Power Cable Insulation Research Articles

Ultra-High Frequency Sensors for Detecting Partial Discharge in Power Cables

Partial discharge (PD) detection is vital for evaluating the health of power cable insulation, where failure can lead to significant disruptions. This study investigates the use of Ultra-High Frequency (UHF) sensors to detect PD signals, which typically occur in nanoseconds. The sensors operate in the GHz range and minimize interference by selecting frequencies above 400 MHz, where background noise is reduced. Through comparison with other detection methods, UHF sensors demonstrate superior sensitivity in measuring minor discharges, providing a reliable means for on-site condition assessment of high-voltage equipment. The study concludes that UHF sensors offer a practical solution for improving PD detection accuracy, particularly in challenging field conditions.

ЕЛЕКТРИЧНЕ ПОЛЕ НАПІВПРОВІДНОГО ЕКРАНА СИЛОВОГО КАБЕЛЮ З ПОЛІМЕРНОЮ ІЗОЛЯЦІЄЮ З УРАХУВАННЯМ СТРУКТУРНИХ НЕОДНОРІДНОСТЕЙ

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 macro-level 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 cross-linked polyethylene insulation. References 23, figures 8, table 1.

Structure, mechanical, and dielectric properties of polypropylene blended with ethylene and propylene‐based elastomers

AbstractPolypropylene (PP) has been widely researched in power cable insulation due to its excellent resistance against high temperatures and high voltages. Since PP is too stiff for power cable extrusion, elastomers have been blended with PP to improve its stiffness. Although effects of elastomers on electro‐mechanical properties of PP have been widely studied, fundamental issues governing changes in dielectric properties of PP/elastomer blends have yet to be fully understood. This paper therefore reports on the properties of PP blended with ethylene‐based elastomer (EBE) and propylene‐based elastomer (PBE) by correlating their structural, mechanical, and dielectric investigations with respect to elastomer types and contents. The results show that blending increasing amounts of EBE and PBE improves mechanical flexibility of PP, with Young's modulus reduces by 53% at 40 wt% of elastomer content. Morphology‐wise, PBE demonstrates better compatibility with PP and less disrupted crystallinity compared to EBE. Furthermore, PP/PBE has better breakdown performance over PP/EBE, albeit that their breakdown strengths reduce with increasing elastomer contents. Specifically, direct current breakdown strength of PP/PBE reduces by only 21% at 40 wt% of PBE loading compared to 31% at equivalent EBE loading. Potential mechanisms governing breakdown changes are discussed with structural, mechanical, and dielectric interpretations.

Diagnostics of power cable insulation by using the methods of dielectric spectroscopy: overview of physical basis and features of practical application

The article provides an overview of the physical foundations and features of the application of diagnostic methods for the insulation of power cables using dielectric spectroscopy methods in the frequency and time domains. The relationship between the depolarization currents and the frequency spectrum of the complex dielectric constant is shown. An analysis of the factors determining the frequency dependence of the tangent angle of dielectric losses of paper and polyethylene insulation of power cables is given. The main types of reaction of dielectric materials with different levels of development of water channels at the level and frequency of the applied voltage are listed. According to the results of the analysis, it is shown that for high-voltage measurements, one of the factors that complicates the diagnosis of the insulation of power cables by analyzing the frequency dependences of the capacitance and the tangent of the dielectric loss angle is the distortion of the sinusoidal current through the dielectric due to the nonlinear dependence of the complex dielectric constant on the level of the applied voltage. A comparative analysis of dielectric spectroscopy methods in the frequency domain, involving high-voltage and low-voltage measurements of the complex dielectric constant, was carried out. The correlation between the tangent of the dielectric loss angle of paper insulation and its mechanical characteristics is shown

Novel dual‐resonance damped alternating current testing system for offline partial discharge measurement of power cables

AbstractTo accurately detect the early deterioration of electrical insulation in power cables, an energizing system is required for offline partial discharge (PD) measurements. The damped alternating current (DAC) testing system has emerged as an effective tool for inducing PD events. However, the existing systems often suffer from limitations such as signal interference, low sensitivity, and high costs. To address these issues, this study proposes a novel dual‐resonance DAC testing system that is simple in structure and cost‐effective. The prototype was built for testing 10‐kV distribution cables, and its effectiveness was validated through experimental tests on a cable sample. The results show that this approach significantly improves PD detection sensitivity and successfully completes PD localization. This research contributes to the development of more efficient and affordable DAC generation technology for power cable testing applications.

Dielectric properties of polypropylene blended with copolymers of varying ethylene contents

AbstractPolypropylene (PP) has recently been actively investigated as a potential power cable insulation substitute for crosslinked polyethylene (XLPE). This is mainly due to PP's higher thermal withstand capability over XLPE. Notably, PP has much higher stiffness than XLPE and therefore needs to be modified with tougher materials to reduce its overall stiffness while maintaining its desirable dielectric properties. To date, many investigations have been conducted on the mechanical and dielectric effects of PP blended with various copolymers. Nevertheless, systematic investigations on the dielectric effects of PP blended with ethylene‐based copolymers having different ethylene contents are less explored. The current work therefore reports on the impact of different ethylene contents of ethylene‐based copolymers on the breakdown performances of PP. The findings reveal that PP blended with a copolymer having a low ethylene content (68.7 wt%) results in at least 11% higher breakdown performance than PP containing a copolymer having a high ethylene content (77.0 wt%). Specifically, PP containing 10 wt% of copolymers having 68.7 wt% of ethylene content results in comparable breakdown performance to XLPE (325 kV mm−1). These results suggest that ethylene‐based copolymers with an appropriately low ethylene content can be blended with PP to achieve desirable breakdown properties.Highlights PP is blended with copolymers of varying amounts and ethylene contents. PP blended with low amounts of copolymers has good breakdown strength. PP blended with low ethylene level copolymers has favorable breakdown strength. PP blended with copolymers of low ethylene contents is desirable. The breakdown mechanisms are related with the structure and permittivity.

İSTİSMARDAKI KABELLӘRDӘ ZӘDӘLӘRİN ARADAN QALDIRILMASININ MÜASİR ÜSULLARI

XLPE insulated power cables serve as essential components in medium and high voltage power transmission lines, yet maximizing their resource duration poses a significant challenge for consumers. Issues such as water treeings, electric treeings, and partial discharges within the insulation system accelerate cable aging over time. In response, a novel approach has been proposed in this study to mitigate these detrimental factors. The method involves injecting a specially formulated liquid into the cable insulation to address inhomogeneities, effectively rejuvenating the cable and extending its service life by 20-30 years, as indicated by the technology's name. Furthermore, to provide context on the practical implications, a succinct analysis of the Azerbaijani cable network is presented in this article. Also, in order to explain the real situation of power cables, a brief analysis of the Azerbaijani cable network was conducted in the article.

КОМП'ЮТЕРНЕ МОДЕЛЮВАННЯ ЕЛЕКТРИЧНИХ ПРОЦЕСІВ ПІД ЧАС ВИНИКНЕННЯ ЧАСТКОВИХ РОЗРЯДІВ У СУЧАСНІЙ ПОЛІМЕРНІЙ ІЗОЛЯЦІЇ СИЛОВИХ КАБЕЛІВ

A Simulink model of modern polymer insulation of power cables with a spherical gas micro-inclusion, in which high-frequency partial discharges (PDs) occur, has been developed. The magnitude of the voltage both at the beginning of the PD appearance and during its decay was taken into account during numerical calculations and research of such threshold electro-physical processes as PD in solid polymer insulation. The dependence of the voltage drop on the gas micro-inclusion on its size, as well as the time interval between discharges, which is necessary for the formation of free electrons in this gas micro-inclusion, as a necessary condition for the appearance of the next PD, was also taken into account. Based on the results of the calculations, the electro-physical dependences that occur during the PD, such as the influence of the size of the inclusion, the amplitude and frequency of the applied sinusoidal voltage on the above-mentioned characteristics were investigated. It has been revealed that with an increase in the diameter d of a gas mi-croinclusion, such characteristics as the number of discharges per period and the charge of one PD also increase, and this charge increases in proportion to a power function . When the voltage on the cable insulation increases, the number of PDs per period increases, which causes an increase in other characteristics, and when the frequency of the applied voltage increases, the average value of the PDs current increases almost proportionally to the increase in this frequency. Having obtained the results of the calculation of the level of PDs that occur when high-frequency voltage is applied, it is possible to obtain results for the main characteristics of PDs that occur at other frequencies, in particular at the industrial frequency of 50 Hz, which will make it possible to predict the technical condition of the insulation in terms of the residual resource of its trouble-free operation. References 18, figures 6, table 1.

Electric Field Assist on Enhancing the Electrical Breakdown Strength of Cross-Linked Polyethylene for Power Cable Insulation

Electric Field Assist on Enhancing the Electrical Breakdown Strength of Cross-Linked Polyethylene for Power Cable Insulation

Effects of nanomagnesia and polypropylene-graft-maleic anhydride on the dielectric breakdown properties of polypropylene/ethylene propylene diene monomer blend

Thermoplastic polypropylene (PP) has garnered a significant attention in power cable insulation research because of its exceptional thermal tolerance and dielectric properties. Due to its poor impact strength at room temperature, PP has been blended with various elastomers, including ethylene-propylene-diene monomer (EPDM), to improve the mechanical stiffness of the final material. This, however, comes with compromised dielectric properties of the material. Recently, the addition of nanofillers to polymers has demonstrated promising properties that can be tailored for various dielectric applications, provided that nanofiller and polymer interactions are appropriately formulated. Nevertheless, the effect of nanostructuration in PP/elastomer blends, especially from the perspective of dielectrics, have yet to be systematically explored. In the current work, magnesia (MgO) nanofiller is added to a model PP/EPDM blend system to determine the effect of MgO on the breakdown properties of PP/EPDM. The results show that adding 0.5 wt% of MgO to PP/EPDM reduces the AC and DC breakdown strengths by 7% and 16%, respectively. As the amount of MgO increases to 3 wt%, the AC and DC breakdown strength reduces further by 25% and 29%, respectively. Significantly, appropriate modification of the nanocomposites with polypropylene-graft-maleic anhydride (PP-g-MAH) can result in 5% higher breakdown strength of the nanocomposites with respect to comparable nanocomposites without modification. The mechanisms surrounding these breakdown effects are discussed with the aid of materials structure interpretations. Overall, the results demonstrate that appropriate modification of nanocomposites with PP-g-MAH is crucial in tailoring breakdown properties of PP blend nanocomposites.

Effect of Ethylene-Propylene-Diene Monomer Blending on the Dielectric Properties of Polypropylene for Power Cable Insulation

Thermoplastic materials such as polypropylene (PP) are ideal candidates to be used as power cable insulation materials. However, the mechanical properties of PP, which is brittle and stiff, need to be modified to meet the requirements of power cable insulation applications. To overcome this, ethylene-propylene-diene monomer (EPDM) can be melt blended with PP to improve PP’s mechanical properties. In the current work, the effect of blending different contents of EPDM with PP was investigated in terms of the morphology, chemical structure, dielectric response, electrical, and mechanical properties. The results show that the EPDM blended well with the PP as the EPDM dispersed in the PP structure. Meanwhile, the chemical structure and dielectric response of the EPDM and PP blend became slightly different with high contents of EPDM, which subsequently affected the breakdown strength and mechanical properties. Nevertheless, it is worth noting that PP blended with low contents of EPDM has the potential to be used as recyclable power cable insulation materials.

Alternative Concepts for Extruded Power Cable Insulation: from Thermosets to Thermoplastics.

The most common type of insulation of extruded high-voltage power cables is composed of low-density polyethylene (LDPE), which must be crosslinked to adjust its thermomechanical properties. A major drawback is the need for hazardous curing agents and the release of harmful curing byproducts during cable production, while the thermoset nature complicates reprocessing of the insulation material. This perspective explores recent progress in the development of alternative concepts that allow to avoid byproducts through either click chemistry type curing of polyethylene-based copolymers or the use of polyolefin blends or copolymers, which entirely removes the need for crosslinking. Moreover, polypropylene-based thermoplastic formulations enable the design of insulation materials that can withstand higher cable operating temperatures and facilitate reprocessing by remelting once the cable reaches the end of its lifetime. Finally, polyethylene-based covalent and non-covalent adaptable networks are explored, which may allow to combine the advantages of thermoset and thermoplastic insulation materials in terms of thermomechanical properties and reprocessability.

НАУКОВА КОНЦЕПЦІЯ CТВОРЕННЯ ВИСОКОВОЛЬТНИХ МОБІЛЬНИХ ЕЛЕКТРОТЕХНІЧНИХ СИСТЕМ РЕЗОНАНСНОГО ТИПУ ЗІ ШВИДКОДІЮЧИМИ КЕРУВАННЯМ І ПАРАМЕТРИЧНОЮ СТАБІЛІЗАЦІЄЮ РЕЖИМІВ НАВАНТАЖЕННЯ

A new scientific concept has been developed for the creation of high-voltage electro-technical systems (ETS) of a reso-nant type based on the implementation in them of series high-quality inductive-capacitive circuits (ICC) and high-frequency (HF) resonant currents. This makes it possible to repeatedly increase the alternating voltage on the reactive elements of the ICC and on the load connected in parallel to one of the elements, and to ensure a significant decrease in the impulse energy of the ETS without changing their average power, as well as to increase the speed of control and parametric stabilization of the load modes of the ETS even with a rapid decrease in the electrical resistance of this load to almost zero, as in the case of electrical breakdown of its insulation. The generation of resonant currents with a fre-quency of up to 40 kHz in the ICC, which has a coil with an inductance of ~ 25 mH and a Q factor up to 270 (made of multi-core twisted copper wires of the " litzendraht " type) and a ceramic capacitor with a capacity of ~ 3.5 nF and a Q factor > 1000, ensures the realization of the QICC up to 260 and the corresponding increase in the ratio of the ETS out-put voltage to the input voltage without the use of step-up transformers. When connecting such an ETS to a source of alternating voltage of 220 V, a voltage of up to 40 kV can be generated at the output of the ETS. A significant increase in the frequency of currents leads to a significant decrease in the mass-dimensional characteristics of ETS and the pos-sibility of creating their samples mobile (weighing up to 5 kg), and if necessary, autonomous, in particular with power supply from batteries. The new scientific concept is aimed at creating a resonance-type ETS for safe and reliable moni-toring and diagnostics of the technical condition of high-voltage insulation of power cables, powerful electric machines and other energy objects of the critical infrastructure of Ukraine. Such ETS can also be effectively used for charging to high voltages capacitive energy storage (CES) in technological installations for the production of electro-spark micro- and nano-powders with unique properties, as well as for high-voltage electro-hydro-pulse processing of various mate-rials and environments. It has been established that the power of these ETS increases with a decrease in the ratio of the capacitances of the capacitors ICC and CES. References 40, figures 4.

Enhanced Dielectric Breakdown Property of Polypropylene Based on Mesoscopic Structure Modulation by Crystal Phase Transformation for High Voltage Power Cable Insulation

Enhanced Dielectric Breakdown Property of Polypropylene Based on Mesoscopic Structure Modulation by Crystal Phase Transformation for High Voltage Power Cable Insulation

Simultaneous Promotion of the Mechanical Flexibility and Dielectric Strength of Impact Polypropylene Copolymers Containing Multifold H-Shape Long-Chain-Branching Structures for Recyclable Power Cable Insulation Application

Simultaneous Promotion of the Mechanical Flexibility and Dielectric Strength of Impact Polypropylene Copolymers Containing Multifold H-Shape Long-Chain-Branching Structures for Recyclable Power Cable Insulation Application

Influence of assisted electric field on the microstructure evolution and direct current electrical properties of low-density polyethylene

Low-density polyethylene (LDPE) is the basic material of the high-voltage direct current (DC) power cable insulation. The assisted electric field is a common way to regulate the microstructure of polymers, but its application in the field of electrical insulating polymers is rarely reported. In order to study the influence of the assisted electric field on the microstructure evolution and DC electrical properties of LDPE, the LDPEs without and with being treated with assisted electric field are prepared in the melting stage, cooling stage, and the whole stage (i.e. the melting stage and cooling stage), respectively. The influence of the assisted electric field applied in the different stages on the microstructure evolution of LDPE is characterized by the scanning electron microscopy (SEM) and differential scanning calorimetry (DSC). The DC electrical properties of the untreated LDPE and the treated LDPE are investigated via measuring their breakdown strengths, conductivities, space charges and surface potential decays. The results show that, compared with the untreated LDPE, the LDPE treated with the assisted electric field in the whole stage has the smallest spherulite size and the largest spherulite number, followed by the LDPE treated in the cooling stage and the melting stage. The assisted electric field applied in different stages can significantly improve the DC electrical properties of LDPE. Compared with the untreated LDPE, the LDPE treated in the melting stage, the cooling stage and the whole stage increases the breakdown strength but greatly reduces the conductivity and space charge accumulation. The DC electrical properties of LDPE treated with the assisted electric field in the whole-stage are the best. Compared with untreated LDPE, the LDOE treated in whole stage increases the breakdown field strength by 35.8%, reduces the conductivity by 72.0%, and the space charge accumulation by 20.2%. More and smaller spherulites lead to the formation of more interface paths and introduce more deep-traps, which contributes to improving the DC electrical characteristics of the electric field assisted LDPE. This work provides a new idea for improving the DC electrical properties of polymers.

An improved Power Cable Insulation Monitoring Method for Inverter-fed Machines Using Switching Oscillation Damping Feature

An improved Power Cable Insulation Monitoring Method for Inverter-fed Machines Using Switching Oscillation Damping Feature

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

Reduction of High-Voltage Cable Line Capacity Caused by Implementation of Magnetic Field Shielding Techniques

The paper deals with a capacity of high-voltage cable line made of three single-core cross-linked polyethylene insulated power cables. We consider three cases. First is a single-point bonded cable system when no magnetic field shielding technique is implemented and the capacity achieves maximum values. Second is a solidly bonded cable system when a thermal effect of induced shield currents causes a capacity reduction. The third case under study is a single-point bonded cable system covered by the passive loop. The passive loop mitigates the cable line magnetic field as well as the solidly bonding does, but also the thermal effect of passive loop currents reduces the capacity. The goal of the paper is to evaluate the relative change of cable line capacity when implementing magnetic field shielding techniques comparably to unshielded case. To achieve the goal we use a standard IEC 60287 when calculating the cable line capacity in the first and the second cases, and a thermal field simulation in the third case. The capacity is evaluated by successive approximations. Iterations are stopped when the conductor reaches the maximum operating temperature. We show that the increase in cable spacing does not guarantee the capacity increase when the solid bonding of cable shields or the passive loop is used. The most significant result is the substantiation of the advantages of passive loop, which provides the greater capacity in comparison with solid bonding at equivalent magnetic field shielding efficiencies. The obtained results can be used when choosing the type of bonding and the technique of cable line magnetic field mitigation.

Decision support system for power cable insulation vulcanization production line management

The paper proposes a structural model of a decision support system for controlling a cable insulation continuous vulcanization line. The proposed decision support system is based on a mathematical model of the cable insulation continuous vulcanization technological process, a database, and a mode correction algorithm. The DSS will make it possible to quickly develop a new regime in case of using new materials or structures, as well as to correct the current regime in case of unplanned changes during the production process. The core of the DSS is the proposed mathematical model, which is based on conservation laws and is presented as a system of differential equations closed by boundary conditions. The vulcanization process is described taking into account the temperature-time dependence of the kinetic parameters, which made it possible to take into account the uneven heating of the cable, both in the radial direction and along the length. The numerical implementation of the differential mathematical model made it possible to carry out a systematic analysis of the nature of the processes in the vulcanization pipe and to evaluate the influence of various technological, structural and material parameters on the cable insulation vulcanization completion degree. As a result of the analysis, significant parameters were identified that significantly affect the vulcanization process completion degree. Based on the obtained numerical results, technological parameters dependence technological surfaces on the geometry of the product and the properties of the materials used were constructed, a regression mathematical model was proposed that allows determining the values of the process control parameters without resorting to the use of a differential mathematical model. Based on the results of the analysis, an algorithm for correcting the technological regime is proposed, taking into account only significant process parameters. The proposed algorithm allows you to adjust the value of the isolation rate, depending on external influences and deviations from the specified parameters. The results of the study can be used in the production of cable and wire products with vulcanizable insulation, when it is necessary to quickly select the optimal technological mode, take into account changes in the cable design, properties of the insulation material, as well as possible pressure deviations inside the vulcanization pipe.