High Voltage Electrical Insulation Research Articles

Assessment of the Arc Resistance of 3D-Printed Insulation Materials for Outdoor High-Voltage Applications

High-voltage electrical equipment insulation often uses composite materials like epoxy resin, cross-linked polyethylene, polyurethane, and silicone rubber as encapsulation. 3D printing technology offers a more efficient and cost-effective solution, producing intricate elements without cutting and casting. Research shows that 3D printed materials have comparable properties to polymer-based insulation, but further testing is needed to evaluate their resistance to harsh environmental conditions. This research investigates the arc resistance properties of 3D printed insulation materials for outdoor high-voltage applications, assessing their suitability for outdoor applications. The wet and dry arc resistance tests were performed in accordance with ASTM D495-99 and IEC-60587. The present work investigated three varieties of samples: polylactic acid, epoxy resin, and silicone rubber. The results of the tests reveal that polylactic acid test samples have average wet and dry arc resistance times of 2.5 hours and 1.4 seconds, which is less than silicone rubber and epoxy resin. Additional research is required to comprehend the behavior of arc formation in polylactic acid insulation materials for high-voltage 3D printing applications.

Partial Discharge-Originated Deterioration of Insulating Material Investigated by Surface-Resistance and Potential Mapping

The endurance of medium- and high-voltage electrical insulation is a key reliability element in a broad spectrum of applications that cover transmission and distribution levels, the transportation segment, the industrial environment, and power electronics-based energy-conversion systems. The high electric-field stress and high-frequency switching phenomena as well as the impact of environmental conditions lead to the occurrence of partial discharges (PD) and the subsequent deterioration of electrical insulation. Partial discharges usually occur inside solid insulation materials in tiny voids that may either be located adjacent to the electrodes or in the bulk of dielectric material. This effect refers to both AC and DC systems; however, AC voltage is usually much more intensive as compared to DC voltage. This paper describes a novel combined approach based on surface-resistance and potential mapping to reveal the effects of internal processes and the deterioration of insulating material due to the actions of partial discharges. To realize the research objective, the following two-step approach was proposed. Multi-point resistance mapping enables us to identify the spots of discharge channels, manifesting a-few-orders-of-magnitude-lower surface resistance as compared to untreated areas. In addition, surface-potential mapping that was stimulated by corona-charge deposition reflects quasi-equipotential clusters and the related polarity-dependent dynamics of charge decay. A high spatial and temporal resolution allows for the precise mapping and tracing of decay patterns. Experiments were carried out on polyethylene (PE) and Nomex specimens that contained embedded voids. During PD events, the effective discharge areas are identified along with the memory effects that originate from the accumulation of surface charges. Long-term aging processes may drive the formation of channels that are initiated from the deteriorated micro clusters, in turn, penetrating the bulk isolation. The presented methodology and experimental results extend the insight into PD mechanisms and internal surface processes.

The design and test of the electrical insulation break for the EAST Divertor primary heat transfer system

Experimental Advanced Superconducting Tokamak (EAST) is one of the important steady-state divertor Tokamak physical experiment platforms in the world. The main functions of the high-temperature and high-pressure Divertor Primary Heat Transfer System (DIV PHTS) are to provide high-pressure cooling water for the divertor to remove the heat load deposited on the divertor under the plasma operation mode and to provide high-temperature nitrogen gas for the divertor system to achieve vacuum condition during the baking mode. The stability and reliable operation of the DIV PHTS play an important role in the EAST tokamak plasma physics experiment. The high-temperature and high-voltage electrical insulation break are one of the important components of the system. The main function of the Electrical Insulation Break (EIB) is to break the closed circuit of the heat transfer system to avoid eddy current during plasma discharge affecting the magnetic field distribution characteristics of the tokamak. On the other way, it also needs to meet the requirement, there is no leak of the cooling water and nitrogen gas during cooling and baking operation mode. This paper proposes the design of an electrical insulating break (EIB) to meet the design requirements of EAST tokamak at first. Then the electric field analysis is carried out by using a finite element model to evaluate its electrical insulation characteristics. And the sealing structural characteristics are verified by applying the finite element method under two design modes. Finally, the sealing test result under the high-temperature baking and high-pressure cooling modes are presented to validate the design.

Characteristics of 3D Printed Biopolymers for Applications in High-Voltage Electrical Insulation.

Three-dimensional printing technology is constantly developing and has a wide range of applications; one application is electrical insulation, where the standard technology uses polymer-based filaments. Thermosetting materials (epoxy resins, liquid silicone rubbers) are broadly used as electrical insulation in high-voltage products. In power transformers, however, the main solid insulation is based on cellulosic materials (pressboard, crepe paper, wood laminates). There are a vast variety of transformer insulation components that are produced using the wet pulp molding process. This is a labor-intensive, multi-stage process that requires long drying times. In this paper, a new material, microcellulose-doped polymer, and manufacturing concept for transformer insulation components are described. Our research focuses on bio-based polymeric materials with 3D printability functionalities. A number of material formulations were tested and benchmark products were printed. Extensive electrical measurements were performed to compare transformer components manufactured using the traditional process and 3D printed samples. The results are promising but indicate that further research is still required to improve printing quality.

High Performance Epoxy Composites Containing Nanofiller Modified by Plasma Bubbles.

The thermal conductivity of polymer materials is a fundamental parameter in the field of high-voltage electrical insulation. When the operating frequency and power for electrical equipment or electronic devices increase significantly, the internal heat will increase dramatically, and the accumulation of heat will further lead to insulation failure and serious damage of the whole system. The addition of filler with high thermal conductivity into polymer is a common solution. However, the interfacial thermal resistance between filler and bulk materials is the major obstacle to improve thermal conductivity. Herein, in order to reduce the interfacial thermal resistance, nanofillers are modified by plasma technology. The surface modification of nano-Al2O3 is carried out using plasma bubbles with three atmospheres (Ar, Ar+O2, air) as well as coupling agent. The situation of surface grafting before and after the modification is characterized using FTIR, XPS, and SEM. The effect of the mechanism of modification on the thermal conductivity and reaction pathway is investigated. The results showed that the thermal conductivity after plasma modification is increased significantly. Especially, the thermal conductivity is increased by 35% for the sample modified by Ar+O2 atmosphere. This results because more hydroxyl is introduced on the filler surface by the plasma bubbles, which enhance the interface compatibility between filler and epoxy. In addition, surface insulation performance for the modified samples also is enhanced by 14%. This is associated with the change of surface resistance and trap distribution. These results provide potential support for the development of fabrication for high performance epoxy composites.

Effects of nanosecond impulse and step excitation in pulsed electro acoustic measurements on signals for space charge determination in high-voltage electrical insulation

The presence of space charges in high-voltage insulation can influence the operational stresses of the dielectric materials; the topic is present in various, even distant domains such as power grids or transportation segments that are represented by electromobility, rail, more-electric aircraft, and space systems. In this article, the effects of nanosecond impulse and step excitation in the pulsed electro-acoustic measurements (PEA) of space charges in high-voltage electrical insulation have been investigated. Various parameters of a pulser (such as impulse width, rise time, and sensor thickness) have been investigated by using a designed programable pulser. The investigations have been performed on a polyethylene sample in one- or double-layer configurations. In the latter, an interlayer sprinkled charge was analyzed. The experimental results have shown the main PEA effect during the transition phase of the applied voltage. It was observed that the pulse transition has a critical importance for stimulating space-charge vibrations and generating elastic waves. Hence, the slope’s rise and fall times are crucial in pulser design. The pulser width also has an impact on a signal’s magnitude as well as on its dispersion and attenuation. The correspondence between a pulse and step excitation was presented. Some advantages are attributed to the step-based excitation in terms of fewer wave reflections and interferences as well as the avoidance of the wavelet cancelation effect for a very narrow pulse width. Hence, step excitation can result in the easier postprocessing and interpretation of individual peaks in the acquired PEA signal. Another advantage may be recognizing the space-charge polarity instead of the net result. Important recommendations refer to the tuning of pulser timing settings with respect to signal attenuation (especially in thicker specimens) and the adequate adjustment of the sensor’s thickness. The presented analysis and experimental results extend the insight into PEA measurement – especially with a focus on diagnostic applications.

Investigation of dielectric and mechanical properties of Lignocellulosic Rice Husk Fibril for high and medium voltage electrical insulation applications

The insulating material is made from rice husk and epoxy resin which are ecologically friendly and incredibly durable. When coarse Rice husk is mechanically disintegrated, fibrils are formed. By weaving together fibrillated threads, and robust biodegradables, lightweight dielectric fibers are created. Then the Composites are examined utilizing a blend of agave Rice husk fibers (10–35%) and an epoxy resin solution. The Chemical treatment of the Rice husk fibers increases the composites’ mechanical strength and electrical insulating properties. The tensile strength of Rice husk in epoxy composites is increased from 37.84 MPa to 48.32 MPa. The experimental results are compared using well-known prediction models such as the rule of mixture (ROM), Halpin–Tsai, and Nielson–Chen using regression analysis with other insulting materials used in state of the art. The Nielson-Chan model predicts experimental data effectively with an average relative error of 14.64%. The proposed composite material has excellent insulating properties because of its conductivity and high dissipation factor. The composite material exhibits high stability when the frequency is in the range of 1–10 kHz than at lower frequencies.

Aging of Polymeric Insulators under Various Conditions and Environments: Another Look

Polymeric insulators have lightweight, excellent hydrophobicity and convenient transportation and installation. They are widely used in the external insulation for distribution and transmission lines. However, due to the long-term effects of pollution, ultraviolet radiation, discharge, temperature, humidity, altitude and other natural and complex environmental and service factors, the silicone rubber and other materials of polymeric insulators gradually age and lose their hydrophobicity and electrical insulation characteristics. The operability is significantly reduced, which seriously affects the safety and reliability of the power system. Hence, there is a need for assessing and evaluating the long-term aging and degradation of polymeric insulators under various operating conditions and environments. In this review, the various aging and characterization techniques of the polymeric insulators and their aging performance under the action of multiple factors are discussed. To enhance the performance of polymeric insulators, nano-coating, surface treatment and other techniques are also indicated. In addition, future potential fields that should be explored from a high-voltage electrical insulation perspective are also presented.

Book Reviews [6 Books Reviewed

The following six books are reviewed: High Voltage Electrical Insulation Engineering, 2nd Edition (R. Arora and W. Mosch; 2022); Batteries—Materials Principles and Characterization Methods (C. Liao; 2021); Practical Terahertz Electronics: Devices and Applications—Volume One (V. K. Khanna; 2021); Simulation of Complex Systems (A. Argun, et al; 2021); Elegant Circuits—Simple Chaotic Oscillators (J. C. Sprott and W. J. Thio; 2022); and Power System Protection, 2nd Edition (P. M. Anderson, et al; 2022).

Factory Acceptance Test and Delivery of the First Two Poloidal Field Coils to ITER Fusion Facility

Fusion for Energy (F4E), the European Domestic Agency for the International Thermonuclear Experimental Reactor (ITER), is responsible for the supply of 5 out of the 6 Poloidal Field (PF) Coils: PF2-PF6. One coil, PF1, is being manufactured by the Russian Federation Domestic Agency (RFDA). While the 10 m diameter PF6 was manufactured by the Institute of Plasma Physics Chinese Academy of Sciences (ASIPP) and tested in the cold test facility at Cadarache under a collaboration agreement with F4E; coils PF2-PF5 are currently being manufactured on site, close to the Tokamak building, their size ranging from 17 to 24 m diameter and weights from 200 to 400 T. This article describes the final acceptance tests performed on the coils PF5 and PF6, the testing setup, paying special attention to the tests performed before, after and during the cool-down at 80 K. The tests cover a wide range of aspects of the operation at cryogenic temperatures: ranging from the high voltage electrical insulation performance during the potential fault conditions during plasma operation, leak tightness under vacuum and pressure drop behavior of its hydraulic system during operation with forced flow helium. In addition, we will briefly introduce the results for the current center line (CCL) calculation obtained for PF5 and PF6.

Evaluation of the Dielectric and Insulating Properties of Newly Synthesized Ethylene/1-Hexene/4-Vinylcyclohexene Terpolymers

Terpolymerizations of newly synthesized ethylene (E), vinylcyclohexene (VCH), and 1-hexene were carried out with symmetrical metallocene catalysts rac-Me2Si(2-Me-4-Ph-Ind)2ZrCl2 (catalyst A) and rac-Et(Ind)2ZrCl2 (catalyst B). X-ray diffractometry (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), high-temperature gel permeation chromatography (GPC), and nuclear magnetic resonance (NMR) spectroscopy were used to evaluate the behavior and microstructure of the polymers. The activity of catalyst B was 1.49 × 106 gm/mmolMt·h), with a Tm of 73.45 (°C) and ΔHm of 43.19 (J/g), while catalyst A produced first higher 1-hexene, 19.6 mol %, and VCH contents with a narrow molecular weight distribution (MWD). In previous reports, ethylene propylene monomer dienes (EPDM) had a low content and were used for dielectric and insulating properties with nanomaterials. Second, this paper presents a kind of elastomeric polymers based on E/1-hexene and VCH with a high dielectric constant (k = 6–4) and mechanical properties. In addition, low dielectric loss suggests the suitable application potential of these polymeric materials for the fabrications of capacitors. Also, this work reveals that these polymers can be a better candidate for high-voltage electrical insulation due to their enhanced dielectric, mechanical, and thermal characteristics. To examine the insulating property, the interface characteristics of the polymer were evaluated using electrochemical impedance spectroscopy (EIS) with a frequency range of 1 × 105–0.01 Hz and an amplitude of 5.0 mV. EIS is an effective method to investigate the polymers’ interfacial electron transfer characteristics. The EIS Nyquist plot showed high Warburg impedance features in the low-frequency domain with straight lines without a semicircle, suggesting that the property of the polymer owing to the high electrical resistance and poor conductivity for ionic kinetics in the electrolyte may have surpassed that of the semicircle. Although the slope of low frequencies in polymers holding potent exoelectrogenic bacteria (Shewanella oneidensis MR-1) as a charge carrier in the electrolyte could significantly reduce the Warburg resistance, it still could not improve the conductivity, which demonstrated that the external charge supply could not alter the insulating property in the used polymers.

Flexible nanocomposite paper with superior fire retardance, mechanical properties and electrical insulation by engineering ultralong hydroxyapatite nanowires and aramid nanofibers

With the increasing popularity of modern electronic devices in the fifth-generation (5G) era, high-performance and high-safety electrically insulating materials with good mechanical flexibility and strength, high thermal stability and fire resistance are urgently needed. Herein, we report a highly flexible, thermally stable, and fire-retardant nanocomposite paper with high dielectric breakdown strength and mechanical strength by synergistically integrating one-dimensional ultralong hydroxyapatite (HAP) nanowires and aramid nanofibers (ANFs) through the vacuum-assisted filtration process. The as-prepared HAP/ANF nanocomposite paper has a nanowire/nanofiber networked framework and a layered structure, and exhibits high tensile strength (73.5 MPa), fracture strain (7.4 %), folding durability (1396 times under a loading weight of 9.8 N), excellent flexibility, and good processibility. Notably, the HAP/ANF nanocomposite paper has a superior dielectric breakdown strength (92.4 kV mm−1), high thermal stability and flame retardancy in comparison with the commercial Nomex T410 electrical insulation paper. The multifunctional HAP/ANF nanocomposite paper is promising for applications in miniaturized and flexible electronic devices, high-voltage electrical insulation equipments, and fire-retardant and high-temperature fields.

The Behavior of Polyurethane Foam-Filled Glass-Fiber-Reinforced Polymer Crossarm Subjected to Lightning Transient Voltage.

The demand for composite materials in high-voltage electrical insulation is escalating over the last decades. In the power system, the composite glass-fiber-reinforced polymer has been used as an alternative to wood and steel crossarm structures due to its superior properties. As a composite, the material is susceptible to multi-aging factors, one of which is the electrical stress caused by continuous and temporary overvoltage. In order to achieve a better insulation performance and higher life expectancy, the distribution of the stresses should firstly be studied and understood. This paper focuses on the simulation work to better understand the stress distribution of the polyurethane foam-filled glass-fiber-reinforced polymer crossarm due to the lightning transient injection. A finite-element-based simulation was carried out to investigate the behavior of the electric field and voltage distribution across the sample using an Ansys Maxwell 3D. Electrical stresses at both outer and inner surfaces of the crossarm during the peak of lightning were analyzed. Analyses on the electric field and potential distribution were performed at different parts of the crossarm and correlated to the physical characteristics and common discharge location observed during the experiment. The results of the electric field on the crossarm indicate that both the outer and internal parts of the crossarm were prone to high field stress.

Experimental Investigation of the Triple-Junction Effect on the Electric Discharge Characteristics and Modeling of the Maximum Discharge Current

The electrical discharge and breakdown characteristics of a triple junction (TJ) in high voltage (HV) electrical insulation are becoming an important issue in recent industrial applications. In this paper, a comparative study is conducted between three insulation materials used in HV: silicone, porcelain, and heat tempered glass, with electrode shape parameters such as inter-electrode distance (d), applied voltage (V), and geometry investigated for positive polarity, using an experimental approach. For optimum test organization to support our research and highlight the parameters and their interactions, we have established a mathematical regression model of the discharge current. It is polynomial, with good performance and a high level of precision. Besides, this yields one monovariable and another two-variable quadratic model. The latter can simulate the electric discharge simultaneously with two variables: V and d, and an adjusted determination coefficient () of nearly 0.99. Consequently, the two-variable quadratic model has been adapted to V and d ranges of 10 to 50 kV and 1.9 to 8 cm, respectively. Finally, this study provides us with new applicable knowledge about the TJ effect on electrical insulation with recommendations to optimize the design for higher performance.

News From Japan

Power electronics have been playing a big role in many fields of our daily lives. However, as has been well known, at least among high voltage electrical insulation engineers for these two decades, this situation brings about a drastic increase in the risk of partial discharges (PDs). That is, compared with ac voltages with sinusoidal wave shapes at frequencies of 50 or 60 Hz, voltages fed from or induced by power electronic circuits or devices such as converters and inverters contain much shorter fronts and tails in their waveforms. In addition, such devices generate surge voltages with higher amplitudes. Therefore, as power electronic devices are used more and more widely, PDs could be induced much more frequently. This, in turn, increases the importance of monitoring the occurrence of PDs in electric power apparatus such as transformers and rotating machines like motors and generators. However, it is in general difficult for conventional PD testers to monitor PDs generated by such converter-fed voltages. With this background, ECG Kokusai Co., Ltd., Tokyo, has developed a variety of PD testers. In this short article, two of them are briefly introduced.

Partial Discharges Classification Methods in XLPE Cable: A Review

Partial discharge (PD) signal classification analysis on cross-linked polyethylene (XLPE) cables is complex, requiring a comprehensive understanding of the characteristics of PD patterns. In the realm of high-voltage electrical insulation, PD pattern characteristics, such as PD charge and inception voltage, are essential as assessment criteria in diagnostics systems using PD classifiers. This paper provides a review of the various PD patterns and classifiers used by previous researchers, specifically for XLPE cables. In addition, the differences of the studies on various sensor developments based on PD detection in the past 27 years are also discussed. The repeatability, recognition accuracy, recognition speed, and effect of feature sizes on each PD classification method are reviewed and explained. This review indicates that the pattern recognition for PD signal using artificial neural network (ANN) exhibits better performance than the other methods in terms of accuracy and repeatability, and the reduction of feature size does not affect the accuracy of ANN.

Classification of Partial Discharge Images Using Deep Convolutional Neural Networks

Artificial intelligence-based solutions and applications have great potential in various fields of electrical power engineering. The problem of the electrical reliability of power equipment directly refers to the immunity of high-voltage (HV) insulation systems to operating stresses, overvoltages and other stresses—in particular, those involving strong electric fields. Therefore, tracing material degradation processes in insulation systems requires dedicated diagnostics; one of the most reliable quality indicators of high-voltage insulation systems is partial discharge (PD) measurement. In this paper, an example of the application of a neural network to partial discharge images is presented, which is based on the convolutional neural network (CNN) architecture, and used to recognize the stages of the aging of high-voltage electrical insulation based on PD images. Partial discharge images refer to phase-resolved patterns revealing various discharge stages and forms. The test specimens were aged under high electric stress, and the measurement results were saved continuously within a predefined time period. The four distinguishable classes of the electrical insulation degradation process were defined, mimicking the changes that occurred within the electrical insulation in the specimens (i.e., start, middle, end and noise/disturbance), with the goal of properly recognizing these stages in the untrained image samples. The results reflect the exemplary performance of the CNN and its resilience to manipulations of the network architecture and values of the hyperparameters. Convolutional neural networks seem to be a promising component of future autonomous PD expert systems.

Development Status of High Voltage Insulation Technology

High-voltage insulation technology is a technology related to the development, selection, design, manufacture, operation and maintenance of high-voltage electrical equipment insulation structures. In high-voltage electrical equipment, insulation structures are used to separate conductors with different potentials, so the insulation structure is an important part of electrical equipment. With the increase of power consumption and the increase of transmission distance, the maximum voltage level of the power system will be further increased, and it is becoming more difficult to solve the insulation problems related to high-voltage electrical equipment. This article gives a brief description of sulfur hexafluoride gas insulation, power cable and power transformer insulation technologies. In addition, new insulation materials and improved manufacturing processes can be introduced to improve the electrical insulation strength.

Electrical tree growth in microsilica-filled epoxy resin

Epoxy resin is widely deployed as a high voltage electrical insulation material when compounded with inorganic fillers. However, in the laboratory, the filler prevents visual observation of the long-term degradation known as electrical treeing. To date therefore, much laboratory testing has been conducted on unrepresentative unfilled materials. Here, the impact of micro-sized fillers on the treeing phenomenon in an epoxy system has been explored. Sub-micrometre resolution 3D reconstructions of electrical trees are reported from X-ray computed tomography (XCT) using an advanced ‘pink beam’ synchrotron light source imaging system. The role of filler particles between 1 and 10 μm in size on tree channel propagation is reported. In highly filled materials (30% by weight) a radical change in tree growth behavior is seen, leading to bush tree rather than branch tree growth. The dielectric breakdown time at constant stress was also found to increase as the square root of the filler level. The change in geometry of tree growth may explain the extended life of filled materials in high voltage applications.

A Variation Model of Thermal Breakdown of a High-Voltage DC Cable Electrical Insulation

On the basis of the presented differential form of the mathematical model describing the steady-state thermal conductivity in the layer of electrical insulation of a single-core high-voltage dc cable, the variation form of this model is elaborated. The analysis of stationary points of the functional obtained is carried out and a critical combination of the main parameters preceding the thermal breakdown of this layer has been determined. To find the best trial functions allowable for the functional, which approximate the stationary temperature distribution in the polymer layer of electrical insulation, residuals are compared that arise when substituting these functions into an original differential equation.