Breakdown Tests Research Articles

Discovery of a novel binary azeotrope with positive synergistic insulation strength as eco-friendly SF6-alternative

Abstract Sulfur hexafluoride (SF6), as the arc extinguishing and insulating medium, is broadly applied in power equipment. While it is very essential to find an environmentally friendly substitute gas for SF6 due to its strong greenhouse effect. Although there are many potential alternatives, most have relatively high boiling points that cannot meet the minimum operating temperature of the power equipment. In the past, the liquefaction temperature of the mixture was reduced by mixing with buffer gases, such as CO2, N2, or dry air. But this method cannot take the insulation performance requirements of eco-friendly insulating gas into account. Therefore, given the current problems and challenges, a novel approach is presented to exploring new eco-friendly gases by incorporating the azeotropic theory. The liquefaction temperature of the gas mixture can be reduced simultaneously while the insulation strength is increased. In this approach, a theoretical prediction model E-PPR78 was introduced to predict the vapor-liquid equilibrium data and RC318 was found to exhibit azeotrope behavior with HFO-1336mzz(E) at 17%. Furthermore, the predicted vapor-liquid equilibrium data obtained were validated against cyclic-analytical experimental results, affirming the efficacy of the proposed model. Subsequently, to assess its insulation performance, breakdown tests were conducted under both AC and lightning impulse voltages, revealing significant positive synergistic effects in the gas mixture. The possible mechanisms of this positive synergistic effect were also discussed. This study offers an innovative way of tackling high boiling point issues plaguing eco-friendly gases. The findings may also enlighten the design of eco-friendly switchgear that utilizes HFO-1336mzz(E) mixtures to replace traditional SF6 gases.

Impact of damaged housing on the performance of field aged composite High Voltage Insulators

Composite High Voltage Insulators (HVIs) are lightweight, inexpensive, and offer superior pollution performance. Consequently, they have replaced ceramic HVIs in highly contaminating coastal and desert regions. However, they are prone to degradation in harsh environments. In this paper, we assess the performance of three identical field-aged 380 kV composite HVIs with a service life of twelve years near the western coastal region of the Kingdom of Saudi Arabia. The housing of all the HVIs showed widespread damage, including cracks on sheds and shanks, partially or fully broken sheds, and rusted end fittings. The changes in morphology and material composition were assessed through SEM and EDX. An electrical breakdown test in the presence of steam fog revealed lowered withstand strength. Electric field distribution, a key design criterion for an HVI, was studied using the Finite Element Model (FEM) of the insulator bearing physical defects. The results reveal localized electric field intensification caused by all types of defects, notably smaller and narrower ones. Our findings indicate that while physical defects in HVIs can cause localized electric field intensification, they are not a significant concern unless accompanied by severe hydrophobicity loss, compromised electrical withstand levels, or extensive erosion exposing the fiberglass rod and jeopardizing mechanical stability.

Design Optimization and Reliability Evaluation in 1.2 kV SiC Trench MOSFET with Deep P Structure

In this paper, 1.2 kV SiC trench MOSFET with deep P structure has been proposed to effectively shield the trench bottom oxide. The various design splits, such as N concentration between deep P and deep P to trench distance, were experimentally evaluated and TCAD simulations were performed to extract maximum oxide electric field at trench bottom. Based on trade off results, critical design parameters were optimized to obtain low Rdson and stable breakdown voltage with acceptable oxide electric field. To evaluate trench gate oxide reliability in wafer level, gate oxide integrity (GOI/Vramp), charge to breakdown (QBD), and time dependent dielectric breakdown (TDDB) tests were conducted. Also, high temperature gate bias (HTGB) and high temperature reverse bias (HTRB) stress tests were carried out for assembled samples to compare device reliability depending on different designs. For the target design, the promising reliability results were confirmed in both wafer level and assembled samples.

Influence of Epoxy Resin Interlayer Interfaces on Electrical Tree Growth and Breakdown Characteristics.

The solid-solid insulation interface structure is a typical interface in extra-high-voltage power equipment, in which the multilayer epoxy resin material is a key component in the insulation structure of the power equipment, and the study of its interface characteristics is the most important. In this paper, epoxy-epoxy cross-linking interface specimens were prepared through experiments, and the degree of cross-linking between the interfaces was analyzed by changing the ratio of the curing agent and adding hydroxyl-terminated liquid nitrile rubber (HTBN) particles; it can be concluded that there exists a weak cross-linking reaction between the interfaces. The electrical tree measurement and alternating current (AC) breakdown test platform were set up, and three different cases of no interface, the electric field direction parallel to the interface, and the electric field direction perpendicular to the interface were tested, through which it was concluded that the existence of the interface inhibited the development of the electrical tree. For the three different cases of AC breakdown tested, it was concluded that the presence of an interface enhances the AC breakdown strength when the electric field direction is parallel to the interface and decreases the AC breakdown strength when the electric field direction is perpendicular to the interface through the interface, affecting the charge transport.

Design of a high‐frequency transformer based on amorphous cut cores for insulation breakdown testing

AbstractInnovative test methods are required to keep up with the increased demand for insulation materials which can withstand the high‐frequency square‐wave voltages generated by power‐electronic equipment. Test systems using high‐voltage, high‐frequency transformers have proven versatile and easy to realise. The authors investigate the application of amorphous cut cores in such transformers. Analytical and numerical models for the transformer and its frequency response are developed, aiding the design process. An amorphous core‐based transformer is designed for 8 kVpk output at 100 kHz and compared to two previous designs based on ferrite cores. The frequency and pulse response, as well as the high‐voltage and thermal performance, are evaluated. The comparison shows that while the low parasitics of the amorphous‐based transformer allow for superior frequency response, they are unsuitable for long‐duration tests with high pulse repetition frequencies (25–100 kHz) due to increased core losses. The partial discharge inception and flashover voltage are comparable to the ferrite‐based transformers.

Atomic diffusion and electrical reliability of NiAl/SiO2 interconnect: Breakdown voltage and TDDB characteristics

This study reports the effects of post-annealing on the electrical reliability of a NiAl/SiO2 interconnect structure for potential use as post-Cu interconnect. Our materials characterization using transmission electron microscopy and secondary ion mass spectrometry discloses that annealing at elevated temperatures induced the diffusion of Al into SiO2: Al, for a 400 °C-annealed sample, diffused only to a few nanometers from the interface, forming a thin aluminum-rich oxide layer, while samples annealed at higher temperatures show an extensive Al diffusion and interfacial reactions. In a voltage ramp dielectric breakdown test, the 400 °C annealed sample shows the lowest breakdown voltage, possibly, due to the aluminum-rich oxide layer serving as a self-forming barrier while the samples annealed at higher temperatures display a drastic reliability degradation with the annealing temperature increasing. In addition, analyzing data acquired from time-dependent dielectric breakdown tests using the E-model helps us predict the lifetime of the 400 °C sample to be longer than 105 h at 1 MV/cm.

Analysis of Deterioration Characteristics of Service-Aged XLPE Cables According to Installation Location of Combined Heat and Power Plant

The number of XLPE cables being used near or beyond their design life is increasing. The importance of timely cable replacement is necessary. Therefore, research is actively being conducted using VLF Tan δ diagnostic technology to assess the insulation condition of cables. Present studies lack in measuring and analyzing the VLF Tan δ of service-aged XLPE cables. Additionally, there is a research gap considering the operating environment. Therefore, it is needed to diagnose and analyze the insulation condition of the same service-aged cable when it is operated in a different environment. This paper assesses and analyzes the insulation condition of cables installed in the BFP, cooling tower, and deaerator booster pump of a combined heat and power plant. Each cable was evaluated by measuring the VLF Tan δ, the dielectric breakdown test of the cable, and the tensile strength, elongation at break, crystallinity, and dielectric strength of the XLPE specimens. Additionally, the correlation between the VLF Tan δ and other characteristics was also analyzed. It was found that degradation progressed in the order of the BFP, the cooling tower, and the deaerator booster pump. Therefore, it was confirmed that even for the same cable, deterioration varies depending on the installation location.

Electric-Tree Resistant Performance and Thermal Charge-Carrier Dissipation Mechanism of Voltage Stabilizer-Modified EPDM

In order to improve electric-tree resistant performance and dielectric breakdown strength of ethylene-propylene-diene misch-polymere (EPDM) material used for cable accessory reinforce insulation, the two specific aromatic ketone compounds—vinylphenylacetone (VPE) and 4-propylene oxyxy-2-hydroxydibenzenone (AOHBP) are employed as two paradigms of voltage stabilizer for chemical-graft modifications. Electric-tree resistances and insulation performances of modified EPDM materials and their charge trapping mechanism of thermoelectron inhibitions are studied by the accelerated electric-tree aging experiments, alternating current (AC) dielectric breakdown tests, surface potential trap-level analyses and first-principles calculations. Both the two species of voltage stabilizers are effective for promoting electric-tree inception voltage and dielectric breakdown strength, leading to a high extension of electric-tree morphology and smaller dimension of electric-trees growth, in which AOHBP is more significant. The two species of voltage stabilizers have been successfully grafted onto EPDM molecular-chains in thermal-chemistry crosslinking reactions of EPDM, introducing multiple shallow levels of charge traps, which reduces the energy released by trapping charge carriers and thus alleviates electric-tree aging of EPDM. The AOHBP and VPE represent a high electron affinity and a small electronic energy gap, which is competent of assimilating the kinetic energies of hot charge carriers whilst restricting Auger electronic excitation. Especially, the benzene group in voltage stabilizer renders shallow level charge traps with a larger carrier capture cross-section than deep traps and simultaneously possesses the high atomic vibration frequencies similar as electronic-transition energies, which results in effective dissipation on the kinetic energies of hot charge carriers. This mechanism dominates to increase electric-tree resistance and insulation strength of EPDM. The present study proves the important role of voltage stabilizers in improving insulation performance of EPDM material, and reveals the refrigeration mechanism on hot charge carriers for restricting electric-tree growth, which provides a significant strategy of chemical modifications for developing high-insulation cable accessory materials.

Novel HPLC Method Validation for Quantification of Dapagliflozin in Bulk Drug and Formulation

A new, steady, easy-to-use, and straightforward high-performance liquid chromatography (HPCL) technique was also tested to determine dapagliflozin concentration in medicinal and API forms. For the chromatographic extraction study, a Phenomenex Gemini-NX C18 Column was used. This column was filled with a mobile phase that was 70:30 v/v methanol to sodium 1-octanesulphonate. This experiment used a 20-liter syringe amount and a flow rate of 1-mL per minute. A bunch of factors were used to make sure the new method worked. The drug dapagliflozin was released at a wavelength of 203 nm after 6.5 ± 0.5 minutes. A correlation coefficient (r2) of 0.9994 between 15 to 55 μg/mL shows that the planned process is linear. The theoretical plates and peak tailing were found to be 4129 and 1.03, respectively. In terms of healing, the percent accuracy that was reached was within the acceptable range of 98 to 100. New suggestions say that the regular testing of dapagliflozin in large amounts must be done using a proven method that is unique and easy to repeat. Forced breakdown tests with drugs were used to show that the proposed method is stable. The product was tested according to the steps laid out in the ICH Q2R1 Guidelines. The test looked at many chemical processes, such as oxidation, photolysis, heat stress, and acids and alkaline hydrolysis.

Improved Vth Stability and Gate Reliability of GaN-Based MIS-HEMTs by Employing Alternating O2 Plasma Treatment.

The Vth stability and gate reliability of AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs) with alternating O2 plasma treatment were systematically investigated in this article. It was found that the conduction band offset at the Al2O3/AlGaN interface was elevated to 2.4 eV, which contributed to the suppressed gate leakage current. The time-dependent dielectric breakdown (TDDB) test results showed that the ALD-Al2O3 with the alternating O2 plasma treatment had better quality and reliability. The AlGaN/GaN MIS-HEMT with the alternating O2 plasma treatment demonstrated remarkable advantages in higher Vth stability under high-temperature and long-term gate bias stress.

Covalently cross-linked CaCu3Ti4O12 and poly(arylene ether nitrile) hybrids with enhanced high temperature energy storage properties

Ensuring polymer dielectrics with stable high energy storage density at high temperatures via improving interfacial compatibility remains a challenge. Based on this principle, calcium copper titanate and poly(arylene ether nitrile) (CCTO-PEN) hybrids dielectrics are developed to exhibit improved high temperature energy storage properties through the interfacial cross-linked high-temperature resistant cyano. Herein, CCTO-PEN hybrid dielectrics are fabricated through the thermal induced self-crosslinking reaction of phthalonitrile between the phthalonitrile modified CCTO (CCTO-CN) and phthalonitrile end-capped PEN (PEN-CN). SEM, XPS, FTIR, mechanical, dielectric, and breakdown tests of the CCTO-PEN hybrids reveal that the phthalonitrile modified CCTO-CN possessed superior interfacial compatibility in PEN dielectrics, together with enhanced dielectric, breakdown, mechanical, and energy storage properties compared to CCTO directly doped PEN dielectrics. Benefitting from the improved interfacial compatibility and the appropriate distribution of CCTO-CN within PEN-CN matrix, the CCTO-PEN hybrids demonstrate stable dielectric properties from room temperature to 200 °C, and the energy storage density of CCTO-PEN hybrid reaches up to 0.785 J/cm3, suggesting that the CCTO-PEN hybrids can be utilized as high temperature dielectric materials.

AC-DC breakdown characteristics of oil-paper insulation at low temperature

New energy sources such as wind energy are mainly distributed in low temperature areas such as high altitude and high dimensionality in inland China, which has higher requirements for the low-temperature insulation characteristics of power equipment. This poses higher demands for the low-temperature insulation capabilities of power equipment. However, the existing research on the low temperature breakdown characteristics of oil-impregnated paper is limited. In this study, the authors constructed an AC-DC combined power supply and a specialized low-temperature breakdown testing platform. Various oil-impregnated paper samples with different moisture contents were prepared. The paper investigated the AC-DC breakdown characteristics of these samples under low-temperature conditions, focusing on the effects of temperature, moisture content, and DC component on the breakdown strength. The findings serve as a valuable design reference for the application of oil-impregnated power equipment in low-temperature environments.

Multi-expert GMM decision support system with AHP method for determining weight of transformer oil insulation quality index

The transformer is important and quite central in the power system for distributing energy from generators to consumers through electrical substations. Good transformer oil isolation is needed to protect the transformer to function optimally and prevent fatal interference. Over time, insulating oil experiences aging which can cause transformer damage and disruption in energy distribution to consumers. There are three things that affect the condition of transformer oil insulation, namely chemically testing for acidity, sediment (SED) and water content, from an electrical point of view testing for breakdown voltage (BDV) and testing dielectric dissipation factor (DDF), and from a physical point of view, color, and interfacial tension (IFT) tests are carried out. In dealing with this problem, a Decision Support System (DSS) is needed to calculate the oil quality index based on the given parameters. The method used is Analytical Hierarchy Process (AHP) with multi-expert GMM. The results show that the system is running well, and the calculation method is appropriate. Tests show 100% accuracy in comparing manual calculations with the Confusion Matrix system. Users give an average satisfaction of 92.94%. In conclusion, this system effectively meets the need and helps to determine the quality index of insulating oil in transformers.

Investigation on different materials after pulsed high field conditioning and low-energy H- irradiation

During operation, the radio-frequency quadrupole (RFQ) of the LINAC4 at CERN is exposed to high electric fields, which can lead to vacuum breakdown. It is also subject to beam loss, which can cause surface modification, including blistering, which can result in reduced electric field holding and an increased breakdown rate. First, experiments to study the high-voltage conditioning process and electrical breakdown statistics have been conducted using pulsed high-voltage DC systems in order to identify materials with high electric field handling capability and robustness to low-energy irradiation. In this paper, we discuss the results obtained for the different materials tested. To complement these, an investigation of their metallurgical properties using advanced microscopic techniques was done to observe and characterize the different materials and to compare results before and after irradiation and breakdown testing.

Time-dependent dielectric breakdown of SiC-CMOS technology for harsh environments

To estimate the failure time of silicon carbide (SiC) integrated circuits in harsh environments, the activation energy (Ea) and field acceleration factor of SiC n-channel MOS (nMOS) and p-channel MOS (pMOS) were measured using time-dependent dielectric breakdown testing at constant voltage stress in the range of 25–350 °C. Ea around 300 °C was 0.7 eV for nMOS and 0.66 eV for pMOS, which was about twice as high as that below 150 °C and did not differ greatly depending on the conductivity type. The gate dielectric breakdown mechanism shifted from the 1/E model to the E model as the temperature rose, and this is thought to have caused the Ea to change. The field acceleration factor in the E model at 300 °C was 2.7 and 2.3 cm/MV for nMOS and pMOS, respectively. The maximum operating electric fields of nMOS and pMOS for a 100-year lifetime are 6.8 and −7.2 MV/cm, which are over 25% lower than the fields at room temperature, mainly due to a shift in the dominant breakdown model. A more conservative failure time design will be required for SiC-ICs exposed to high temperatures.

Ta/Al/CuW low temperature ohmic contacts for GaN-on-Si HEMT

We proposed a low temperature Au-free ohmic contacts of GaN-on-Si HEMT with the Ta/Al/CuW metal stack. The CuW was deposited by using the dual-target magnetron sputter deposition method. The annealing conditions and recess depth of ohmic area were systematically investigated. By utilizing the Ta/Al/CuW structure, an improved contact characteristic (0.49 Ω·mm) is obtained following annealing at 550 °C for 10 min in vacuum, with the recess depth of 30 nm(±2 nm). This performance surpasses that of Ta/Al/W Au-free contacts (1.07 Ω·mm). Furthermore, both the Ta/Al/CuW ohmic contacts (RMS = 6.3 nm) and the Ta/Al/W ohmic contacts (RMS = 6.0 nm) exhibit smooth surface morphology. Compared to Ti contact layer, Ta demonstrates superior performance in low temperature contact and breakdown test. Amorphous Ta layer can effectively suppress Cu diffusion. The GaN-on-Si HEMT was also fabricated based on Ta/Al/CuW Au-free ohmic contacts, exhibiting excellent DC characteristics.

Investigation of Novel Solid Dielectric Material for Transformer Windings.

Improvement techniques aimed at enhancing the dielectric strength and minimizing the dielectric loss of insulation materials have piqued the interest of many researchers. It is worth noting that the electrical breakdown traits of insulation material are determined by their electrochemical and mechanical performance. Possible good mechanical, electrical, and chemical properties of new materials are considered during the generation process. Thermoplastic polyurethane (TPU) is often used as a high-voltage insulator due to its favorable mechanical properties, high insulation resistance, lightweight qualities, recovery, large actuation strain, and cost-effectiveness. The elastomer structure of thermoplastic polyurethane (TPU) enables its application in a broad range of high-voltage (HV) insulation systems. This study aims to evaluate the feasibility of using TPU on transformer windings as a solid insulator instead of pressboards. The investigation conducted through experiments sheds light on the potential of TPU in expanding the range of insulating materials for HV transformers. Transformers play a crucial role in HV systems, hence the selection of suitable materials like cellulose and polyurethane is of utmost importance. This study involved the preparation of an experimental setup in the laboratory. Breakdown tests were conducted by generating a non-uniform electric field using a needle-plane electrode configuration in a test chamber filled with mineral oil. Various voltages ranging from 14.4 kV to 25.2 kV were applied to induce electric field stress with a step rise of 3.6 kV. The partial discharges and peak numbers were measured based on the predetermined threshold values. The study investigated and compared the behaviors of two solid insulating materials under differing non-electric field stress conditions. Harmonic component analysis was utilized to observe the differences between the two materials. Notably, at 21.6 kV and 25.2 kV, polyurethane demonstrated superior performance compared to pressboard with regards to the threshold value of leakage current.

Dielectric Breakdown Testing of Insulation Materials Under High-Frequency Bipolar Square Wave Voltage by Repetitive Pulses

Dielectric Breakdown Testing of Insulation Materials Under High-Frequency Bipolar Square Wave Voltage by Repetitive Pulses

Electrospray deposition ofin‐situ UV‐photoactivatedpolyimide films

AbstractIn electrospray deposition, a precursor solution, composed of a solute material in a volatile carrier solvent, is atomized into a spray of charged microdroplets under the influence of a strong electric field. As the droplets are in‐flight, the carrier solvent evaporates, leaving behind the solute material that can be delivered to a target surface to create a film. In this work, we employ electrospray deposition to create films of UV‐photosensitive polyimide. Films were deposited using in‐situ UV exposure, where the in‐flight droplets and deposited material were exposed to UV during deposition. The characteristics of these films were compared to films exposed to UV only after deposition (referred to as post‐UV exposure). The microstructure of the deposited films was notably different for the two exposure modes, in which the in‐situ UV exposed films have a wavy/dimpled surface, compared to the flat and smooth surface of the post‐UV exposed films. However, thermogravimetric analysis and Fourier transform infrared spectroscopy showed that the UV activation of the in‐situ UV and post‐UV exposed films was nearly identical. Breakdown testing was conducted to evaluate the dielectric strength of the films. Overall, the in‐situ UV and post‐UV exposed films exhibited similar breakdown strengths of approx. 430–450 V/μm. The use of in‐situ UV exposure cuts in half the processing time for producing thin polyimide films.

Study on Power Frequency Breakdown Characteristics of Nano-TiO2 Modified Transformer Oil under Severe Cold Conditions

With 45# transformer oil as the base fluid, different concentrations of TiO2 nanomodified transformer oil were prepared via the thermal oscillation method. Nanomodified transformer oil with a concentration of 0.01 g/L was selected for evaluation via the breakdown test. Then, 0.01 g/L nanomodified transformer oil and ordinary 45# transformer oil were subjected to the variable control of different moisture contents and different temperatures, and breakdown tests under different types of electrodes were performed within the temperature range of −30 °C to 30 °C. The test results showed the following: Under severe cold conditions, the improvement effect of the breakdown voltage in different temperature ranges was different. Within the temperature range of −30 °C to −10 °C, the enhancement effect could reach 13% to 15%. Within the temperature range of −10 °C to 0 °C, the enhancement effect could reach 8% to 9%. Within the temperature range of 0 °C to 30 °C, the enhancement effect could reach 18% to 21%. Compared with the test results at high water contents, the improvement in the breakdown voltage amplitude of transformer oil by nanomaterials was more obvious at low water contents. In addition, nanomaterials could reduce the dispersion of the breakdown voltage to make the breakdown voltage more stable. Lastly, COMSOL was used to simulate the polarization process of nanoparticles under a uniform electric field and the influence of the trajectory of charged particles in the oil to further analyze the mechanism of the influence of nanoparticles in oil on the breakdown voltage of the oil gap. The simulation results showed that, when the particles were accelerated by the electric field, they moved irregularly. After adding nanoparticles, the charged particles were adsorbed by the nanoparticles when passing through the nanoparticles, which reduced the migration rate of charged particles in the oil. The breakdown voltage of the oil gap increased.