Partial Discharge Development Research Articles

Introducing deep trap states for high dielectric strength of aramid‐based composite films

AbstractAramid nanofiber (ANF)‐based composites have drawn tremendous interest in high‐voltage electrical systems due to their superior insulation strength, thermal stability, and mechanical endurance. However, the filler agglomeration and interface compatibility have retarded further improvement of the dielectric performance. Herein, the nano‐titanium dioxide (TiO2) particles treated by aminopropyl triethoxysilane (APTES) serve as the inorganic fillers, which are doped in the ANF to prepare the composite nano‐paper via the blade coating method. The electrostatic interaction between the ANF and fillers highly promotes their uniform distribution. Compared to the pure ANF paper, the composite paper has a denser structure with reduced pores and defects, which significantly improves its dielectric performance with inhibited partial discharge development. At a filler loading of 3 wt% (mass fraction), the breakdown strength is increased by 70.5% to a maximum value of 358.1 kV/mm, while the bulk conductivity is minimised to 5.2 × 10−17 S/m, representing an 88.1% decrease. By analysing the energy band structure of each component, energy barriers at the interface for electrons (1.48 eV) and holes (0.40 eV) are determined. These values indicate deepened trap energy levels, which greatly strengthen the carrier trapping effect for improved dielectric performance.

Determination of partial discharge development stage of oil-paper insulation based on sparse decomposition considering the effect of aging

Determination of partial discharge development stage of oil-paper insulation based on sparse decomposition considering the effect of aging

Investigation of Partial Discharge Transformation Characteristics in Polyimide (PI) Insulations under High-Frequency Electric Stress.

This research delves into the primary issue of polyimide (PI) insulation failures in high-frequency power transformers (HFPTs) by scrutinizing partial discharge development under high-frequency electrical stress. This study employs an experimental approach coupled with a plasma simulation model for a ball-sphere electrode structure. The simulation model integrates the particle transport equation, Poisson equation, and complex chemical reactions to ascertain microscopic parameters, including plasma distribution, electric field, electron density, electron temperature, surface, and space charge distribution. The effect of the voltage polarity and electrical energy on the PD process is also discussed. The contact point plays a pivotal role in triggering partial discharges and culminating in the breakdown of PI insulation. Asymmetry phenomena were found between positive and negative half-cycles by analyzing the PD data stage by stage. A significant number of PDs increased at every stage and the PD amplitude was higher during the negative cycle at the initial stage, but in later stages, the PD amplitude was found to be higher in the positive half-cycle, and scanning electron microscopy (SEM) revealed that the maximum damage occurred near the contact point junction. The simulation results show that the plasma initially accumulates the electron density near the contact point junction. Under the action of the electric field, plasma starts traveling at the PI surface outward from the contact point. Before the PD activity, all parameters have higher values in the plasma head. The microscopic parameters reveal maximum values near the contact point junction, during PD activities where significant damage takes place. These parameter distributions exhibit a decreasing trend over time as when the PD activity ends. The model's predictions are consistent with the experimental data. The paper lays the foundation for future research in polymer insulation design under high-frequency electrical stress.

Influence of overvoltage waves on the development of partial discharges

A theoretical study of the development dynamics of partial discharges in defects in cable insulation of medium voltage networks in the presence of an overvoltage wave has been carried out. Simulation modeling of the development of partial discharges was performed on the basis of a model with three capacitors, supplemented by a model for the appearance of a seed electron. A single-phase short circuit to earth with several breaks in the electric arc was the source of the overvoltage wave. Simulation modeling showed that the number and power of partial discharges significantly increased over the period of the fundamental harmonic. The amplitude of the periodic component of the transient process was already enough to recharge the defect for large insulation defect and it is the highest harmonic that becomes decisive in the formation of partial discharges. This fact may be one of the explanations for a possible trend in medium voltage cable networks, where a failure on one cable is followed by a group of subsequent failures in nearby cable lines within a few days.

Investigation of air breakdown and plasma evolution on microstrip antenna surface using the particle-in-cell method

This paper investigates the breakdown of two microstrip antennas through experiments and particle-in-cell simulations. The breakdown thresholds of a microstrip dipole antenna and a double-layer patch microstrip antenna are investigated experimentally and found to be 15.6 and 30.8 kW, respectively. Ablation is observed on the surface of the antennas, indicating that the local electric field is particularly intense. To further understand the breakdown process, the particle-in-cell and Monte Carlo collision methods are combined to investigate the inception and development of partial discharge on the surface of the antennas. Under the criterion of continuous electron density growth, the breakdown thresholds of the dipole and double-layer patch antennas are estimated to be 19.4 and 52.9 kW in our simulations. The simulation results are in reasonable agreement with the experimental measurements. In the microstrip dipole antenna, the plasma evolution of the partial discharge is initiated near the tip, while the electric field close to the tip is distorted and a positive streamer directed toward the tip is observed. In the double-layer patch microstrip antenna, a more uniform discharge is observed at the edge of the circular patch in the simulations.

Study on Development Characteristics of Partial Discharge in Oil-Pressboard Insulation under Constant DC Voltage

The converter transformer is the core equipment of HVDC transmission system, the valve-side winding of which needs to withstand DC voltage. Partial discharge is one of the main threats to the safe operation of converter transformer, yet the characteristics of partial discharge development of the oil-pressboard insulations under constant DC voltage are insufficiently understood. In order to better understand the partial discharge characteristics of the oil-pressboard insulation under DC voltage and provide deeper theoretical support for insulation diagnosis of converter transformers, development characteristics including the time-varying tendency of discharge magnitude and repetition rate of partial discharge in oil-pressboard insulation under constant positive and negative DC voltage were studied. The results indicate that the development of partial discharge in a needle-plane oil-pressboard insulation model under constant DC voltage has three stages: the intensive discharging stage, the silent-burst stage, and the breakdown stage. Throughout all stages, the partial discharge magnitude and repetition rate first decrease and increase afterwards. At the silent-burst stage, the partial discharge appears in the form of a “cluster” with very large magnitude and repetition rate. Each cluster exists for tens of seconds but with at a very long interval with each other. Further analysis shows that the repeated accumulation and dissipation of free charges on the surface of the pressboard cause the above phenomena. Negative charges are easy to accumulate and difficult to dissipate under the same voltage amplitude compared to positive charges, leading to a weaker actual electric field at the needle tip and thus partial discharges under negative DC voltage with a lower magnitude and longer interval.

An improved technique for quantifying PD activity in cross-linked polyethylene (XLPE) power cables

The presence of air-filled cavities within the insulation of active power cables affects the electric field distribution in the insulation bulk and increases the electrical stress inside and around the cavities. This causes accelerated ageing of the materials and creates regions for partial discharge (PD) development that may subsequently result in cable failure. In this paper, an improved PD quantifying technique applied for insulated power cables is first presented. Its effectiveness is demonstrated through an in-depth study of electric field distribution across a defective cross-linked polyethylene (XLPE) power cable with practical dimensions for HV applications and by analysing the PD behaviour under different ageing conditions. In realizing the aforementioned, the cable model with different arrangements, in series and parallel, of two discharging air-filled cavities was implemented in COMSOL software. The simulated cable fields are analysed for different separations and positions of the cavities before and after PD activity. The cavity fields are extracted in MATLAB and utilized for PD pattern characterization under three ageing conditions. Through the PD patterns and statistical quantities measured from simulated PD behaviour, the severity of PD in the cable model was quantified over the different ageing periods. It was found that the series configuration of the cavities was the most harmful configuration due to its high-field magnitude and greater tendency to initiate a PD propagation. Furthermore, the PD behaviour changes during ageing and the highest PD activity, greater PD magnitude and rate, were recorded at the most advanced ageing stage. Thus, indicating that PD characteristics can be used for inferring the ageing stage.

ТЕРМОФЛУКТУАЦИОННАЯ ТЕОРИЯ РАЗРУШЕНИЯ И ОЦЕНКА ДОЛГОВЕЧНОСТИ ЭЛЕКТРИЧЕСКОЙ ИЗОЛЯЦИИ СПЭ КАБЕЛЕЙ

The article is devoted to research on the creation of a method for assessing the durability ofthe main insulation of power cable lines based on the thermofluctuation theory of destruction of solids.The features of breakdown development in homogeneous and inhomogeneous dielectrics areconsidered. The problematic issues of insulating materials of power cable systems (PCS) are consideredon the basis of the development and development of non-destructive testing methods. The maincomponents that destroy the insulation of the PCS are installed. The thermofluctuation theory ofdestruction and the evaluation of the durability of electrical insulation of power cables are described.An analytical method is proposed for evaluating the processes of cellulose oxidation with the determinationof the most probable. The proposed approach to identifying the main processes of insulationdestruction allows us to present in more detail the prerequisites for the development of partial discharges(PD) in isolation and to determine measures to minimize the processes leading to the destructionof PCS insulation. The results of experiments on the study of the service life of the insulatingmaterial of aged ends of a power cable in a thermal cabinet, to determine the aging criteria, arepresented. The experimental data are interpreted from the standpoint of the thermofluctuation theory.The dependence of the increase in the temperature difference ΔT on the degree of wear of the electricalinsulating properties of the material is revealed and investigated, which makes it possible to predictits resource. The thermofluctuation theory of the destruction of insulating materials caused bythe thermofluctuation rupture of chemical bonds and the evaluation of the durability of electricalinsulation of cables made of cross-linked polyethylene are considered. It is shown that, in order tocalculate the average energy of the monomeric link of various polymer materials, it is necessary toknow: the chemical formula of the monomeric link and the values of the binding energies. In thework, the time before the breakdown of the main insulation of the PCS was determined under theaction of temperature. The model can be used in devices and systems for continuous diagnosis ofpower cables according to temperature conditions.

Breakdown Performance and Partial Discharge Development in Transformer Oil-Based Metal Carbide Nanofluids.

In this work, the influence of semi-conductive SiC nanoparticles on the AC breakdown voltage and partial discharge development in natural ester oil FR3 is examined. Primarily, the dielectric constant and the electrical conductivity of the nanoparticles are measured following the broadband dielectric spectroscopy technique. The nanoparticles are added into the matrix following the ultrasonication process in three weight percentage ratios in order for their effect to be evaluated as a function of their concentration inside the base oil. The processing of the results reveals that the nanofluid containing SiC nanoparticles at 0.004% w/w demonstrates the highest AC dielectric strength improvement and shows the greatest resistance to the appearance of partial discharge activity. The mechanisms behind the aforementioned results are discussed in detail and confirmed by the broadband dielectric spectroscopy technique, which reveals that this particular nanofluid sample is characterized by lower dielectric constant and electrical conductivity than the one with double the weight percentage ratio.

Effect of Aging Degree on Partial Discharge Degradation of Oil-paper Insulation

This study conducts thermal aging treatment to study the effect of thermal aging on the PD degradation process of the oil-paper insulation. The partial discharge inception voltages, extinction voltages, carbon mark, and microscopic morphology of samples are analyzed. The results show that thermal aging does not reduce the partial discharge inception voltages of oil-paper but can make the spark produced in the oil-paper more difficult to extinguish. At the initial stage, thermal aging has little effect on the development of partial discharge in normal direction of samples, while in later stages, the effect begins to appear; thermal aging reduces the insulation performance between layers of oil impregnated paper and accelerates the carbon trace growth rate in the horizontal direction. In this model, the first layer is most severely bombarded by electrons, and this layer is most obviously affected by the electric field in the normal direction at the contact point between the electrode and the insulating paper. The lower layer is affected by the horizontal and vertical electric fields; therefore, a large area of fiber looseness occurs on the surface of the oil impregnated paper. The degree of deterioration is proportional to the endurance time and aging time, and the damage degree of oil impregnated paper decreases with the increase of the number of layers.

Detection of Electrical Tree Formation in XLPE Insulation through Applying Disturbed DC Waveforms

Initiation and growth of electrical trees can be linked to the development of partial discharge (PD) activity within an insulation system. We present in this paper changes in PD characteristics that appear during the electrical tree growth in a crosslinked polyethylene (XLPE) based insulation at different stages of its degradation. A DC voltage with superimposed high frequency component is applied to the material specimens for the detection and characterization of PD traces observed during the degradation. The method is flexible and offers a possibility to vary DC voltage level independently of the superimposed disturbance, its frequency and rise time, including rapid voltage steps. It also enables to create a phase-locked phase-resolved PD pattern (PRPD) facilitating various analyses of the characteristics. It is postulated that measurements of the changes in PD characteristics found under such excitations can be used for performing diagnostics and prognostics of material condition. This approach also implies new possibilities to evaluate different material concepts.

Anomaly Detection, Trend Evolution, and Feature Extraction in Partial Discharge Patterns

In the resilient and reliable electrical power system, the condition of high voltage insulation plays a crucial role. In the field of high voltage insulation integrity, the partial discharge (PD) inception and development trends are essential for assessment criteria in diagnostics systems. The observed trend to employ more and more sophisticated algorithms with machine learning features and artificial intelligence (AI) elements is observed everywhere. The classification and identification of features in PD images is perceived as a critical requirement for an effective high voltage insulation diagnosis. In this context, techniques allowing for anomaly detection, trends observation, and feature extraction in partial discharge patterns are important. In this paper, the application of few algorithms belonging to image processing, machine learning and optical flow is presented. The feature extraction refers to image segmentation and detection of coherent forms in the images. The anomaly detection algorithms can trigger early detection of the trend changes or the appearance of a new discharge form, and hence are suitable for PD monitoring applications. Anomaly detection can also handle transients and disturbances that appear in the PD image as an indication of an abnormal state. The future monitoring systems should be equipped with trend evolution algorithms. In this context, two examples of insulation aging and application of PD-based monitoring are shown. The first one refers to deep convolutional neural networks used for classification of deterioration stages in high voltage insulation. The latter one demonstrates application of optical flow approach for motion detection in partial discharge images. The motivation for the research was the strive to machine-controlled pattern analysis, leading towards intelligent PD-based diagnostics.

PROCEDURE FOR CONTROL OF POLYMER ELECTRICAL INSULATING MATERIALS

The article describes the directions and features in the field of control of power lines. A method is created for determining the prebreakdown state. The dependence of the development of partial discharges in polymeric materials is studied. The process of exposure to high-frequency currents before the onset of a breakdown state under constant operating modes of electrothermal high-voltage equipment is described. The results of the dynamics of the emergence of discharges under high-frequency exposure are given in the form of graphic images. The graph of the dynamics of partial discharges is described. In this work, a methodology for monitoring and protecting against electrical breakdown, when the frequency of occurrence of partial discharges changes. The results of practical tests for diagnosing the residual life of insulation are presented.

Оценка электрической прочности опорных изоляторов в условиях загрязнения и увлажнения

Based on the known theoretical concepts about the partial arc discharge development process and the data on the main design features of support insulators, numerical studies of their electrical strength under pollution and moistening conditions were carried out. The conditions under which the electrical strength of insulators can or cannot achieve its maximum possible value were analyzed. It is shown that the highest electrical strength of contaminated insulators is obtained at the optimal value of the ratio of the creepage distance to the height of the insulators along their insulating part (L/H)opt. The value of (L/H)opt is determined by the edge profile design features. As a rule, for insulators with a simple edge profile, the value of (L/H)opt = 2.45, and for insulators with a complex edge profile (L/H)opt = 3.1. In the region L/H ≤ (L/H)opt the effective use of the creepage distance by the discharge channel is ensured. It is shown that excessive increasing of the L/H ratio above the optimal value leads to inefficient use of the creepage distance by the discharge channel, which entails a noticeable decrease in the electrical strength of insulators. By using the proposed calculation estimates, it becomes possible to a priori determine the expediency of applying a particular insulator for being used in areas with various normalized pollution degrees.

Influencing of water droplets on corona inception characteristics of composite insulator recorded by UV imager

Water droplets on the surface of insulators can distort the electric field and cause the generation of surface partial discharge or flashover. In this study, the inception and the development of surface partial discharges on a 110 kV composite insulator were evaluated by using a solar-blind ultraviolet imager. Several experiments were conducted by using water droplets differing in volume, conductivity, and position on an insulator housing. The results showed that the corona inception voltage decreases with the increasing volume of the water droplets. The relative permittivity of the water droplet decreases with the increase of the conductivity and then reduces the electric field intensity and increases the corona inception voltage. Installing the grading ring can increase the value of the corona inception voltage by 38% at most. To investigate the influence of the water droplets on the corona inception characteristics of the insulator, the sheath and shed models were proposed according to the feature of the electric field distribution. By changing the parameters of the water droplets, the corona inception voltage, discharge position, and electric field were analysed. Furthermore, the flashover voltage of the water droplets is influenced by its conductivity, while the corona inception voltage by its relative permittivity.

Partial Discharge Development in Oil-Based Nanofluids: Inception, Propagation and Time Transition

Oil-based nanofluids have been indicated to enhance the breakdown strength and dielectric behavior of mineral oil. However, partial discharge (PD) development in these new materials has not yet been clarified. This study aims to deeply investigate PD development in nanofluids considering the role of the electrical double layer (EDL) around nanoparticles. Two types of nanoparticles (TiO2 and Al2O3) with different EDL thicknesses were used. Nanofluids were prepared using the two-step method, and their proper composition was adopted after considering their stability and avoiding the drawbacks that are present when surfactants are used. The prepared nanofluids together with the base oil were tested for PD development. First, the PD inception voltage was evaluated and analyzed using the Weibull distribution. Then, PD parameters including the PD magnitude and repetition rate were obtained for both types of nanofluids; these values were compared with the corresponding results of the base oil. Finally, the PD time transition was acquired over ten minutes of applied voltage using the segmented memory mode of the oscilloscope. Based on obtained results, physical mechanisms behind PD activity are proposed and discussed. It was found that nanoparticles with a large EDL thickness could more effectively suppress PD activity.

Development of smart online partial discharge monitoring system for medium voltage power cable

This paper presents, the development of smart online partial discharge (PD) monitoring system for medium voltage (MV) underground power cable. PD monitoring is the highly efficient tool to monitor insulation degradation for high voltage (HV) equipment in order to avoid failures or breakdown. Selection of improved technology and performance of PD detection sensor, effective measurement technique and smart user friendly of graphical user interface (GUI) system are contributed towards the development of efficient monitoring system. This paper addresses three main aspects which are needed in completing the monitoring system. They are, the use of Rogowski coil (RC) as detection sensor, processing unit using Alterra board and integrated with GUI PD monitoring system for underground cable using LabVIEW. The monitoring system is compared to the conventional method with the PD signal used is measured from the real on-site measurement in order to analyse its performance. The analysis is performed in MATLAB and LabVIEW software’s environment and the maximum peak of PD signal is enabled to view using GUI which complete with the location information of PD source. Furthermore, this paper has contributed to solve the problem in selection the simplified and practical approach for PD sensor and monitoring system. In the perspective of automated condition monitoring, this smart online PD monitoring system provides a complete solution towards latest industrial revolutions

Partial discharge development stage division based on multi-classifier fusion

The oil-paper insulation air gap discharge experiment was carried out by the step-up method, and the 29-dimensional discharge characteristic parameters were extracted. The oil-paper insulation air gap discharge experiment was carried out by the step-up method, and the 29-dimensional discharge characteristic parameters were extracted. According to K-means clustering, the partial discharge development stage is divided into four stages: initial discharge stage, discharge development stage, discharge stability stage and near breakdown stage. The three basic classifiers of random forest, support vector machine and back propagation neural network are trained by the credibility-based adaptive weighted voting algorithm to train a new fusion classifier. Compared with the traditional classification fusion device, the proposed classifier fusion model can effectively improve the accuracy of the identification of the discharge development stage, up to 87.5% or more.

Dielectric properties of epoxy resin impregnated paper insulation in different stages of partial discharge development

AbstractTo investigate the variation of dielectric properties of epoxy resin impregnated paper insulation in different stages of partial discharge (PD) development, a PD experimental platform was established and epoxy resin impregnated paper insulation samples were prepared. According to the discharge amount, the number of discharges and discharge phenomena during the PD process, the PD process is divided into an initial stage, development stage, burst stage, and near‐breakdown stage. The variations of dielectric constant and dielectric loss factor of the sample during different PD development stages were measured by frequency domain dielectric spectrum tester. Scanning electron microscopy was used to observe the microscopic morphological changes of the samples at different stages of PD development. The surface characteristic functional groups at different stages of PD development of the sample were determined by Fourier transform infrared spectroscopy. The results show that: as the PD progresses, the insulation performance deteriorates; under continuous bombardment by high‐speed electrons, the network structure of the fiber surface and the epoxy molecular chain are destroyed, causing the weakening of the binding force between the molecular chains, and the short‐chain structure formed by cracking has a stronger steering ability. Under the continuous action of PD, the inside of the long‐chain molecule breaks and oxidizes, and a large number of small molecules, such as free radicals and monoglucose, are formed. The decrease in the molecular weight of the polymer leads to the weakening of the interaction between the molecules, resulting in an increase in polarization, a large dielectric constant, and an increase in the dielectric loss factor.

Development process of micropores partial discharge of silicon rubber in prefabricated cable joint

Abstract To clarify the relationship between microporous defects and the development of partial discharge(PD) in silicone rubber, meanwhile evaluate insulation state of the prefabricated power cable joints quantitatively, the microporous defect is made based on real power cable joint, and PD signals are measured by step test method with the development of the defect. The discharge number, total energy and average energy of PD is gained to calculate the curves changed over time, based on which the breakdown process is divided into 4 stages, then phased spectra and grayscale maps are calculated for reflection of PD repetition rate and average energy in phase domain. Phase width, skewness of spectrum and coefficient of variation of parameter are employed to indicate the spectra statistical shape feature in each stage. The study indicates that the shape features of spectra are changed during the development of defect, the 3 features parameters are monotonously changed, and the changing rate is significantly higher at the end of the breakdown process. Evaluation method for micropores PD of silicon rubber is proposed based on the analysis of the parameters and the trend of PDs development.