Epoxy Insulation Research Articles

Pulse current injection platform with consecutive early-time and intermediate-time high-altitude electromagnetic pulse conducted currents for immunity test of electrical equipment.

High-altitude electromagnetic pulse (HEMP) has attracted considerable attention for its influence on electrical equipment. HEMP is divided into three parts: early time HEMP (E1), intermediate-time HEMP (E2), and late-time HEMP (E3). Most studies focused on E1 alone, while few investigated others. However, the electrical equipment may be disturbed by more than one part since these three parts co-exist in a HEMP environment. The pulse current injection (PCI) test is an effective immunity test method for evaluating the sensitivity and susceptibility of electrical equipment. To investigate the responses of electrical equipment excited by the consecutive E1 and E2 and compare with those under the individual E1 or E2, this paper builds a PCI platform that can carry out PCI tests with the consecutive E1 and E2 conducted current. To output the E1 current and the E2 current consecutively, which exhibit significant differences in the rise time (20ns and 1.5 μs), peak current (2500 and 250A), and full width at half maximum (FWHM, 500-550ns and 3-5ms), an E1&E2 coupler with a fast-closing high-current trigger switch is designed in this paper. Finally, some 10-kV epoxy insulators are tested in the developed platform, which shows the capacity of the proposed platform to test the immunity of electrical equipment with the consecutive E1 and E2 conducted current.

Preparation and performance comparison of low‐dielectric epoxy resins cured by naphthalene‐ and phenyl‐based active esters

AbstractThe poor dielectric properties of epoxy resins limit their application in microelectronics, and active ester curing agent is an effective means to enhance the dielectric properties of epoxy resins. However, the phenyl active ester curing resins nowadays have the problem of low mechanical properties. In this work, a novel naphthalene‐based active ester‐cured resveratrol epoxy resin system (REP/NDA) was prepared for the first time. Compared with the phenyl‐active ester‐cured epoxy resin (REP/PDA), the naphthyl‐active ester prepared epoxy resin has obvious advantages in mechanical properties. The experimental results indicated a tensile strength measurement for REP/NDA at 91.9 MPa, the tensile strength of REP/PDA was 65.3 MPa, and the tensile strength of REP/NDA was 141% of that of REP/PDA. The prepared REP/NDA epoxy resin exhibits favorable dielectric properties, evidenced by a dielectric constant of 3.02 at 10 MHz and a dielectric loss of 0.0042, very good thermal stability (T5% of 379°C), excellent water absorption (only 0.49% for 7 days from 2 to 8°C) and good dimensional stability (coefficient of thermal expansion below Tg of 77 ppm). The first synthesis of naphthalene‐based active ester curing agent offers a reference for creating new low dielectric epoxy resin materials that work out exceptionally.

Nonlinear dielectric response and conductivity characteristics of epoxy resin in high voltage AC electric field

Abstract High-voltage dielectric and AC conduction behaviors of epoxy resin (EP) insulation are beneficial for the design and application of solid-state power electronic devices. This study investigates the nonlinear dielectric response and AC conduction characteristics of EP. The dielectric relaxation characteristics, including permittivity and AC conductivity of the EP samples, were investigated using high-voltage dielectric spectroscopy and the ionic polarization model. The results demonstrate a nonlinear increase in the relative permittivity and AC conductivity concerning the AC electric field. The increase in AC conduction under a high-frequency electric field is attributed to the reduction in the threshold field for charge injection caused by elevated temperatures. Considering the dielectric response and carrier hopping, it is evident that the nonlinear dielectric response of EP primarily originates from the ionic process under high electric fields. Ionic polarization, in conjunction with ion-hopping conduction, enhances the dielectric loss at high frequencies and electric fields, thereby facilitating the nonlinear conversion of AC conduction. The equivalent free volume is likely to increase in high-frequency fields. This phenomenon leads to an increase in AC conduction and even dielectric breakdown. This study offers a pivotal theoretical framework for the design and application of high-frequency insulation.

Improved Corona Resistance of Epoxy Resin for Gas‐Insulated Equipment in Nitrogen Gas by Direct Fluorination

Direct fluorination has demonstrated efficacy in modulating the surface electrical properties of epoxy insulators and preventing surface charge accumulation. Comparative corona treatments were conducted on both surface fluorinated (modified) epoxy samples and untreated (virgin/original) samples using a modified electrode setup in a nitrogen (N2) atmosphere. The purpose was to evaluate the resistance of the modified epoxy surface layer against corona discharge. The results of ATR‐IR analysis and SEM surface and cross‐sectional imaging indicate that corona treatment did not alter the chemical composition of the fluorinated sample or the thickness of the fluorinated layer. Based on assessments of potential decay and water contact angle measurements, the surface conductivity of the modified sample was decreased by corona treatment. The wettability of fluorinated sample remained unchanged after corona treatment, and no soluble degradation products were produced. Conversely, the surface conductivity of the virgin sample exhibited an increase following corona treatment, accompanied by the formation of soluble degradation products. These results confirm that direct fluorination improves the epoxy insulator's discharge resistance in N2 and provides technical support for enhancing the electrical performance of epoxy insulators in gas insulated equipment. © 2024 Institute of Electrical Engineers of Japan and Wiley Periodicals LLC.

Mechanism exploration of ion-implanted epoxy on surface trap distribution: An approach to augment the vacuum flashover voltages

Abstract The augmentation of the epoxy (EP) resin surface to advance flashover performance has become a pivotal point of global interest. This research introduces a novel surface modification method and its mechanism for insulation materials. The research follows an electron cyclotron resonance ion implantation system to subject the surface of EP insulation to ion beams with diverse energies, i.e., 6, 10, 20, 40, 50, and 60 keV for a consistent time of 300 s at an angle of 90°. The experimental phase includes the DC flashover examination under negative polarity. Besides, the simulation phase includes the Monte Carlo model constructed using SRIM software to examine the range and distribution of bombarded ions in the targeted insulation. Results reveal that the flashover properties are affected by the surface potential, surface conductivity, trap distribution, water contact angle, and elemental composition. Likewise, based on the outcomes and theoretical point of view, it is revealed that the bombardment of energetic ions enhances the trap depth, assisting in a reduction in surface conductivity, confining the surface charge movements, and extensively suppressing the secondary electron emission yield. Also, the enhanced trap depth induces homo-charge formation near triple junctions. Synergistically, the factors contribute to high flashover voltages.

Unraveling High Temperature-Induced Glass Transition Effect on Underlying Multitimescales Dynamic Mechanisms of Epoxy Resin Insulation in Power Electronic Applications

Unraveling High Temperature-Induced Glass Transition Effect on Underlying Multitimescales Dynamic Mechanisms of Epoxy Resin Insulation in Power Electronic Applications

Phase Dependence of Surface Charge Measurement on Epoxy Insulator in C4F7N/CO2 under AC Voltage.

The application of binary gas mixtures consisting of heptafluorobutyronitrile (C4F7N) and carbon dioxide (CO2) in AC GIS is currently attracting much attention. Therefore, the evaluation of the gas-solid interface charge distribution characteristics of epoxy resin is indispensable. Additionally, the phase-dependency of the charging behavior remains not fully understood. We simulated coaxial electrode structure in GIS and investigated the surface charge distribution on a down-scaled epoxy insulator. The influence of the truncated phase angle and duration of AC voltage on charge behavior were analyzed, and the charge transport mechanism under AC voltage was theoretically analyzed. The results showed that there was a noticeable negative charge speckle with the presence of the metal particle and the accumulated negative charge on the insulator surface far exceeded that of the positive charge. The maximum surface charge density and the amount of surface charge accumulated first increased and then decreased over time. It was found that the phase angle has a negligible influence on the surface charge distribution at the cut-off moment.

Novel recyclable epoxy resin with releasable residual stress and synergistically enhanced dielectric properties and healing ability

It has been a challenge to improve the performance of epoxy insulation in the whole life cycle by achieving the reduction of residual stress during manufacturing, the healing of damages during application, and the recycling after decommissioning. In this paper, a novel recyclable epoxy resin (SEP) with releasable residual stress and synergistically enhanced dielectric properties and healing ability was successfully developed by introducing dynamic thiocarbamate bonds (DTBs). A reduction in residual stresses by 45 % was detected after SEP was annealed at 30 °C below the glassy transition temperature (Tg) for 8 h, during which the mechanical properties remained unchanged. Synergistically improved dielectric properties and damage-healing ability were also observed in SEP. A high healing efficiency of 94.4 % for electrical breakdown damage was found in SEP, meanwhile its dielectric properties were superior to commercial epoxy resin. Additionally, SEP featured good recyclability, including reprocessability and degradability. All those excellent properties were ascribed to the dissociation and recombination of DTBs triggered by thermal stimulation. This work provides an effective solution to a series of issues throughout the full lifecycle of epoxy materials.

Surface degradation of epoxy resin exposed to corona discharge under bipolar square wave field: From phenomenon to the insights

The unavoidable corona discharge induced by distorted field is detrimental to the safety of power equipment, especially the equipment with high voltage magnitude and high frequency. In this paper, the degradation morphology, residual components, lifetime of endurance, partial discharge characteristics, and evolution of surface traps of epoxy insulation under bipolar square wave field is investigated. The results show that degraded zone exhibits as three layers with round pits and channel-like ravines on the surface of epoxy resin exposed to corona discharge. It is demonstrated that more oxygen element during corona discharge while more carbon element during breakdown appeared, and nano-Al2O3 fillers migrates to the discharged zone. The maximum temperature and number of emitted phonons increase with voltage amplitude and frequency in power law and exponential form, respectively, corresponding to the fitting function of endurance lifetime. The emitted light is concentrated on the near ultraviolet (UV) and infrared ray (IR) band, indicating the energy pooling and thermal effect of corona discharge, which interprets the distinct degradation behavior of samples under sinusoidal and bipolar square wave voltage. The effect of space charge and thermal conductivity should be considered simultaneously in the degradation of epoxy insulation under bipolar square wave field due to polarity reversal and high frequency, which is proved by the disparate behavior of EP/nano-Al2O3 composites resistance to corona discharge and the breakdown moment at falling edge of bipolar square wave voltage. This work may contribute to the advancement of resistance to corona discharge degradation in equipment with high power density, high voltage amplitude and high frequency.

Enhanced breakdown strength of epoxy composites by constructing dual-interface charge barriers at the micron filler/epoxy matrix interface

For the advanced energy systems with ultra-high voltage and frequency, in order to improve the thermal conductivity, arc resistance and mechanical strength of epoxy-based dielectric materials, the addition of micron inorganic fillers is necessary. However, this will inevitably degrade their breakdown strength. In this work, the example of constructing dual-interface charge barriers by optimizing molecular structure at micron filler/epoxy matrix interface to capture charge and then enhance the breakdown strength of epoxy composites is reported. Results show that the Al2O3@PVDF-6/BPA system with optimized interfacial structure exhibits the breakdown strength of AC and DC voltages of 37.5 and 67.8 kV/mm, respectively, far outperforming current epoxy composites containing micron fillers. The charge trapping effects in the dual-interface charge barriers are comprehensively investigated, which is confirmed to be the reason for the improved breakdown strength. In particular, the construction of dual-interface charge barriers hardly sacrifices the thermal and mechanical properties of epoxy composites. This work unveils a scalable approach to exploring satisfied dielectric epoxy composites by dual-interface charge barriers construction at the micron filler/epoxy matrix interface.

Detection of defect-induced luminescence in epoxy-based insulation materials via phase-resolved photon counting method

Electroluminescence (EL) has shown promise in detecting micro-defects in epoxy-based insulation materials. Understanding the various luminescence mechanisms caused by defects is crucial for improving the characterization and analysis of insulation defects. In light of this, this study proposes a photon counting-based approach to investigate the impact of defects on the entire evolutionary process of the luminescence mechanism. A phase-resolved photon counting (PRPC) method is proposed to examine the polarity and periodicity of photon counting results influenced by defects. Additionally, a simulation model based on the finite element method is established to analyze how defects modify the distribution of electric field and space charges. Observations suggest that the PRPC-based approach holds promise for advancing the defect analysis of epoxy insulation used in gas-insulated equipment.

Probing the Epoxy Insulation of Smoothing Reactors With Graphene Ink

Probing the Epoxy Insulation of Smoothing Reactors With Graphene Ink

The effect of different active diluents on the properties of epoxy materials

Abstract Epoxy resin is widely used in the insulation packaging field of electrical equipment due to its advantages such as low cost, excellent insulation, and mechanical properties. However, the thermal conductivity and the heat resistance of domestic epoxy insulation packaging materials make it difficult to meet the increasingly demanding operating conditions of electrical equipment. This article investigated the effects of active diluents with different functional group numbers on the glass transition temperature, mechanical strength, and low-temperature cracking resistance of epoxy materials. Four functional group active diluents were selected as additives to reduce the viscosity of epoxy resin, and the influence of diluent content on the comprehensive performance of epoxy resin was studied and analyzed.

A Study on Simultaneous Measurement of Partial Discharge in Epoxy Resin Insulator using IMC and Rogowski Coil

In practice, field measurement of partial discharge is easily suffered by interferences due to the noisy signal has been mixed with the resulting partial discharge signal. Therefore, the detection and measurement of PD are important to monitor the insulation life in high voltage (HV) power equipment. The paper presents the simultaneous measurement of partial discharge (PD) pulse parameters using the impedance matching circuit and the Rogowski coil sensor to study the features of partial discharge on the epoxy resin insulator. Two different thicknesses of samples were used to observe the PD pulse parameters with the voltage applied vary depending on the thickness of the sample to attain constant electric field intensity for both samples. The step response parameters resulted from the measurement can be used as a time domain features to discriminate various types of PD in HV power equipment. Thus, the PD can be observed clearly, maintenance can be performed, and the performance of the power system can be improved.

Cyber-Physical Systems for Epoxy Resin Insulators: Development and Study

Cyber-Physical Systems for Epoxy Resin Insulators: Development and Study

Effect of Micro and Nano Particles of Al<sub>2</sub>O<sub>3</sub> and SiO<sub>2</sub> on Electrical Tree Inhibition in Epoxy Resin Insulator

Electrical tree is a topic that has been extensively studied in recent years. Electrical tree is considered a deterioration of the electrical insulator due to the high voltage field's distortion. Solid insulating materials used in high voltage applications, such as epoxy resin are widely employed due to their high dielectric strength and excellent mechanical properties. This research studies the effect of micro and nanoparticles of Al2O3 and SiO2 on electrical tree inhibition in epoxy resin insulators. Electrical tree inhibition is achieved by incorporating micro and nanoparticles into the polymer material, which possess different properties. Following ASTM D 3756-97, the experiment is conducted with a constant 22 kV voltage and frequency of 50 Hz. Both Al2O3 and SiO2 possess the ability to inhibit the growth of the electrical tree. Experimental results revealed that the addition of Al2O3 and SiO2 to the epoxy resin affected the formation of electric trees. As the quantity of filler increases, fewer electric trees are produced. Additionally, It has an effect on the initial formation time of electric trees. The initial time of the electric tree with the addition of micro/nano(1/3) Al2O3 additives at a ratio of 0.1 wt% was 3.5 times longer when compare with pure epoxy resin.

Spatial-Temporal Kinetic Behaviors of Micron-Nano Dust Adsorption along Epoxy Resin Insulator Surfaces and the Physical Mechanism of Induced Surface Flashover.

The advanced Gas Insulated Switchgear/Gas Insulated Lines (GIS/GIL) transmission equipment serves as an essential physical infrastructure for establishing a new energy power system. An analysis spanning nearly a decade on faults arising from extra/ultra-high voltage discharges reveals that over 60% of such faults are attributed to the discharge of metal particles and dust. While existing technical means, such as ultra-high frequency and ultrasonic sensing, exhibit effectiveness in online monitoring of particles larger than sub-millimeter dimensions, the inherent randomness and elusive nature of micron-nano dust pose challenges for effective characterization through current technology. This elusive micron-nano dust, likely concealed as a latent threat, necessitates special attention due to its potential as a "safety killer". To address the challenges associated with detecting micron-nano dust and comprehending its intricate mechanisms, this paper introduces a micron-nano dust adsorption experimental platform tailored for observation and practical application in GIS/GIL operations. The findings highlight that micron-nano dust's adsorption state in the electric field predominantly involves agglomerative adsorption along the insulator surface and diffusive adsorption along the direction of the ground electrode. The pivotal factors influencing dust movement include the micron-nano dust's initial position, mass, material composition, and applied voltage. Further elucidation emphasizes the potential of micron-nano dust as a concealed safety hazard. The study reveals specific physical phenomena during the adsorption process. Agglomerative adsorption results in micron-nano dust speckles forming on the epoxy resin insulator's surface. With increasing voltage, these speckles undergo an "explosion", forming an annular dust halo with deepening contours. This phenomenon, distinct from the initial adsorption, is considered a contributing factor to flashovers along the insulator's surface. The physical mechanism behind flashovers triggered by micron-nano dust is uncovered, highlighting the formation of a localized short circuit area and intense electric field distortion constituted by dust speckles. These findings establish a theoretical foundation and technical support for enhancing the safe operational performance of AC and DC transmission pipelines' insulation.

Enhancement of DC Flashover Voltage of Epoxy Insulators and Gap Breakdown Voltage in SF6 Gas by Direct Fluorination of Metal Electrodes

Enhancement of DC Flashover Voltage of Epoxy Insulators and Gap Breakdown Voltage in SF₆ Gas by Direct Fluorination of Metal Electrodes

Flexible smart surface coating for GIS/GIL epoxy insulators

AbstractA flexible smart coating with electroluminescence effect was designed and fabricated on the surface of gas insulated switch gear (GIS)/gas insulated transmission line (GIL) epoxy insulators based on two‐step curing process. As the AC voltage increases, the luminous area on the insulator surface expands from the centre to the periphery, and the light intensity shows a linear relationship with the applied voltage. Besides, the flexible smart coating can effectively identify the location of metal particle defects and the degree of electric field distortion. The flexible smart coating enhances the surface flashover voltage due to its higher dielectric constant. Simultaneously, metal particle contamination can substantially reduce the insulation performance of epoxy insulators, particularly when they are located near the high‐voltage side. It is hoped that this study can provide a reference for the smart detection of surface defects GIS/GIL basin insulators.

Partial discharge characteristics of epoxy insulation surface under AC/LI superimposed voltages in SF6/N2 gas mixtures

Partial discharge characteristics of epoxy insulation surface under AC/LI superimposed voltages in SF₆/N₂ gas mixtures