Silicone rubber (SiR) is a fundamental electrical insulating material. For its use in nuclear power plants, the degradation induced by heat, gamma-ray irradiation, and steam exposure could be a concern. Therefore, their synergism on the degradation of SiR was examined experimentally. When SiR is first exposed to the steam at 200 °C, it melts and its tensile strength becomes impossible to measure. However, if the gamma-ray irradiation was given in advance, SiR is not destroyed so badly by the high-temperature steam. The reason for the above is that the formation of tight cross-linked structures via oxygens, induced by the irradiation of gamma rays, prevents the progress of hydrolysis.
Overhead transmission line has always been the major approach for large capacity power transmission over long distances, which takes a great deal of steel and land source. Therefore, composite cross arms are introduced to a full-scale AC 500 kV model tower, which could save the transmission corridor by 10%• The switching overvoltage flashover characteristics of the air gaps are investigated. Three flashover paths are observed and the flashover processes are recorded. Also, the influence of air humidity and air density is considered. And the test results are corrected to standard conditions. By comparison with other air gaps, the switching overvoltage withstand ability of composite cross arm is slightly higher than the typical V -string line insulators, which totally meets the requirement of AC 500 kV transmission tower.
To study the electrical tree growth and partial discharge (PD) characteristics of cross-linked polyethylene (XLPE) under the DC electric field, the XLPE insulation was made into needle-plate electrode samples to carry out experiments at 25°C and 50 °C. The results show that the electrical tree grows at 50°C accompanied by PD, and the PD amplitude positively correlates with the tree length. However, under the same voltage condition, the DC electrical tree does not grow at 25°C, and there is only a small amount of PD observed. The elevated temperature not only promotes the growth of the electrical tree but also enhances the amplitude and frequency of PD signals. In addition, when the power is turned off and the applied DC voltage begins to decay to zero, PD with the reversal polarity can be detected in the sample with an electrical tree defect at both 25°C and 50 °C. With the exponential decline of the applied voltage, the PD amplitude increases, as well as the discharge interval, until the applied voltage is close to zero. This may be due to the formation of a reverse electric field at the needle tip during the applied voltage drop, resulting in PD in the electrical tree.
There is no doubt that transformer plays a fundamental role in power system. At the same time, transformer winding fault diagnosis is an important topic. Many works put the most emphasis on the identification of fault type and degree, while ignoring the fault location. However, fault location is an urgent problem to be solved, which is worth studying and discussing. The contribution of this paper lies in the location of Disk space variation (DSV) fault The introduction of digital twin can solve the problem of insufficient fault cases, and pave the way for the intellectualization of fault diagnosis. In this paper, the digital twin of transformer winding is established based on double ladder network, in which the distributed parameters are calculated by finite element method. Frequency response analysis (FRA) is one of the most widely accepted methods for transformer winding mechanical deformation fault diagnosis. By extracting the mathematical index of FRA, multi-layer perceptron (MLP) is trained and DSV fault location is realized. In addition, the popular support vector machine is also compared with the MLP model in this paper, which further highlights the advantages of MLP. The proposed method is verified by an actual transformer, and the results are satisfactory.
The silicone rubber of the composite insulator is critical to the silicone rubber's operation time. To study the changing pattern of silicone rubber composition and silicone rubber operation process, 2, 6 and 10 years of composite insulator silicone rubber were chosen for testing, which included scanning electron microscopy analysis, thermogravimetric analysis, differential scanning calorimetric analysis, fourier infrared analysis, and X-ray spectroscopy analysis. The correlation results show that the integrity of the silicone rubber molecular chains deteriorates during operation, and an increasing number of cracks and holes appear on the silicone rubber surface. The operation of silicone rubber is related to the change and precipitation of aluminum hydroxide in silicone rubber components, and aluminum hydroxide changes the most during operation. This research can better reflect the surface aging state of silicone rubber sheds, which can be used for formulation preparation, quality inspection, operation condition assessment, and aging failure analysis of composite insulators.
This work evaluates the influence of typical first return-stroke current waveforms of negative downward lightning flashes, as recorded in literature, on the computed fast-front overvoltages on a typical 150 kV overhead transmission line. The critical flashover currents are also assessed. The investigation is performed through ATP-EMTP simulations considering lightning strikes to towers (backflashover) and phase conductors (shielding failure). Results for recorded lightning current waveforms are compared with those obtained for the widely used CIGRE waveform; the front time, maximum steepness, and time to half value of the latter are varied according to their statistical distributions. A comparison between CIGRE and double-peak waveforms is also performed. It is shown that the use of actual recorded return-stroke current waveforms may affect considerably the computed overvoltages and critical currents. The leader development models employed for flashover prediction are discussed in terms of the criterion used to terminate leader propagation for withstand cases.
Insulator arrangement has significant influence on pollution flashover voltage under natural pollution condition. In this paper, the pollution discharge process of an inverted T - type insulator string is simulated in the artificial climate chamber, and the pollution discharge voltage is compared with the suspended I string. The difference of pollution flashover voltage gradient E50 between two different series types is not obvious. According to the analysis, since the creepage distance, material coefficient and shape coefficient are consistent, the pollution flashover voltage gradient will not be much different.
The streamer inception voltage simulation method is described as implemented in the post processing of Ansys Maxwell electrostatic solver. Physical model-based streamer simulation demands tremendous simulation time and is hard to apply for real engineering cases. The streamer criteria approach described here provides a fast, accurate and easy to use method to evaluate the streamer inception voltage for gas insulation. The simulation is based on electrostatic simulation for 2D/3D models. From the electrostatic simulation results, the electric field line tracing is performed from defined starting points. Field line tracing has two methods: 1) insulation gas space 2) along the solid insulator surface. Based on the electric field value along this field line and the streamer inception criteria, the streamer inception voltage can be calculated, which is influenced by effective ionization coefficient properties of insulation gas, the streamer constant, the electric field distribution, the pressure of the insulation gas. Three validation simulations, Plate/Plate, Rod/Plate and Sphere/Sphere are made and compare the results from literature, all have good agreement with the results from literature. Apart from the above-mentioned three configurations, two industry application examples were simulated and compared with test results, the simulated and test results agreed with each other. It provides an easy accurate and fast way to calculate the streamer inception voltage which can support the design of high voltage devices in general.
Coupling agents can be key for the electrical performance of BN/ meta-aramid paper. In this article, triethoxy-silane coupling agents with different organophilic groups, including mercapto-propyl (MP), glycidylether-propyl (GP), amino-propyl (AP) and trideca-fluoro-octyl (TFO) were studied. The structural and electrical properties of modified papers were compared, and the molecular simulation was conducted to reveal the interface interaction of modified BN and aramid. The results show that AP and TFO have a better enhancing effect of insulation performance of composite paper than GP and MP. By choosing TFO and 15 wt% filler content, the optimal breakdown strength of paper was obtained as 28.17 kV /mm, 1.8 times that of the hydroxylated BN/ aramid paper.
The stem evolution during the dark period is important for subsequent corona pulses or leader initiation. To this end, a physical model is built to simulate the stem evolution, in which the migration process of space charge and thermodynamic processes of the stem channel (heat conduction, heat convection and thermal diffusion) are both considered. The effect of voltage rise rate, electrode shape, and air pressure on the stem evolution during dark period is investigated. Results show that the space charge migration contributes to the stem elongation on the axial length and be more influential than thermodynamic processes at high voltage rising rates. Moreover, the stem elongation in the axial direction is more evident with a smaller curvature radius of the electrode tip. In addition, as the air pressure decreases, the central temperature of the stem channel rapidly decreases, and the heat dissipation is dominant. This study can help to further understand the characteristics of the dark period and its effect on subsequent discharges.
Breakdown and aging properties of five insulating liquids have been discussed and compared. Additionally, the characteristics in their properties under different voltage polar-ities were analyzed to study the effect of aging on the polarity effect under LI voltage in semi-uniform field. These finding were compared to standard compliant AC breakdown test. After 2330 h and 4350 h, respectively, of aging a change in the aging markers water content (absolute and relative), total acid number and color was seen in all liquids. Viscosity increased only in natural esters up to 10 %. The aging related increase in water content was only alarming for mineral oil, being above 20 %. The effect of aging on the breakdown voltage differed depending on the voltage type and polarity applied. Ageing had the least effect with negative lightning impulse voltage. For the synthetic ester MIDEL 7131 strongest reduction in breakdown voltage was seen under positive lightning impulse voltage. It decreased more than 24 %, from a breakdown voltage above 560kV to 428kV. The change in breakdown voltage in mineral oil amounted to only 3 %. For all other oils decrease of breakdown voltage due to aging accelerated degradation was most pronounced under AC voltage. With the natural esters the decline amounted to 17 %, with the synthetic esters to 26 % and a 38 % decrease of AC breakdown voltage was observed in mineral oil.
Silicone rubber (SIR) has been widely used in the insulation of cable accessories due to its excellent performance. In this paper, pure SIR and nano $\boldsymbol{\text{Al}_2 \mathrm{O}_3 / \text{SIR}}$ composites are thermally aged for 0–80 days at $\boldsymbol{200^{\circ} \mathrm{C}}$. The effects of long-term thermal aging on the space charge transport are analyzed. The results show that with the increase of thermal aging time, the accumulation of heteropolar charge of pure SIR and nano $\boldsymbol{\text{Al}_{2}\mathrm{O}_{3}/\text{SIR}}$ composites gradually decreases and changes to the accumulation of homopolar charge. Compared with pure SIR, the space charge accumulation of $\boldsymbol{\text{Al}_{2}\mathrm{O}_{3}/\text{SIR}}$ composites decreases significantly and changes little with the increase of thermal aging time. It is believed that when doped nano $\boldsymbol{\text{Al}_{2}\mathrm{O}_{3}}$ in SIR, the increase of carrier mobility and the introduction of metal oxides reacting with fallen free radicals to form stable compounds both lead to less space charge accumulation of $\boldsymbol{\text{Al}_{2}\mathrm{O}_{3}/\text{SIR}}$ composites.
As a renewable and environmentally friendly liquid dielectric, natural esters are widely used in oil-immersed power transformers because of their anti-aging and high ignition point properties. However, the presence of large amounts of unsaturated fatty acids in natural ester increases their chemical activity and deteriorates their oxidative stability. Currently, the initial oxidation temperature of the natural ester can be increased by adding the composite antioxidant. Therefore, the microscopic molecular simulation of the process of polysilsesquioxane (POSS) modified natural ester oxidation was studied in this paper. natural ester and POSS additive models were established and simulated via molecular dynamics (MD) simulations based on ReaxFF (Reactive Force-Field). The results showed that the increase in temperature and heating time will promote the oxidation of natural ester, while POSS can effectively prevent this process. This article reveals the mechanism by which POSS postpones the oxidation of natural ester and provides certain guidance for the related experiments and theoretical studies of subsequent antioxidants.
Continuous promotion and sustainable development of ultra-high voltage(UHV) transmission engineering construction in China has brought significant attention to the UHV post composite insulator owing to its unique advantages. However, the core diameter of ±800kV post composite insulator used in UHV engineering is almost larger than φ280mm.From the aspects of structural design, component preparation and performance test, the research of ‘large-diameter’ is highly significant. In terms of structural design, the researchers mainly use the mechanical load theory calculation or finite element simulation to explore the key nodes and the overall stress of the post composite insulator, and put forward the theory of optimizing the section design and the fixture fixing method, which lays the foundation for the structural design, improvement and optimization of large-diameter post composite insulator. The research on component preparation could be divided into two aspects: material formulation and molding process. For ‘large-diameter’ core cracking, insulation degradation and other issues, many studies have been carried out on toughening modification of epoxy resin, hydrophobic migration and recovery ability of sheds materials (high temperature vulcanized silicone rubber, hydrophobic aliphatic epoxy resin (HCEP)), optimization of curing conditions, and improvement of interfacial strength. However, there is still progressive space. The long-term operation reliability of toughened large-diameter core has not been studied yet. Moreover, the application of HCEP has not yet formed a general formula system. In terms of performance testing, have been done and obtained engineering conclusions research on the mechanical and electrical properties, seismic performance and aging characteristics of large-diameter post composite insulators. With the development of UHV transmission projects, the Chinese national standards have been gradually improved, while the post composite insulator materials still need to be continuously studied. In this work, the development trend of UHV large-diameter post composite insulators research were prospected. The summary of these research results would provide reference for the development of UHV large-diameter post composite insulators in the future.
With the rapid development of clean energy,three-phase three-limb transformer is widely used in offshore wind power systems. However, the classical BCTRAN model can not accurately simulate the deep saturation phenomenon at each terminal. In this paper the improved BCTRAN model of three-phase three-limbs transformer has been built. The improved BCTRAN matrix of three-phase three-limbs transformer can accurately describe the coupling relationship between different windings. Deep saturation inductances are measured and determined using the hybrid source method to create the magnetizing branch, including the deep saturation region. Inrush current experiments on a 12.5MVA three-phase three-limb transformer in offshore wind power systems show that the first peak error of inrush current of the improved BCTRAN model is reduced from 24.9% to -1.7 % , comparing with the traditional model, whichcan accurately represent the saturation characteristics and provide a basic model for hree-phase three-limb transformers in offshore wind power systems
Natural ester, as a kind of renewable and environmental insulating material, has created broad opportunities for the development of electrical industry. To better explore the mechanism and principle of natural ester discharge, the effects of electrical field the space configuration, ionization energy, excitation energy and frontier orbital of the natural ester molecules were studied by density functional theory. The results show that the natural ester molecular chains deflect toward the electric field and its dipole moment increases with the increase of electric field intensity. The ionization energy of natural ester molecules decreases significantly with increasing electric field intensity. Among all molecules, the ionization energy of glycerol triolein has the most obvious decrease. The electric field has great influence on the excitation process of natural ester. The excitation energy of natural ester molecules will decrease in different electrical field. The HOMO of natural ester molecules gradually moved in the direction of the electric field, while its LUMO gradually moved towards the source of the electric field. The energy gap of natural ester decreased significantly under the influence of electric field. This paper provides a strong theoretical guidance for the research of natural ester discharge and improving its breakdown voltage.
Transmission line is an important infrastructure to ensure China's energy security. In recent years, rainstorm and waterlogging disasters have occurred from time to time, resulting in the increasing geological disasters of transmission lines, which seriously threatens the operation safety of high-voltage transmission lines. Traditional monitoring methods (GPS and leveling) have limitations in monitoring the deformation of transmission pole tower. In this paper, the cumulative tower foundation variables of a 500kV Line from November 2020 to June 2021 were retrieved by using the small baseline set (SBAS) technology and sentinel-1a satellite radar data. The comprehensive analysis and monitoring results show that the overall foundation of the line is stable, and the tower speed change rate of pole 7 is the largest, which is 25 mm / A. Among them, the deformation in May 2021 has an obvious acceleration process. Combined with the local meteorological conditions and the monitoring and analysis of manual activities, it is inferred that the deformation of the land subsidence area is related to the ground or underground construction process. The results verify the feasibility and effectiveness of this method in surface deformation monitoring and transmission tower structure monitoring along the transmission line..
Overheating faults within GIS equipment occur frequently, which has a negative impact on the normal operation of the equipment, and it is of great significance to the safe and reliable operation of GIS to discover and eliminate the hidden dangers of thermal faults in advance. The closed structure of GIS equipment makes it very difficult to detect its internal state. It is of great significance to invert and reconstruct the internal state of the equipment through external detection signals for equipment state evaluation and fault diagnosis. At present, the digital twin technology of power equipment is developing at a high speed, and digital twin is to establish a dynamic virtual model of physical entities in a digital way with multidimensional, multi temporal and spatial scales, multi disciplines, and multi physical quantities to simulate and depict the attributes, behaviors, rules, etc. of physical entities in the real environment, and fully reproduce the actual operation of physical entities in the real environment. Based on the evaluation of the heat state of the device, this paper proposes a visual display and evaluation method of the heat state applied to the GIS digital twin, which integrates the internal overtemperature diagnosis of GIS with the digital twin technology to realize the efficient application of the diagnosis of the heat state of GIS equipment..
