Showing papers on "Partial discharge published in 2010"

Effects of nano-filler addition on partial discharge resistance and dielectric breakdown strength of Micro-Al 2 O 3 Epoxy composite

Abstract: It is often observed that the insulation structure for an insulated gate bipolar transistor (IGBT) suffers from dielectric failure, when the insulation is made of epoxy resin to which micro fillers with a high thermal conductivity were added. In order to reveal the above phenomena and to clarify the breakdown (BD) mechanism, we have carried out experiments using an MB-PWB (metal-base printed wiring board) insulation simulated structure. As a result, it was clarified that the IGBT insulation breaks down after successive partial discharges (PDs). It was also elucidated that BD strength becomes lower, when epoxy resin was loaded with high content of micro-fillers. A trial was made to raise the once-lowered BD strength by adding nano-Al2O3 fillers. Three kinds of experiments were carried out, i.e. an MB-PWB insulation simulated structure for dielectric failure, a rod-to-plane electrode for PD erosion resistance, and a sphere-to-sphere electrode for BD strength for four kinds of insulation samples, i.e. neat epoxy, 5-wt% nano- Al2O3/epoxy composite, 60-wt% micro-Al2O3/epoxy composite, and combined 2-wt% nano- and 60-wt% micro-Al2O3/epoxy composite. It was clarified that the nano-micro-composite is higher in both BD strength and PD resistance than the micro-composite. It should be noted that the addition of nano-fillers would provide an excellent approach that can increase the dielectric BD strength and time of micro-filled epoxy composites.

Partial discharge source discrimination using a support vector machine

Abstract: Partial discharge (PD) measurements are an important tool for assessing the health of power equipment. Different sources of PD have different effects on the insulation performance of power apparatus. Therefore, discrimination between PD sources is of great interest to both system utilities and equipment manufacturers. This paper investigates the use of a wide bandwidth PD on-line measurement system consisting of a radio frequency current transducer (RFCT) sensor, a digital storage oscilloscope and a high performance personal computer to facilitate automatic PD source identification. Three artificial PD models were used to simulate typical PD sources which may exist within power system apparatus. Wavelet analysis was applied to pre-process measurement data obtained from the wide bandwidth PD sensor. This data was then processed using correlation analysis to cluster the discharges into different groups. A machine learning technique, namely the support vector machine (SVM) was then used to identify between the different PD sources. The SVM is trained to differentiate between the inherent features of each discharge source signal. Laboratory experiments where the trained SVM was tested using measurement data from the RFCT as opposed to conventional measurement data indicate that this approach has a robust performance and has great potential for use with field measurement data.

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

Abstract: 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.

Dielectric properties and partial discharge endurance of polypropylene-silica nanocomposite

Abstract: This paper presents the results of the dielectric properties and partial discharge endurance measurements conducted on polypropylene (PP)-silica nanocomposite. The material compounds were analyzed with micro-Raman spectroscopy, X-ray tomography and transmission electron microscopy (TEM). ac and dc breakdown strength of the materials was measured. Dielectric response, capacitance and loss factor of the film samples were measured as a function of temperature and frequency. Partial discharge (PD) endurance of the reference PP and PP Silica nanocomposite was studied as a function of ac voltage. Material surfaces were analyzed after PD stress with optical microscopy. All dielectric measurements were done for oriented thin films with a thickness of 11-23 μm. The results were analyzed statistically to determine the effects of the additive on the properties of PP. The paper discusses the potential of PP Silica nanocomposite with a view to high voltage applications, especially power capacitors.

Partial discharge control in a power electronic module using high permittivity non-linear dielectrics

Abstract: High electric fields at the edge of the substrate metallization can give rise to partial discharge within power electronic modules and can lead to eventual failure. This paper examines the use of silicone gels filled with barium titanate to reduce the electric field enhancement at the edge of substrate metallization and therefore increase partial discharge inception voltages. The barium titanate filled gel produces a dielectric in which the relative permittivity is increased over a plain gel and that also exhibits a dependence on electric field. The theoretical electric field reduction that can be achieved in a power electronic module through the use of filled gels is demonstrated and compared against experimental measurements including the trial of the technique in some commercial modules. As promising results are achieved, consideration is also given to the effect of the barium titanate filler on the viscosity of the gel and the thermal conductivity, two key manufacturing issues.

Creepage discharge on insulation barriers in aged power transformers

Abstract: This paper presents experimental research of creepage discharge on insulation barriers in power transformers. Using point-to-plate electrode configurations under AC voltages creepage discharge is studied for both single flashover breakdown and partial discharge induced failure modes. It is confirmed that the dielectric strength of oil gap will not be reduced with introducing dry new pressboard surface into the oil gap, indeed the flashover breakdown voltage is hardly compromised by introducing aged pressboard with up to 3% moisture. However, increased moisture content in pressboard reduces partial discharge inception voltage (PDIV) significantly, i.e. ~30% PDIV reduction for pressboard of ~3% moisture as compared with dry pressboard. More importantly, high moisture contents in pressboard increase PD activities in oil pores which allow gasses to be trapped inside to develop gaseous channels which eventually lead creepage discharge to breakdown.

Behavior of machine insulation systems subjected to accelerated thermal aging test

Abstract: Accelerated aging tests have been extensively used on motor and generator insulation systems to simulate in a short time period the deterioration mechanisms occurring during normal operation of many years, to identify insulation system designs with longer life time and to support the qualification of a new system. The contribution presents results from extensive investigations on the behavior of two VPI machine test insulation systems (reference and candidate) with thermal class F (155°C), which were subjected to three thermal overstresses in repeated cycles. After each thermal cycle the insulation system is subjected to mechanical stress, moisture, and voltage. In order to check the condition of the insulation systems in a non-destructive manner several properties of insulation like dissipation factor, insulation resistance and partial discharge quantities were measured after each thermal cycle. After that the end of life of the insulation systems were checked with ac voltage and impulse voltage. The results support the qualification by comparative evaluation and they indicate, how the changes in electrical and dielectric properties of insulation take place during the accelerated aging test.

Power electronics and electrical insulation systems ߝ Part 1: Phenomenology overview

Abstract: It is well known that the wide use of power electronic converters (PEC) is one of the main causes of current and voltage distortion in the electrical networks. These converters generate harmonic components propagating toward the supply network side and nonsinusoidal voltage at the load side. Distorted waveforms generated by power electronics can dramatically reduce the reliability of insulation systems. Such systems should be designed bearing this important factor in mind.

Cross-wavelet transform as a new paradigm for feature extraction from noisy partial discharge pulses

Abstract: In this work a new approach based on cross-wavelet transform towards identification of noisy Partial Discharge (PD) patterns has been proposed. Different partial discharge patterns are recorded from the various samples prepared with known defects. A novel cross-wavelet transform based technique is used for feature extraction from raw noisy partial discharge signals. Noise is a significant problem in PD detection. The proposed method eliminates the requirement of denoising prior to processing and therefore it can be used to develop an automated and intelligent PD detector that requires minimal human expertise during its operation and analysis. A rough-set theory (RST) based classifier is used to classify the extracted features. Results show that the partial discharge patterns can be classified properly from the noisy waveforms. The effectiveness of the feature extraction methodology has also been verified with two other commonly used classification techniques: Artificial Neural Network (ANN) based classifier and Fuzzy classifier. It is found that the type of defect within insulation can be classified efficiently with the features extracted from cross-wavelet spectra of PD waveforms by all of these methods with a reasonable degree of accuracy.

Mandrel-Based Fiber-Optic Sensors for Acoustic Detection of Partial Discharges—a Proof of Concept

Abstract: Acoustic emission monitoring is often used in the diagnosis of electrical and mechanical incipient faults in high-voltage apparatus. Partial discharges are a source of failure in power transformers, and the differentiation from other sources of acoustic emissions is of the utmost importance. This paper reports the development of a new sensor concept-mandrel-based fiber-optic sensor-for the detection of incipient faults in oil-filled power transformers, taking direct measurements inside a transformer. These sensors can be placed in the inner surface of the transformer tank wall, not affecting the insulation integrity of the structure, and improving fault detection and location. The applicability of these acoustic sensors in air, water, and oil is investigated and the paper presents the promising results obtained, which will enable the industrial development of practical solutions.

Excitation of atmospheric pressure uniform dielectric barrier discharge using repetitive unipolar nanosecond-pulse generator

Abstract: Dielectric barrier discharge (DBD) excitation by unipolar high voltage pulses is a promising approach for producing non-thermal plasma at atmospheric pressure. In this study, a magnetic compression solid-state pulsed power generator was used to produce repetitive nanosecond pulses for the excitation. The DBD is created using two liquid electrodes. The electrical characteristics of the discharge voltage and current are illustrated under different experimental conditions. The nanosecond-pulse discharge current is of the order of tens of amperes. This differs from common DBD current excitated by high-voltage ac sources. Compared with the characteristics of two current pulses corresponding to two discharges for unipolar pulsed-excitation, the secondary discharge in this study is minor owing to the pulsed power and discharge configuration. Under the experimental conditions, the luminous emissions from the front and side views of the liquid electrodes show that no filament is observed and the discharge is homogeneous and diffuse in the whole discharge region. The effects of applied voltage amplitude, repetition rate, and air gap spacing on the discharge characteristic are investigated. The discharge mode does not change with the variation of the investigated parameters. A comparison of high voltage ac and nanosecond-pulse excitation is also presented. In addition, discussion of the experimental results is presented.

Analysis and Prevention of Vortex Breakdown in the Simplified Discharge Cone of a Francis Turbine

Abstract: We perform a numerical analysis of the decelerated swirling flow into the discharge cone of a model Francis turbine operated at variable discharge and constant head, using an axisymmetric turbulent swirling flow model and a corresponding simplified computational domain. Inlet boundary conditions correspond to velocity and turbulent kinetic energy profiles measured downstream the Francis runner. Our numerical results are validated against experimental data on a survey section further downstream in the cone, showing that the Reynolds stress turbulence model with a quadratic pressure-strain term correctly captures the flow field. It is shown that the diffuser performance quickly deteriorates as the turbine discharge decreases, due to the occurrence and development of vortex breakdown, with a central quasistagnant region. We investigate a novel flow control technique, which uses a water jet injected from the runner crown tip along the axis. It is shown that the jet discharge can be optimized for minimum overall losses, while the vortex breakdown is eliminated. This flow control method is useful for mitigating the Francis turbine flow instabilities when operating at partial discharge.

Influence of rise time on partial discharge extinction voltage at semi-square voltage waveforms

Abstract: This work presents measurements of the partial discharge (PD) extinction voltage in three different types of test objects, using semi-square voltages with 2 ?s and 100 ?s rise time. A needle creating corona discharges, a twisted pair specimen commonly used for testing motor insulation and a paper/oil test object modelling the turn-to-turn insulation of a transformer winding were investigated, presenting extinction voltages between approximately 1 kV and 8 kV. For the twisted pair specimen the PD extinction voltage was significantly lower at the shorter rise time, whereas for the other test objects, just a small or no difference could be detected. The conclusion is that depending on what range of rise times and what insulation system that are studied, there may be an influence of the rise time of the applied voltage on the PD extinction voltage.

A frequency-based RF partial discharge detector for low-power wireless sensing

Abstract: Partial discharge (PD) monitoring has been the subject of significant research in recent years, which has given rise to a range of well-established PD detection and measurement techniques, such as acoustic and RF, on which condition monitoring systems for highvoltage equipment have been based. This paper presents a novel approach to partial discharge monitoring by using a low-cost, low-power RF detector. The detector employs a frequency-based technique that can distinguish between multiple partial discharge events and other impulsive noise sources within a substation, tracking defect severity over time and providing information pertaining to plant health. The detector is designed to operate as part of a wireless condition monitoring network, removing the need for additional wiring to be installed into substations whilst still gaining the benefits of the RF technique. This novel approach to PD detection not only provides a low-cost solution to on-line partial discharge monitoring, but also presents a means to deploy wide-scale RF monitoring without the associated costs of wide-band monitoring systems.

Leakage current as a predictor of failure in dielectric elastomer actuators

Abstract: Dielectric breakdown often leads to catastrophic failure in Dielectric Elastomer Actuator(s) (DEA). The resultant damage to the dielectric membrane renders the DEA useless for future actuation, and in extreme cases the sudden discharge of energy during breakdown can present a serious fire risk. The breakdown strength of DEA however is heavily dependent on the presence of microscopic defects in the membrane giving its overall breakdown strength inherent variability. The practical consequence is that DEA normally have to be operated far below their maximum performance in order to achieve consistent reliability. Predicting when DEA are about to suffer breakdown based on feedback will enable significant increase in effective DEA performance without sacrificing reliability. It has been previously suggested that changes in the leakage current can be a harbinger of dielectric breakdown; leakage current exhibits a sharp increase during breakdown. In this paper the relationship between electric field and leakage current is investigated for simple VHB4905-based DEA. Particular emphasis is placed on the behaviour of leakage current leading up to and during breakdown conditions. For a sample size of nine expanding dot DEA, the DEA that failed at electric fields below the maximum tested exhibited noticeably higher nominal power dissipation and a higher frequency of partial discharge events than the DEA that did not breakdown during testing. This effect could easily be seen at electric fields well below that at which the worst performing DEA failed.

Influence of disconnecting part on propagation properties of PD-induced electromagnetic wave in model gis

Abstract: Partial discharge (PD) detection using a UHF (ultra high frequency) band signal is a well known advanced insulation diagnosis method in gas insulated switchgear (GIS), and has been actively studied. Detailed investigation of electromagnetic (EM) wave propagation inside the GIS tank is required for significant improvement of detecting PD signal by UHF method. When practically applying the UHF method to GIS insulation diagnostics, it is necessary to examine the effects of GIS components such as circuit breakers, isolators and disconnectors on EM wave propagation properties. In this paper, attention is paid to the effects of a disconnecting part of a high voltage (HV) conductor like a circuit breaker or a disconnector in GIS. To examine the effects of disconnecting part, the gap length of the disconnecting part was set as parameter, and waveforms and frequency spectra of the propagation PD-induced EM wave were measured with UHF sensors. For the purpose of discussing the effects of the disconnecting part theoretically, a finite difference time domain (FD-TD) simulation was also carried out. The experimental results show that the PD-induced wave could propagate through the disconnecting part with higher frequency components over the cutoff frequency components of TE11 mode for disconnecting part, i.e. cylindrical shape formed by GIS tank without HV conductor. The propagation of the lower frequency components below the TE11 mode depended on the gap length of the disconnecting part.

Impact of low pressure aerospace environment on machine winding insulation

Abstract: The concept of More Electric Aircraft is chiefly concerned with the replacement of heavy non-electrical systems with electrical systems. For the aerospace industry to move forward to the More Electric Aircraft and its partner concepts such as More Electric Engine, structures of the electrical, hydraulic, pneumatic and mechanical power transmission systems on board need to be modified and optimized. Therefore, the insulation system used in the full range of electrical components is going to face more challenging working conditions which include higher voltage, extreme temperatures and pressures, etc. One important feature of the working environment for aircraft insulation system is the pressure range can vary from approximately 10,000 Pa to 400,000 Pa. Given the importance to deliver a long insulation life, the impact of this pressure variation on the electrical degradation of insulation must be understood. This paper describes the tests that have been carried out to examine the impact of voltage and pressure on the partial discharge behaviour of different types of machine winding insulations.

Advanced modeling of electron avalanche process in polymeric dielectric voids: Simulations and experimental validation

Abstract: This paper deals with aging phenomena in polymers under electric stress. In particular, we focus our efforts on the development of a novel theoretical method accounting for the discharge process (partial discharge) in well known defects present in polymers, which are essentially tiny air gaps embedded in a polymeric matrix. Such defects are believed to act as trigger points for the partial discharges and their induced aging process. The model accounts for the amplitude as well as the energy distribution of the electrons during their motion, particularly at the time in which they impact on the polymer surface. The knowledge of the number of generated electrons and of their energy distributions is fundamental to evaluate the amount of damage caused by an avalanche on the polymer-void interface and get novel insights of the basic phenomena underlying the relevant aging processes. The calculation of such quantities would require generally the combined solution of the Boltzmann equation in the energy and space/time domains. The proposed method simplifies the problem, taking into account only the main phenomena involved in the process and provides a partial discharge (PD) model virtually free of adjustable parameters. This model is validated by an accurate experimental procedure aimed at reproducing the same conditions of the simulations and regarding air gaps embedded in polymeric dielectrics. The experimental results confirm the validity and accuracy of the proposed approach.

DC corona discharge ozone production enhanced by magnetic field

Abstract: We have studied the effect of a stationary magnetic field on the production of ozone from air at atmospheric pressure by a negative corona discharge in a cylindrical electrode configuration. We used a stainless steel hollow needle placed at the axis of the cylindrical discharge chamber as a cathode. The outer wall of the cylinder was used as an anode. The vector of magnetic induction was perpendicular to the vector of current density. We found that: (a) the magnetic field extends the current voltage range of the discharge; (b) for the discharge in the Trichel pulses regime and in the pulseless glow regime, the magnetic field has no substantial effect on the discharge voltage or on the concentration of ozone that is produced; (c) for the discharge in the filamentary streamer regime for a particular current, the magnetic field increases the discharge voltage and consequently an approximately 30% higher ozone concentration can be obtained; (d) the magnetic field does not substantially increase the maximum ozone production yield. A major advantage of using a magnetic field is that the increase in ozone concentration produced by the discharge can be obtained without additional energy requirements.

A large gap of radio frequency dielectric barrier atmospheric pressure glow discharge

Abstract: A large gap was acquired between electrodes (up to 5.5 mm) of Ar atmospheric pressure glow discharge in radio frequency dielectric barrier discharge (rf-DBD). The discharge of Ar plasma was characterized by I-V curve and Lissajous plot, and the effective power of the discharge was calculated based on the measured Lissajous plot and found to be higher than 90% of the input power. To gain a thorough understanding of the mechanism, the rf-DBD with a single dielectric barrier layer operating in γ mode glow discharge of N2 plasma was diagnosed in spatial resolution through optical emission spectroscopy. It was concluded that secondary electron emission might be responsible for the sustainable glow discharge in the large gap rf-DBD plasma.

PD apparent charge estimation and calibration: A critical review

Abstract: This paper focuses on the limits of partial discharge apparent charge estimation and calibration using an unified approach. The fundamental problems that prevent accurate apparent charge estimates (resonances, attenuation and partial discharge pulse splitting) are tackled through this approach, highlighting the physical limitations that prevent partial discharge charge to be measured properly. The feasibility of calibration of ultra-wide bandwidth measurement systems, something that is not treated in the IEC 60270 standard, is also discussed.

The influence of impurities on the performance of the dielectric barrier discharge

Abstract: In this letter, we investigate the effect of various levels of nitrogen impurity on the electrical performance of an atmospheric pressure dielectric barrier discharge in helium. We illustrate the different current profiles that are obtained, which exhibit one or more discharge pulses per half cycle and evaluate their performance in ionizing the discharge and dissipating the power. It is shown that flat and broad current profiles perform the best in ionizing the discharge and use the least amount of power per generated charged particle.

Partial discharge detection as a tool to infer pollution severity of polymeric insulators

Abstract: This paper deals with the analysis of partial discharge characteristics of silicone rubber insulators, with the aim to develop a better diagnostic tool to identify the pollution severity of outdoor insulators. In this work, laboratory-based pollution performance tests are carried out on silicone rubber insulators under ac voltage at different pollution levels and relative humidity conditions, using sodium chloride as a contaminant. Partial discharge (PD) is acquired through an innovative PD detection system which is able to collect PD waveforms beside PD patterns. Time domain and frequency domain characteristics of PD pulses at different surface pollution conditions are studied. Statistical parameters of PD patterns are also evaluated in order to achieve a quantitative assessment of pollution severity of polymeric insulators. The results on silicone rubber insulators show that the pollution severity of outdoor polymeric insulators could be identified from the partial discharge pattern analysis.

Microscopic view of aging mechanism of polyimide film under pulse voltage in presence of partial discharge

Abstract: Inverter-fed motors are damaged due to pulse voltage. The situation leads to early failure of insulation. Polyimide is an important insulating material in the inverter-fed motors. Its insulation aging process and failure mechanism are different from traditional AC and DC voltage. In this paper, structure change of polyimide film aging under pulse voltage above partial discharge inception voltage (PDIV) is investigated through scanning electron microscopy (SEM), thermally stimulated current (TSC) and lifetime test. It reveals that the degradation of structure in polyimide propagates from surface to interior with continuous aging, creating three layers in section. In the TSC spectrum, two main well-resolved peaks, namely ? and s, exist in the 20-200°C range. The configuration corresponding to ? peak in polyimide is damaged more severely than the configuration corresponding to s peak and its degradation is accelerated with increase in frequency.

Dielectric response and partial discharge measurements on stator insulation at varied low frequency

Abstract: This is a study of potential improvements of diagnostic methods used on high-voltage generators and motors. It considers offline electrical measurements on the main insulation of stator windings, ...

Diagnosis of EHV and HV Transformers Through an Innovative Partial-Discharge-Based Technique

Abstract: Online partial discharge (PD) analysis of power transformers is sometimes complex due to the presence of large disturbance and noise as well as to uncertainty in PD source identification. In this paper, a novel approach to PD detection and analysis in online power transformers is presented. The proposed approach provides hardware and software tools to remove disturbance, noise, separate contributions from different sources and, eventually, identify PD sources. Besides, a description of the hardware tools used to assemble the diagnostic system, the tests (in the lab and on real transformers) carried out to build the reference database needed for identification system training will be discussed, providing rules for PD source identification. A number of working cases will be presented to show the effectiveness of the proposed method.

Off-line PD testing of converter-fed wire-wound motors: when IEC TS 60034-18-41 may fail?

Abstract: This paper reports and discusses qualification and type test procedures for random wound motors as specified in IEC Technical Specification 60034-18-41. Since laboratory tests dealing with off-line partial discharges measurements followed by life tests showed that motors qualified as good can fail in very short times, an extensive investigation on the causes of such discrepancy and, in particular, on the differences existing between the stresses applied during off-line tests and in service is described. In addition, the results of partial discharge measurements performed on crossed pairs are presented, highlighting how the differences in the applied voltage waveform can influence the Repetitive Partial Discharge Inception Voltage. Suggestions to improve the off-line test procedure and related equipment are eventually discussed.

Partial Discharge Pattern Characteristic of HV Cable Joints with Typical Artificial Defect

Abstract: Insulation failure of XLPE cable system, particularly in joints and terminations, mostly attributes to local defects resulted from inadequate manufacturing or poor installation workmanship. Since it is well-acknowledged that partial discharge (PD) has a relationship with the discharge source (fault or defect), PD detection and pattern recognition have been widely accepted as a means to provide information on both the type and severity of defects or potential failures, which is further expected to give advice on repair or replacement of cable accessories. This paper presents a laboratory experiment on HOkV XLPE cable joints with artificial typical defects and their partial discharge pattern characteristic. PD patterns and statistical operators of these defects shows dissimilarity, which can be utilized as samples for further on-site PD pattern recognition.

Simulation of transient earth voltages aroused by partial discharge in switchgears

Abstract: Switchgears are the key equipments in the distribution network. Operating switchgear with active Partial Discharge (PD) increases the risk of failure occurring at the time of switching leading to increased risk to the operator. PD in switchgears can be considered to take two forms, surface discharge and internal discharge, if allowed to continue, eventually causes the insulation to break down catastrophically. The electromagnetic pulses produced by PD are in large part conducted away by the surrounding metalwork but a small proportion impinges onto the inner surface of the casing. These charges escape through joints in the metalwork, or a gasket on a gas insulated switch, and pass, as local raised voltages, across the surface of the switch to earth. These pulses of charge were named by Transient Earth Voltages (TEV), and the level of these TEV signals are proportional to the condition of the insulation for switchgear of the same type and model, measured at the same point. So TEV is a very powerful comparative technique for noninvasively checking the condition of switches. In this paper, the Finite-Difference Time-Domain (FDTD) method was employed to simulate the propagation law of TEV in the switchgear. The simulation results show that, the TEV amplitude is proportional to the PD pulse amplitude, increases with PD pulse width decrease and decrease with the distance between detection point and PD source.

Characterization and mechanism studies of dielectric barrier discharges generated at atmospheric pressure

Abstract: A dielectric barrier discharge (DBD) device operated at ambient air with an ac power supply was designed and examined. The discharge power and active current of DBD were characterized. Experimental results show that the discharge power does not proportionally increase all along with voltage. Through in-depth analysis of typical waveforms of instantaneous applied voltage and discharge current, and images of microdischarges in the gas gap, it is inferred that considerable reduction in charges transferred through discharge channels is most likely due to recombination and attachment to electronegative molecules, nonuniform highly distorted electric fields, and repulse of more homogeneous electric charges.