Insulation Of Equipment Research Articles

Analysis of the dynamics of changes in gas content in oil-filled equipment with defects of various types

The article presents the results of analysing the dynamics of changes in the values of the ratios of characteristic gases, the percentage of gases, and defect nomograms in the process of developing electrical discharges, local overheating, and combined defects in high-voltage oil-filled equipment. During the analysis, the value of gas concentrations was evaluated for compliance with different levels regulated in the current Ukrainian standard at different stages of defect development. To determine the type of defect based on the values of the ratios of characteristic gases at different points in time, the norms regulated by the IEC 60599 standard and the ETRA square were used. The dynamics of changes in the percentage of gas was analysed using the Duval triangle. The results of the analysis showed that the primary defects during the development of electric discharges can be not only electric discharges with lower intensity, but also thermal (in particular, in the temperature range of 150-300 ℃) and combined defects. At the same time, in the process of discharge development, the nature of defects may change from measurement to measurement. Thus, when assessing the possibility of further operation of transformers, in addition to the degree of danger of the defect and the rate of its development, it is necessary to take into account the possibility of transforming the defect from a less to a more “dangerous” one that develops rapidly. During the development of thermal defects, the primary defect is usually a thermal defect with a lower hot spot temperature. It was found that in equipment with overheating above 700 ℃, the change in gas content during the development of the defect has a similar character. In particular, a mirror image of the change in the percentage of methane in relation to ethylene is observed. This effect can be used to detect high-temperature overheating at an early stage of its development, even before the gas concentrations exceed the limit values, which will help to avoid the destruction of equipment insulation and extend its service life. During the development of combined defects (overheating accompanied by discharges or discharges accompanied by heating), the main defect (e.g., discharge) first appears, and in the process of development, an additional defect (e.g., heating) develops. The results obtained indicate the possibility of detecting and recognizing defects in oil-filled equipment at different stages of their development.

Dielectric Performance of Natural- and Synthetic-Ester-Based Nanofluids with Fullerene Nanoparticles

According to the latest research, nanofluids as a possible future substitution for high-voltage equipment insulation have the potential to enhance the heat transfer and insulation properties of their base fluids. Dielectric properties are represented by breakdown strength (AC, DC, lightning) and dielectric performance as a set of quantities including dissipation factor, permittivity, and volume resistivity. In this study, natural and synthetic esters were mixed with C60 nanoparticles. Samples were examined for dissipation factor, relative permittivity, and volume resistivity at temperatures between 25 °C and 140 °C to monitor changes in dielectric performance with rising temperature, in accordance with IEC 60247. In addition, the samples were tested for AC breakdown voltage (using mushroom-like electrodes with a gap distance of 1 mm) and evaluated using the Weibull distribution statistical method. These measurements allowed complex evaluation of the examined mixtures and the determination of optimal concentration for each ester-based nanofluid.

Low Frequency Waterborne Sound Insulation Based on Sandwich Panels With Quasi-Zero-Stiffness Truss Core

Abstract Due to the negative correlation between pressure resistance and waterborne sound insulation, low-impedance soundproof materials can hardly work in deep water. Here, we propose a new mechanism to circumvent this problem by employing a sandwich panel with designed dynamics quasi-zero-stiffness (QZS) truss cores. The latticed cores are made of programable curved beams, whose shape is carefully designed to meet the demand of both high-pressure resistance and dynamics QZS. An analytical model is developed to evaluate sound transmission of such panel. It is shown that the low-frequency sound insulation performance of the customized panel increases with the hydrostatic pressure and reaches its maximum when the QZS state is triggered. The effective pressure range of the proposed sandwich panel can be further programed by stacking QZS beam lattices of different static load plateaus. The proposed design strategy stems solely from the structural geometry of the curved beams and is therefore materials-insensitive. The linear/inverse relationships between static loading feature and characteristic mechanical properties/geometrical parameters, and the stacking arrangement of lattice bring out the programability of the panel’s bearing capacity. The design strategy, together with the established database, provides a feasible approach for underwater sound insulation of equipment subjected to elevated pressures.

Особенности оценки пожарной опасности и выбора теплоизоляционных материалов для трубопроводов и оборудования в зданиях и сооружениях

Thermal insulation of pipelines, in addition to energy-saving functions, must ensure the operational reliability and safety of the functioning of heating systems, water supply, heating networks, technological systems and air conditioning in industrial, public, and residential buildings and structures. Use of fire-hazardous thermal insulation of the pipelines and equipment during an ignition creates conditions for the development of a fire, the manifestation of its hazardous factors, which can lead to material damage and death of people. Analysis of the normative documents regulating the installation and operation of thermal insulation for pipes and equipment showed that the fire safety requirements are established only with respect to the combustibility group of thermal insulation materials. At the same time, their ability to spread flame over the surface, smoke formation and the release of gaseous toxic combustion products are not considered. The article presents the results of experimental studies of the complex of fire hazard characteristics of pipe insulation materials, and the study of methodological features of assessing their combustibility group according to GOST 30244 (method 2). The expediency is identified concerning the formulation of the principles of fire-fighting rationing of the pipelines and equipment for industrial, production, residential and public buildings (premises) and structures. These criteria set limits on combustibility, flammability, flame spread, smoke generation and the release of toxic combustion products. It is determined that the selection and justification of fire hazard indicators can be performed for thermal insulation of pipes and equipment with various functional purposes, applications, and technological features.

Improving the Efficiency of Acoustic Insulation for Power Equipment

Improving the Efficiency of Acoustic Insulation for Power Equipment

Thermal insulation of engineering structures with mineral wool based on basalt fiber

The most vulnerable link of central heating systems are heat pipelines. Steam and condensate pipelines devoid of thermal insulation are a constant source of heat loss, which can be easily eliminated. In most cases, the thermal insulation of all heated surfaces does not present significant difficulties. There may be situations when the insulation was removed during maintenance or repair and not restored at the end of the work. Removable thermal insulation elements of valves and other devices may also be missing. To ensure the economic efficiency and reliability of heat supply, it is necessary to intensively modernize heating networks. The most effective way to increase the energy efficiency of engineering structures is the use of modern structural solutions using thermal insulation materials. In addition, it allows you to reduce operating costs, that is, to achieve significant savings in fuel resources. The economical efficiency of district heating systems at the current scale of heat consumption largely depends on the thermal insulation of equipment and pipelines. The struggle to reduce transport heat losses in pipelines is the most important means of saving fuel resources. The paper considers the possibility of improving the energy efficiency of engineering structures through the use of modern structural solutions using thermal insulation materials based on basalt fiber.

Development in Emergency Device of Live Deficiency Elimination for SF6 Electrical Equipment

With the increase in the operating life of SF6 gas insulation equipment, the issues of excessive SF6 micro-water content, its excessive decomposition products, and its decreased purity have serious repercussions for safe and stable equipment operation. The conventional treatment is affected by the power outage and cannot completely eliminate the deficiencies. A set of the SF6 online dialysis device that can be operated without power failure needs designing and processing to realize online purification of micro-water with ultra-standard SF6 gas and impurity gases in it; when the high-voltage equipment leaks and cannot be powered off, this device can automatically control the air supply to ensure the safe equipment operation and earn time for subsequent repairs. The lightweight design and self-loading and unloading configuration of this device can satisfy the needs of special operating environments and sites.

Capture Mechanism and Optimal Design of Micro-Particle Traps in HVAC/HVDC Gas Insulated Equipment

Gas-insulated equipment such as GIS (Gas-Insulated Substation) and GIL (Gas-Insulated transmission lines) faces critical insulation failure challenges caused by particles inside. However, the particle traps, as key devices available to inhibit the movement of particles, lack theoretical basis and quantitative methodology for trap design especially with high voltage ratings. In this paper, a particle motion excitation and observation platform is established to physically simulate the actual online operating conditions of HVAC/HVDC GIS/GIL and study the capture mechanism of particle traps. Experimental results illustrate that, the collision motion style is a principal factor to affect the particle capturing capability, and the capture behavior of AC and DC particle traps can be classified into three separate modes, depending on variation of the collision process which can be characterized by random probability and the lognormal distribution rebound angle. A particle trajectory simulation model incorporating motion randomness is thereby presented to realize quantitative analysis and further optimize the trap parameters. A hazard index and minimum collision times are defined and calculated to quantitatively evaluate the particle collision effect on trapping capability. Further, a novel trap design topology is proposed to enhance the anti-motion efficiency of the particle traps. Targeted at high objective capture probability, the particle trap parameters are optimized to reduce the hazard index and improve the minimum collision times by the Monte Carlo scheme. The obtained results indicated that, the capture probability of AC traps can reach 86.5% at a gap spacing of 5 mm, while that of DC traps can reach 74.1% with an 8 mm-width slot and a 50-degree inclination angle. Verification of the novel article trap is implemented on a test rig, which gives an increased capture probability by 30% compared with the traditional trap design. The proposed new trap topology and corresponding methodology present quantitative guidance for particle traps optimization and render application potential for different voltage levels.

Very fast transient overvoltage calculation and evaluation for 500‐kV gas insulated substation power substation with double circuit and long gas insulated substation busbar

The operation of disconnectors in gas insulated substation (GIS) or power plant will produce very fast transient overvoltage (VFTO), which is considered to have serious harm to transformer longitudinal insulation and other high-voltage equipment insulation. VFTO may also lead to secondary circuit failure. In this paper, the holistic modelling of 500 kV GIS step-up substation equipment with a double circuit and long GIS busbar in a coastal power plant is established using Electromagnetic Transient Program (EMTP). The authors calculated the VFTO waveform that may be generated in different operations of the GIS substation. The authors analyze the amplitude and frequency characteristics of the VFTO waveform at lightning arresters and the entrance of transformers and find that the amplitude of VFTO at the entrance of #1 MT is less than its impulse withstand voltage. In some cases, the VFTO waveform at the entrance of #1 MT has high-frequency content with fast attenuation. The VFTO waveform generated when operating the disconnector close to the arrester will cause the arrester to act many times and count frequently in a short time.

Assessing the effectiveness of energy efficiency measures in the residential sector gas consumption through dynamic treatment effects: Evidence from England and Wales

Improving energy efficiency (EE) is vital to ensure a sustainable, affordable, and secure energy system. The residential sector represents, on average, 18.6% of the total final energy consumption in the OECD countries in 2018, reaching 29.5% in the UK (IEA, 2020a). Using a staggered differences-in-differences approach with dynamic treatment effects, we analyse changes in residential gas consumption five years before and after the adoption of energy efficiency measures. The analysis includes energy efficiency interventions involving the installation of new heating-related insulation equipment—i.e., of loft insulation and cavity walls, supported by energy efficiency programmes in England and Wales between 2005 and 2017—using a panel of 55,154 households from the National Energy Efficiency Data-Framework (NEED). We control for, among other factors, energy prices and the extent to which gas consumption changes are dependent on household characteristics and variations in weather conditions. Our results indicate that the adoption of EE measures is associated with significant reductions in household residential gas consumption one year after their implementation. However, the effect does not last in the long run and energy savings disappear four years after the retrofitting of cavity wall insulation measures and after two years following the installation of loft insulation. The disappearance of energy savings in the longer run could be explained by the energy performance gap, the rebound effect and/or by concurrent residential construction projects and renovations associated with increases in energy consumption. Notably, for households in deprived areas, the installation of these efficiency measures does not deliver energy savings. These results confirm the existence of effects that reduce the energy savings from the adoption of these efficiency technologies over time and indicates that, for some groups, these net savings do not seem to materialize.

Localization of Partial Discharge Using All-Fiber System Based on Crystal Fluorescent Fiber

Partial discharge (PD) is a common defect to determine the quality of high-voltage power equipment insulation systems. Localization of PD is very important for equipment maintenance and risk assessment. A localization algorithm of received signal strength (RSS) using demodulating PD optical signal is proposed. This is based on the optical effects caused by PD, which influence the optical signal that is transmitted through an optical fiber sensor placed inside the equipment. Compared with plastic fluorescent fiber, SiO2 cladding YAP:Ce crystal core fluorescent fiber (SYCF) with high luminous efficiency, low loss, and strong anti-electromagnetic interference capability is selected as the sensing unit to detect the received optical signal strength of PD, through the all-fiber optic sensing system to achieve the PD location in 3-D space. Based on the optical RSS localization method, the range of localization deviation of PD under 37-kV applied voltage is measured and studied. The average localization deviation and the error are 6.9 cm and 7.4%, respectively. Comparing the optical signal location method based on RSS with other methods of PD localization, the advantages and accuracy of the optical location method proposed in this article are outstanding. Therefore, the all-fiber system with SYCF via optical signal has a wide application prospect in the spatial localization of PD.

The influence of aging time and moisture content on the tensile strength of transformer bushing insulating paper

The parameter of tensile strength for transformer bushing insulating paper occupies an important position in the structural design and life evaluation of transformer bushing. In order to precisely achieve the effect of aging time and moisture content on the tensile strength of transformer bushing paper, transformer insulating paper samples with a thickness of 0.13 mm were prepared for tensile strength and dielectric strength testing under different moisture contents and aging states. The results show that the tensile strength (MPa) of insulating paper decreases linearly in the range of 0–648 h under accelerated thermal aging at 130 °C. However, there is a more serious exponential decline in the tensile strength (MPa) of insulation paper with its moisture content is boosted. The moisture content in insulation paper is the most important factor for insulation paper deterioration in oil-impregnated paper insulation equipment, which could accelerate the end of insulation service life. The value of capacitance increment ΔC of the insulation paper samples displayed closely linear growth with a moisture content from 0.5% to 5.9%. Strictly controlling the moisture content by monitoring the ΔC value of transformer insulation paper is of significance for prolonging its service life.

The detection of SF6 decomposition components SO2F2, SOF2 using mid-infrared TDLAS at 6.635 µm and 7.462 µm

SO2F2 and SOF2 are the main SF6 decomposition products, and the accurate detection of trace SO2F2 and SOF2 is of great significance to evaluate the internal insulation of the electrical equipment. In general, gas molecules have strong absorption coefficient in the mid-infrared spectral range, which can achieve very low detection limit and has great advantages in the detection of trace gases. In this paper, the quantum cascade lasers at 6.635 µm and 7.462 µm in the mid-infrared band are used as the light source of tunable diode laser absorption spectroscopy (TDLAS) to detect trace SO2F2 and SOF2. The results show that the second harmonic signal peak values of SO2F2 and SOF2 have a good linear relationship with the gas concentration. The linear fits of SO2F2 and SOF2 are excellent at 0.99374 and 0.99785 respectively. The experimental platform has good stability, and the maximum errors are 0.00109 V, 0.00208 V, and 0.00125 V. Allan analysis shows that the detection limit of SO2F2 is 0.1628 μL/L when the integration time is 7.44 s. The detection limit of SOF2 is 0.0167 μL/L at 2.8 s. The research results can provide technical reference and support for the effective detection of SF6 decomposition components.

Influence of dielectric barrier effect and thermally‐conductive network on thermal and electrical properties of epoxy under different frequencies and temperatures

AbstractEpoxy resin (EPR) insulations play a vital role in the insulation of modern power electronic equipment owing to their excellent dielectric properties. However, due to the high‐power density and miniaturization of power equipment which causes high heat fluxes under high voltage and high‐frequency stresses, EPR with good thermal and insulation properties is urgently needed. In this study, the polydopamine functionalized micro‐BN and core‐shell nano TiO2–SiO2 particles are dispersed in EPR to simultaneously improve thermal and dielectric insulation properties. It is revealed that the addition of micro‐nano particles significantly improves the thermal and dielectric performance. Particularly, the high thermal conductivity of micro‐BN and the dielectric barrier effect due to the core‐shell structure of nano TiO2–SiO2 are the main reasons for improved thermal and dielectric insulation performance, respectively. The EPR composite containing 3 wt% of micro‐BN and 1 wt% of nano TiO2–SiO2 exhibits the optimal performance with 0.49 W/mK thermal conductivity and the highest dielectric strength among all the samples, that is, 60.61 kV/mm even at 10 kHz and 90°C. This study found that the crucial factors are the surface encapsulation, weight percent, and homogeneous dispersion of particles in EPR, the dielectric barrier effect, thermal conductivity, and the mismatch between the dielectric constant of EPR and particles. This study proposes the optimal weight percent of suitable micro‐nano particles for EPR to produce suitable composites for high‐frequency and high‐temperature applications.

The Improved Design of a Mist Dust Removal Device for Coal Mining

With the development of a fully mechanized mining face, comprehensive mechanized mining face, and high-capacity and high-efficiency mining face in the coal mine, the level of mechanization and productivity is being improved, as well as dust capacity. If dust density is not reduced, it will be a hazard to the respiratory system of the miners seriously, even trigger pneumoconiosis, and the normal running of pieces of equipment will be affected, accelerating insulation equipment aging, and causing an explosion. Miners’ health and safety, normal running of equipment, and economic efficiency are being injured severely.
 Mist dust removal is the most widely used in coal mining, and it has been proven very effective. But the dust removal effect is affected because of the low interference resistance of the light control sensor, and small application scope of the solenoid valve, low agility of the spray device. In the paper, mist dust removal from coal mining was selected as the research background, and dust concentration detection and mechanism of mist dust removal were studied. The light control sensor, dust concentration sensor, and spray device were improved. By the mist dust removal device, online and real-time dust concentration monitoring can be achieved, and automatic dust removal can be realized according to the dust concentration. So, the dust concentration can be effectively reduced, working conditions can be improved, and safe production in enterprises and miners’ health can be guaranteed. The main work of the paper includes the following aspects.
 ① the paper studied the application background and research actuality of dust removal at home and abroad, and analyzed the existing technology of dust removal, and pointed out the research aim and main content.
 ② to provide academic support for the improved design of a mist dust removal device, the paper analyzed dust concentration detection, mechanism of mist dust removal and main affecting factors of dust removal.
 ③ Through needs analysis, the paper presented overall architecture and functional module design.
 ④ Control module, dust concentration sensor, light control sensor, and spray device were improved. at the same time, the performance tests were also discussed.
 ⑤ the paper run the laboratory tests and field tests, the test results showed that the device can measure dust concentration truly, and realize automatic dust removal, and reduce the dust concentration effectively.

Ultralight aerogel textiles based on aramid nanofibers composites with excellent thermal insulation and electromagnetic shielding properties

Ultralight, flexible and robust aerogel fibers based on aramid nanofiber/modified carbon nanotubes are prepared via a facile wet spinning method following with a freeze-drying technique. The aerogel textiles based on the strong aerogel fibers exhibit excellent thermal insulation properties within a wide range of temperature (−30–200 °C), which can be attributed to their ultralow density (5–12 mg/cm3) and high specific areas (123–219 m2/g). Moreover, the optimized aerogel textiles (with a thickness of 0.92 mm) show high-efficient electromagnetic shielding performance with a value exceeding 30 dB in the X-band. Overall, those aerogel textiles exhibit great potential for applications as thermal insulation and electromagnetic shielding equipment under harsh environments.

Electrical Tree Characteristics of Epoxy Resin Under Lightning Impulse at Cryogenic Temperature

As the key cryogenic insulating material for high-temperature superconductivity equipment, epoxy resin works in the harsh environment of strong electric field and extremely cryogenic temperature, and its operational reliability faces severe challenges. In this article, aiming at bisphenol F epoxy resin for cryogenic insulation of super-conducting power equipment, researches on electrical trees in epoxy resin under lightning impulse voltage at room temperature and cryogenic temperature were carried out. The effects of temperature, impulse voltage amplitude, and polarity on the initiation characteristics, growth morphology, growth rate, and expansion coefficient of electrical trees are discussed. The results show that the electrical tree initiation under impulse voltage in a cryogenic environment also has a polarity effect. The voltage is higher than that under negative impulse voltage, the shape of electrical trees is a typical branch, the color is darker, the tree channel is wider, and the branches next to the channel are simpler. There are fewer branches, and many darker spherical or ellipsoidal cracks appear in the electrical branch channel.

Research on intelligent photovoltaic control and protection switch based on fuzzy PID controller

In recent years, intelligent electrical equipment has been widely used. Control and protection switches (CPS) have the functions of circuit breakers, relays, disconnectors and many other products, etc. The intelligent PV low-voltage switch based on fuzzy PID controller designed in this study is applicable to the low-voltage PV distribution network with rated voltage of 500V and rated current up to 1200A with direct grounding of the neutral point of three four wires. The intelligent photovoltaic low-voltage switch designed in this paper can provide indirect contact protection to the distribution network, which can reduce the occurrence of grounding accidents caused by equipment insulation damage; the intelligent photovoltaic low-voltage switch designed in this paper is equipped with a wireless transmission module, which applies the wireless communication technology to the power equipment, so that the power equipment can realize the functions of remote monitoring the operation status of the power grid and controlling the switch breaking and closing. Finally, the fuzzy PID controller is introduced to improve the reliability of switch operation.

Audible acoustic characteristics of epoxy resins with partial discharge

The epoxy resin is the main solid insulating material for electrical equipment. PD (partial discharge) is an important factor leading to epoxy resin aging or failure. Fault detection technology based on audible acoustic imaging has the advantages of real-time monitoring, visibility, and flexibility and is gradually being used in the field of electrical equipment insulation state monitoring. However, the audible voiceprint features of epoxy resins with typical PD defects are not clear, which is not conducive to effective detection and fault diagnosis. Therefore, in this study, the study of audible voiceprint features of epoxy resins with a metal burr, pollution, metal foreign matters, and surface discharge defects was carried out. The discharge audible signals were obtained, and their time and frequency domain features were analyzed. The results show that the discharge audible signals of four PD defects can reflect the occurrence of PD simultaneously with pulse current signals. But the characteristics are obviously different in the time domain, which are embodied in listening perception, persistence, amplitude, and phase. In the frequency domain, the frequency spectra of discharge audible signals of four defects are mainly 5–10 and 13–24 kHz. Furthermore, the three feature vectors of frequency spectrum complexity, high-frequency energy factor, and maximum frequency point are extracted, which can well distinguish the discharge audible signals of four PD defects.

Detection of trace carbon monoxide based on cantilever enhanced photoacoustic spectroscopy at 2.33 μm

The composition gases internal SF6 insulation equipment is closely related to the insulation state of the equipment. According to relevant regulations, CO is an important component, and its concentration can be used as the basis for judging the internal insulation state of SF6 equipment. Gas detection based on photoacoustic spectroscopy is an effective means of online monitoring. The study adopts the 2.33 μm distributed feedback semiconductor laser as light source and the cantilever as acoustic sensor to develop the photoacoustic spectroscopy detection system, performs the photoacoustic spectroscopy detection of CO, and studies the influence mechanism of the background gas and temperature on the excited photoacoustic signals. The results show that the signal has high stability and a good linear relationship with the gas concentration. The lowest detection limit of CO in SF6 is 5.1 ppm, and the background gas and temperature mainly affect the excited signals by the difference of the cell constant.