that, despite the occurrence of microdamages on the surface of the sample and the formation of local oxide layers, the discharge energy during 4 h of exposure to the plasma products remains unchanged.

Recording Radiation in the Near-Ultraviolet Range to Determine the Initial Ignition Voltage of Surface Discharge in Air

The method of radiation recording in the near-ultraviolet range arising at the surface electric discharge. In the experiment, a double-electrode cell is used in the mode of a power supply by a single rectangular pulse of positive polarity. Using a photoelectric multiplier, a coincidence between the moment of appearance of the discharge current and moment of appearance of the radiation arising at it is specified, which is important for determination of the initial voltage of appearance of the discharge.

On the Determination of the Initial Ignition Voltage of a Surface Discharge in Air

The experimental and calculated values of the initial ignition voltage of a surface barrier discharge in atmospheric air in a plane–parallel electrode system with a Plexiglas barrier are presented. It is shown that the calculation of the initial voltage based on a simplified procedure, in which the criterion of the discharge initiation is the realization of the Townsend condition, provides the calculated dependence of the initial voltage on the barrier thickness, which coincides with the experimental data.

Resistance Models Applied to the Return Stroke Phase of Negative Pulsed Surface Discharges in Air

The energy deposition during the return stroke phase of a pulsed surface discharge is driven by the electrical circuit and the electrical properties of the discharge. To control these factors, a parametric study is performed with varying the circuit parameters, for different discharge lengths and voltages between -19 to -26 kV. The electrical characteristics of the discharge are then simulated using different plasma resistance models, which assume a time-varying resistance: the Toepler model, the Rompe-Weizel model, and the Vlastós model. The model parameters are optimized to fit the experimental results. The analysis shows that for long pulses obtained with large inductance, the three models fare equally well, since the discharge resistance is mainly constant during the pulse. In low-inductance cases, the Toepler model leads to larger errors during the initial current pulse, whereas the Rompe-Weizel and Vlastós models describe with a good agreement the experiments. The discharge resistance evolves during the first 300 ns, then remains mostly constant until the end of the pulse. The constant part of the resistance gives the surface-averaged conductivity of the discharge, which increases linearly with the linear energy dissipated in the discharge. Finally, theoretical estimates of the varying resistance parameters are in fair agreement with the parameters obtained while fitting the experiments, in particular in the Rompe-Weizel case. These findings can be used to estimate the channel resistance of a pulsed surface discharge, and to help optimizing the high-voltage circuit.

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.

Surface discharge in air at high temperatures

The electrical characteristics of surface discharge in air and the intensity of charged species formation in this discharge at high temperatures have been studied experimentally. Current pulses of microdischarges from the edges of a multistripe electrode placed on the surface of a ceramic plate (dielectric barrier) were measured for a.c. voltage with a frequency of 14 kHz and an amplitude up to 3 kV. The analysis of the experimental data shows that with an increase of the gas temperature in the discharge cell up to 500°C and additional heating of the barrier there is a change in the parameters and shape of microdischarge current pulses and a significant increase of charged species formation.

Feature extraction of partial discharge signals using the wavelet packet transform and classification with a probabilistic neural network

Partial discharge (PD) classification in power cable accessories and high voltage equipment in general is essential in evaluating the severity of the damage in the insulation. In this article, the PD classification was realised as a two-fold process. Firstly, measurements taken from a high-frequency current transformer (HFCT) sensor were represented as features by means of a transformation to the classifier and secondly, the probabilistic neural network (PNN) classifier itself was capable of effectively recognising features coming from different types of discharges. The feature that was used as a fingerprint for PD characterisation was extracted from the moments of the probability density function (PDF) of the wavelet coefficients at various scales, obtained through the wavelet packets transformation. The PNN classifier was used to classify the PDs and assess the suitability of this feature vector in PD classification. Four types of artificial PDs were created in a high voltage laboratory, namely corona discharge in air, floating discharge in oil, internal discharge in oil and surface discharge in air, at different applied voltages, and were used to train the PNN algorithm. The results obtained here (97.49, 91.9, 100 and 99.8% for the corona, the floating, the internal and the surface discharges, respectively) are very encouraging for the use of PNN in PD classification with this particular feature vector. This article suggests a feature extraction and classification algorithm for PD classification, which when combined together reduced the dimensionality of the feature space to a manageable dimension, and achieved very high levels of classification.

Spatio-temporal breakdown in surface DBDs: evidence of collective effect

This paper presents an experimental investigation of the plasma ignition in a dielectric barrier surface discharge in air at atmospheric pressure. CCD pictures of the discharge are compared with electrical measurements. A detailed study of the current peaks during the positive half period of the applied voltage has been performed. CCD pictures of single discharges events have been taken. They show synchronous breakdowns of plasma filaments, corresponding to current intensities of several amperes. It is shown that each plasma filament transfers a current of about 40 mA. The influence of adsorbed electrons on the synchronization of the plasma filaments is discussed. The length of the filaments increases during the half period and can be plotted as a linear function of the difference between applied and ignition voltages. The differences between the discharges of positive and negative half periods are presented. The discharges of the negative half period consist of diffuse spots of shorter lengths and are characterized by low currents (several milliamperes), and individual breakdowns.

Excited Electron Temperature and Molecular Vibration Temperature During Transition from Filamentary Discharge to Glow Discharge in Surface Discharge in Air

A dielectric barrier surface discharge device was used toinvestigate the transition from a filamentary discharge to a glowdischarge in air at different gas pressures. Discharge images andwaveforms of the applied voltage and discharge current were recordedsimultaneously, and it was found that the discharge could transitfrom filamentary to glow with the decrease in pressure. Opticalemission spectra during the transition from a filamentary dischargeto a glow one were recorded. Excited electron temperature can bedetermined from the ratios of the relative intensities of spectrallines while molecular vibration temperature can be measured byanalysing spectral lines of the N2 second positive band system.The results show that both the excited temperature and molecularvibration temperature increase with the decrease in the gaspressure. Qualitative explanations are given.

Transition from diffuse to filamentary domain in a 9.5GHz microwave-induced surface discharge

The transition from the low-pressure diffuse to the high-pressure filamentary domain of a 9.5GHz microwave-induced surface discharge in air is recorded. The discharge employs several half-wavelength initiators that locally enhance the electric field to achieve breakdown in the higher-pressure subcritical region. Visible light imaging illustrates the qualitative changes in discharge morphology over the pressure range 4.5to760Torr (0.6to100kPa).

Effects of frequency on the electric strength of polymers

The electric strength of air, in millimeter gaps, decreases at frequencies exceeding 100 kHz, but the effect on the discharge inception voltage V/sub i/ in solid insulation is too small to explain the reduction in the short-time breakdown voltage V/sub st/ of solids at radio frequencies. When breakdown is caused by internal discharges or by surface discharges in air, V/sub st/ at 50 Hz is usually between 5 V/sub i/, and 20 V/sub i/, so the reduction in V/sub st/ when the frequency is raised may be explained by the increased discharge repetition frequency causing more rapid degradation with a risk of cumulative heating at lower stresses. When tests are made in oil, V/sub st//V/sub i/ is smaller than in air, so in this case a tenfold reduction in V/sub st/ at higher frequencies may be caused by a reduction in the electric strength of the oil.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Degradation and breakdown of solid dielectric materials resulting from surface discharges in air and in insulating liquids

An effort is made to identify some of the common aspects of the behavior of PDs (partial discharges) originating in different conditions and interacting with different solid dielectrics (SDs) in media of different density. Emphasis is placed on the behavior of PDs in the SD arrangement with a view to its use as a standard model system for testing the comparative resistance of various dry and impregnated solids to PDs appearing in flat and broad slits, such as those due to delamination and other defects which occur in many kinds of insulation. Observations were made on the propagation and intensity of the discharges as well as their effect on the solid dielectric surface. Results of measurements of light output in the optical range and of magnitude of the PDs are reported, and the resulting damage patterns and the breakdown probability characteristics are described.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

気中沿面放電におけるバリア効果

気中沿面放電におけるバリア効果

Mechanisms of spark propagation in ambient air at the surface of a charged dielectric. II. Theoretical modeling

Experimental investigations on linear surface discharges in air at atmospheric pressure have shown three main regions displayed at the advancing tip of these discharges. Theoretical models of the evolution of the ionized medium along these three succeeding regions are now established. They show how the matching between the coronalike head of the negative gliding spark and the thermalized leader channel occurs via a turbulent plasma region of small dimensions, where the energy of the electrical field is transferred into ionization within a duration of about 10 ns.

Empirical Formula and Polarity Effect of the Impulse Surface Discharge in Air

Empirical Formula and Polarity Effect of the Impulse Surface Discharge in Air

The resistance of sheet insulation to surface discharges

Investigations show that a satisfactory classification of insulating materials with respect to their resistance to deterioration and breakdown by surface discharges in air is given by time-to-breakdown tests using simple rod and plate electrodes. It is necessary to circulate dry air over specimens to avoid the formation of semiconducting films, and comparison should be made only between specimens of similar thickness. The discharge resistance of most materials is reduced by increasing the ambient temperature or by applying mechanical strain. Results of tests on thin films and sheets of several polymers and on both glass and paper laminates of 1–3 mm thickness are given.Recommendations for standard tests for comparing the discharge resistance of materials are given in the Appendices.