High Voltage Bushings Research Articles

Numerical Investigations into the Homogenization Effect of Nonlinear Composite Materials on the Pulsed Electric Field

Pulsed power equipment is often characterized by high energy density and field intensity. In the presence of strong electric field intensity, charge accumulation within insulators exacerbates electric field non-uniformity, leading to potential insulation breakdown, thereby posing a significant threat to the safe operation of pulsed power equipment. In this manuscript, we introduce nonlinear composite materials with field-dependent conductivity and permittivity to adaptively regulate the distribution of the pulsed electric field in insulation equipment. Finite-element modeling and analysis of the needle-plate electrodes and high-voltage bushing are carried out to comprehensively investigate the non-uniformity of the distribution of the electric field and the homogenization effect of various nonlinear materials in the presence of pulsed excitations of different timescales. Numerical results indicate that the involvement of nonlinear composite materials significantly improves the electric field distribution under pulse excitations. In addition, variations in the rising time of the pulses affect the maximum electric field intensity within the insulators considerably, but for pulses of nanosecond and microsecond scales, the tendencies are the opposite. Finally, via the simulations of the bushing, we illustrate that some measures proposed for improving the uniformity of the electric field under low frequencies, e.g., increasing the length of the electric field equalization layer and the distance of the underside of the electric field equalization layer from the grounding screen, are still effective for the homogenization of pulsed electric field.

Investigating the effects of corrosion parameters on the surface resistivity of transformer’s insulating paper using a two-level factorial design

The integrity of the insulation in oil-filled power transformers, shunt reactors, and high voltage bushings can be affected when copper dissolves in the insulating oil and then deposits onto the paper insulation. The presence of dissolved copper in the oil increases dielectric losses, while copper deposition significantly improves the conductivity of the paper insulation. Various factors, including temperature, oxygen, sulfur groups, passivators, and ageing time, have been found to contribute to the acceleration of corrosion activity in transformer insulating oils. Unfortunately, there is a lack of extensive research focused on systematically analysing and measuring the impact of corrosion-related factors on the dissolution of copper in transformer insulating oils and the deposition of copper onto solid insulation surfaces (Kraft paper). Therefore, this study aims to thoroughly examine the effects of corrosion factors on copper and sulfur deposition on Kraft paper insulation when it is submerged in transformer mineral oil (TMO). Using a two-level (2k) factorial design, we investigated three crucial factors: i) oil temperature, ii) elemental sulfur concentration, and iii) ageing time. It is worth mentioning that the results obtained from the two-level factorial design indicate that the surface resistivity is primarily affected by the temperature of the oil. This factor alone explains a significant 38.68% of the observed variation. In order to improve predictability, a regression model was created to estimate the surface resistivity of TMO-impregnated paper insulation. This model takes into account factors such as oil temperature, elemental sulfur concentration, and ageing time.

Study on preparation and properties of reversible discoloration coatings for transformer bushing temperature detection

Abstract Influenced by seasonal fluctuation and stringent operation requirements of transformer bushing, overheating often occurs. In order to detect the heating phenomenon, the reversible discoloration coating is prepared and its characteristics are investigated. The result shows that as the temperature increases, the color-changing material changes obviously from blue to colorless. With the increase of bisphenol A (BPA), the sample color is gradually deepened. With the rise of octadecyl alcohol, the color gradually becomes lighter, and the change range is smaller than BPA. By SEM images and laser particle size images of color-changing material, the size distribution of microcapsules is relatively concentrated and the dispersion is great. The color change temperature of reversible discoloration coating ranges from 48°C to 58°C. The discoloration is obvious. It is distributed that the reversible discoloration coating is thermally stable by the DSC test. As a result, a reference for the temperature detection of transformer high-voltage bushing is provided.

Analysis of electrical contact characteristics of strap contacts used in high voltage bushings under eccentric conditions

AbstractThe contact finger electrical connection structure is a crucial component of high voltage bushings, and its safety and reliability directly impact the operational stability of the bushing. To investigate electrical contact performance of the contact finger under eccentric conditions, a three‐dimensional electrical, thermal, and force multi‐physics coupling calculation model was established. Additionally, a test platform was constructed to measure electrical contact characteristics of the contact finger. The contact characteristics of the contact finger when the male head was axially deflected and radially offset compared to the female head were obtained. The research findings indicate when the male head deflects axially, the contact force changes of the contact finger blades on both sides are opposite. Moreover, as the axial deflection angle of the male head increases, the resistance of the electrical connection structure shows a rising‐slow decreasing‐fluctuating trend. The resistance is highest at 3°, with a resistance increase rate of 7.35%. Furthermore, the resistance of the electrical connection structure varies with the radial offset of the male head, following a power function. Contact failure occurs when the radial offset is 1.31 mm, and the resistance increase rate reaches 24.9% at a radial offset of 1.58 mm.

Molecular dynamics study on the influence of thermal aging on the mechanical properties of epoxy resins for high voltage bushing.

Thermal aging significantly deteriorates the mechanical properties and service performance of epoxy resins used for the high-voltage bushing. Current studies on the thermal aging behavior of epoxy resins mainly focus on experimental observations. However, an in-depth understanding of the mechanism of thermal aging of epoxy resins requires the monitoring of structural evolution of epoxy resins during thermal aging at the molecular level. To thoroughly analyze the intrinsic factors affecting structural evolution and the effect of thermal aging on the mechanical properties of epoxy resin for high-voltage bushing, epoxy resin models with different crosslinking degrees were established and thermal aging treatments at various temperatures and time periods were carried out by molecular dynamics simulation. It was found that the tensile strength of the epoxy resin was enhanced with the increase of the crosslinking degree, which was related to the elevation of the proportion of C-N and O-H bonds in its structure. With the increase of thermal aging temperature, the tensile strength of the epoxy resin decreased, which was related to the formation of weak bonds. At the early stage of thermal aging and after a period of high-temperature thermal aging, the strength of epoxy resin significantly decreases. The thermal aging of the epoxy resin is accelerated under external loading. In addition, the crosslinking degree and curing agent also affect the thermal aging resistance of epoxy resins. The results of this study can provide guidance for predicting and improving the thermal aging resistance of epoxy resins. Materials Studio was used to construct molecular models and complete crosslinking reactions. DGEBA and 44DDS (or 33DDS) were mixed at a ratio of 2:1, followed by crosslinking reaction. During this process, the Nose method was used to control temperature, the Berendsen method was used to control pressure, and the polymer consistent force field (PCFF) was used to control the motion and force of atoms. Isobaric-isothermal ensemble (NPT ensemble) was used to heat up epoxy resin models to various thermal aging temperatures of 400K, 500K, 600K and 700K. The models were maintained at these temperatures for different thermal aging times of 100ps, 200ps, 300ps, 400ps, 500ps, 600ps, 700ps and 800ps. Afterwards, the models were cooled down to 300K and subjected to uniaxial tensile testing at this temperature with a strain rate of 1 × 109s-1. The structural configurations and stress-strain data during the tensile process were recorded. The flow stress of the material was derived by counting the average stress in the 20-50% strain interval.

Effect of vertical electric field components on the local arc development along contaminated surfaces

During operation, a vertical-component electric field emerges on the surface of high-voltage AC bushings. This unique electric field structure renders the bushing more susceptible to discharge and flashover. However, limited attention has been paid to studying the flashover characteristics resulting from surface pollution in such electric fields. This investigation, involving four differently structured bushings as well as post insulators, delves into the impact of pollution, creepage distance, and electric field structure on bushing flashover characteristics. The study reveals that increasing the creepage length of heavily polluted bushings does not significantly enhance their flashover voltage. Moreover, the role of the vertical electric field in the local arc development was analysed. This research could provide valuable references for future bushing design in polluted areas.

A method for nonlinear electric-thermal coupling calculations of bushings based on unbiased gradient-free smooth domains.

High-voltage dry-type bushings, serving as the crucial junctions in DC power transmission, represent equipment with the highest failure rate on the DC primary side, underscoring the critical importance of monitoring their condition. Presently, numerical simulation methods are commonly employed to assess the internal state of bushings. However, due to limitations in the efficiency of multi-physics field computations, the guidance provided by numerical simulation results in the field of power equipment condition assessment is relatively weak. This paper focuses on solving the electrical-thermal coupling in high-voltage dry-type bushings. Addressing the most widely used tetrahedral mesh in numerical computations, we propose an efficient solution method based on the concept of "smooth domains." This method involves partitioning the volume centroids of the elements into multiple smooth domains within the computational domain. Electric and thermal conduction matrix calculations occur within these smooth domains, rather than within the grid or element interiors. This approach eliminates the need for traditional element mapping and complex volume integration. To demonstrate the effectiveness of this method, we use high-voltage dry-type bushings as a case study, comparing the performance of our approach with traditional finite element algorithms. We verify the algorithm's computational efficiency and apply it to the analysis of typical temperature anomalies in bushings, further illustrating its suitability for electrical equipment condition assessment.

Analysis of the results of preventive testing of bushings using elements of the theory of statistical hypothesis testing

The article presents the results of a study of the dependence of insulation indicators on the duration of operation for serviceable and faulty high-voltage oil-filled bushings, both of hermetic and non-hermetic construction. The results of periodic tests of oil-filled bushings, with a voltage of 110 kV of hermetic design with paper-oil insulation of the capacitor type, as well as non-hermetic construction, were used as initial data. Three statistical criteria were used to form statistically homogeneous data sets: the Wilcoxon rank test, the Z-test, and the Fisher-Snedecor test. The values of the sample mean, sample variance, as well as coefficients of asymmetry and excess of insulation indicators of high-voltage bushings were obtained for the array of initial data and arrays obtained during statistical processing. The values of the sample averages for the arrays obtained as a result of the statistical processing procedure differ significantly. There is a significant decrease in the sample variance values for tgd1 compared to the original arrays. To check the homogeneity of the data in the obtained arrays, the one-factor variance analysis model is used. The practical use of this algorithm made it possible to significantly reduce the heterogeneity of the results of periodic tests of the state of insulation of high-voltage bushings. The analysis of the composition of the arrays with homogeneous values of the indicators made it possible to establish that the values of the indicators of bushings from different regions of Ukraine, of different types and made with different numbers of factory drawings, got into the homogeneous data arrays. It is noted that for high-voltage bushings that do not have insulation defects, the values of the mathematical expectation of the same indicator for different arrays of preventive tests of capacitor-type insulation have a shift relative to each other. From this it follows that the load factor and the operating time of the transformer significantly affect the determination of the maximum allowable value of the insulation index of the high-voltage bushing.

Experimental study and numerical analysis of thermal hazard for fire accident in converter transformers

Converter transformers are widely used in high voltage direct current (HVDC) transmission systems. Due to its large storage capacity and relatively high failure probability of the insulation, pool fires are a common type of accidents for this type of transformers, which could pose a significant threat to the safety of personnels and the integrity of nearby transformers. During normal operation, the temperature of the transformer oil can vary between 80 and 90 °C. It is known that the oil temperature can have a significant impact on its burning characteristics. However, most of previous simulations of transformer fires utilized the material properties of transform oil obtained at ambient temperature to determine the heat release rate (HRR). In this study, experimental data (D = 0.2–1.0 m) at an initial oil temperature of 85 °C were employed to determine the correlation between HRR and burner diameter, which was subsequently used to validate the numerical model. 14 typical fire scenarios were examined to understand the accident development process of transformer pool fires. The results showed that a merged flame was observed at the inner side for the case when the fire occurred both on the oil tank upper surface and in the oil storage pit. The radiation impact on (and thus the risk of failure of) key transformer components was found to vary considerably across the different fire scenarios. The radiative heat flux at the outlet of the enclosure where the fire is located was found to exceed 5 kW/m2 and the recommended safety distance for firefighting can reach 6.6 m. It was also found that the maximum heat radiative flux received by the high voltage bushing of an adjacent transformer can reach 46.2 kW/m2 in the worst-case scenario, with a probability of escalation to the adjacent transformer approximately 3.50×10−4. Three distinctive areas (safety area, risk area, and dangerous area) were identified to determine firefighting positions and strategies for transformer substation fires. The present results could not only enhance the understanding of the accidental development of converter transformer fires but also provide valuable guidance in firefighting in various fire accident scenarios.

Investigation on Hot Spot Temperature of Resin-Impregnated Paper High-Voltage Bushing Based Upon Dielectric Loss

The resin impregnated paper high voltage bushing (RHB) has explosion-proof and flame-retardant advantages compared with the oil-impregnated paper bushing. However, the RHB failure is frequently caused by high temperatures, so it is essential to investigate the hot spot temperature of the transformer RHB. Thus, the multi-physics field simulation model of the transformer RHB is developed. Furthermore, the hot spot temperature distribution pattern is obtained. In terms of the transformer RHB temperature rise test, the transformer RHB frequency domain spectroscopy (FDS) is carried out under load and oil temperature variables. In addition, relationships between the transformer RHB hot spot temperature and FDS curves are established. It is illustrated that the inversion method of the transformer RHB hot spot temperature is based on the dielectric loss tangent integral. According to the tanδ curves, the dielectric loss tangent integral and the square of the dielectric loss tangent integral are used as the characteristic parameters for the inversion of the transformer RHB hot spot temperature. The results show that both characteristic parameters have a well-fitting exponential correlation with the transformer RHB hot spot temperature. In addition, this conclusion enables non-destructive measurement of the transformer RHB hot spot temperature to improve the thermal reliability of its operation.

Research on the Characteristic of the Electrical Contact Resistance of Strap Contacts Used in High Voltage Bushings

As an important electrical connection component in electrical equipment, the strap contact is directly related to the long-term operation stability of equipment. The electrical contact resistance (ECR) of the electrical connection structure is an important indicator for evaluating the reliability of the electrical contact system. In this research, the theoretical calculation of ECR of the strap contacts used by the G-W theoretical model and the fractal theoretical model is improved and compared. After comparison with the experimental measurement values, the rationality and accuracy of the two theoretical models are discussed. The results show that when the load is small (1–3 N), the maximum error of G-W model is 41%, while the fractal model method has a maximum error of 9%. When the load is large (4–10 N), the results of the two are almost the same, and the errors are both within 14%. In summary, the error range of the fractal model is smaller and the change trend is closer to the experimental value, which is suitable for a relatively better ECR analytical calculation theory. The research results can provide a theoretical basis for research on the electrical contact performance of the electrical contact structure of electrical equipment.

Research progress and prospect of insulation characteristics of HVDC converter transformer bushing

The paper mainly analyzes the development of the high voltage bushing is closely related to the development of power industry. With the gradual rise of the voltage level in power industry, bushing has experienced the development process from low voltage, high voltage, ultra-high voltage to ultra-high voltage. In order to meet operation requirements under the different voltage levels, the pure porcelain bushing, metal shielded bushing and capacitive bushing have also appeared in the bushing body structure, and the core material has gradually changed from the oil impregnated paper and the adhesive paper to adhesive impregnated paper. In the process of the continuous development of bushing structure and main insulation materials, the research on the high-voltage bushing mainly focuses on the material performance test of bushing, the improvement of the main insulation structure design method, and the simulation analysis of bushing voltage and heat sharing.

Problems of adaptation of the electrical industry to sanction limitations (on the case of Izolyator Group)

The article discusses the main problems that the Russian electrical industry faces in the modern period of sanctions restrictions. The article analyzes the situation with the provision of electrical engineering with imported materials on the example of the production of high-voltage cable fittings and high-voltage bushings, and also considers the current possibilities for their import substitution. The authors analyzed the possibility of supplying materials from new Russian suppliers of materials and suppliers from friendly countries, and came to the conclusion that under the current conditions, companies in the industry have the ability to fulfill the tasks of producing electrical equipment for the Russian power grid complex.

Electric Field Improvement for High-Voltage Bushings

Resin-impregnated paper (RIP) bushing has gained significant interest due to its extended application in Extra High Voltage (EHV) and Ultra High Voltage (UHV) electricity transmission systems. However, the design criterion of its overall structure, the geometry parameters of the condenser layers, and stress release devices, etc., are still not fully understood. This article proposes a unique electric field optimization technique to integrate both the analytical and the numerical methods. The charge simulation method (CSM) is employed to create the overall equipotential surface, within which the finite element analysis (FEA) is adapted to study the localized field enhancement effects, taking into consideration the multi-physics coupled fields. A case study is performed on an actual UHV bushing. The results are compared to the traditional methods, to demonstrate the benefit of the hybrid method.

Simulation Based Design of A 275kv High Voltage Bushing

Simulation Based Design of A 275kv High Voltage Bushing

Simulation Based Design of A 275kv High Voltage Bushing

Simulation Based Design of A 275kv High Voltage Bushing

Simulation Based Design of A 275kv High Voltage Bushing

Simulation Based Design of A 275kv High Voltage Bushing

High-Voltage Bushings and Their Production in Russia

The state of production of high-voltage bushings for rated voltages of 35 kV and higher in Russia is assessed. Attention is focused on bushings of various designs and purposes, the competitiveness of domestic production of bushings, the use of imported materials and components in them, as well as the extent to which the domestic production covers the country’s own needs in these items. The manufacture of these products around the world, its largest brands and manufacturers' specializations are specially considered. Much attention is paid to the science supporting the production of high-voltage bushings. Problems and achievements in the field of production technologies are outlined. Problems concerned with personnel training for this branch of electrical engineering, starting with vocational guidance at school, are discussed. In conclusion, information is given about the Izolyator (Insulator) Works, the flagship of the domestic production of high–voltage bushings. The article is written in the form of answers given by A.Z. Slavinsky, General Director of the Izolator Works, on the questions of P.A. Butyrin, Editor-in-Chief of the Elektrichestvo (Electrical Technology) journal.

Fast electrothermal coupling calculation method for supporting digital twin construction of electrical equipment

AbstractThe failure of electrical equipment directly or indirectly caused by overheating has become one of the main reasons for equipment accidents. The real‐time condition monitoring method of electrical equipment based on digital twin (DT) has received extensive attention and is considered as a technology with great engineering values and excellent application prospects. However, the current calculation of DT mostly relies on the traditional finite element method (CFEM). This method becomes less computationally efficient as the size of the DT increases, especially for electrical equipment with high complexity. It is difficult to meet the requirements real‐time calculation in DT. Therefore, starting from the algorithm optimization and parallel architecture, based on the weighted residual method and stabilised conforming nodal integration, a novel discrete method of electrothermal coupling equation is proposed and the data storage structure of the algorithm from the bottom layer is redesigned, and the corresponding GPU and multi‐core CPU parallel framework are proposed. Finally, taking the high voltage bushing as an example, the correctness of the method in this paper is verified by the CFEM code and commercial software ABAQUS. Under the same grid and accuracy requirement, the calculation time is shortened by at least five times than ABAQUS. And the method is easy to extend to other types of multi‐physics calculations.

Application of Comprehensive Diagnosis Technique in Fault Analysis of FRP Bushing of 110kV Transformer

FRP high-voltage bushing is widely used in power system because of its advantages of good mechanical strength, short production cycle and free maintenance. Due to the immobility of solid insulation such as glass fiber reinforced plastic and epoxy resin, once there is a local hidden danger, it will not heal itself, which is bound to develop into insulation breakdown. In this paper, starting from the creepage fault of a 110kV transformer FRP high-voltage bushing, comprehensive diagnosis techniques such as test detection, online monitoring, disintegration analysis and simulation calculation are adopted. Different diagnosis methods confirm each other and determine the cause of the fault. The analysis method in this paper has important reference value for fault analysis of high voltage equipment.