XLPE Material Research Articles

Electrical Tree Image De-Noising using Threshold Wavelet Transform and Wiener Filter

Electrical treeing occurred in solid dielectric materials, especially in electrical application with high voltage. The occurrence of electrical tree happens when high electric fields applied, causing tiny channels or paths to form. The main issue during the data collection process is the changes of lighting, making it difficult to study the tree's propagation length, fractal dimension, and growth rate due to corrupted images. This research aims to analyse electrical tree structure images in XLPE material using a CCD camera and develop image de-noising techniques to suppress noise on the electrical tree image. The performance was then analysed using the Otsu thresholding algorithm for accurate segmentation. The methodology was divided into four phases: sample preparation, experimental setup, image pre-processing in MATLAB, and testing four de-noising filters: Wiener, median, NLM, and Gaussian. The Wiener filter with higher PSNR, SNR, and RMSE was selected and using superimposed method, both threshold wavelet transforms and wiener was combined to eliminate the noise. Finally, the proposed method of superimposed was tested with the Otsu thresholding method to evaluate accuracy, sensitivity, and specificity of the combination filter. Based on the analysis of PSNR, SNR, and RMSE, the performance of the threshold wavelet and Wiener filter (TWWF) de-noising technique improves the image quality of the electrical tree structure. Thus, for the Otsu thresholding segmentation algorithm analysis, it also had the highest values in terms of accuracy, sensitivity, and specificity.

Maintenance Practices of High-Voltage Cross-Linked Polyethylene (XLPE) Cable Buffer Layers

As urbanization accelerates globally, the demand for electricity continues to rise, especially within high-voltage power transmission systems. Cross-linked polyethylene (XLPE) cables have become crucial due to their exceptional insulation properties and mechanical characteristics. However, the buffer layers of XLPE cables may undergo aging and faults caused by various factors, including electrical aging, thermal aging, chemical impacts, and improper design. This paper synthesizes existing literature to provide an in-depth analysis of the material properties, aging mechanisms, fault causes, design principles, and maintenance practices related to XLPE cable buffer layers. Through finite element method (FEM) simulations, it evaluates the electric field distribution across XLPE cables under different operating voltages and the contact state between the buffer layer and the metal sheath. Additionally, this study explores the recyclability and environmental impact of XLPE materials, as well as how improvements in material properties and detection technologies can enhance cable reliability and safety. The findings offer comprehensive theoretical and practical guidance to the power industry, aiding in optimizing cable design, improving system reliability, and reducing failure rates, while also suggesting future research directions.

Self-Healing Properties of Water Tree with Microcapsule/Cross-Linked Polyethylene Composite Material Based on Three-Layer Core-Shell Structure.

To overcome the degradation of insulating properties caused by the water tree aging of cross-linked polyethylene (XLPE), a self-repairing material for XLPE based on a microcapsule system is proposed. Three-layer shell nucleus microcapsules/XLPE composites with different microcapsule doping content are prepared. The water tree aging experiments are carried out using the water-needle electrode method to analyze the ability of microcapsules to repair the damaged areas of water trees. The results show that, compared with the XLPE material without microcapsules, the electrical properties of composites decline significantly when the doping concentration of three-layer shell nucleus microcapsules is large. When the doping concentration is 1.0 wt%, the microcapsule/XLPE composite breakdown strength has no noticeable change, and the dielectric loss factor does not change significantly, the space charge density decreases, and the space charge properties have been improved considerably. When the water tree branch develops to the position where the microcapsules are located, the microcapsules will rupture and release their internal repair materials and catalysts and react with water to produce an organic silicone resin to fill the water tree cavity, which can achieve an excellent self-healing effect. In addition, the nano-SiO2 on the surface microcapsules can make the microcapsules and matrix better integrated, which avoids the microcapsule accumulation that tends to occur when incorporating microcapsules, thus improving the repair rate.

Effect of temperature on partial discharges activity and electrical trees propagation in XLPE

AbstractCross‐linked polyethylene (XLPE) cables are commonly used for constructing urban power lines due to their superior properties. Insulation defects can cause partial discharge (PD) and electrical tree, which can negatively impact the insulation performance of the cable and even lead to insulation failure. During operation, cables undergo hot and cold cycles, and the temperature of the insulation layer can affect the PD and electrical tree. An experimental platform with a needle‐plate electrode was developed to investigate this phenomenon. The platform was used to detect PD activity and electrical tree propagation in XLPE under a 50 Hz voltage at various temperatures. The results indicate that an increase in insulation temperature leads to an increase in the number of PDs and a decrease in the inception voltage. Simultaneously, it has been observed that a rise in temperature can facilitate the spread of electrical trees. To explicate the aforementioned PD result, a finite element analysis (FEA) model has been developed. Additionally, a molecular dynamics (MD) model of XLPE material was developed to clarify the phenomenon of electrical tree propagation. This study's findings aid in investigating the impact of temperature on XLPE defects, which is critical for assessing power cable performance.

Trial Manufacture and Performance Research of Hydraulic Oil Tank for Three Kinds of Non-Metallic Materials

With the increasing demand for lightweight construction machinery, it is of great significance to study non-metallic materials that can replace steel plates to make hydraulic oil tanks (HOTs). To explore the feasibility of making HOTs with three materials—cross-linked polyethylene (XLPE), polypropylene (PP), and nylon (PA)—this paper takes 28 L and 115 L volumes commonly used in construction machinery, such as forklifts and loaders, as the design volume and obtains non-metal HOT products of good forming quality by regulating the process parameters. Based on the test methods and evaluation bases of the fuel tank in the national standard, the normal-temperature pressure test, high-temperature pressure test, and low-temperature impact test are designed according to the working conditions of the HOTs. Finally, the non-metallic HOT products are tested. The results show that the rotational molding of XLPE material is the easiest, and products of all sizes can be molded, but the mechanical properties and thermal stability of the products are poor. The low-temperature impact resistance of PP products is poor. PA material can be used to create small HOTs, and the product performance is excellent. This research serves as a valuable reference for the non-metallic and lightweight design of HOTs.

Electrical Resistance Performance of Cable Accessory Interface Considering Thermal Effects.

Power cables are widely used in various fields of power transmission, and cable accessories are the weakest link in power cable systems due to their complex structure and multi-layer insulation coordination issues. This paper investigates the changes in electrical properties of the silicone rubber/cross-linked polyethylene (SiR/XLPE) interface at high temperatures. The physicochemical properties of XLPE material under thermal effects with different times are characterized through FTIR, DSC, and SEM tests. Finally, the mechanism of the effects of the interface state on the electrical properties of the SiR/XLPE interface is analyzed. It is found that with the increase in temperature, the changes in electrical performance of the interface do not show a monotonic downward trend, while interestingly, they can be divided into three stages. Under the thermal effects for 40 d, the internal recrystallization of XLPE in the early stage improves the electrical properties of the interface. In the later stage of thermal effects, the amorphous region inside the material is severely damaged and the molecular chains are severely broken, resulting in a decrease in the electrical properties of the interface. The results above provide a theoretical basis for the interface design of cable accessories at high temperatures.

EFFECTS OF WASTE CROSSED-LINKED POLYETHYLENE ELECTRICAL WASTE COATING ON THE PROPERTIES OF BITUMEN

The high cost of construction materials and increased axle loads has motivated researchers to seek alternative cost-effective materials for road construction. Studies on the use of waste thermoplastic polyethylene material to improve bitumen properties have been investigated. However, few studies on the use of thermoset polyethylene (cross-linked polyethylene) to modify bitumen have been carried out. This research investigated the use of waste cross-linked polyethylene (XLPE) cable coating on bitumen properties. An FTIR analysis carried out on waste XLPE cable coating revealed that it is predominantly composed of XLPE material. A comparative study carried out on the bitumen properties revealed that the modifier had a decreasing effect on its penetration and ductility but, had an increasing effect on softening point and specific gravity; Hence, a considerable improvement in the temperature susceptibility and stability of the bitumen. The short-term ageing analysis carried out revealed that the modified bitumen can withstand short-term ageing requirements at 2% and 4% by weight of pure bitumen. FTIR analysis carried out on the pure and modified bitumen revealed that changes observed in bitumen properties with increasing modifier content were a result of physical changes and not chemical changes. A one-way ANOVA carried out on the properties of various bitumen content revealed that the modifier had a significant effect on the properties of pure bitumen with increasing bitumen content. The regression models developed properly described the relationship between the modifier content and the bitumen properties as they expressed very good R2 values.

Experimental evaluation of the effect of recycled cross-linked polyethylene on the performance of grouted macadam mixtures

ABSTRACT Grouted Macadam (GM) mixtures – recognized as semi-flexible pavement (SFP) materials – offer strong stability in high temperatures, good durability and high load-bearing capacity. However, these materials are prone to environmental and traffic-induced cracking. Cross-linked polyethylene (XLPE), a common high-voltage cable insulation, faces disposal challenges due to limited recycling technology, often leading to burning or burial of these waste materials. In this study, to enhance GM mixture crack resistance and mitigate the environmental impact of XLPE waste accumulation, XLPE material was used in GM mixtures in two methods. In the first group, 15%, 30%, and 45% of 4.75 to 9.5 mm natural aggregates were replaced in volume, with XLPE pseudo-aggregates of the same size. In the second group, XLPE pseudo-fibers (1.9–2.2 cm in length, 1.5 mm thickness) were incorporated as additives in 0.5, 0.7, and 1 volume percentages. The results of mechanical tests on treated GM mixtures showed that adding recycled XLPE improved durability, with a 24.5% and 29.9% enhancement in samples with the most pseudo-aggregates and pseudo-fibers contents. The fracture strain tolerance (FST) index in low-temperature bending tests also increased by 53.8% and 108.9% in mixtures containing XLPE, highlighting its potential to enhance GM mixture performance in various service conditions.

Dielectric Characteristics of Crosslinked Polyethylene Modified by Grafting Polar-Group Molecules.

Polar group-modified crosslinked polyethylene (XLPE) materials are developed with a peroxide thermochemical method of individually grafting chloroacetic acid allyl ester (CAAE) and maleic anhydride (MAH) to polyethylene molecular-chains, which are dedicated to ameliorating dielectric characteristics through charge-trapping mechanism. By free radical addition reactions, the CAAE and MAH molecules are successfully grafted to polyethylene molecular chains of XLPE in crosslinking process, as verified by infrared spectroscopy molecular characterizations. Dielectric spectra, electric conductance, and dielectric breakdown strength are tested to evaluate the improved dielectric performances. Charge trap characteristics are investigated by analyzing thermal stimulation depolarization currents in combination with first-principles electronic-structure calculations to reveal the polar-group introduced mechanisms of contributing dipole dielectric polarization, impeding electric conduction, and promoting electrical breakdown field. The grafted polar-group molecules, especially for MAH, can introduce deep-level charge traps in XLPE materials to effectively restrict charge injections and hinder charge carrier transports, which accounts for the significant improvements in electric resistance and dielectric breakdown strength.

Comparative Analysis of XLPE and Thermoplastic Insulation-Based HVDC Power Cables

The application of cross-linked polyethylene (XLPE) cables to voltage sourced converter (VSC)-based high voltage direct current (HVDC) systems has already been technically verified and has become common, and thermoplastic (TP) is attracting attention as an insulation material for next-generation cables due to the recent development of material-related technologies. However, studies related to TP cables are mainly focused on improving material properties, and studies related to cable systems are insufficient. In this paper, XLPE and TP cables were designed for application to VSC-based HVDC systems, and major characteristics such as electric field distribution and thermal stability were compared and analyzed through overvoltage simulation. The insulation design method of HVDC cable was presented, and the design was performed using XLPE and TP insulation materials. The temperature and electric field profiles of the cables were also analyzed through a finite element method simulation. To analyze the performance of the designed cable, it was simulated with the PSCAD/EMTDC program. Based on the simulation results, the major characteristics of XLPE and TP cables were compared and analyzed. Results showed that in the case of TP cables, insulation properties were excellent, but thermal conductivity was relatively low; therefore, countermeasures are needed.

Thermal Aging Properties of 500 kV AC and DC XLPE Cable Insulation Materials.

Despite similar material composition and insulation application, the alternating current (AC) cross-linked polyethylene (XLPE) and direct current (DC) XLPE materials cannot replace each other due to different voltage forms. Herein, this work presents a systematical investigation into the effects of thermal aging on the material composition and properties of 500 kV-level commercial AC XLPE and DC XLPE materials. A higher content of antioxidants in the AC XLPE than in the DC XLPE was experimentally demonstrated via thermal analysis technologies, such as oxidation-induced time and oxidation-induced temperature. Retarded thermal oxidation and suppression of space charge effects were observed in thermally aged AC XLPE samples. On the other hand, the carbonyl index of DC XLPE dramatically rose when thermal aging was up to 168 h. The newly generated oxygen-containing groups provided deep trapping sites (~0.95 eV) for space charges and caused severe electric field distortion (120%) under -50 kV/mm at room temperature in the aged DC XLPE samples. For the unaged XLPE materials, the positive space charge packets were attributed to the residue crosslinking byproducts, even after being treated in vacuum at 70 °C for 24 h. Thus, it was reasoned that the DC XLPE material had a lower crosslinking degree to guarantee fewer crosslinking byproducts. This work offers a simple but accurate method for evaluating thermal oxidation resistance and space charge properties crucial for developing high-performance HVDC cable insulation materials.

Experimental Study to Evaluate the Wear Performance of UHMWPE and XLPE Material for Orthopedics Application.

The main objective of this study is to perform an abrasive wear resistance study of UMHWPE and XLPE by using different grades of abrasive paper (grade 100 (190 µm), grade 220 (50 µm), and grade 400 (40 µm)) with minor (10 N) and major (15 N) loading conditions. In this article, wear performance of the UMHWPE and XLPE materials compared to the bio-tribological data as reported earlier in the clinical studies has been investigated. The experimental result shows that the loss of materials for the XLPE was much higher than the UHMWPE under similar loading conditions. UHMWPE shows a 34% reduction in wear at minor loading conditions and a 53% reduction in wear at major loading conditions. From experimental results it was concluded that Cross-link PE has better wear resistance than UHMWPE in minor wear conditions, whereas UHMWPE shows better wear resistance under major loading conditions. Based upon these results, UHMWPE and XLPE have been recommended for use as bearing materials in orthopedics. The experimental results of this study were validated using results from the available literature.

Study on thermal degradation and kinetic characteristics of insulating materials used in high voltage switchgear

This study adopts the FT-IR, DSC, TG and other methods, studied the commonly used in high-voltage switchgear XLPE, EP and organic silicone materials in the same heating rate under thermal degradation properties of three kinds of insulating materials by calculation under different temperature of pyrolysis reaction apparent activation energy E and refers to the former factor to determine its dynamic characteristics. The results showed that the activation energies of epoxy resin, crosslinked polyethylene and silicone rubber were 63.53 kJ·mol-1, 99.66 kJ·mol-1, 62.59 kJ·mol-1, respectively. The pre-exponential factors were 3.2×105·s-1, 4.3×107·s-1 and 1386.9·s-1, respectively.

Study on thermal degradation and kinetic characteristics of insulating materials used in high voltage switchgear

This study adopts the FT-IR, DSC, TG and other methods, studied the commonly used in high-voltage switchgear XLPE, EP and organic silicone materials in the same heating rate under thermal degradation properties of three kinds of insulating materials by calculation under different temperature of pyrolysis reaction apparent activation energy E and refers to the former factor to determine its dynamic characteristics. The results showed that the activation energies of epoxy resin, crosslinked polyethylene and silicone rubber were 63.53 kJ·mol-1, 99.66 kJ·mol-1, 62.59 kJ·mol-1, respectively. The pre-exponential factors were 3.2×105·s-1, 4.3×107·s-1 and 1386.9·s-1, respectively.

Water-Tree Characteristics and Its Mechanical Mechanism of Crosslinked Polyethylene Grafted with Polar-Group Molecules.

In order to restrain electric-stress impacts of water micro-droplets in insulation defects under alternating current (AC) electric fields in crosslinked polyethylene (XLPE) material, the present study represents chemical graft modifications of introducing chloroacetic acid allyl ester (CAAE) and maleic anhydride (MAH) individually as two specific polar-group molecules into XLPE material with peroxide melting approach. The accelerated water-tree aging experiments are implemented by means of a water-blade electrode to measure the improved water resistance and the affording mechanism of the graft-modified XLPE material in reference to benchmark XLPE. Melting–crystallization process, dynamic viscoelasticity and stress-strain characteristics are tested utilizing differential scanning calorimeter (DSC), dynamic thermomechanical analyzer (DMA) and electronic tension machine, respectively. Water-tree morphology is observed for various aging times to evaluate dimension characteristics in water-tree developing processes. Monte Carlo molecular simulations are performed to calculate free-energy, thermodynamic phase diagram, interaction parameter and mixing energy of binary mixing systems consisting of CAAE or MAH and water molecules to evaluate their thermodynamic miscibility. Water-tree experiments indicate that water-tree resistance to XLPE can be significantly improved by grafting CAAE or MAH, as indicated by reducing the characteristic length of water-trees from 120 to 80 μm. Heterogeneous nucleation centers of polyethylene crystallization are rendered by the grafted polar-group molecules to ameliorate crystalline microstructures, as manifested by crystallinity increment from 33.5 to 36.2, which favors improving water-tree resistance and mechanical performances. The highly hydrophilic nature of CAAE can evidently inhibit water molecules from aggregating into water micro-droplets in amorphous regions between crystal lamellae, thus acquiring a significant promotion in water-tree resistance of CAAE-modified XLPE. In contrast, the grafted MAH molecules can enhance van der Waals forces between polyethylene molecular chains in amorphous regions much greater than the grafted CAAE and simultaneously act as more efficient crystallization nucleation centers to ameliorate crystalline microstructures of XLPE, resulting in a greater improvement (relaxation peak magnitude increases by >10%) of mechanical toughness in amorphous phase, which primarily accounts for water-tree resistance promotion.

Radical Composition and Radical Reaction Kinetics in the Probe-Irradiated XLPE Samples as a Potential Source of Information on Their Aging Degree

Polyethylene is a model polyolefin, and a widely used material for the manufacture of many products, including cable sheaths. Understanding degradation mechanisms at the atomic scale leading to oxidation during aging is crucial for many long-term applications. The concentrations of radicals derived from oxidation and chain scission during radio-oxidation, as well as their ratio, are important parameters controlling the predominance of chain scission or crosslinking of the polymer. In this work, we propose a cryogenic EPR technique for measuring oxidation- and fragmentation-derived radicals as a less-destructive method for the evaluation of cable insulation aging and performance capability. We investigate the effect of the low-dose and high-dose radiation aging on the formation of free radicals in the polymer matrix that are both unprotected and protected by antioxidants. The stability of radicals after aging is a determinant of macroscopic processes and structural changes during aging. Under the conditions of the higher dose rate, the peroxy radical buildup is lower per dose. Peroxy radical buildup is followed by decay during aging, in accordance with POOH content. Our results allow the prediction of the capability of the antioxidant to protect the XLPE material in the function of dose and time.

Evaluation of graphene/crosslinked polyethylene for potential high voltage direct current cable insulation applications

This paper evaluates the potential usage of graphene/crosslinked polyethylene (graphene/XLPE) as the insulating material for high voltage direct current (HVDC) cables. Thermal, mechanical and electrical properties of blends with/without graphene were evaluated by differential scanning calorimetry (DSC), tensile strength, DC conductivity, space charge measurements and water tree aging test. The results indicate that 0.007–0.008% weight amount of graphene can improve the mechanical and electrical insulation properties of XLPE blends, namely higher tensile/yield strength, improved space charge distribution, and shorter/fewer water tree branches. The improvements mainly attribute to the high stiffness of graphene, deep traps introduced by the interaction zones of graphene and XLPE, and the blockage effect of graphene within XLPE. For thermal performance of XLPE blends, graphene nano-fillers have but limited improvement. The crystallinity of the blends barely changes with the addition of graphene. However, the crosslinking degree increases as the additive-like amounts of graphene doped. The above findings provide a guide for tailoring lightweight XLPE materials with excellent mechanical and electrical performances by doping them with a small amount of graphene.

Electrical treeing behavior in XLPE insulation due to content AL2O3 nanoparticles

XLPE is currently commonly used in high voltage underground cables. Several researchers recently chose several nanofillers to improve the electric tree’s strength in the polymer matrix. Alumina AL2O3 nanofiller have been utilized to investigate the effects on the electrical treeing in XLPE. The percentage concentration were used as follows with different amounts “0.3wt.” % and “1wt.”% from weight of base material. The needle-plane electrodes were used in this investigation and gap selected between needle and plane earth is 3 mm. The growth and morphology of treeing in XLPE insulation have been observed by using charge coupled device camera CCDc and microscope system. Scanning of electron microscopes SEM has been investigated the nanoparticles spread in base material. The outcomes show the tree inception voltage TIV values 12.5, and 14.8 KV “0.3wt.” % and “1wt.”%, respectively in XLPE composites that is mean the TIV increase with increase concentration nanofiller, while the tree propagation time at 2mm length increase about 40 min and 2 hours in “0.3wt.” % and “1wt.”% AL2O3/XLPE, respectively compared with unfilled XLPE, as well as the breakdown time BDT enhancement by4.347% and 13.043% for 0.3wt% and 1 wt% nano AL2O3 composites compared with unfilled XLPE insulation. And showed pictures taken with a SEM Diffusion and accumulation of nanoparticles in the XLPE material.

Investigation of the effect of roughness value on the wettability behavior under electric field in XLPE materials used in medium and high voltage applications

Investigation of the effect of roughness value on the wettability behavior under electric field in XLPE materials used in medium and high voltage applications

Effect of degassing treatment durations on physico-chemical and electrical properties of 500 kV extra HVDC XLPE cable insulation

• This paper analyzes the effect of different degassing duration on the content of cross-linking by-products, morphological structure and insulation properties of 500 kV EHVDC XLPE insulation. • The measured content of the crosslinking by-products is consistent with the theoretical values calculated by Fick's second law. • The electrical performance of the XLPE material exhibited a trend of first increasing and then decreasing with the increase in the degassing treatment duration. • 36 h of degassing treatment is found to be an optimal duration to obtain the enhanced overall properties. An optimal degassing treatment duration for the preparation of commercial 500 kV extra high voltage direct current (EHVDC) cross-linked polyethylene (XLPE) insulation can improve its overall properties, reduce the manufacturing cost and time, which is urgently needed for high voltage cables suppliers. This paper analyzes the effect of different degassing duration on the content of cross-linking by-products, morphological structure and insulation properties of 500 kV EHVDC XLPE insulation. The raw pellets of commercial 500 kV EHVDC XLPE cable material are used to prepare the test samples by the hot-pressing method. Five samples with the different degassing durations of 0 h, 12 h, 36 h, 90 h, and 200 h were at 70°C. Physico-chemical and electrical methods are used to characterize the overall properties of the material under the different degassing durations. The results show that the measured content of the crosslinking by-products is consistent with the theoretical values calculated by Fick's second law. The oxidation induction time of the samples is reduced and tensile properties are improved with the increase of the degassing time. Furthermore, degassing treatment increased the lamellae thickness in the early stages and reduced the difference in the internal aggregation structure of the material. It was found that the degassing treatment significantly suppressed the space charge accumulation inside the material. Moreover, the degassing treatment of 36 h can increase the dielectric breakdown strength and reduce the current density of the samples.