High Voltage
Volume 5, Issue 6, December 2020
Volumes & issues:
Volume 5, Issue 6
December 2020
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- Author(s): Shengtao Li ; Dongri Xie ; Qingquan Lei
- Source: High Voltage, Volume 5, Issue 6, p. 643 –649
- DOI: 10.1049/hve.2019.0122
- Type: Article
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p.
643
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Owing to the formation of interface and new feature of which, the properties of nanodielectrics can be improved. ‘Hard/soft interface’ and its trap distribution can be tailored by functionalised groups. Molecular simulation results show that the interaction energy and electrostatic potential are larger for the soft interface, which indicates the greater bonding strength with the polymer matrix and electrostatic force on charge carriers. Charge transport simulation indicates that the accumulation of homo-charges would form a reverse electric field and distort electric field distribution. The injection depth would be restricted at the vicinity of sample/electrodes due to the greater trapping effect of deep traps, thus weakening the distortion in the sample bulk, thereby decreasing carrier energy and delaying the formation of impact ionisation. Based on the accumulation of carrier energy Φ = Eeλ, the idea of suppressing electron free path and carrier energy to enhance the insulation breakdown is confirmed. The classified effects of nanofillers during dc breakdown and corona-resistant are further understood from carrier energy. The introduced interfacial trap is effective in trapping carriers due to the low carrier energy under dc voltage, while ineffective in blocking the energetic charges during corona-discharge, but nanoparticles exert blocking and scattering effect against the energetic charges.
Understanding insulation failure of nanodielectrics: tailoring carrier energy
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- Author(s): George V. Naidis and Natalia Yu Babaeva
- Source: High Voltage, Volume 5, Issue 6, p. 650 –653
- DOI: 10.1049/hve.2020.0065
- Type: Article
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p.
650
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Results of simulations of streamers propagating along the atmospheric-pressure helium plasma jets ejected from a thin tube into ambient air are presented. The computational model includes the equations governing the helium–air mixture composition along and across the jet, as well as the equations, describing streamer propagation in the mixture, for the electric field and the charged species densities. Streamer velocity and spatial–temporal profiles of plasma parameters are obtained for various values of the helium flow rate. It is shown, in agreement with available experimental data, that the electric field values in the heads of streamers increase nearly linearly with the distance from the tube exit and that the slope of this dependence decreases with the growth of the helium flow rate.
- Author(s): Xianrui Liu ; Zefeng Yang ; Song Xiao ; Xuwei Duan ; Guoqiang Gao ; Wenfu Wei ; Guangning Wu ; Mihai Rotaru ; Jan K. Sykulski
- Source: High Voltage, Volume 5, Issue 6, p. 654 –661
- DOI: 10.1049/hve.2019.0388
- Type: Article
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p.
654
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A pantograph–catenary system (PCS) – an essential component to supply a high-speed train (HST) – faces a variety of new challenges due to the continuously increasing train speeds. The HST traction system receives power via an electrical contact between the pantograph strip and the high-voltage contact wire. This electrical contact is subject to serious mechanical shocks and significant electrochemical corrosion, making the modelling of the dynamic processes complicated, especially under high-speed and heavy-load conditions. The damage to the PCS – which is particularly noticeable at the edges of the pantograph strip – may become severe as the speed of the train rises. Moreover, as the speed increases, the distribution of the electrical current in the strip becomes uneven due to the velocity skin effect (VSE). To assess the impact of the VSE on the performance of PCSs, a multi-physics model has been created and is reported in this study. The model has been validated through experiments and the main aspects of its functionality – such as the VSE, friction, and air convection – have been identified and analysed at different speeds. The impact of speed on the traction current and the behaviour of thermal sources have been explored. With the increasing speed, the phenomenon of current clustering at the trailing edge of the strip becomes quite dramatic, resulting in a thermal surge in the region of the strip with high current density. To mitigate the negative impact caused by VSE in the PCSs, an improved kriging optimisation methodology has been utilised to optimise the parameters of the PCS. Recommendations regarding the optimal design of the PCS are put forward to improve the current-carrying performance and reduce the local temperature rise in the strip.
- Author(s): Allison V. Shaw ; Phichet Ketsamee ; Thomas Andritsch ; Alun S. Vaughan
- Source: High Voltage, Volume 5, Issue 6, p. 662 –668
- DOI: 10.1049/hve.2019.0376
- Type: Article
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p.
662
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The addition of organoclay to a polypropylene-rubber (PP-rubber) blend, primarily introduced to compatibilise the immiscible polymer blend, invokes contrasting dielectric and charge dynamic behaviour depending on the filler loading level. The authors report that at 0.5 wt.% loading, the organoclay decreases the DC conductivity, causes no significant dielectric losses, makes no significant difference to the space charge results compared to the unfilled system, and increases the reproducibility of the breakdown strength results, and hence the reliability of the material. These somewhat surprising results, contrasted by measurements of samples with 2.5 and 5 wt.%, lead us to conclude that trace amounts of organoclay improve the otherwise immiscible polymer blend making organoclay a suitable additive for HVDC applications.
- Author(s): Zhuodong Yang ; Xuebao Li ; Xiangrui Meng ; Zhibin Zhao ; Pengyu Fu ; Bin Zhai ; Xiang Cui
- Source: High Voltage, Volume 5, Issue 6, p. 669 –678
- DOI: 10.1049/hve.2019.0292
- Type: Article
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669
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In this study, the surface discharge current pulses of polyetheretherketone (PEEK) material under positive repetitive square voltage in a nitrogen atmosphere are measured. The influences of different voltage amplitudes and frequencies on the detail parameters of forward discharge and backward discharge current pulses are statistically analysed. The results show that as the square voltage amplitude increases, the current pulse amplitude, fall time and pulse width of both forward and backward discharge current increase, and the rise time does not change significantly. As the voltage frequency increases, current pulse amplitude, fall time and pulse width of both forward and backward discharge current decrease, and the rise time does not change significantly. Due to the independence of the discharge at different repetitive cycles, the specific discharge process in one cycle is analysed in detail to explain the influence mechanism of the voltage amplitude and frequency on the discharge current. By mean of the Richardson–Schottky and the Cavallini relaxation model, the relationship between discharge voltage ratio and surface charge, and the decay process of surface discharge are analysed. Furthermore, the influences of amplitude and frequency of the positive repetitive square voltage on the PEEK surface current pulses are explained qualitatively.
- Author(s): Caowei Huang ; Han Yin ; Pengfei Xu ; Bo Zhang ; Jinliang He ; Jianben Liu
- Source: High Voltage, Volume 5, Issue 6, p. 679 –687
- DOI: 10.1049/hve.2019.0050
- Type: Article
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p.
679
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Many research works have proved that it is viable to predict the radio interference (RI) of high-voltage alternating current transmission lines by corona cage test. However, it is uncertain whether the same method can be adopted for RI prediction of high-voltage direct current (HVDC) transmission lines, since the corona performance of HVDC lines is obviously affected by the widely distributed space charge. In this study, the detailed corona current characteristics, such as the current pulse amplitude, rise time, half-wave time, and repetition frequency are systematically studied by the reduced-scale experiment and the relationship between the average corona current and the RI excitation current is confirmed. Furthermore, based on the experimental study, a method for predicting the RI level of HVDC transmission lines by the corona cage test is proposed. The RI level of a ±800 kV bipolar HVDC transmission line is predicted and compared with the measured result, which verifies the validity of the proposed method.
- Author(s): Feng Bin ; Feng Wang ; Qiuqin Sun ; She Chen ; Jingmin Fan ; Huisheng Ye
- Source: High Voltage, Volume 5, Issue 6, p. 688 –696
- DOI: 10.1049/hve.2019.0098
- Type: Article
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p.
688
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The feature extraction and pattern recognition techniques are of great importance to assess the insulation condition of gas-insulated switchgear. In this work, the ultra-high-frequency partial discharge (PD) signals generated from four types of typical insulation defects are analysed using S-transform, and the greyscale image in time-frequency representation is divided into five regions according to the cutoff frequencies of TE m 1 modes. Then, the three low-order moments of every subregion are extracted and the feature selection is performed based on the J criterion. To confirm the effectiveness of selected moment features after considering the electromagnetic modes, the support vector machine, k-nearest neighbour and particle swarm-optimised extreme learning machine (ELM) are utilised to classify the type of PD, and they achieve the recognition accuracies of 92, 88.5 and 95%, respectively. In addition, the results show that the ELM offers good generalisation performance at the fastest learning and testing speeds, thus more suitable for a real-time PD detection.
- Author(s): Jiangrong Cheng ; Yang Xu ; Dengwei Ding ; Weidong Liu
- Source: High Voltage, Volume 5, Issue 6, p. 697 –703
- DOI: 10.1049/hve.2019.0261
- Type: Article
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p.
697
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The ultra-high frequency (UHF) method has been widely used in a gas-insulated system (GIS) for partial-discharge detection, and many achievements have been realised. In addition, many studies based on artificial defects have been made to confirm its validity. Therefore, the UHF method is generally believed to be sufficiently effective for GIS monitoring. However, in practical application, the authors find that for some micro-crack discharge in GIS insulator, the UHF method has low sensitivity. To fully study the characteristics of the micro-crack discharge in the GIS insulator, an experiment is conducted in this study using an actual post insulator with a micro-crack defect. The current signal based on IEC 60270 standard and the radio-frequency electromagnetic signal is simultaneously measured for thorough analysis. The results show that some submillimetre crack defects may occur in the GIS insulator. Its discharge is mainly presented as glow discharge, and the discharge signal frequency usually cannot reach the UHF band; thus, it cannot be effectively detected by the UHF method. This study provides complementary information to the applicability of the UHF method and inspires further study of the GIS insulator and its monitoring technology.
- Author(s): Xiaozhou Mao ; Zhongdong Wang ; Peter Crossley ; Paul Jarman ; Andrew Fieldsend-Roxborough ; Gordon Wilson
- Source: High Voltage, Volume 5, Issue 6, p. 704 –715
- DOI: 10.1049/hve.2019.0294
- Type: Article
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p.
704
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Frequency response analysis (FRA) is regarded as the most effective technique to detect mechanical faults of transformers. Over the years, FRA measurement data have been collected by utilities into transformer asset databases. The characteristic of FRA data is fundamentally determined by the transformer's equivalent electrical circuit, which consists of inductance and capacitance parameters that are windings' design and structure dependent. Different winding types tend to have different FRA characteristics, and a transformer's design information such as winding type, dimension etc. is often not known to the utility but critically important for asset management. This study reviews the state-of-the-art transformer FRA databases and application of machine learning techniques in this field, and proposes to apply a support vector machine (SVM) model onto the FRA data to identify the winding type. The SVM model is first trained by FRA traces of transformers with known winding types, and after testing, the SVM model is then applied to FRA traces with unknown winding information. A set of data from the UK's National Grid FRA database, was used to demonstrate and verify the SVM model. All transformers used in this study are 400/275/13 kV transmission transformers, which were designed using four different winding types, namely multiple layer, plain disc, interleaved disc and single helical windings. The proposed method can successfully identify the correct winding type.
- Author(s): Kamran Dawood ; Ahmet Kerem Köseoğlu ; Güven Kömürgöz
- Source: High Voltage, Volume 5, Issue 6, p. 716 –723
- DOI: 10.1049/hve.2019.0149
- Type: Article
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p.
716
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The transformer is one of the main components in the power network and transformer windings are one of the most expensive elements in the power transformer. Optimisation of winding distances is one of the most important parameters during the manufacturing of transformer. The distance between the windings in the two winding transformers is well known to transformer designers and manufacturers. However, insulation of the high voltage transformer with additional winding and tap winding is still a major problem for transformer designers. In this study, the additional winding to tap winding distance optimisation is made for a high voltage power transformer. Optimisation of the transformer's windings just not minimises the cost of the transformer but also increases the lifetime of the transformer. With additional winding and tap winding in high-voltage transformers, insulation distance is a major concern for minimising the cost and size of the high voltage transformer. In this study, an approach is made to balance the cost, size, and safety of high voltage transformers. The optimised distance and position between tap winding and additional winding are determined by using the finite element analysis. The finite element method results were also verified by making a prototype transformer.
- Author(s): Jing Yuan ; Wenjun Zhou ; Xiaobing Xu ; Yanqun Liao ; Chengke Zhou
- Source: High Voltage, Volume 5, Issue 6, p. 724 –730
- DOI: 10.1049/hve.2020.0024
- Type: Article
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724
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The associated daily maintenance effort and cost has been increasing with the growing use of high-voltage (HV) cable circuits. This study proposes a time-delay concept-based approach to maintenance scheduling of individual HV cable components, to allow periodicity of inspection to be optimised with consideration of time-delay interval between the instant of defect inception and final failure. Here, the progress from a defect to its resultant final failure can be represented as a two-stage process, one being a stochastic process of defect arrival and the other being a delay-time interval from defect to failure. Then an optimisation model is established to schedule maintenance activities based on the two statistical processes, where the objective function is set as the minimal maintenance cost. Cable circuits are divided into five components in accordance with the objects of inspection and testing. The components within different service ages are considered individually in the statistical models, and their accumulate failure numbers during each service year are used to automatically formulate and update periodicity of inspection. To illustrate the feasibility of the approach proposed, theoretical analysis on thousands of cable circuits are carried out. Results show that the economic expenditure could be reduced by 22.2% after optimisation.
- Author(s): L. Loiselle ; U. Mohan Rao ; I. Fofana
- Source: High Voltage, Volume 5, Issue 6, p. 731 –738
- DOI: 10.1049/hve.2019.0291
- Type: Article
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731
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In this work, mineral oil and synthetic esters were selected at different ageing factors (based on acidity values). Fresh and aged oils have been subjected to high-energy discharges (repeated 100 breakdowns) to simulate electric faults of highly vulnerable intensity. The intent of this work is to understand the influence of high-energy electric faults on oil degradation and gassing tendency at different ageing conditions. In this study, the influence of the high-energy discharges on degradation and gassing tendency at different ageing factors is reported for mineral oil and synthetic esters. Oil degradation is reported by adopting ultraviolet spectroscopy, turbidity and particle counter as per american society for testing and materials (ASTM) standard test methods. Gassing tendencies and fault gas analysis are understood by dissolved the gas analysis using Duval's triangle and Duval's pentagon methods for mineral and non-mineral oils. It is found that the influence of high-energy discharges on oil degradation is higher in mineral oils to that of the synthetic esters. The intensity of the gassing tendency is higher for ester fluids; however, as per the Duval methods, the faulty conditions are at lower levels as compared to mineral oils.
- Author(s): Adnan Krzma ; Maurizio Albano ; Abderrahmane Haddad
- Source: High Voltage, Volume 5, Issue 6, p. 739 –746
- DOI: 10.1049/hve.2019.0189
- Type: Article
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739
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Surface tracking and erosion is an irreversible degradation occurring on the insulator surface, and this can ultimately lead to failure of the insulator. Polymeric materials such as silicone rubber have many advantages; including a superior hydrophobic surface. However, polymers are exposed to ageing and degradation resulting from electrical and environmental stresses. The rotating wheel dip test is adopted to conduct a comparative study of surface conduction on the two insulators. A conventional design has been selected and compared with insulators having textured surface. Monitoring of the shed surface and insulator trunk using an IR camera were carried out to assess the temperature distribution along insulator profiles. A spatial analysis was also performed to identify key features of the two designs. Localised surface conductance measurements are proposed in this study. This helps to understand and distinguish the trends of conductance and its distribution on each surface, helping to predict the future surface degradation associated to each design.
- Author(s): Yangyang Wang and Xingliang Jiang
- Source: High Voltage, Volume 5, Issue 6, p. 747 –752
- DOI: 10.1049/hve.2019.0279
- Type: Article
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p.
747
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To calculate the distribution of the magnetic field and eddy current density on the surface of an aluminium plate, a method that couples the face-smoothed finite element method (FS-FEM) to the boundary element method (BEM) is proposed in this study. This method combines the advantages of the FS-FEM and BEM, which can rapidly and accurately calculate the distributions of vertical magnetic field and eddy current field on the surface of an aluminium plate. The structural parameters and material properties of the coil and aluminium plate are considered. An accurate three-dimensional calculation model is established. Then, the vertical magnetic field and eddy current field distributions are calculated in this study. In the case of the same grid density, compared with the finite element–boundary element coupling algorithm, the simulation results show that the FS-FEM and the boundary element coupling method have obvious advantage in improving the calculation accuracy. The maximum relative error between the calculated results and measured results is only 4%. The proposed method in this study is available for reference to the transient open-domain eddy current field analysis.
- Author(s): Jing Hao ; Xiangdong Xu ; Nathaniel Taylor
- Source: High Voltage, Volume 5, Issue 6, p. 753 –761
- DOI: 10.1049/hve.2019.0334
- Type: Article
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Dielectric response measurement is a widely used technique for characterising dielectric materials in terms of their capacitance and dielectric loss. However, the widely used approach with contact between samples and electrodes can in some cases limit the accuracy of the measurement. The authors introduce an easily realised electrode arrangement for non-contact measurements, which avoids these contact problems. The performance of the electrode arrangement in terms of the edge effect is assessed. The non-contact and contact methods are compared based on error-sensitivity analysis and experimental results. Differences are studied further, with attention to contact pressure. The non-contact method is also compared experimentally with the one-sided non-contact method. Air-reference measurements, comparing the sample to an air-gap for improved calibration, are used for all measurements. The results show that the non-contact method can be an alternative to reduce contact problems between the sample and electrodes, although error sensitivity can be higher when the non-contact method is used. The non-contact method can decrease the influence of the pressure applied to the sample compared to the contact method, and can also reduce the problem of poor contact that can arise from the absence of pressure in the one-sided non-contact method.
- Author(s): Rong Chen ; Jianhua Yang ; Xinbing Cheng ; Baoliang Qian
- Source: High Voltage, Volume 5, Issue 6, p. 762 –767
- DOI: 10.1049/hve.2019.0138
- Type: Article
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p.
762
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Marx generator is a voltage boosting device for power pulse compression, in which its capacitors are charged in parallel and discharged in series. To get a higher voltage boost ratio, high-voltage silicon stacks have been applied to substitute the isolated inductances in this study. Experiments with two isolation modes in the Marx generator have been carried out. Experimental results reveal that the high-voltage silicon stacks with the parameters of 50 kV/1 kA used in the Marx generator can increase the voltage step-up ratio to 168.6:1, up from 141:1 and 162.9:1 when isolating inductances and silicon-stacks with parameters of 50 kV/3 kA are applied, respectively. Moreover, the silicon stack-isolating-type Marx generator can almost eliminate the pre-pulse existing on the load if the isolated inductances employed. Therefore, it is crucial to choose appropriate high-voltage silicon stacks as the isolating devices in the Marx generator designed in this study.
Electric field distributions along helium plasma jets
Multi-physics analysis and optimisation of high-speed train pantograph–catenary systems allowing for velocity skin effect
Effect of organoclay loading on the dielectric properties and charge dynamics of a PP-rubber nanocomposite
Influence of frequency on the surface discharge characteristics of PEEK under positive repetitive square voltage
Prediction of radio interference from HVDC transmission lines based on corona discharge characteristics
Identification of ultra-high-frequency PD signals in gas-insulated switchgear based on moment features considering electromagnetic mode
Investigation of sensitivity of the ultra-high frequency partial-discharge detection technology for micro-crack in epoxy insulator in GIS
Transformer winding type recognition based on FRA data and a support vector machine model
Design optimisation for distance between additional and tap winding in high-voltage transformers
Time-delay concept-based approach to maintenance scheduling of HV cables
Influence of ageing on oil degradation and gassing tendency under high-energy electrical discharge faults for mineral oil and synthetic ester
Comparative characterisation of conventional and textured 11 kV insulators using the rotating wheel dip test
Calculation of 3D transient Eddy current by the face-smoothed finite element–boundary element coupling method
Non-contact method to reduce contact problems between sample and electrode in dielectric measurements
Study on a Marx generator with high-voltage silicon-stacks instead of isolating inductances
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- Source: High Voltage, Volume 5, Issue 6, page: 768 –768
- DOI: 10.1049/hve.2020.0326
- Type: Article
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Corrigendum: Partial discharge characteristics of an air gap defect in the epoxy resin of a saturable reactor under an exponential decay pulse voltage
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