Showing papers on "Partial discharge published in 2014"
TL;DR: In this article, a review of the available partial discharge detection methods (involving high voltage equipment) such as electrical detection, chemical detection, acoustic detection, and optical detection have been explored and compared.
Abstract: When operating an equipment or a power system at the high voltage, problems associated with partial discharge (PD) can be tracked down to electromagnetic emission, acoustic emission or chemical reactions such as the formation of ozone and nitrous oxide gases. The high voltage equipment and high voltage installation owners have come to terms with the need for conditions monitoring the process of PD in the equipments such as power transformers, gas insulated substations (GIS), and cable installations. This paper reviews the available PD detection methods (involving high voltage equipment) such as electrical detection, chemical detection, acoustic detection, and optical detection. Advantages and disadvantages of each method have been explored and compared. The review suggests that optical detection techniques provide many advantages in the consideration of accuracy and suitability for the applications when compared to other techniques.
136 citations
TL;DR: The dependence of endurance test results on repetitive square wave voltage waveform parameters is investigated in this article focusing on crossed pair specimens made of polyamide-imide enameled wires.
Abstract: The dependence of endurance test results on repetitive square wave voltage waveform parameters is investigated in this paper focusing on crossed pair specimens made of polyamide-imide enameled wires. Endurance tests carried out on crossed pairs above partial discharge inception voltage using both sinusoidal and square wave voltages show that lifetimes can be influenced significantly by voltage waveform parameters (rise time and frequency). Partial discharge statistics, recorded from test beginning to breakdown, are used to explain the remarkable differences associated with voltage waveform parameters. According to this study, the influence of voltage waveform parameters should be carefully considered in order to obtain effective evaluation of inverter-fed motor insulation systems.
76 citations
TL;DR: Results show that the features of repetitive voltage impulse affect PD time and frequency characteristics, PD phase distribution, and endurance, and evaluation of insulation subjected to power electronics waveforms should take into account the appropriate choice of impulsive voltage parameter to fit to the type of PD phenomenology occurring in service conditions.
Abstract: To address the reliability of rotating machine insulation, the International Electrotechnical Commission implemented new standards and technical specifications that are relevant to low-voltage and medium-voltage inverter-fed motors. Insulation evaluation under such power supply relies upon partial discharge (PD) measurements and accelerated life tests, which should be conducted (at least for the turn-to-turn insulation) under impulsive voltage waveform. The effect of impulsive voltage parameters on PD inception voltage and, in particular, endurance tests must be investigated to design test procedures that can indicate insulation quality and its behavior in service. This paper examines the effect of repetitive impulsive voltage waveform parameters on PD and the endurance (life) of organic insulation for rotating machine wires based on experiments performed on single-contact crossed pairs. Results show that the features of repetitive voltage impulse affect PD time and frequency characteristics, PD phase distribution, and endurance. Consequently, evaluation of insulation subjected to power electronics waveforms should take into account the appropriate choice of impulsive voltage parameter to fit to the type of PD phenomenology occurring in service conditions.
71 citations
TL;DR: In this article, a high voltage power supply PWM has been built in order to test, offline, electric stators in conditions as close as possible to real electrical conditions and on-line PD measurements have also been successfully carried out, in an engine test bench used to test and control electric vehicle (EV) powertrain.
Abstract: This paper deals with Partial Discharge (PD) detection in Pulse Width Modulation (PWM) inverter fed electric motors. The aim of this work is to detect PD activity in random wound motors, which is the main cause for premature breakdown of insulation system. Detection is performed thanks to a non-intrusive electromagnetic sensor. A high voltage power supply PWM has been built in order to test, offline, electric stators in conditions as close as possible to real electrical conditions. Then, on-line PD measurements have also been successfully carried out, in an engine test bench used to test and control electric vehicle (EV) powertrain.
69 citations
TL;DR: In this article, the Rogowski coil is employed as a PD measuring sensor and a comparative study of variation in mechanical design features provides a brief guideline to select the optimal design of the coil.
58 citations
TL;DR: In this article, the partial discharge characteristics of natural esters as a dielectric fluid for power transformer and other electric power apparatus insulation applications are analyzed using time and frequency domain analysis at both needle-plane and rod-plane electrode configurations.
Abstract: Petroleum based mineral oils are generally used for electric power apparatus insulation and cooling applications. Since the conventionally used mineral oils are not biodegradable and difficult to decompose, there is a need for the development of alternate vegetable based insulation oils for such applications. Formation of partial discharges plays a major role in determining the life time of liquid insulation. Reports on partial discharge characteristics of thermal aged natural ester fluids for high voltage applications are scanty. The major aim of this research work is to understand the partial discharge characteristics of natural esters as a dielectric fluid for power transformer and other electric power apparatus insulation applications. Laboratory experiments are performed as per IEC (International Electro technical Commission) test procedures in order to understand the breakdown voltage and partial discharge characteristics of vegetable oils such as corn oil and palm oil under both virgin and thermal aged conditions. This paper presents a comparative assessment of the PD characteristics of thermal aged natural ester fluids with respect to mineral oil. Time and frequency domain analysis of PD pulse at both needle-plane and rod-plane electrode configurations are studied. Statistical analysis of PD pattern is also carried out. This analysis collects the typical PD patterns from natural ester fluids in order to find its suitability for power transformer and electric power apparatus applications.
52 citations
TL;DR: In this paper, the acquisition of the PD characteristics caused by four typical insulation defects forms φ-v-n 3D PRPD pattern plots sample matrix and the largest Lyapunov exponent of each column of matrix is calculated.
Abstract: Partial discharge (PD) is a key parameter which describes insulation condition of gas-insulated switchgear GIS, GIS internal defects can be discovered in time with the interferences such as corona discharge from the power system using Ultra-high frequency (UHF) method. Traditional method based on statistical characteristics is limited to the analysis of image features that describe the PD pattern plot, causing low recognition rate of some kinds of PD. In this paper, the acquisition of the PD characteristics caused by four typical insulation defects forms φ-v-n 3D PRPD pattern plots sample matrix. The largest Lyapunov exponent of each column of matrix is calculated. A 36-dimension vector is then obtained as the chaotic characteristics of the PD in different voltage phases. The experimental results show that the recognition method based on the chaotic characteristics performs well on all four kinds of insulation defects and can satisfy the recognition order. The method based on the chaotic characteristics has a strong recognition ability for the discharge physical models of gas gap, which is an advantage over the traditional method. The two recognition methods have a good complementary property. Combining the complementary chaotic and statistical characteristics in a decision-making level by using the Dempster-Shafer evidence theory results in an accuracy of above 98%.
52 citations
TL;DR: In this article, the severity levels of partial discharge initiated by free moving metallic particles on GIS insulator surface were evaluated on a well-established 252 kV GIS experiment platform, and the experimental results indicated that partial discharge provoked by free-moving metallic particles in GIS goes through three severity levels, namely, minor discharge, moderate discharge, and threatening discharge.
Abstract: Free moving metallic particles are one of the most common defects leading to insulation failures in gas insulated substation (GIS) equipment. The present research is designed to diagnose and assess the severity levels of partial discharge (PD) initiated by free moving metallic particles on GIS insulator surface. On a well-established 252 kV GIS experiment platform, long term tests were conducted to observe the entire development process of partial discharge from its very initiation stage till eventual flashover as the applied voltage gradually boosted. Real time measurement was undertaken during the tests to capture the trend curve of partial discharge as a result of test time, scatter plot, histogram, grey-scale map, and time-frequency map of partial discharge. The experimental results indicate that 1) partial discharge provoked by free moving metallic particles in GIS goes through three severity levels, namely, minor discharge, moderate discharge, and threatening discharge; 2) as partial discharge develops, the phase distribution is widening and corresponding shape changes occur in the scatter plot, histogram, grey-scale map, and time-frequency map. It is recommended that the features of phase distribution and the corresponding spectra could be used as important criteria in diagnosing and assessing the severity levels of partial discharge initiated by free moving metallic particles on GIS insulator surface.
49 citations
TL;DR: In this paper, a neuro-fuzzy technique that uses unsupervised pattern recognition was proposed to localize partial discharge (PD) source in power transformers, which showed a significant improvement in localizing PD for major types of PD compared to currently available techniques, such as orthogonal transforms and the calibration line method.
Abstract: Partial discharge (PD) is the most common sources of insulation failure in power transformers. The most important tools for quality assessment of power transformers are PD detection, measurement, and classification. As for the maintenance and repair of transformers, the major importance is the techniques for locating a PD source. The transfer function-based (TF) method for power transformers' winding in the high-frequency range is commonly used in power engineering applications, such as transient analysis, insulation coordination, and in transformer design. Although it is possible to localize PD in transformer winding using the transfer function (TF) method, this method cannot be used for transformers with no design data. Previous attempts toward finding a feature that localizes PD in transformers in general that lineate with PD location were found to be less successful. Therefore, in this paper, a neuro-fuzzy technique that uses unsupervised pattern recognition was proposed to localize PD source in power transformers. The proposed method was tested on a medium-voltage transformer winding in the laboratory. The results showed a significant improvement in localizing PD for major types of PD compared to currently available techniques, such as orthogonal transforms and the calibration line method.
48 citations
TL;DR: In this paper, a novel hydrogen sensor is designed on the basis of Fiber Bragg grating (FBG) sensing technique, which can be arranged inside the transformer and has several advantages, such as fast fault detection and location, immunity to electromagnetic interference, quasi-distribution measurement and real-time monitoring.
Abstract: A novel hydrogen sensor is designed on the basis of Fiber Bragg grating (FBG) sensing technique. The sensor can be arranged inside the transformer. It has several advantages, such as fast fault detection and location, immunity to electromagnetic interference, quasi-distribution measurement and real-time monitoring. The principle of the proposed FBG hydrogen sensor is based on changes of the physical properties of palladium films which absorb hydrogen. A thick palladium layer prepared by magnetron sputtering is used to achieve high sensitivity. Meanwhile, polyimide is added into the adhesive layer to improve the reliability of the sensor. Partial discharge experiments demonstrated that the wavelength shift of the FBG hydrogen sensor varies linearly with the concentration of hydrogen dissolved in the transformer oil. It is hardly disturbed by other factors. The hydrogen sensing experiment in oil at a temperature of 80°C revealed that the sensitivity of the sensor remains same as the temperature varies, ranging from room temperature to operating temperature of the power transformer. Thus, the proposed sensor can work properly under the operating temperature of power transformers.
47 citations
TL;DR: An academic review about partial discharge in polymer nanocomposites used as electrical insulating material from previous research is provided, covering aspects of preparation, characteristics of the nanocomPOSite based on experimental works, application in power systems, methods and techniques of experiment and analysis, and future trends.
Abstract: Polymer nanocomposites have recently been attracting attention among researchers in electrical insulating applications from energy storage to power delivery. However, partial discharge has always been a predecessor to major faults and problems in this field. In addition, there is a lot more to explore, as neither the partial discharge characteristic in nanocomposites nor their electrical properties are clearly understood. By adding a small amount of weight percentage (wt%) of nanofillers, the physical, mechanical, and electrical properties of polymers can be greatly enhanced. For instance, nanofillers in nanocomposites such as silica (SiO2), alumina (Al2O3) and titania (TiO2) play a big role in providing a good approach to increasing the dielectric breakdown strength and partial discharge resistance of nanocomposites. Such polymer nanocomposites will be reviewed thoroughly in this paper, with the different experimental and analytical techniques used in previous studies. This paper also provides an academic review about partial discharge in polymer nanocomposites used as electrical insulating material from previous research, covering aspects of preparation, characteristics of the nanocomposite based on experimental works, application in power systems, methods and techniques of experiment and analysis, and future trends.
TL;DR: In this article, a new idea is presented providing generalization and practicality of the method in selection of singular values for detection and/or reconstruction of de-noised PD pulses.
Abstract: Noise reduction is one of the important tasks of partial discharge (PD) detection and investigations in the process of cable insulation assessment. Singular Value Decomposition (SVD) is an algorithm, which can be employed in noise reduction from partial discharge signals, based on separation of singular values corresponding to noise and PD signal. In this paper, a new idea is presented providing generalization and practicality of the method in selection of singular values for detection and/or reconstruction of de-noised PD pulses. This procedure named as Adaptive Singular Value Decomposition (ASVD) has been examined on field measured, laboratory recorded and simulated signals and its results have been compared with the results of some published methods. The proposed method cleans up polluted PD pulses, even in excessive noisy conditions, resulting in higher signal-to-noise ratios (SNRs) rather than the results of other mentioned methods. Comparing in terms of magnitude, falltime, and pulse-area of PD signals after de-noising, the proposed method also preserves the features of PD pulses from distortions and errors much better than the compared methods.
TL;DR: In this article, two types of mother wavelet, that is, db and sym, were applied to decompose the signals and extract the signal features in terms of their skewness, kurtosis and energy.
Abstract: Partial discharge (PD) is a symptom of insulation defect or degradation in high-voltage equipment. Thus, PD detection is an important diagnostic tool. Furthermore in practical situations, the PD can be generated from a single or multiple sources. Being able to detect and classify such PD events will help to determine the necessary corrective action to prevent insulation breakdown. To demonstrate, three different simulated discharge conditions in transformers were investigated: void, floating metal and their combination. The PD signals were captured using an ultra-high frequency (UHF) sensor and denoised using wavelet transform method by application of Matlab wavelet multi-variate denoising tool. Two types of mother wavelet, that is, db and sym, were applied to decompose the signals and extract the signal features in terms of their skewness, kurtosis and energy. These features were then used as input to train a neural network to analyse and determine the PD source type. Results show this technique is able to classify and recognise single and multiple PD source types with a high degree of success.
TL;DR: In this article, the authors defined the effective energy characteristic ratio (ERRMS) and analyzed the relationship between ERRMS and partial discharge energy in sulfur hexafluoride (SF6) insulating equipment.
Abstract: Partial discharge (PD) with different energy always occurs before a serious breakdown in sulfur hexafluoride (SF6) insulating equipment. The high electromagnetic energy of PD can cause the insulation gas SF6 to decompose into various components. Component types and their formation rate are directly related with insulation fault severity. Hence, PD energy can be evaluated based on the characteristics of SF6 decomposition, which could be further used to diagnose insulation status. This paper focuses on the SF6 decomposition mechanism under PD, establishes the feature parameter to describe PD energy, and clarifies the feature parameter?s physical significance. In addition, this paper defines the effective energy characteristic ratio ERRMS and analyzes the relationship between ERRMS and PD energy. Finally, this paper discusses the influence regularity of trace H2O and O2 on ERRMS.
TL;DR: In this article, the authors measured the severity of PD defects using UHF method in gas-insulated switchgear (GIS) and the GIGRE method for the verification of sensitivity.
Abstract: The measurement of partial discharge (PD) using ultra-high frequency (UHF) method is considered an effective approach to monitor the online condition of the equipment, which is used to facilitate the detection of incipient defects in gas-insulated switchgear (GIS). In this paper, in order to assess the severity of PD defects using UHF method, the actual 220-kV GIS were subjected to experimentation. The PD was measured simultaneously by using the UHF method and the IEC60270 measurement technique. The combined measurement has been carried out on different defects in PD test cells, including the floating metal, metallic protrusion, and void in epoxy resin. The inner coupler installed in the GIS tank, and the outer coupler placed outside the spacer, are used to measure the UHF signal. The relationship of the apparent charge and the amplitude of the time-domain signal, and the integral energy from 300 MHz to 1.6 GHz of the signal induced by PD in GIS are analyzed thoroughly. In this way, the severity of PD can be quantified using the UHF signal. In addition, to verify the sensitivity of the UHF detection method, a pulse generator with a rise time of about 500 ps is designed. The GIGRE method for the verification of sensitivity, which is used worldwide, is applied in the experiment. The results of the pulse generator experiment are compared to the results produced by the actual discharge sources, and several possible approaches of improving this method are proposed.
TL;DR: In this paper, the damage to the structure of polyimide nano-composite film under impulse voltage is concentrated on the surface layer of the sample Moreover, the results indicate that with the increase of aging time, the discharge phase distribution becomes broader.
Abstract: Polyimide nano-composite film (Kapton 100CR) is a special type of engineering plastic film, which is widely used in turn insulation of form-wound inverter-fed motor Partial discharge (PD) caused by high-frequency surge impulse is one of the key factors leading to premature failure of turn insulation of inverter-fed motors Aging experiments on turn insulation samples under repetitive bipolar square impulse voltage were carried out in this study Experimental results show that, in the presence of PD, the damage to the structure of the polyimide nano-composite film under impulse voltage is concentrated on the surface layer of the sample Moreover, the results indicate that with the increase of aging time, the discharge phase distribution becomes broader Therefore, the appearance of the discharge at higher phase would be the reflection that the insulation of the sample reaches its terminal stage Surface microscopic images taken by the scanning electron microscope (SEM) show that, because of PD erosion, the polymer matrix was carbonized and volatilized, the residual nano-fillers remained on the surface and formed a screen layer to resist further damages caused by PDs It is a symbol that faults expand rapidly when the floccules and voids appear on the surface layer, which indicates the insulation could be breakdown soon
TL;DR: In this article, the authors provided a timely research into the issues of partial discharge in oil-paper insulation under the combined AC-DC voltage, and nine possible configurations, which intent to simulate different defects in the transformer, have been investigated.
Abstract: Heretofore, unlike HVAC transformers, there is not much experience in both insulation design guides and test methods for ultra HV converter transformers. This special insulation phenomenon is very prominent due to the complication of voltage applied on valve-side windings of converter transformers. There is a severe lack of empirical research on partial discharge in oil-paper insulation under the combined ACDC voltage. The study in this paper provides a timely research into the issues. Nine possible configurations, which intent to simulate different defects in the transformer, have been investigated. The PD inception voltages varied ratios of combined AC-DC voltages were conducted. The discharge magnitude and its relation with the applied voltage for selected four common configurations were obtained during voltage increasing and decreasing respectively, which presented the PD initiating process and also reflected the insulation behavior of dielectrics. Besides, the Finite Element Analysis Soft was used to propose the effect of morphology of electrode surface (3 dimensional roughness is approximately 0.03 mm) on PD characteristics, which is very lacking in the previous references. The roles of DC and AC component in PD characteristics were discussed in the context of the relevant work in literatures.
TL;DR: In this paper, the authors investigated the characteristics of partial discharge (PD) within dielectric-bounded and electrodebounded cavities which are embedded in Ethylene Propylene Rubber (EPR) by using plane to plane electrode.
Abstract: The aim of this paper is to investigate the characteristics of partial discharge (PD) within dielectric-bounded and electrode-bounded cavities which are embedded in Ethylene Propylene Rubber (EPR) by using plane to plane electrode. The theoretical analysis is carried on the electric field strength and PD inception voltage of cylindrical and ellipsoidal cavities in different dimensions. The samples with the different dimensions of artificial spherical cavities in EPR are made and the PD characteristics in the cavities, such as PD number, amplitude and phase, are measured by professional instrument in laboratory. It has been found by the experiments that the symmetric PD distribution changes from “rabbit-like” to “turtle-like” shape with the time of applied voltage. With the increase of applied voltage on the samples, the PD inception phase becomes prior to the zero crossing of positive and negative half-cycle. Meanwhile, PD pulse repetition rate has an increase trend with increasing the experimental voltage and the amplitude of PDs occurred in dielectric-bounded cavities changes from a higher value to normal during a short time. However, no obvious amplitude change of PDs occurred in electrode-bounded cavities has been observed in the experiment. As a result, internal PDs occurred in cavities is one of the prime reasons resulted in the degradation and corrosion of EPR.
TL;DR: In this article, the authors investigated the nonlinear dynamics characteristics of the partial discharge (PD) sequence measured during the propagation of typical electrical trees in XLPE cable insulation and provided strong evidence for the existence of deterministic chaos in the PD phenomenon of electrical trees.
Abstract: This paper presents an investigation into the nonlinear dynamics characteristics of the partial discharge (PD) sequence measured during the propagation of typical electrical trees in XLPE cable insulation. Calculation of the correlation dimension and the largest Lyapunov exponent from the PD sequence is used to illustrate the nonlinear characteristics of the PD behavior in the electrical tree growth. The results provide strong evidence for the existence of deterministic chaos in the PD phenomenon of electrical trees, where the correlation dimension and the largest Lyapunov exponent are related with the PD activity of the tree growth, rather than a presence of random stochastic process. The fluctuating correlation dimension of the PD sequence during the branch-pine tree growth is associated with the transition of PD patterns and the change of the channel conductivity of the tree structure. It is also found that the nonlinear dynamics characteristics of the PD sequence are influenced by the applied voltage, the channel conductivity and the electrical tree shape. A possible mechanism is presented for the formation of different chaotic extents of typical electrical trees in XLPE cable insulation.
TL;DR: In this paper, the authors developed further knowledge in PD signal propagation in power cables and attenuation by the PD monitoring system devices to address the localization and criticality issues, which can be useful to PD denoising and for development of a PD localization technique.
Abstract: Partial discharge (PD) based condition monitoring has been widely applied to power cables. However, difficulties in interpretation of measurement results (location and criticality) remain to be tackled. This paper aims to develop further knowledge in PD signal propagation in power cables and attenuation by the PD monitoring system devices to address the localization and criticality issues. As on-line or in-service PD monitoring sensors commonly comprise of a high frequency current transformer (HFCT) and a high-pass filter, the characteristics of detected PD pulses depend on the attenuation of the cable, the HFCT used and the filter applied. Simulation of pulse propagation in a cable and PD monitoring system are performed, based on analyses in the frequency domain using the concept of transfer functions. Results have been verified by laboratory experiments and using on-site PD measurements. The knowledge gained from the research on the change in pulse characteristics propagating in a cable and through a PD detection system can be very useful to PD denoising and for development of a PD localization technique.
01 Dec 2014
TL;DR: In this article, a microstrip patch antenna has been designed in a suitable manner for detection of UHF signals, emitted due to occurrence of partial discharges in HV power apparatus.
Abstract: High Voltage (HV) power apparatus are usually, the most critical and costly component in any power system. Sudden failure of such component leads to unwanted interruptions and catastrophic losses. Partial Discharges (PD) are reported as main reason for degradation of insulation system in any HV power apparatus. A successive occurrence of such discharges eventually leads to complete failure of the equipment. Therefore, it becomes important to monitor the PD in all HV power apparatus in order to detect incipient insulation problems, and to prevent further tragic failure. In the work, microstrip patch antenna has been designed in suitable manner for detection of Ultra High Frequency (UHF) signals, emitted due to occurrence of PD in HV power apparatus. An experimental study has been conducted in laboratory environment for testing of proposed sensors. Experimental results also correlated with the standard PD detection system (IEC60270). Result shows that, the proposed microstrip patch antenna can be effectively used as UHF sensor, and PD can be detected in the HV power apparatus in non-contact mode from a long distance. PD measurement with microstrip patch antenna is easy to install and also a cost effective solution for online condition monitoring of HV power apparatus.
TL;DR: In this article, a multi-band UHF sensor based on the loop antenna theory and meandering technique was proposed, which reduces the sensor size, provides high sensitivity and exhibits omnidirectional performance.
Abstract: To design high-sensitivity sensors is one of the critical issues to be solved for ultra-high-frequency (UHF) partial discharge (PD) detection in substations. Commonly-used UHF sensors usually use ultra-wideband antennas for the frequency bands ranging from 300 MHz to 1.5 GHz. To avoid interference in the frequency bands, such as signals generated from mobile phones, a new multi-band UHF sensor is proposed based on the loop antenna theory and meandering technique, which reduces the sensor size, provides high sensitivity and exhibits omnidirectional performance. The sensor works in the bandwidth ranges of 480–520, 800–850 and 1100–1200 MHz, and has sensitivity of more than 10 mm. The PD detection platform was set up, three typical insulation defects, such as corona discharge, surface discharge and free metal particle discharge, were designed, and then the tests were performed to compare the performance of the multi-band sensor and broadband sensor. The results show that the multi-band sensor's bandwidth covers the main spectra of PD signals, thereby can be used for detecting most kinds of PD signals. The sensor's sensitivity is higher than that of the broadband sensor with its size occupying only 5% of the latter, meeting the requirements for detection of PD sources in substations.
TL;DR: In this article, a system has been developed that allows to simulate partial discharge and overheating in transformer insulation, which is useful in detecting internal defects in oil-filled electrical equipment.
Abstract: The power transformer is one of the most important equipment in the electrical power system due to its cost and potential failure????s consequences. To ensure a continuous energy supply, it is needed to assess abnormal condition such as thermal and electrical behavior. From this viewpoint, dissolved gas analysis (DGA) is very useful in detecting internal defects in oil-filled electrical equipment. A system has been developed that allows to simulate partial discharge and overheating in transformer????s insulation. By using this system, we have studied on DGA under low temperature overheating in mineral oil and vegetable oil.
Abstract: Most of the 110 and 220 kV cables are in service till the end of life, but part of them would be out of service by refurbishment This research is focused on evaluating the cable insulation and determining whether the cable can be reused All the cables used in this research satisfactorily passed the AC voltage and partial discharge tests Then the fourier transform infrared spectroscopy, thermogravimetry analysis, differential scanning calorimetry, dynamic mechanical analysis, and tensile machine were used to analyze the insulation morphological structure and performance of 20 retired 110 and 220 kV crosslinked polyethylene cables obtained from the Beijing and Zhuhai districts The results show that the structure parameters which can represent the physical change and the irreversible chemical change of cables have obvious time dependence characteristic DSC result shows that crystallinity, melting range, and crystallization rate increase slightly with service years DMA experiment illustrates that the temperature of mechanical loss peak, Tγ, shifts to a higher temperature while the mechanical loss increases slightly and temperature dependency of storage modulus increases with service years The electrical treeing experiment utilized cable operated for 17 years, which is the longest operation year for the samples Compared with new cable, the cable operated for 17 years has a slight decrease in tree initiation time and an obvious increase in tree propagation time These experiment data show that the insulation material morphological structure is mainly stable, and the test results are also a contribution to the lifetime expectancy evaluation of the 110 and 220 kV XLPE cable
TL;DR: In this paper, an approach to determining classification of partial discharge (PD) events in Gas Insulated Load Break Switches (GILBS) using probabilistic neural networks (PNN) and fuzzy C-means (FCM) clustering approach is presented.
TL;DR: In this paper, a two-dimensional axial-symmetric model of a cylindrical void in polyethylene layers has been developed using finite element analysis software, which was used to simulate PD activity in the void under square waveform applied voltage under different amplitudes of the voltage.
Abstract: There are many factors, which influence the behaviours of partial discharge (PD) within a void located in a solid dielectric material. One of the important factors is the waveform of the applied voltage on the electrode of a system, such as its amplitude and frequency. In this study, a two-dimensional axial-symmetric model of a cylindrical void in polyethylene layers has been developed using finite element analysis software. The model was used to simulate PD activity in the void under square waveform applied voltage under different amplitudes of the voltage. The model has considered the effect of charge propagation along the void surface during a PD occurrence. The obtained simulation results were compared with the measurement results reported from previous literature to validate the PD model that has been developed in this work. It was found that the simulation and measurement results are within reasonable agreement with only slight disagreement. From the comparison, critical parameters from the model that affect PD behaviours under square waveform applied voltage were found to be the electron generation rate and the inception, extinction and critical charge propagation fields. These findings may increase an understanding of PD behaviours within a void in a dielectric material under square waveform applied voltage, which is important for insulation diagnosis.
TL;DR: In this paper, a 3-mm-thick air gap at atmospheric pressure using two plane parallel electrodes each covered by one specific alumina plate with a thickness of 2.3 mm was identified with Townsend discharge.
Abstract: Diffuse dielectric barrier discharge was first produced in 3-mm-thick air gap at atmospheric pressure using two plane parallel electrodes each covered by one specific alumina plate with a thickness of 2.3 mm. Based on the discharge photographs of 10 ns exposure time taken with an intensified CCD camera, the diffuse discharge was identified with Townsend discharge. The Townsend breakdown voltage for this 3-mm air gap is about 5.7 kV, significantly lower than 11.2 kV, the streamer breakdown voltage of the air gap. If the alumina plate is too thin, the discharge transits to filamentary discharge. If it is too thick, the discharge is too weak to observe. Thermally stimulated current experiments revealed that there exist more shallow traps in the ceramic than in quartz plate after discharge pretreatment. The uniqueness of the shallow traps in the surface of the specific alumina plate, as well as the effect of the current limitation by dielectric leads to a Townsend discharge.
TL;DR: In this paper, the authors provide an overview on the factors affecting the initiation and propagation of electrical tree, including applied voltage, electric field enhancement, partial discharge, frequency of applied voltage and temperature.
Abstract: Nowadays, the most widely used insulating materials in high voltage equipment such as cables are polymeric insulations due to the numerous merits they possess with regards to electrical performance compared to paper insulations. However, electrical treeing, one of the dielectric pre-breakdown phenomena, has been considered as a major contribution to the failure of insulating polymeric materials. Thus, this paper provides an overview on the factors affecting the initiation and propagation of electrical tree. Discussions on parameters that affect the growth of electrical treeing such as applied voltage, electric field enhancement, partial discharge, frequency of applied voltage and temperature are given. Some discussions on the various models are also highlighted. The tree related models being discussed herein include Weibull, Lognormal, Johnson SB, Dielectric Breakdown Model, Discharge-Avalanche Model, and Field-Driven Tree Growth. In addition, discussions on the use of nano-sized fillers in polymeric insulating material to inhibit electric treeing are highlighted.
TL;DR: Two inductive sensors with different frequency responses to pulsed signals, a high frequency current transformer and an inductive loop sensor are analyzed to test their performance in detecting and separating the sources of partial discharges.
Abstract: Partial discharge (PD) detection is a standardized technique to qualify electrical insulation in machines and power cables. Several techniques that analyze the waveform of the pulses have been proposed to discriminate noise from PD activity. Among them, spectral power ratio representation shows great flexibility in the separation of the sources of PD. Mapping spectral power ratios in two-dimensional plots leads to clusters of points which group pulses with similar characteristics. The position in the map depends on the nature of the partial discharge, the setup and the frequency response of the sensors. If these clusters are clearly separated, the subsequent task of identifying the source of the discharge is straightforward so the distance between clusters can be a figure of merit to suggest the best option for PD recognition. In this paper, two inductive sensors with different frequency responses to pulsed signals, a high frequency current transformer and an inductive loop sensor, are analyzed to test their performance in detecting and separating the sources of partial discharges.
TL;DR: In this article, a hybrid partial discharge transducer based on the Rogowski coil is developed for online PD detection on a 10kV XLPE covered conductor to prove the effectiveness of this technique.
Abstract: This letter presents an improved technique to identify the traveling direction (TD) of the partial discharge (PD) on the overhead covered conductors. A hybrid PD transducer based on the Rogowski coil is developed for online PD detection. An experimental study is performed on a 10-kV XLPE covered conductor to prove the effectiveness of this technique.