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The non-homogeneous electric field distributions in the cross-linked polyethylene insulation of 330 kV power cable with multi-conductor core depending on the electrical conductivity and thickness of the semiconducting screen as well as at different frequency of applied voltage (from 50 to 104 Hz) are studied by finite-element analysis. As shown, taking into account the periodic structure of core surface, the electrical conductivity of the material of internal semiconducting screen should exceed 10–6 S/m and its thickness should be at least 1.5 mm in order to obtain the uniform electric field in the basic insulation of the cable at the boundary with the screen. The paper also considers the effect of various types of the surface and volumetric defects in the semiconducting screen on the electric field inhomogeneity in cable insulation. It is shown that the defects in the screen can lead to a significant increase of the electric field in the local zones of their location (up to 5 times as compared to the field without defects) and therefore contribute to the formation and development of treeing structures in the insulation. The revealed results explain the reasons for the micro- and macrolevel degradation of power cable insulation and confirm the need to ensure the uniform structure, smooth surface of both semiconducting screen and core during the technological process of manufacturing the power cables with crosslinked polyethylene insulation [ABSTRACT FROM AUTHOR]

To investigate the pattern recognition of complex defect types in XLPE (cross-linked polyethylene) cable partial discharges and analyze the effectiveness of identifying partial discharge signal patterns, this study employs the variational mode decomposition (VMD) algorithm alongside entropy theories such as power spectrum entropy, fuzzy entropy, and permutation entropy for feature extraction from partial discharge signals of composite insulation defects. The mean power spectrum entropy (PS), mean fuzzy entropy (FU), mean permutation entropy (PE), as well as the permutation entropy values of IMF2 and IMF13 (Pe) are selected as the characteristic quantities for four categories of partial discharge signals associated with composite defects. Six hundred samples are selected from the partial discharge signals of each type of compound defect, amounting to a total of 2400 samples for the four types of compound defects combined. Each sample comprises five feature values, which are compiled into a dataset. A Snake Optimization Algorithm-optimized Support Vector Machine (SO-SVM) model is designed and trained, using the extracted features from cable partial discharge datasets as case examples for recognizing cable partial discharge signals. The identification outcomes from the SO-SVM model are then compared with those from conventional learning models. The results demonstrate that for partial discharge signals of XLPE cable composite insulation defects, the SO-SVM model yields better identification results than traditional learning models. In terms of recognition accuracy, for scratch and water ingress defects, SO-SVM improves by 14.00% over BP (Back Propagation) neural networks, by 5.66% over GA-BP (Genetic Algorithm–Back Propagation), and by 12.50% over SVM (support vector machine). For defects involving metal impurities and scratches, SO-SVM improves by 13.39% over BP, 9.34% over GA-BP, and 12.56% over SVM. For defects with metal impurities and water ingress, SO-SVM shows enhancements of 13.80% over BP, 9.47% over GA-BP, and 13.97% over SVM. Lastly, for defects combining metal impurities, water ingress, and scratches, SO-SVM registers increases of 11.90% over BP, 9.59% over GA-BP, and 12.05% over SVM. [ABSTRACT FROM AUTHOR]

The aging of cable insulation presents a significant threat to the safe operation of cables, with space charge serving as a crucial factor influencing cable insulation degradation. However, the characteristics related to space charge and conduction current behavior during thermal aging remain unclear. This study focused on the thermal aging of cross-linked polyethylene (XLPE) material and utilizes a combined pulse electro-acoustic (PEA) and conduction current testing system to analyze the space charge and conduction current characteristics in the sample under varying electric fields and temperatures. The average charge density, short-circuit residual electric field, electric field distortion rate, and conduction current were studied. The findings indicate that the space charge in the samples following thermal aging is predominantly governed by the injected charge. The amorphous region of XLPE decreases, while the cross-linking degree increases after aging, thereby facilitating charge carrier migration within the sample and reducing the generation of charge carriers through thermal pyrolysis. The minimum temperature required for charge injection is reduced by thermal aging. Furthermore, modifications in conduction current, residual electric field, and average charge density indicate that thermal aging has the potential to alter the microstructure and trap characteristics of XLPE. This study provides empirical evidence to elucidate the underlying mechanism of cable insulation aging. [ABSTRACT FROM AUTHOR]

Moisture of high voltage distribution network cables will cause major safety hazard, but there is no effective means to detect and analyze the internal humidity state of the cables. Therefore, it is urgent to develop a new nondestructive detection method to evaluate the waterproof performance of distribution network cables and their connectors. The internal structure of the cable is a multilayer structure composed of wires, cross-linked polyethylene insulation layer, and silicone rubber insulation sheath. We used the reflective terahertz pulse signal to detect the internal states of the cable, and judge whether it contains water stains according to the echo characteristics. In addition, three-dimensional data was obtained through cylindrical coordinate scanning and terahertz images were reconstructed based on feature information, which were consistent with the distribution of water stains between the cable insulation sheath and cross-linked polyethylene insulation layer. The results show that the terahertz technology can realize the high sensitivity detection of cable moisture state, which is of great significance in the power and transmission industry. [ABSTRACT FROM AUTHOR]

The overview of fiber-optic technologies for real-time monitoring of the technical condition and operational characteristics of modern power cables with cross-linked polyethylene insulation and with the fiber-optic module integrated into their structure is presented. In particular, the new intelligent means for monitoring of the temperature, load current, deformation (mechanical damages), partial discharges in the insulation, moisture penetration inside the cables and control over sheath voltage limitation are described. The topicality of using and developing the technologies of smart diagnostics for power cable lines in order to achieve the effective and safe operation of cables as well as the high reliability of networks is shown. Ref. 47, fig. 7.

This article presents a mathematical model for evaluating the dielectric properties of inner layers of insulation in three-core belted cables. It proposes a modified inspection scheme that allows for the evaluation of partial capacitances and dielectric dissipation factor. The article discusses the challenges in measuring individual dielectric parameters due to parasitic capacitive coupling between adjacent conductive elements. The proposed approach utilizes aggregate measurements and the least squares method to mitigate measurement errors and improve accuracy. The article also references three other articles related to capacitive mass sensors, monitoring insulation in multicore cables, and measuring the dissipation factor in three-core belted cables. The document includes the ISSN number and publication details for the journal "PRZEGL¿D ELEKTROTECHNICZNY." [Extracted from the article]

The paper presents a review and analyzes of the principal factors for reliable operation of the power cables with polymer insulation. The basic conditions for long-term operation of the insulation, typical defects in its structure and the causes of their occurrence, which eventually lead to insulation failure, are defined and summarized. According to scientific data, the influence of different electrical modes of the cable operation on cable line service is described, the effects of the higher harmonics, asymmetry and non-sinusoidal voltage on the state of the insulation, its accelerated aging, the increase in cable temperature, and therefore the need to correct the current loading are studied. Such impacts can cause the risk of failure of the cables, their operation and the breakdowns of the electrical network as well as additional economic costs. The new intelligent systems for on-line control of electrical, thermal and mechanical characteristics and partial discharges in power cable lines are presented. These systems are intended to control automatically the insulation state and cable line operation, to protect power cable lines against emergency situations. Ref. 53, fig. 3, tables 2.

. It is noted that at present, 10 and 35 kV overhead power transmission lines are being laid outside the settlements of the Republic of Belarus on reinforced concrete vibrated (10 kV) and centrifuged (35 kV) poles that are characterized by low reliability and damaging the environment (on account of alienation of land for poles, the need to make a wide clearing for laying in the forest, obstructions by poles and wires of lines to the operation of agricultural machinery, the danger of electric shock to personnel and the public). It is possible to avoid these disadvantages if, instead of overhead lines, power transmission cables with cables insulated by cross-linked polyethylene are used which are characterized by a very low failure flow parameter. Contrary to the prevailing opinion about the higher cost of cable power transmission lines compared to overhead ones of the same rated voltage, it turned out that, taking into account reliability, the cost of electricity lost in the lines for a year, damage to the environment and to the power system caused by the need to perform more expensive emergency repairs (as compared to a planned one), laying cable lines with three-core and single-core cables of a voltage of 10 and 35 kV instead of overhead cables outside the populated area is fairly justified. In this connection, the laying of three-core cables is more preferable. It should be also borne in mind that with an increase in the length of cable lines, the capacitive earth fault current increases, to compensate for which additional devices are needed to be installed in power centers, viz. arc-extinguishing reactors or resistors, accounting for the cost of which (up to 22 % of the cost of one kilometer of cable line) does not significantly affect the conclusions we have drawn regarding the effectiveness of using 6–35 kV cable power lines in an unpopulated area instead of overhead ones, however.

Polypropylene (PP), a thermoplastic material that can be recycled by melting, is viewed as a potential alternative to cross‐linked polyethylene for insulation. In this work, PP‐based composites were fabricated with surface‐modified silicon dioxide (SiO2), organized montmorillonite (OMMT), and polyolefin elastomer (POE) as fillers via a two‐step melt blending method. The dispersion states of SiO2 nanoparticles, OMMT, and POE in PP and their effects on PP crystallization were investigated. Moreover, the elongation at break, yield stress, energy storage modulus, damping loss factor, broadband dielectric spectrum, bulk resistivity, and alternating current (AC) breakdown strength of the specimens were tested. POE significantly increased the composite toughness, whereas the AC breakdown field strength and volume resistivity of POE/PP were lower. The homogeneously dispersed SiO2 and OMMT in the matrix acted as heterogeneous nucleation sites and reduced the grain size. To varying degrees, they effectively improved the dielectric properties, volume resistivity, and breakdown field strength of the composites. Hence, the composites simultaneously had excellent mechanical and dielectric properties. The volume resistivity of SiO2‐OMMT‐POE/PP with higher crystallinity was 15.4 times higher than that of POE/PP, and the breakdown field strength increased by 16.4%. [ABSTRACT FROM AUTHOR]

The widespread use of cross-linked polyethylene (XLPE) as insulation in cables may be attributed to its outstanding mechanical and dielectric properties. In order to quantitatively evaluate the insulation status of XLPE after thermal ageing, an accelerated thermal ageing experimental platform is established. Polarization and depolarization current (PDC) as well as elongation at break of XLPE insulation under different ageing durations are measured. XLPE insulation state is determined by the elongation at break retention rate (ER%). Based on the extended Debye model, the paper proposed the stable relaxation charge quantity and the dissipation factor at 0.1 Hz to evaluate the insulation state of XLPE. The results show that the ER% of XLPE insulation decreases with the growth of ageing degree. The polarization and depolarization current of XLPE insulation will increase obviously with thermal ageing. Conductivity and trap level density will also increase. The number of branches of the extended Debye model increases, and new polarization types appear. Stable relaxation charge quantity and dissipation factor at 0.1 Hz proposed in this paper have a good fitting relationship with ER% of XLPE insulation, which can evaluate the thermal ageing state of XLPE insulation effectively. [ABSTRACT FROM AUTHOR]

This paper investigated the influence of three aromatic voltage stabilizers (4‐n‐propylbenzoic acid, 2‐methoxyphenylboronic acid, and 3‐aminobenzoylmethylamide) on insulating properties of cross‐linked polyethylene (XLPE) at high temperatures for high voltage direct current (HVDC) applications. The XLPE blends containing 1 wt% voltage stabilizers were prepared through a solution‐blending method. The addition of voltage stabilizers suppressed the space charge inside the XLPE at high temperatures. The DC conductivity of XLPE and its blends increased with temperature. The DC conductivity of the XLPE blended with the 4‐n‐propylbenzoic acid was lowest at the different temperatures and electric fields. The DC breakdown strength of the tested materials continually decreased as the temperature increased. Notably, the DC breakdown strength of XLPE with the addition of 4‐n‐propylbenzoic acid and 3‐aminobenzoylmethylamide was higher than the reference XLPE at high temperatures. Moreover, the thermal stability of the XLPE remained unaffected after the voltage stabilizer's addition, whereas the thermal conductivity was improved. Quantum chemical calculations showed that the addition of voltage stabilizers with lower LUMO could effectively buffer the high‐energy electrons and improve the DC breakdown strength of the XLPE. A buffering mechanism of high‐energy electrons demonstrated the effect of the voltage stabilizers on the DC breakdown strength in the XLPE. [ABSTRACT FROM AUTHOR]

This paper investigates the influence of voltage stabilizer and nanofiller addition on the insulation performance of the cross‐linked polyethylene (XLPE). The test samples of XLPE/stabilizer blends consisting of 1 wt% m‐aminobenzoic acid, XLPE nanocomposites consisting of 0.5 wt% nano MgO and XLPE hybrid composite consisting of both voltage stabilizer and nanofillers were prepared. Various physicochemical and electrical properties were measured to analyze the performance of prepared samples. The obtained results show that the addition of nanofillers deteriorates the electrical insulation performance of the XLPE. On the other hand, the voltage stabilizer addition proves to be suitable for enhancing the electrical insulation performance of the XLPE. Meanwhile, the hybrid XLPE composites have shown medium behavior. The voltage stabilizer addition reduces, but the nanofillers increase the space charge density inside the XLPE compared to pure XLPE. It is also found that the dispersion of the voltage stabilizer in the material is uniform, whereas the nanofillers are aggregated. Furthermore, both additives slightly improve the thermal stability of the XLPE. The trap level theory based on quantum chemical calculation is proposed to explain the influence mechanism of the additives on the XLPE. [ABSTRACT FROM AUTHOR]

The ageing characteristic of XLPE insulation of operating a 110 kV power cable with different service time is studied in this paper. The microscopic morphology of XLPE films from different cables were characterized by using Differential Scanning Calorimetry (DSC), X-ray Diffraction method (XRD), and Fourier Transform Infrared Spectroscopy (FTIR) methods, and the dielectric, mechanical, and electrical properties of XLPE were also measured. The relationship of several typical property parameters with the cable service time were established, and the ageing mechanism of XLPE insulation of the operating cable was also analyzed. It was found that XLPE insulation would endure a recrystallization process in the initial operation stage during which the microscopic morphology would become more perfect with higher crystallinity and denser crystal structure. Then, the thermal oxidation would dominate the ageing process of XLPE with the molecular chains broken and more micromolecular products generated after the cable had operated for more than 10–15 years. The AC breakdown strength decreases with the increase of cable service time, with lower decreasing rate in the initial operation stage and a larger rate after 10–15 years. The Pearson correlation coefficient between the cable service time with the characteristic parameters were calculated, and some of them were found to be effective to be used as indicators for operation state detection of operating power cables. [ABSTRACT FROM AUTHOR]

One of the main phenomena that contributes to the non-success of cable insulation made of cross-linked polyethylene (XLPE) is electrical treeing. To improve the XPLE cable insulation, the use of nanofiller has been introduced. Adding the nanofiller in the based composite offers better cable lifetime and resistance to deal with the cable failure. One of the potential nanofillers that can increase the insulation performance of XLPE cable is silica nanofiller. To this extent, the studies on silica nanofiller in XLPE are focusing on the impulse breakdown strength, dielectric loss, permittivity, space charge, alternating current (AC), and partial discharge. The studies reveal that the dielectric properties of the XLPE nanocomposite have significant improvement. Therefore, this work investigates the effect of various concentrations of silica nanofiller in XLPE composite as electrical tree inhibitor. The concentrations of silica nanofiller in XLPE were 0.25 wt%, 0.5 wt%, 0.75 wt%, 1.0 wt%, 1.25 wt%, 1.5 wt%, and 1.75 wt%. The silica nanofillers have 96%-99% purity, 20-30 nm sizes and the shapes are spherical. As a result, the XLPE composite containing 1.5 wt% silica nanofiller demonstrate higher tree inception voltage and detaining the tree propagation speed, which could be considered as an inhibitor medium of electrical tree growth. [ABSTRACT FROM AUTHOR]

This study investigated the electric field distribution of underground cable insulation in cross-linked polyethylene/zinc oxide (XLPE/ ZnO) nanoparticles (NPs) for medium-voltage (MV) cables. The ZnO NPs that were obtained by three methods of preparation were classified using transmission electron microscopy (TEM). The obtained ZnO NPs were semi-spheres with sizes of 35–55 nm on TEM images. XLPE/ ZnO films with various ZnO NP weight contents (i.e., 0, 1, 3, and 5%) were exposed to varied dosages of 3-MeV electron beam (EB); 0 kGy, 15 kGy, 20 kGy, and 25 kGy. The optimum film XLPE/ 5-ZnO, which has ZnO NP content (5 wt%), irradiated at 25 kGy, according to alternating current (AC)/ DC conductivity (AC: 1 × 10−4 S/m; DC: 12.44 × 10−2 S/m) in minimum relative permittivity (2.24), was obtained. COMSOL Multiphysics was used to simulate the electric field distribution within an MV cable of 25-kGy XLPE/ 5-ZnO insulation. The maximum uniform electric field was found in the middle of the 25-kGy XLPE/5-ZnO film sample, rather than at the top or bottom, which might be attributed to the significantly low relative permittivity of the new 25-kGy XLPE/5-ZnO film cable. [ABSTRACT FROM AUTHOR]

It is well-known that there is no PLAN-DO-CHECK-ACT (PDCA) approach that is used by electricity distribution network operators and asset managers of power cable systems. Accordingly, this paper proposes a novel application of the PDCA approach to thermal aging management of underground power cables in electricity distribution networks. Another novelty of the proposed approach is that the finite element method (FEM) is used in combination with the traditional Arrhenius model to calculate the unknown temperature of cable conductors under service conditions. In particular, this means that the FEM-based Arrhenius model can involve the effects of other heat sources, wind, solar irradiation, etc., in procedures for qualification of underground power cables. The Arrhenius model is applied to an actual hot spot of a 110 kV underground cable line of most importance to reliable operation of the electricity distribution network of the city of Belgrade. In the hot spot, the 110 kV cable line is installed in parallel with the group of 35 kV cables and crosses an underground heating pipe-line. The proposed approach is successfully validated using the existing experimental data on cross-linked polyethylene insulation. Finally, it is found that the hot spot effect can shorten the expected total service lifespan of the 110 kV cables in the hot spot area by 36.84%, as well as that the largest consumption of total thermal lifespan occurs in the presence of all the existing thermal effects. [ABSTRACT FROM AUTHOR]

To fully understand the distribution network cable accessories’ moisture fault, the variation in insulation parameters of the cable main insulation of cross-linked polyethylene (XLPE) and the cable accessory reinforced insulation of silicone rubber (SIR) under different moisture conditions are studied experimentally. Furthermore, the effects of typical moisture defect forms and moisture positions on electric field distributions are studied by establishing the interface defect model. The experimental results show that the insulation properties of XLPE after water immersion are more seriously reduced than SIR. The resistivity of XLPE and SIR specimens decreases significantly with the increase in moisture time, decreasing by 90.3% and 48.3% after 720 h, respectively. The relative dielectric constants of the two kinds of specimens increase with different degrees after moisture, increasing by 5.16% and 7.83%, respectively, and the breakdown strength decreases by 18.3% and 13.1% after 720 h, respectively. The simulated results show that the moisture form and position have a great influence on electric field distribution. The electric field distortion caused by water trees’ defect is the most serious, followed by water film defects and water droplet defects. Besides, for different types of moisture defects, the position of the maximum distortion electric field is different. [ABSTRACT FROM AUTHOR]

The studies of the service life and residual life of various insulating materials are described. The known mathematical models of insulation aging applicable to AC power cable lines are considered. Based on the models and the previously proposed approach, the service life and residual life of cables with XLPE, EPR and PVC insulation are estimated. The assessment is carried out using the data from monitoring the voltage and current of a 6 kV cable transmission line laid at one of the electric power enterprises. Air temperature obtained from open sources. The results showed the applicability of all models for estimating the residual life due to the small difference in the predicted life. In real conditions, the service life of the listed types of insulation can be different due to their dielectric and design features.

Cross‐linked polyethylene (XLPE) cables are a critical component of power transmission systems. As operating conditions sometimes exceed the thresholds set in discipline, some cables fail to reach their designed lifespan, and consequently evaluating the aging degree of cables is particularly necessary. Here ten cables with an operating duration between 1 and 11 years from adjacent lines were sampled. Investigations were performed through various aging evaluation methods. Then typical lifespan prediction indices were concluded from test results and filtrated through correlation calculation. Meanwhile, a lifespan prediction method based on GM (1, N) model was proposed to establish the equivalent relationship between operating time and these indices. The research results indicated that, lifespan prediction indices obtained were all significantly correlated with operating time, which can be used to characterize aging degree of XLPE cables. Besides, due to the high prediction accuracy of experimental verification, the GM (1, N) model was proved to be applicable to evaluate the aging degree quantitatively and determine the remaining lifespan (relative to the designed lifespan) of XLPE cables. In future research, this method can be used to formulate a reasonable and economic withdrawal strategy for XLPE cables operating in conditions that exceed the thresholds set in the discipline. [ABSTRACT FROM AUTHOR]

The review concerning application of fiber-optic technologies in power industry, in particular, for monitoring of modern power cables with cross-linked polyethylene insulation and integrated fiber-optic module is carried out. The new intelligent tools for control of electrical, thermal and mechanical characteristics and partial discharges in power cable lines are presented. The current operational experience for the system of Smart Cable Guard in an emergency is described. The prospects to develop and use the intellectual technologies for monitoring of technical state of up-to-date high-voltage cable power lines and their operate reliability are grounded by analysis of new diagnostic methods controlling the level of partial discharges, temperature distribution and mechanical damage in polyethylene insulation and other elements of the high- and extra-high-voltage cables with integrated fiber-optic modules. References 51, figures 8. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study of the effects of thermal aging on the insulation characteristics of cross-linked polyethylene (XLPE) medium voltage cables. These cables are installed in Algeria where they are designed to withstand high temperatures and humidity levels. Therefore, the main objective of this work is to report experimental results concerning the effects of accelerated thermal aging and water adsorption on the XLPE insulation properties. For this purpose, mechanical characterization and visual observation analysis are performed. In addition, complementary diagnostic measurements, including Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR) and Differential Scanning Calorimetry (DSC), are carried out. Furthermore, a correlation between XLPE mechanical, physical, and physico-chemical changes due to thermal and water adsorption is deduced. [ABSTRACT FROM AUTHOR]

Voltage endurance coefficient (VEC) is a parameter used in the design of withstand test and insulation thickness of cross‐linked polyethylene (XLPE) cables. Thermal ageing is inevitable in operation of cable, but the thermal ageing effect on the VEC is rarely considered. In this study, the trend of VEC of XLPE films under DC voltage during thermal ageing is investigated by 120 and 135°C thermal ageing experiments. The results show that, after 14 days of 120 and 135°C thermal ageing, the VEC decreases from 20.74 to 7.05 and 3.93, respectively. To understand the effect of thermal ageing on the VEC, the VEC is described as a function of the free energy increment which is proportional to the degree of polymerisation (DP) and the electric field. A simulation calculating the free energy increment of several molecular chains is conducted to confirm the proportional relationship between the free energy increment and the DP, the electric field. Based on the function of the VEC, a predicting method for the VEC under thermal ageing is developed. The experimental results of 120 and 135°C thermal ageing are used to confirm the preciseness of the proposed predicting method. [ABSTRACT FROM AUTHOR]

Introduction. The main direction of technical policy in the design, construction and technical re-equipment of transmission lines is the modernization of electrical networks and increase their energy efficiency in order to increase the throughput and reliability. Problem. Existing calculation methods do not take into account the influence of insulation thickness on the long-term current load of the wires according to the values of the maximum permissible working temperature of the conductors. Purpose. The investigation of the influence of insulation thickness of the protected wires of high-voltage electric transmission lines on their current carrying capacity. Methodology. The long operating temperature of the wire when the rated load current flows is determined based on the heat balance equation. Results. A method has been developed for determining the optimum thickness of polyethylene cross linked and oxide insulation to provide the lowest thermal resistance to the heat transfer of protected wires, the use of which allows increasing the current carrying capacity by 20 % compared to bare wires. It is shown that the internal temperature drop in cross linked polyethylene insulation is an order of magnitude smaller in comparison with the oxide insulation at identical values of the dielectric loss tangent. Originality. The calculations take into account the presence on the surface of a non-insulated aluminum conductor of a natural dense film based on aluminum oxide, which protects it from further contact with air. The capacitance of a single phase conductor with insulation is determined on the basis of the calculation of the electric field in a piecewise homogeneous medium by the method of secondary sources.

In medium voltage cables, partial discharges (PD's) are the major problems that trigger electrical insulation failures. Therefore, classification of PD source type and failure localization in medium voltage cables are significant issues of medium voltage engineering. Therefore, in this study, both detection and localization of PD are studied. As a first step, 4 different kind of defects are artificially generated at the same length of the same kind of medium voltage cross-linked polyethylene (XLPE) cables. Consequently, an experimental setup is built. During the experiments, different medium voltage levels are applied to the cables, then the PD signals are measured and recorded. To classify the signals of different defects, different statistics of frequency spectrum of the signals are considered as features. As a final task of this step, multiclass support vector machine is employed and the PD signals are classified. In the second step, one kind of defect is generated at different locations of same kind of longer XLPE cable. Consequently, the cable exposed to different medium voltage levels and PD signals are measured and recorded. The statistics of the data are employed as features. Finally, PD signals measured from different lengths are classified by the help of multiclass support vector machine. [ABSTRACT FROM AUTHOR]

Polymeric nanocomposite insulations are receiving the widespread attention of the electrical cable industry. This paper presents the electrical insulation performance of as‐received commercial 320 kV high‐voltage direct‐current (HVDC) cross‐linked polyethylene (XLPE)/MgO nanocomposite material with reference to the pure XLPE. The results of this commercial‐grade electrical insulation material are not reported hitherto. The scanning electron microscopy confirms the well‐dispersed nanofiller inside the polymer matrix. The DC electrical insulation performance is investigated by DC breakdown strength, space charge, DC electrical conductivity, and surface potential decay measurements. The test samples are subjected to the thermal aging at 135°C for 30 days. The un‐aged nanocomposite exhibits 20% higher DC breakdown strength, negligible hetero space charge accumulation, and the lower DC conductivity by one order than the un‐aged pure XLPE. Moreover, thermally aged nanocomposite shows more restraint to the deterioration of its properties. After the thermal aging, the DC breakdown strength decreased by 38% and 20% in the pure XLPE and its nanocomposite, respectively. Thermally aged nanocomposite shows negligible hetero charges and an increase in the DC conductivity by one order. However, the pure XLPE shows higher hetero charge accumulation and the increased DC conductivity by one order. In un‐aged XLPE nanocomposite higher crystallinity, higher deep trap density, and the lower carbonyl index are found to be the primary attributes of its improved performance. It is postulated that these significantly unchanged attributes can be the reason for the better anti‐thermal aging properties of the XLPE nanocomposite. [ABSTRACT FROM AUTHOR]

Copyright of Electrical Engineering & Electromechanics is the property of National Technical University, Kharkiv Polytechnic Institute and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

This study aims at elucidating the correlations between structural changes and the variation of dielectric properties of cross-linked polyethylene (XLPE) during thermal aging. For this purpose, thermal aging experiments were carried out on XLPE samples at 80, 100, 120 and 140 °C for different aging times for a maximum total duration of 5040 hours. Chemical changes were assessed by Fourier transform infrared spectrum (FTIR). Besides, the crystallinity ratio and the melting temperature were evaluated using differential scanning calorimetry (DSC). Frequency domain dielectric spectroscopy was used to investigate the evolution of the dielectric constant and losses of XLPE during aging. The results show that aging at 80 and 100 °C could help to improve the crystalline state of XLPE which leads to the decrease of the dielectric constant. However, for higher thermal stress, the main aging mechanism of XLPE is thermal oxidation which leads to deteriorate the morphology and increase both the polarization and losses, mainly at low frequencies. It has been found also that in some cases, the non-homogeneity of the color of XLPE seems to indicate the increase of interfaces in the material which could lead to increase the dielectric losses due to the interfacial polarization. [ABSTRACT FROM AUTHOR]

Copyright of Technical Electrodynamics / Tekhnichna Elektrodynamika is the property of National Academy of Sciences of Ukraine, Institute of Electrodynamics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Monitoring of electromagnetic (EM) waves due to partial discharge (PD) is a promising tool for condition monitoring of cables. This study presents the development of a modelling scheme for simulation of EM wave propagation due to PDs occurring at cavities in the cross‐linked polyethylene (XLPE) insulation. Simulation models for generation and propagation of PD pulses through the cable geometry are developed. A finite element method (FEM)‐based model is developed to simulate the PD current along cylindrical voids in the cable insulation. The initial fields due to the PD currents in the voids are simulated by an FEM model. The propagated EM fields inside and outside the cable surface due to PD's occurring inside the voids are analysed by a finite‐difference time‐domain model. The analysis of propagated EM fields due to a Gaussian‐shaped PD pulse identifies the dominant components of propagated electric and magnetic fields along the cable geometry. Furthermore, the propagated EM fields at the cable sheath due to different void dimensions are simulated and experimental validation of the propagated magnetic field is conducted with measurement by an high‐frequency current transformer sensor installed around an earth wire from the sheath of an 11 kV XLPE cable. [ABSTRACT FROM AUTHOR]

In this paper, a closed-form solution for traveling wave (TW)-based fault location on non-homogeneous lines (NHLs) with multiple sections is proposed. It is able to accurately estimate the fault location on NHLs, taking into account the different propagation velocities, irrespective of the number of sections, including the effects of line electrical parameters uncertainties. The algorithm can be applied to non-homogeneous transmission networks composed by overhead transmission lines (OHLs), underground cable lines (UCLs), submarine cable lines (SCLs), or by any other line section with considerably different electrical characteristics. A wide variety of fault scenarios were simulated in a 380 kV/50 Hz NHL consisting of multiple OHL, UCL, and SCL sections. In each simulation, the proposed algorithm performance was compared against those obtained from an existing two-terminal TW-based fault location approach. The obtained results reveal that the proposed closed-form TW-based solution is generalist and reliable, being useful for fault location applications on NHLs. [ABSTRACT FROM AUTHOR]

In this paper, the energy distribution of trapped charges on the surface of cross-linked polyethylene (XLPE) thermally aged at 100 °C and 160 °C were studied by the isothermal surface potential decay method. It was found that the surface traps of unaged XLPE were mainly deep ones of both electron-type and hole-type. In the process of thermal aging at 100 °C, the surface traps of XLPE were still mainly deep traps. As the aging time increased, the density of shallow traps increased, and the density of deep traps didn't change much. In the process of thermal aging at 160 °C, the density of shallow traps of both electron-type and hole-type ones increased greatly, and the density of deep traps of both electron-type and hole-type ones decreased sharply. At the same time, the energy levels of hole-type traps decreased. Under the thermal stress, the increase in the density of shallow traps may be due to an increase in aging products such as carbonyl (C=O); the decrease in the density of deep traps should be due to a decrease in chemical defects in the crystalline regions because of the destruction of spherulites. Differences of the energy distribution of trapped charges on the surface of XLPE aged at two different temperatures may be caused by the differences in the way that crystal structures deteriorate. [ABSTRACT FROM AUTHOR]

In order to understand the characteristic of water tree growth for cross-linked polyethylene (XLPE) at different temperatures, here, a new possible explanation is presented for the different characteristic at different temperatures. Water tree aging experiments were performed, respectively, at 0, 20, 40, and 60°C. The shapes of water trees were observed by an optical microscope, and the sizes of water trees at different temperatures were recorded. Based on the molecular dynamics and polymer orientation, the new possible explanation for the characteristics of water tree growth is proposed at high or low temperatures. According to the experiments, the rate of water tree growth first decreases and then increases with the rise of temperature and the transition temperature is about 40°C. The behaviours of thermal motion and orientation of molecules can both influence the water tree growth. The water tree growth at high temperature is mainly determined by the thermal motion, while the water tree growth at low-temperature is mainly affected by the behaviour of molecules orientation. [ABSTRACT FROM AUTHOR]

Space charge accumulation inside the cross-linked polyethylene (XLPE) insulation is one of the most serious problems in HVDC cable operation. In this paper, the voltage stabilizers that have excellent compatibility with XLPE are used to suppress the space charge in XLPE insulation. Three different voltage stabilizers, 4,4'-Difluorobenzophenone, 4,4'-Dihydroxybenzophenone, and 4,4'-Bis (dimethyl amino) benzyl, denoted as A, B, and C, respectively, were added into XLPE material with additive content of 0.5 wt%, and neat XLPE was used as a control. The differential scanning calorimeter (DSC) test, tensile test, DC conductivity and breakdown strength measurements were employed to characterize the thermal, mechanical and electrical properties of the samples respectively. Moreover, the space charge behaviors were investigated using the PEA method, and the trap-controlled carrier mobility was evaluated by the depolarization processes of the space charge. The mechanical and thermal analyses indicate that the presence of voltage stabilizers does not significantly change the microstructure of XLPE, as required for the preparation of HVDC cable insulation. Though the influence of voltage stabilizers on DC conductivity is not obvious, a higher breakdown strength was found in the voltage-stabilizer modified XLPE samples. In addition, XLPE modified by the voltage stabilizers B and C with higher trap-controlled carrier mobility show a good ability to suppress space charge in XLPE insulation, that is, less space charge accumulation and faster space charge dissipation than the neat XLPE. The experimental results reveal that the voltage stabilizers B and C show great promise for use in HVDC cable application. [ABSTRACT FROM AUTHOR]

Cross-linked polyethylene (XLPE) is often manufactured as pipe, film and foam products and used as electric insulation material. To improve the dielectric properties of XLPE film, CF4 dielectric barrier discharge (DBD) is applied as a surface modification method. The surface of XLPE film was modified at the low pressure of 1 kPa with different treatment time (15s, 30s, 60s, 120s, 240s and 480s). Electrical and optical characteristics are observed during DBD process, including applied voltage, measured current, photograph and emission spectra. Then, the surface properties, which are hydrophobicity, chemical composition, surface morphology, trap depth, dielectric loss and AC breakdown voltage, have been measured or observed by water contact angle test, X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), isothermal relaxation current (IRC), frequency domain spectroscopy (FDS) and withstand voltage test. After the surface modification, the water contact angle, trap depth and breakdown voltage increase first and then decrease with treatment time extending. Meanwhile, the dielectric loss has an opposite trend, which represents better dielectric properties. The reason is that fluorine can reduce the surface energy, which can significantly influence the water contact angle. Better hydrophobicity can restrain the accumulation of outside pollution on the surface. Moreover, fluorine has strong electronegativity, so amorphous crystalline and impurities interface trap depth become deeper and the dielectric loss becomes lower. Therefore, appropriate DBD treatment conditions can apparently improve XLPE dielectric properties. [ABSTRACT FROM AUTHOR]

Cross-linked polyethylene (XLPE) insulation is successfully used for high-voltage AC transmission. However, it is still under development for high-voltage DC application due to space charge accumulation, which distorts the internal electrical field distribution and leads to its aging/failure. Therefore, the space charge should be measured and carefully analysed. On the other side, conductivity measurement helps to forecast the degradation probability of the insulation. Higher conductivity represents the severe degradation. Nanofiller addition, such as SiO2, TiO2, MgO and so on (<5 wt%), particularly surface-modified nanofiller due to its better dispersion significantly suppresses the space charge accumulation and conductivity. Nevertheless, the choice of suitable nanofiller has still remained a challenge. With this context, space charge and conductivity of XLPE-silica and XLPEmagnesium oxide (MgO) surface-modified nanocomposites are measured. This study proposes a parameter for nanofiller selection that will deliver optimal properties for the intended application. Results show that nanocomposites with higher nanofiller permittivity (i.e. MgO) have less space charge accumulation and low conductivity and are justified with the help of a band gap theory model. [ABSTRACT FROM AUTHOR]

Morphology of the contact area between solid insulation materials ultimately determines the short- and long-term electrical properties of the complete insulation system. The main purpose of this paper is to propose a statistical model to examine the real area of contact between solid dielectric surfaces and secondly to verify and correlate the model outputs with experiments. The model computes real area of contact, number of contact spots and average cavity size at the interface as a function of elasticity, contact force and surface roughness. Then, using the average cavity size and the Paschen's law, the discharge inception field of the cavity (CDIE) is estimated. AC breakdown strength (BDS) testing of solid-solid interfaces was carried out, where cross-linked polyethylene (XLPE) samples with four different surface roughnesses were tested at various contact pressures. Following the increased contact force, the calculated average cavity size decreased by a factor of 4.08 − 4.82 from the roughest to the smoothest surface, corresponding to increased CDIEs by a factor of 2.01 − 2.56 . Likewise, the experimentally obtained BDS values augmented by a factor of 1.4 − 1.7 when the contact pressure was elevated from 0.5 MPa to 1.16 MPa. A linear correlation between the CDIE and BDS was assumed, yielding a correlation coefficient varying within 0.8 − 1.3 . When the 90 % confidence intervals were considered, the range reduced to 0.86 − 1.05 . This correlation suggests that interfacial breakdown phenomenon is strongly related to the interfacial cavity discharge. Hence, the proposed model is verified with experiments. [ABSTRACT FROM AUTHOR]

Copyright of Technical Electrodynamics / Tekhnichna Elektrodynamika is the property of National Academy of Sciences of Ukraine, Institute of Electrodynamics and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Medium voltage (MV)/high voltage (HV) cable lines are high-value assets and require substantial costs for their installation or replacement. For this reason, the capability to assess the condition of cable lengths and accessories on site is of great importance. Cross-linked polyethylene (XLPE) insulation is extensively used for MV, HV, and extra-high voltage (EHV) class cables [1] thanks to its excellent voltage-endurance and thermomechanical properties. In particular, XLPE-insulated cables feature substantially lower losses, easier manufacturing and jointing procedures, better environmental compatibility, and higher operating temperature compared with impregnated paper cables, which lead to lower costs in procurement and operation [2], [3]. [ABSTRACT FROM AUTHOR]

This study investigates and compares two different silicone anti-failure rejuvenation fluids based on alumina nanofiller in terms of their capability in rehabilitation and restoration of water tree aged medium voltage cross-linked polyethylene (XLPE) distribution power cable insulations. These two rejuvenation fluids include two types of silane coupling agents used for forming chemical bonds between nanoparticles and cable polymer matrix, filling water tree micro voids and drying the humidity of cable insulation. These two compositions contain γ-alumina nanoparticles which have applications in improving dielectric properties, treating and modifying the surface of the aged insulation and filling water tree micro voids. After injecting the two rejuvenation fluids in two groups of aged cables, dielectric loss factor (tanδ) of the injected samples was measured every week from day 1 to 30 and their results were compared with the new unused and aged samples. Microstructure analysis of the aged and rejuvenated insulations was carried out by scanning electron microscope (SEM) and the chemical bonds of the aged and rejuvenated samples were detected and monitored by Fourier transform infrared (FTIR) spectroscopy. The type of elements and the weight percent of the absorbed elements on the surface of rejuvenated insulations were studied by energy disperse X-ray spectroscopy (EDX). After one month from the injection, it was revealed that tanδ of the injected samples (both rejuvenation fluids) decreased in a way that their tanδ values were even less than the new unused samples. Results of SEM analysis illustrated that rejuvenation fluids filled the water tree micro voids and modified the insulation surfaces. FTIR analysis also indicated that both silicone fluids penetrated in cable insulations and the peaks related to silicone and alumina bonds could be clearly observed. EDX test demonstrated and compared the amount and weight percentage of the rejuvenated elements such as silicone, aluminum and iron. Finally, through the results of these 4 tests, the best rejuvenation composition was selected among these two compositions. [ABSTRACT FROM AUTHOR]

The effect of thermal aging on the charging phenomena in cross-linked polyethylene (XLPE) has been studied under electron beam irradiation in scanning electron microscope (SEM). The dynamic variation of trapped charge represents the trapping process of XLPE under electron beam irradiation. We have found that the trapped charge variation can be approximated by a first order exponential function. The amount of trapped charge presents enhanced values at the beginning of aging at lower temperatures (80 °C and 100 °C). This suggests the diffusion of cross-linking by-products to the surface of sample that acts as traps for injected electrons. The oxidation which is a very important form of XLPE degradation has an effect at the advanced stage of the aging process. For higher temperatures (120 °C and 140 °C), the taken part process in the evolution of the trapped charge is the crystallinity increase at the beginning of aging leading to the trapped charge decreasing, and the polar groups generated by thermo-oxidation process at the end of aging leading to the trapped charge increase. Variations of leakage current according to the aging time have quite similar trends with the dielectric losses factor and consequently some correlations must be made between charging mechanisms and the electrical behaviour of XLPE under thermal aging. [ABSTRACT FROM AUTHOR]

Dielectric response is closely related to the aging status of XLPE cables, and the isothermal relaxation current (IRC) has been applied to find out the change trend of cable insulation as a non-destructive method. In this paper, 4 groups of XLPE cable samples (16 cables in total) are artificially acceleratedly aged with different time interval at 120, 140 and 160°C, respectively, and their IRC curves are measured by a micro-current device. The results show that with the increasing aging time, IRC curves decrease slower and the absolute values of steady current become larger. In order to quantify the aging characteristics of XLPE cables, the trap parameters calculation theory is employed to work out the peak trap level of different polarization types. The experiment results show that the peak trap level of bulk polarization (type 1) remains stable and is around 0.76eV which is considered to be independent of aging degree. As the aging time increases, the peak trap level of amorphous crystalline relaxation (type 2), which is from 0.785eV to 0.82eV, increases at low temperature (120°C) due to the breaking of molecular chain and decreases at high temperature (more than 140°C) due to the over cross-linking. The peak trap level of impurities interface relaxation (type 3) is highly influenced by aging temperature, which is most sensitive to the aging degree of power cable. It is considered that IRC can be used as a practical way to judge cable insulation in the future. [ABSTRACT FROM AUTHOR]

The growth in consumption of electrical energy has stabilzed in many developed countries, e.g., United States, Japan, and Europe. However, the demand is still very high in several countries, especially in China. In addition, power grids have been connected globally for the purpose of enhancing mutual accommodation and stability of electric power over wide areas, especially in Europe. High-voltage direct current (HVDC) power transmission is becoming widespread, especially in Europe and China. [ABSTRACT FROM AUTHOR]

Experimental data on measurements of isothermal relaxation current (IRC) are presented for different kinds of industrial electrical insulation: cross-linked polyethylene (XLPE) 6-kV power cables and thermosetting insulation for the stator windings of high-power rotation machinery. The ageing of and damage to electrical insulation was assessed using indicators derived from the so-called distributed charge current. An analysis of the experimental data shows that the IRC method is highly sensitive for detection of incipient defects in these insulating materials and can be used to determine the indicators of ageing in XLPE insulation and their initial and limiting values. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Copyright of Electrical Engineering & Electromechanics is the property of National Technical University, Kharkiv Polytechnic Institute and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Background: The effect of alternative bearing materials on the risk of revision due to infection after total knee replacement remains uncertain. By reducing the immunomodulating polyethylene wear-particle burden and with different substrate bacterial adhesion properties, Oxinium oxidized zirconium and cross-linked polyethylene (XLPE) could alter infection risk. The purpose of the current study was to analyze the risk of revision for infection in 3 comparisons of bearing combinations.Methods: To evaluate the risk of revision for infection with XLPE, cobalt-chromium (CoCr) on XLPE was compared with CoCr on non-cross-linked polyethylene (NXLPE). To evaluate Oxinium, Oxinium-NXLPE was compared with CoCr-NXLPE, and to evaluate the possibility of an additional beneficial effect of Oxinium on XLPE, Oxinium-XLPE was compared with CoCr-XLPE. The cumulative percent revision (CPR) and hazard ratio (HR) for revision for infection in primary total knee replacement for osteoarthritis were determined from registry data from September 1, 1999, to December 31, 2015. Revisions within 6 months following the primary surgery were censored from the analysis, while procedures with posterior stabilized or fully stabilized total knee replacements as well as prostheses with a known higher risk of revision were excluded. Analyses were stratified by age, sex, and fixation type.Results: Of the 326,603 included primary total knee replacements, 1,511 (0.46%) were revised for infection. The risk of revision for infection was lower for CoCr-XLPE compared with CoCr-NXLPE (HR = 0.74; 95% confidence interval [CI] = 0.65 to 0.84; p < 0.001). This effect was apparent for both male and female patients overall, all fixation types, antibiotic cement use, those <65 years of age, and male patients ≥65 years of age. However, for female patients ≥65 years of age, there was no difference. Overall, Oxinium-NXLPE had the same revision risk as CoCr-NXLPE regardless of fixation; however, for cemented fixation, subanalysis showed a lower risk for Oxinium-NXLPE compared with CoCr-NXLPE (HR = 0.69; 95% CI = 0.51 to 0.94; p = 0.018). Oxinium-XLPE had the same revision risk for infection as CoCr-XLPE overall, among male patients, and when cemented fixation had been used.Conclusions: In this registry analysis, CoCr-XLPE had a 26% lower risk of revision for infection than CoCr-NXLPE, suggesting a reduction of wear particle-induced immunomodulation with XLPE. Oxinium-XLPE had the same risk as CoCr-XLPE. Overall, Oxinium did not reduce the infection risk.Level Of Evidence: Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence. [ABSTRACT FROM AUTHOR]

Electrical cable is a potential ignition source and fire hazard in residential houses, nuclear power plants, aircraft, and spacecraft. In this work, a bench-scale flame-retardant cable, consisted of the outer PVC sheath, middle XLPE insulation, and inner copper core, was heated uniformly inside a novel cylindrical heating chamber. The applied heat flux was transient, which increased with time close to a parabolic function. Once heated, the outer PVC sheath swelled and shrank under multiple stages. Before ignition, the swelling behavior was found to follow the same trend as the mass-loss rate. Analysis showed that the observed spontaneous ignition was likely a result of pyrolysis gas from inner XLPE insulation piloted by the smoldering hot spot (600~700 °C) on the outer charring PVC sheath. For the first time, the spontaneous ignition time was found to linearly increase with the integral heat flux, and it was different from other ignition experiments under the transient heat flux in the literature. Moreover, the measured critical mass flux of ignition increased with the heating power, and the critical surface temperature of PVC was above 500 ° C . The results of this work provide important information about the swelling and ignition behaviors of the flame-retardant cable under a real fire, and may guide the design of future fire-safety cable. [ABSTRACT FROM AUTHOR]