High Voltage Cable Insulation Research Articles

Image De-noising Based on WMF Technique for Electrical Trees Structure in High Voltage Cable Insulation

Electrical treeing is a common problem during the pre-breakdown phenomenon in solid insulations due to the damage caused by Partial Discharge (PD) that progresses through stressed insulation via chemical degradation, which resembles the shape of a tree root. This resulted in a decrease in performance through degrading the insulation, which became a serious problem while dealing with electrical equipment. Hence, a deep understanding of electrical tree structure is vital to improving the quality of solid insulations. Ergo, optical microscopy is primarily used to examine tree structures, shapes, and fractal dimensions to reconstruct electrical tree structures for morphological study. However, optical microscopy images are frequently degraded by noise from readout procedures or image data acquisition systems, noise caused by occlusion, illumination, non-uniform intensity, destroying potential tree pixels, and a critical loss of information about the electrical tree structures. Therefore, this research proposed the Wiener Median Fusion (WMF) filter for electrical tree study. The performance of the WMF de-noising technique improves the image quality for the precise portrayal of the electrical tree structure based on thresholding segmentation algorithm analysis in terms of accuracy, sensitivity, and false positive rate. Based on the analysis of the thresholding segmentation algorithm, Otsu's thresholding exhibits the highest result compared to Niblack. The Otsu's overall percentage in terms of accuracy is 80.2934%, the sensitivity is 99.1513%, and the false positive rate is 82.6265%.

Surface Microstructure Study on Corona Discharge-Treated Polyethylene Using Positron Annihilation Spectroscopy.

The microstructure and chemical properties of the corona discharge process could provide an effective method for predicting the performance of high-voltage cable insulation materials. In this work, the depth profile of the microstructure and chemical characteristics of corona discharge-treated PE were extensively investigated using Doppler broadening of position annihilation spectroscopy accompanied with positron annihilation lifetime spectroscopy, attenuated total reflectance Fourier transform infrared spectra, Raman spectra and contact angle measurement. By increasing corona discharge duration, the oxygen-containing polar groups, including hydroxyl, carbonyl and ester groups, strongly contribute to the deterioration of hydrophobicity and the enhancement of hydrophilicity. And the mean free volume size, with a broadening distribution, decreases slightly. The line shape S parameter decreases because of the decrease in free volume elements and the appearance of oxygen-containing groups. Also, the thickness of the degradation layer, determined from the S parameter with positron injection depth, increases and diffuses into the PE matrix. A linear S-W plot within the degradation layer of different corona treatment duration samples indicates the defect type does not change. The S parameter decreases and the W parameter increases with an increasing corona duration. Using a slow positron beam, the nondestructive probe can be used to profile the microstructure and chemical environment across the corona discharge damage depth, which is beneficial for investigating the surface and interfacial insulation materials.

Largely Improved Creep Resistance and Thermal-Aging Stability of Eco-Friendly Polypropylene High-Voltage Insulation by Long-Chain Branch-Induced Interfacial Constraints.

Polypropylene (PP)-based composites have attracted numerous attention as a replacement of prevailing cross-linked polyethylene (XLPE) for high-voltage insulation due to their ease of processing, recyclability, and excellent electrical performance. However, the poor resistances against high-temperature creep and thermal aging are obstacles to practical applications of PP-based thermoplastic high-voltage insulation. To address these problems, in this Letter, we synthesized an impact polypropylene copolymer (IPC) containing multifold long-chain branched (LCB) structures in phases, especially the interfaces between the PP matrix and the rubber phase. The results indicated that the structural stability of LCBIPC was significantly enhanced under extreme conditions. In comparison to IPC (without LCB structures), 24.1% less creep strain and 75.2% less unrecoverable deformation are achieved in LCBIPC at 90 °C. In addition, the thermal aging experiments were performed at 135 °C for 48 and 88 days for IPC and LCBIPC, respectively. The results show that the resistance against thermal aging was also enhanced in LCBIPC, which showed a 133% longer thermal aging life compared to IPC. Further results revealed that the interfacial layer between the PP matrix and the rubber phase was constructed in LCBIPC. The two phases are tightly linked by chemical bonds in LCB structures, leading to enforced constraints of the rubber phase at the micro level and better resistance performance against creep and thermal aging at the macro level. Evidently, the reported eco-friendly LCBIPC thermoplastic insulation shows great potential for applications in high-voltage cable insulation.

The effect of thermal ageing on electrical and mechanical properties of thermoplastic nanocomposite insulation of power high-voltage cables

This research explores the thermal ageing influence on the Low Density Polyethylene (LDPE) dielectric properties, which is utilised as electrical insulation in high-voltage cables. An accelerated thermal ageing test was done at four temperature ranges ranging from 25 °C to 120 °C to define the degree of material deterioration under thermal ageing and to prevent its failure. LDPE composite samples were made by adding aluminium oxide (Al2O3) inorganic filler in two different grain sizes (nano and micro) with various concentrations. The effect of adding inorganic filler on the acceleration of the thermal ageing of the polymer was studied by heating the samples for different periods of time and measuring the dielectric strength of the samples. The obtained results show that thermal ageing considerably affects the electrical properties of the material. The LDPE/Al2O3 nanofiller sample has the highest dielectric strength value at different temperatures. Thermogravimetric analysis was used to investigate the thermal characteristics of materials. The mechanical characteristics of LDPE polymer are studied using tensile strength and elongation at break tests. References 27, table 4, figures 6.

Insights into Non-uniform Aging Effects on Broadband Dielectric Behaviors for High-voltage XLPE Cable Insulation: A Novel Fractional-order Circuit Modeling Approach

Insights into Non-uniform Aging Effects on Broadband Dielectric Behaviors for High-voltage XLPE Cable Insulation: A Novel Fractional-order Circuit Modeling Approach

Improved Isothermal Relaxation Current Measurement Based on Isolated Circuit for Nondestructive Evaluation of High-Voltage Cable Insulation

Improved Isothermal Relaxation Current Measurement Based on Isolated Circuit for Nondestructive Evaluation of High-Voltage Cable Insulation

Analysis of electrical performance and assessment of aging state for retired high-voltage cable accessory insulation

The cable accessories constitute a vulnerable element and are prone to failures in the operation of power transmission lines. To investigate the changes in the electrical performance and aging state of high-voltage cable accessories with different operating time, the volume resistivity, breakdown electric field, dielectric constant, and trap parameters of insulation samples taken from retired cable accessories were characterized. The results indicate that there is a certain correlation between the macroscopic dielectric characteristics of cable accessory insulation and its aging state. With the increase of operating time, the volume resistivity and breakdown electric field decrease, while the dielectric constant initially increases and then decreases. The trap distribution of cable accessory insulation can effectively reflect its aging state. With the increase of operating time, the trap energy levels of the accessory insulation become shallower, and the trap density increases. The trap results of the accessory insulation show good consistency with the resistivity and breakdown field strength. Clustering analysis is also used to classify the test data, and the results validate that the trap energy levels and trap density of the insulation samples have better correlation with the insulation aging state of cable accessories than macroscopic dielectric parameters.

Electrical-Tree Resistant Characteristics of SEBS and Nano-SiO2 Modified Polypropylene Composites

Polypropylene (PP) composite materials with both high mechanical toughness and electrical insulation performance are prepared by incorporating styrene-ethylene/butylene-styrene (SEBS) block copolymer as a toughening agent and nanoscale silica (SiO2) as a inorganic modifier to enhance electrical-tree and breakdown resistances. The effects and mechanisms of SEBS toughening agent and SiO2 nanofiller on the thermal-mechanical properties and electrical insulation performances of PP material are investigated through the mechanical tests as well as the accelerated electrical-tree aging and alternative current (AC) breakdown experiments. The elastic modulus of SiO2/SEBS/PP composite is slightly lower than that of pure PP material, while the thermal elongation rate remains superior to cross-linked polyethylene (XLPE), which is competent in mechanical performances for main insulation materials in high-voltage cables. The addition of styrene-ethylene/butylene-styrene (SEBS) facilitates electrical-tree growth in PP matrix and thus leads to the reduction in dielectric breakdown strength of PP material. In contrast, the incorporation of nano-SiO2 can effectively improve the electrical-tree resistance and dielectric breakdown strength of PP material, making the SiO2/SEBS/PP composite a promising candidate for high-voltage cable insulation. The tests and analyses of thermal stimulated depolarization current (TSDC) reveal that the SEBS toughing additive introduces the shallow charge traps in PP matrix, making it easier for the trapped charges to transition into charge carriers, thus leading to a considerable decrease in electrical-tree resistance and insulation strength of PP material. Meanwhile, the SiO2 nanofiller can introduce deeper charge traps into PP matrix than the structural-defect intrinsic charge traps, resulting in a significant amelioration in the electrical-tree resistant and insulation performances for SEBS/PP composite. The present study demonstrates that SiO2/SEBS/PP composite possesses sufficiently high electrical-tree resistance and dielectric breakdown strength as well as suitable thermal-mechanical properties, offering a potential application in main insulation of high-voltage cables and providing an effective pathway for developing novel recyclable AC high-voltage cables.

The enhanced physical properties of XLPE insulation for high voltage cable based on LDPE/LLDPE or LDPE/HDPE blends

Exploring methods of improving the performance of high-voltage cable XLPE insulation is a hot issue in high-voltage and insulation technology. This paper presented a new method to improve the physical properties of XLPE by doping low-content polyolefin materials, such as LLDPE or HDPE. The new XLPE insulation has significantly improved high-temperature mechanical properties and slightly improved room-temperature mechanical properties. The optimal thermal elongation properties were achieved with a 1 phr content of HDPE and LLDPE, while DC conductivity, DC breakdown strength, and dielectric properties were stable or slightly improved. The properties mentioned above showed a decreasing trend at higher content. This study demonstrated that adding HDPE or LLDPE to LDPE increases the physical entanglement of XLPE molecular chains, which has a similar effect to crosslinks formed by chemical crosslinking in enhancing the mechanical properties of XLPE insulation. This suggests that there is a potential to reduce the concentration of crosslinking agents during XLPE cable manufacturing while maintaining electrical properties and improving mechanical properties at elevated temperatures. It provides a new idea for improving the properties of XLPE insulation for high-voltage DC cables.

Improved DC Dielectric Performance of Cross-Linked Polyethylene Modified by Free Radical-Initiated Grafting BMIE.

To enhance the direct current (DC) dielectric properties of cross-linked polyethylene (XLPE) for high-voltage (HV) cable insulation, the polyethylene molecular chain is modified by grafting bismaleimide ethane (BMIE), which creates carrier deep traps within the polymer material. Compared to the traditional modified molecule maleic anhydride (MAH), BMIE has a significantly higher boiling point than the production temperature of XLPE. Additionally, it does not release bubbles during the production process and, thus, preserves the dielectric properties. It was proved by infrared spectroscopy and a gel content test that BMIE was successfully grafted onto the polyethylene molecular chain and had no effect on the crosslinking degree of the polymer while reducing the amount of crosslinker, thereby reducing the influence of the by-products of the decomposition of dicumene peroxide (DCP) on the electrical resistance of polymers. The analysis of DC breakdown field strength, current density, and space charge distribution at various temperatures demonstrates that grafting BMIE can greatly enhance the dielectric properties of insulation. Polar groups in the BMIE molecule create deep trap energy levels in XLPE-g-BMIE, and these trap energy levels contribute to the formation of a charged layer near the electrode, which is shielded by Coulomb potential. As a result, the charge injection barrier increases. Additionally, the presence of these polar groups reduces the mobility of charge carriers through trap-carrier scattering, effectively suppressing the accumulation of space charge within the material. First-principle calculations also confirm that bound states can be introduced as carrier traps by grafting BMIE onto polyethylene molecules. The agreement between experimental results and simulation calculations indicates that grafting BMIE to enhance the dielectric properties of polyethylene is a new and feasible research direction in the exploitation of materials for HVDC cables.

Polypropylene nanocomposites doped with carbon nanohorns for high-voltage power cable insulation applications

Polypropylene nanocomposites doped with carbon nanohorns for high-voltage power cable insulation applications

Space Charge Characteristics and Breakdown Properties of Nanostructured SiO2/PP Composites

Polypropylene (PP) has gained attention in the industry as an environmentally friendly material. However, its electrical properties are compromised due to space charge accumulation during operation, limiting its application in high-voltage DC cable insulation. This study investigates the effect and mechanism of SiO2 with a DDS surface hydrophobic treatment on space charge suppression and the electrical properties of PP composites. The PP matrix was doped with SiO2 nanostructures, both with a DDS surface hydrophobic treatment and untreated as a control group. The functional group structure and dispersion of nanostructured SiO2 in the matrix were characterized. The findings reveal that the incorporation of SiO2 nanostructures effectively mitigates charge accumulation in PP composites. However, a high concentration of unsurfaced nanostructures tends to agglomerate, resulting in inadequate space charge suppression and a diminished DC breakdown field strength. Nonetheless, surface treatment improves the dispersion of SiO2 within the matrix. Notably, the composite containing 1.0 wt% of surface hydrophobic SiO2 exhibits the least space charge accumulation. Compared to the base material PP, the average charge density is reduced by 83.9% after the 1800 s short-circuit discharges. Moreover, its DC breakdown field strength reaches 3.45 × 108 V/m, surpassing pure PP by 19.4% and untreated SiO2/PP composites of the same proportion by 24.0%.

Coupling Effect of LDPE Molecular Chain Structure and Additives on the Rheological Behaviors of Cable Insulating Materials.

The rheological behaviors of low-density polyethylene doped with additives (PEDA) determine the dynamic extrusion molding and structure of high-voltage cable insulation. However, the coupling effect of additives and molecular chain structure of LDPE on the rheological behaviors of PEDA is still unclear. Here, for the first time, the rheological behaviors of PEDA under uncross-linked conditions are revealed by experiment and simulation analysis, as well as rheology models. The rheology experiment and molecular simulation results indicate that additives can reduce the shear viscosity of PEDA, but the effect degree of different additives on rheological behaviors is determined by both chemical composition and topological structure. Combined with experiment analysis and the Doi-Edwards model, it demonstrates that the zero-shear viscosity is only determined by LDPE molecular chain structure. Nevertheless, different molecular chain structures of LDPE have different coupling effects with additives on the shear viscosity and non-Newtonian feature. Given this, the rheological behaviors of PEDA are predominant by the molecular chain structure of LDPE and are also affected by additives. This work can provide an important theoretical basis for the optimization and regulation of rheological behaviors of PEDA materials used for high-voltage cable insulation.

High Voltage Cable Fault Location Technology Based on Traveling Wave

High voltage cable line is an important part of power grid; its stable operation is of great significance to urban power system. This paper proposed a high voltage cable insulation monitoring system using traveling wave. The travelling wave data are collected by high precision satellite timing signal and an on-line fault location system for high voltage cable is designed.

The Lifetime Prediction and Insulation Failure Mechanism of XLPE for High-Voltage Cable

The performance parameters and service life of the insulation layer of high-voltage cables are the key to ensure safe cable operation. Through extracting the mechanical parameters of high voltage cable insulation layer under different thermal aging temperatures, a normal linear regression model is established to predict the service life of high voltage cables. Meanwhile, the physicochemical characteristics such as microscopic morphology and molecular structure changes of the cable insulation layer are analyzed, the dielectric properties and breakdown field strength under ac condition are tested and the macroscopic electrical properties of the insulation layer are studied, and the insulation failure mechanism is further analyzed. The experimental results show that the elongation at break retention rate of cross-linked polyethylene (XLPE) increases slowly with the aging time, and then decreases rapidly when it reaches 50% of the initial elongation at break retention rate. The normal linear regression prediction model is established based on the Arrhenius formula, and it can be obtained the life endpoint of XLPE high voltage cable about 65 years at an operating temperature of 70 °C. Further analysis, under the action of heat and oxygen, the crystal zone structure of cable insulation is seriously damaged, and the carbonyl index is significantly increased. Accordingly, when the aging failure point is reached, the dielectric permittivity and dielectric loss of insulation are significantly increased, and the breakdown performance is significantly decreased. The work has an important guiding significance for insulation condition assessment and life prediction of high voltage cable.

Precision and Accuracy of Pulse Propagation Velocity Measurement in Power Cables

The partial discharge (PD) measurement is an important method used in determining the condition of medium- and high-voltage cable insulation. Considering the propagation velocity of PD signals in power cables is necessary for determining the location of PD defects. However, the determination of velocity is not straightforward due to propagation-related attenuation and dispersion, which distorts the PD pulse waveform. This introduces a degree of uncertainty into the pulse velocity as well as the PD source locations determined based on that velocity, which is usually considered to be of constant value in PD analysis. This paper investigates the accuracy of the pulse propagation velocity measurement in power cables. Tests were performed on a medium voltage power cable in a laboratory setting using two sets of PD-specific measurement equipment: a high-frequency current transformer (HFCT) and an IEC 60270-compliant conventional measurement system. The propagation velocities and their statistical variability were determined using both devices to assess the uncertainty of the propagation velocity measurement. The results indicate that the measured velocity is slightly higher in the case of the HFCT and that the 50% peak threshold value should be used rather than the peak value of PD sensor response waveforms to increase the precision of velocity measurements.

Influence of Thermal Aging on Dielectric Properties of High Voltage Cable Insulation Layer

Thermal aging is one of the main reasons for the degradation of insulation properties of high voltage cable. Dielectric properties and breakdown strength are important parameters to reflect the insulation performance of the cable insulation materials. In the work, the influence of thermal aging on dielectric and breakdown performance of the cable insulation layer was studied. Firstly, XLPE cable insulation samples were prepared and the thermal aging treatment was carried out. Secondly, the microstructure and molecular structure of XLPE samples under different thermal aging time were analyzed. The dielectric properties and breakdown characteristics of XLPE samples under different thermal aging times were characterized in macro aspect. Finally, the effects of different temperatures on the molecular microstructure of XLPE were studied. The results show that with the extension of thermal aging time, the microstructure of XLPE molecule is destroyed, the macromolecular chain is gradually cleaved, and the carbonyl absorption intensity increases. At power frequency, the breakdown strength decreases from 75.37 kV/mm to 62.18 kV/mm, the relative permittivity increases from 2.44 to 2.51, and the dielectric loss increases from 1.47 × 10−4 to 3.10 × 10−3. The free volume rate of XLPE molecules increases with the increasing temperature, and the mean square displacement gradually increases. The work has good guiding significance for the safe operation and condition assessment of high-voltage cables.

Effect of thermo-oxidative aging on thermal elongation performance of XLPE insulation for high-voltage cables

The thermal elongation of cross-linked polyethylene (XLPE) insulation for high-voltage cables is an important factor for evaluating the high-temperature mechanical performance, which is an important parameter included in the testing standards of the power cable insulation. Previous studies have found that the thermal elongation of XLPE insulation for high-voltage cable depends on the cross-linking degree, but have not dealt with the effect of the thermo-oxidative aging during the thermal elongation test. In this paper, the thermal elongation experiments of the XLPE samples compounded with different kinds of antioxidants were carried out under both air and nitrogen atmospheres. The molecular structure changes of the XLPE samples after thermal elongation under air atmosphere were examined by gel content, FTIR spectra and X-ray diffraction. The oxidation induction periods were also measured to analyze the antioxidation performance of the phenolic antioxidants and study its contribution to the thermal elongation performance. The results showed that the XLPE samples underwent thermo-oxidative aging in the thermal elongation test under air atmosphere at 200 °C. It caused that the thermal elongation properties can not accurately reflect the cross-linking degree of the original XLPE samples, but has a strong correlation with the gel content of the aged samples. Antioxidants can inhibit the thermo-oxidative aging effect on the network structure, leading to a slower uptrend of elongation under the air atmosphere. This indicates that the thermal elongation performance of XLPE insulation is determined by the synergistic effect of the network structure and the antioxidation performance, and this can provide reference significance for optimizing the evaluation methods of high-voltage cable XLPE insulation performance.

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.

Impact of heterogeneous cavities on the electrical constraints in the insulation of high-voltage cables

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