Partial Discharge Phenomena Research Articles

Identification of Partial Discharge Defects in Gas-Insulated Switchgears by Using a Deep Learning Method

In this study, a novel method based on deep learning was developed for partial discharge (PD) pattern recognition. Traditional PD recognition methods are crucial for extracting features from PD patterns. The method of extracting crucial features is the key to PD pattern identification. The fractal theory is commonly used to determine the features of discharge patterns. The feature distribution of different defect types can be determined according to the fractal dimensions and lacunarity. However, finding fractal features is a complicated process. In this study, a PD image was entered as an input into a deep learning system to reduce the complexity of finding features. First, four defect type of gas-insulated switchgear (GIS) experimental models are established. Then, an LDP-5 inductive sensor (L-sensor) was used to measure the ground line signals caused by PD phenomenon. Second, these electrical signals were transformed into the most representative 3D ($n$ -$q$ -$\varphi$ ) PD patterns. Finally, a convolutional neural network was employed for PD image pattern recognition. A total of 160 sets of PD patterns were measured using a 15-kV GIS. The results obtained with the proposed method were compared with those obtained with the fractal method. The results revealed that the proposed method is easy to use and can easily distinguish various defect types. The proposed approach can determine the GIS insulation status and provide information to construction units for maintenance.

New approach in partial discharge diagnosis and maintenance of 22.9 kV XLPE power cables in service

Partial discharges (PDs) are one of the main causes of cable fault. Early detection and pre-analysis of PD characteristics are paramount in preventing cable breakdown. This paper analyzed the PD characteristics of 22.9 kilovolts (kV) calculated nerve conduction velocity (CN-CV) cross-linked polyethylene (XLPE) cable subjected to various artificial defects, based on the maintenance method by PD diagnosis. Various artificial defects were created in a 3-m CN-CV test cable to which a power frequency voltage of 60 hertz (Hz), 13.2 kV was applied. To compare the PD characteristics difference by cable length, a 3-m cable specimen was connected to a 70-m three-phase cable system using a high-voltage mating connector. A measurement unit and a high-frequency current transformer were used for PD data acquisition. As a result, different PD characteristics were found in each defect type, which provided better understanding of the PD phenomena. A maintenance method of 22.9 kV XLPE power cable through PD diagnosis was developed from the data obtained, which will help to ensure greater accuracy in the on-site diagnosis of a cable in service.

Development of Hankel‐SVD hybrid technique for multiple noise removal from PD signature

Detection and measurement of partial discharge (PD) phenomena combined with the separation and identification of PD sources is the way to achieve effective insulation integrity assessment. However, during measurement, PD signals are coupled with interferences (discrete spectral, pulsive, and white noises). Recovering PD signals from such interferences would improve PD source separation (thus identification), but still remains a challenging task. Several denoising methods have been proposed to suppress interferences. However, using a universal method to achieve interference removal is probably impossible, as the characteristics of the interferences are distinct. This study proposes a novel low-rank H-Matrix-based singular value decomposition (SVD) filter (H-SVD) that removes different types of interferences. Denoising is done by projecting the measured pulse in a lower dimensional signal space. To assess the effectiveness of the proposed method, H-SVD filter is first applied to simulated PD data and later on real-time PD data with the introduction of three different types of synthetic noises. The results of the evaluation metrics confirm that H-SVD has significant performance improvements compared to existing state-of-the-art PD denoising methods.

Classification of Partial Discharge Detection Technique in High Voltage Power Component: A Review

In this study, a review on categorization of partial discharge (PD) detection technique is presented. The PD detection is important in order to monitor and diagnosis the insulation health on high voltage (HV) power component. PD at high voltage transformer occurs due to the unscheduled maintenance, aging of equipment, breakdown of insulation, gas bubbles in insulation liquid, manufacturing error and etc. In order to maintain constant and high as possible of the transformer performance, it is essential to control, detect and measure the PD phenomena. There are many methods have been developed based on point of observation; optical, chemical, acoustic and electrical. However, the different methods have their own advantages and disadvantages.

Numerical modelling, simulation and experimental validation of partial discharge in cross‐linked polyethylene cables

A clear understanding of the partial discharge (PD) phenomena occurring in cavities at various radial locations in the insulation is essential for proper monitoring of cables. This work presents a comparison of finite element method (FEM) model and capacitive model for simulation of PD in the insulation and an attempt to identify reliable parameters for monitoring the condition of cable insulation is done. A three-dimensional FEM-based model of the cable is developed in ANSYS software by including the effects of surface charge accumulation and propagation along with the phenomena of charge decay at the void surface. The induced charge concept which is correlated with changes in capacitance is employed to model a capacitive model for simulation of PD by considering the free electron availability for simulation of PDs in cables in EMTP software. The experimental validation of developed models is done by PD measurement on 11 kV cross-linked polyethylene cables. Analysis of the simulation results recommends the relevance of the capacitive model to be employed for condition assessment of cable insulation in view of its simplicity and appropriateness in the estimation of model parameters from actual cable measurements.

Partial Discharge Detection Using a Spherical Electromagnetic Sensor.

The presence of a partial discharge phenomenon in an electrical apparatus is a warning signal that could determine the failure of the insulation system, terminating the service of the apparatus and/or the network. In this paper, an innovative partial discharge (PD) measurement instrument based on an antenna sensor is presented and analyzed. Being non-intrusive is one of the most relevant features of the sensor. The frequency response of the antenna sensor and the features to recognize different PD sources and automatically synchronize them with the supply voltage are described and discussed in details. The results show the performance of the instrument can make a fast and correct diagnosis of the health state of insulation systems.

Application of Chaos Synchronization Technique and Pattern Clustering for Diagnosis Analysis of Partial Discharge in Power Cables

This paper primarily discusses the measurement of partial discharge (PD) phenomena and clustering in the defect pattern of a cross-linked polyethylene power cable joint. First, a high-speed data acquisition and pretreatment were performed for PD electrical signals at a sampling rate of 20 MS/s. The crucial characteristic signals were reversed to reduce the calculated amount of noise. A characteristic matrix was created according to the resulting dynamic error of chaos synchronization. The characteristic parameters were extracted using the fractal theory. Finally, the extension theory was used to develop a diagnostic system and anti-interference test. A comparison with the existing Hilbert-Huang transform (HHT) method revealed that the two characteristics extracted from the chaos synchronization results using the fractal theory were recognized at a higher pattern recognition rate by employing the extension theory. The proposed method can extract crucial information concerning PD as a defect in power cable joints.

Observations of Partial Discharge Echo in Dielectric Void by Applying a Voltage Chopped Sequence

This paper describes a novel observation on partial discharges (PDs), which occur despite the absence of an applied voltage, within a chopped sequence. It was found that additional discharge pulses occur when a specimen is subjected to chopped sequences rather than a continuous sinusoid. The discharge pulses, called Partial Discharge Echoes (PDE), appeared in time intervals (where no voltage was being applied), immediately after the specimen had been exposed to a base waveform (e.g., sinusoidal) above a partial discharge inception level. The chopped timing is composed of a multiple series of packets consisting of base waveforms, with each packet being separated in time by a defined delay period. The presented experiments were performed on specimens with an embedded gaseous void, in thermosetting insulation and glass as a non-polar material, for comparison. Acquisition of the echo signal was performed in the phase-resolved mode, modifying the synchronization path and the settings. In contrast to continuous sinusoidal PD measurements, the chopped approach might provide a deeper insight into key PD phenomena, such as inception, propagation, time lag, post-discharge time decay, and effective surface area. Special focus was paid to the transition point between sinusoidal phase and the echo interval. The various scenarios of an echo mechanism, depending on the coincidence of remnant polarization field and the field accumulated on void walls, are discussed.

Design and development of a portable partial discharge generator

Intensive study of Partial Discharge (PD) phenomenon is of great importance for detecting and distinguishing different types of partial discharge. A portable device for partial discharge generation is designed and developed in this paper, which possesses advantage of miniaturization, dependability and flexibility. Such device is composed of power supply module, PD generating module and PD output interface. An implementing example of the partial discharge generator is given here in detail. Simulated high voltage signal is generated by a waveform generator and applied on physical PD generating model after being amplified by power amplifier and being boosted by a high voltage transformer with high transformation ratio. The generated PD pulse sequence are acquired and further analysed by MATLAB. Point to plane discharge is used as an example and verifies the performances of this device.

Electrostatic field theoretic approach to analyze the partial discharge phenomenon pertaining to insulation degradation

This paper elucidates the application of electrostatic field theory to analyze partial discharge due to the void formation inside the insulating material. Formation of voids leads to accumulation of static charges leading to capacitance build-up. The most probable cause of insulation failure is due to the subjection of high voltage. Prolonged high voltage poses a threat and leads to insulation failure. Failures occur in the tip gap between the conductor and insulating material’s inner periphery. Probable causes of such failures are corona discharge, surface discharge and treeing, leading to formation of Lichtenberger figures in the material and cavity discharge. This paper presents a way of fabricating the inner lining of the insulator with a semiconductor layer obeying avalanche breakdown at breakdown voltage or voltages at which partial discharge is likely to occur. With the onset of high voltage which can cause a discharge, the semiconductor experiences avalanche breakdown giving out a single photon ejection by Geiger mode (principle). A superior prevention method of using Teflon for insulation instead of XLPE/PILC has been suggested and simulated using COMSOL. Detection using Avalanche photo-detector(LiDAR) may enable us to track the probable location of the occurrence of partial discharge and isolate the system.

Application of improved Hilbert-Huang transform to partial discharge signal analysis

As a key concern in a power system, a deteriorated insulation will cause a partial discharge phenomenon and hence degrades the power supply quality. Thus, a partial discharge test has been turned into an approach of significance to protect a power system from an unexpected fault. As the first step in this work, a defect cast resin transformer is treated as a test object, and the detected partial discharge data are then transformed into a time-frequency-energy distribution through the Hilbert-Huang-Transform (HTT). The distribution is capable of providing both time-domain and frequency-domain information. It is a highly promising approach to pattern identification of a partial discharge and fault diagnosis. There is an excellent adaptability when applied to a nonlinear as well as nonstationary signal analysis for HHT, but with two major concerns, that is, the determination of optimal shifting number and the identification of unintended illusive components. For this sake, a combination of Kolmogorov-Smirnov (K-S test) and a sorting by signal energy ratio is proposed in the determination of the optimal shifting number. Subsequently, illusive components are ridded through a cumulative K-S test, such that an intrinsic mode function (IMF) is precisely extracted, intrinsic physical meaning contained over each spectral band is well preserved, and a mode confusion problem is removed as well.

Measurements on partial discharge in on‐site operating power transformer: a case study

This study presents the case study of a substation in-service power transformer referred to the on-site partial discharge (PD) detection and evaluation methods. An original methodology for simultaneous application of three methods is proposed: electrical, acoustic and ultra-high frequency. Transformer is powered by the power grid and no external generator is required according to the proposed methodology. Furthermore, several possibilities of applying these concurrent measurements and benefits of such solution in terms of result interpretation, interference resistance and on-site measurement applicability are indicated. The proposed methodology allows for a fast, accurate and secure PD diagnostics in a power transformer under on-site operating conditions. In the described example, a failure as a surface PD in the vicinity of the first phase of high voltage winding output is detected. The research results provide the basis for further works on a diagnostic expert system, which exploits automatic detection and evaluation of the PD phenomenon in power transformers under normal operating conditions.

Denoising different types of acoustic partial discharge signals using power spectral subtraction

Measuring acoustic emission (AE) of partial discharge (PD) phenomena can be adopted to estimate the condition of power transformers. However, the environmental noise encountered with AE of PD measurements negatively affects the accuracy of PD localisation and classification. Thus, efficient signal denoising techniques are required for noise suppression and hence, better detection accuracy. This study deals with white noise and it is a continuation of a previously published work that deals with random noise. The published work addresses the random noise suppression using a method named, power spectral subtraction denoising (PSSD). This study applies PSSD to the PD signals contaminated with white noise and uses a novel scheme of noise power spectrum density estimation. Multiple types of AE signals are examined including signals produced by corona, surface, parallel, and void PDs. Synthetic and real data demonstrate the superiority of the proposed method over the wavelet shrinkage denoising method as it can more effectively eliminate white noise and preserve signals of low signal-to-noise ratio.

Investigating the effect of cavity size within medium‐voltage power cable on partial discharge behaviour

One of the common causes of cross-linked polyethylene (XLPE) insulation ageing and finally cable failure is the presence of a cavity within cable insulation. Gas filled cavities can be initiated in XLPE cables during its manufacturing, installing and operating conditions. Once the size of the cavity reaches the critical limit, noticeable partial discharge (PD) activity develops. Therefore, the size of the cavity is one of the important factors that considered when investigating the PD activity in power cable. This work studies the effect of cavity size on PD behaviour within insulation layer of an 18/30 kV XLPE cable specimen; the changing in an artificial spherical cavity depths and diameters is investigated in the laboratory. In addition, 2D model geometry of a cable insulation having an artificial cavity is also developed using COMSOL software and MATLAB program to simulate the PD measurements from the laboratory experiments to imitate the conditions found during measurements, hence interpreting the obtained experimental results and determining the significant parameters influencing PD activity; hence, more a fuller understanding of PD phenomena within a cavity. The results show good coincidence between experimental and simulated data, in terms of PD magnitude and PD inception voltage.

Simulation of Space Charge Impact on Partial Discharge Inception Voltage in Power Busbars Dedicated to Future Hybrid Aircrafts

Reducing greenhouse gases, saving energy resources and mass optimization require technological changes towards increasingly electric vehicles. At the same time, performance improvement of semiconductor and dielectric materials further promotes electronic components confinement, resulting in a significant increase of embedded power densities. In the particular case of future hybrid propulsion aircrafts, electrical power that intended to supply reactors would be converted through power electronics components mounted on power busbars and insulated by solid dielectrics materials. These dielectrics materials have to respond to various electrical constraints of use (HVDC), in spite of environment change of aircraft parameters such as low pressure, temperature and thermal cycles, humidity... Unfortunately, partial discharges phenomenon is the most problem within electrical insulation system (EIS). Based on a topological model of power busbars designed for power converters dedicated to hybrid aircraft, partial discharge studies were conducted by simulation in various charging conditions of a PTFE insulator. Simulation results, which focus on electric field thresholds criteria of partial discharge inception voltage in air, reveal a net sensitivity of a space charge accumulation and distribution on dielectrics behaviour even for low space charge density, depending on their location in dielectrics. Compared to the behaviour observed with implanted homocharges, when by increasing homocharges density from 0.5 C/m3 to 2 C/m3 we observe a decrease of electric field by 450%, simulation results show a highest risk of partial discharge inception when heterocharges are accumulated inside dielectrics. Their accumulation increases the electric field in triple points beyond electric field thresholds of partial discharge inception in air. The simulated electric field reaching 22 kV/mm with only 2 C/m3 of heterocharges density accumulated in dielectric/busbars interfaces.

Application of Improved Hilbert–Huang Transform to Partial Discharge Defect Model Recognition of Power Cables

As a key concern in a power system, a deteriorated insulation is likely to bring about a partial discharge phenomenon and hence degrades the power supply quality. Thus, a partial discharge test has been turned into an approach of significance to protect a power system from an unexpected malfunction. An improved Hilbert–Huang Transformation (HHT) is proposed in this work as an effective way to address the issues of an optimal shifting number and illusive components, both suffered in a conventional HHT approach, and is then applied to a defect mode recognition for a partial discharge signal analysis in the case of a cross-linked polyethylene insulated power cable. As the first step, the partial discharge signal detected is converted through the proposed improved HHT to a time-frequency-energy 3D spectrum. Then as the second step, the fractal features contained therein are extracted by way of a fractal theory, and in the end the defect modes are recognized as intended by use of an extension method.

Research on Location Method of PD Signal for Metal-Clad Switchgear

It is well known that the occurrence of partial discharge phenomena within switchgears can lead to their destruction. Early detection can avoid failures of electrical equipment. The work of this paper mainly provides theoretic foundation for precise partial discharge (PD) location in switchgears. Hyperboloid method and spatial grid search method are proposed to locate PD source with transient earth voltage (TEV) test. Finite-difference time-domain (FDTD) is used to simulate the propagation process of TEV signal and validate the proposed method. Laboratory test on operating switchgear was conducted and the test results were in consistent with the simulation.

Determining Insulation Condition of 110kV Instrument Transformers Using Gas Chromatography

The paper dwells on determining insulation condition of high voltage instrument transformers and contains both theoretical contributions and measurements (performed on electrical equipment in 110/20kV substations in Sibiu county, Romania) regarding, namely, the partial discharge phenomena, highlighted using gas chromatography. Measurements have shown the negative effects of these internal possible mechanisms, such as arcing, corona discharges, spark discharges (local penetrations of insulation, possessing a high density of ionization or appearance of low energy arcing, sometimes described – not as an absolute rule – as partial discharge), on the solid insulation of high voltage instrument transformers. These conditions occurring singly or as several simultaneous events can result in decomposition of the insulating materials and the formation of various combustible and noncombustible gases. The technique used by the authors proved itself to be up to date, extremely advantageous, with extraordinary precision, speed and handling flexibility. Very reproductive results recommend the use of gas chromatography.

Comparison between three-capacitance, analytical-based and finite element analysis partial discharge models in condition monitoring

An important and essential diagnostic tool for insulation systems in condition monitoring is partial discharge (PD) measurement. Through PD measurement, the results may be used for insulation condition assessment. However, the modelling of PD is important because it is helpful in attaining a better understanding of PD phenomenon. The physical mechanisms and critical parameters influencing PD events under various conditions of defects and stresses can be identified. The relationship between the insulation design parameters, test conditions and defect characteristics with PD activities can also be developed. There have been many researches that reported on simulation of PD events in a void in insulation material. PD models can be categorized in three models, they are the induced charge concept model, three-capacitance model and the finite element method models. Each model has its own strengths and limitations in certain aspects. Therefore, in this paper, comparative studies and simulations for various PD models that have been developed to date are reported and discussed. The disadvantages and advantages of every model are presented in details. The results from the simulation using those models were compared with the measurement data to observe their performance in terms of physical parameters values. From comparative studies between each model, the most suitable PD model can be chosen to simulate PD events depending on the requirement selected by the users.

Analysis of HVDC superimposed harmonic voltage effects on partial discharge behavior in solid dielectric media

This paper presents an investigation of effects of high voltage direct current (HVDC) superimposed voltage harmonics on partial discharge (PD) behavior. Firstly, a single air filled void embedded in a slab of polymeric insulation was modeled using finite element methods (FEM). PD phenomena activated under the influence of rippled DC voltages were simulated using an interlinked environment of MATLAB and multiphysics simulation package COMSOL. Secondly, the results of the modeling were backed up by experimental tests, where HVDC superimposed harmonics were applied to artificial void samples in the lab and trends in the resultant PD characterized with varying harmonic orders and amplitudes. The results of both modeling and experiment are generally in agreement showing that as the harmonic orders and levels increase, the repetition rate of PD pulses rises in comparison to a purely DC applied voltage having the same peak amplitude. The findings of this study will assist in understanding of PD behavior under HVDC conditions where harmonic rippling occurs on the voltage waveform.