Wall Bushing Research Articles

Seismic performance improvement of ±800 kV UHV DC wall busing using friction ring spring dampers

Wall bushings that connect converter valves within hall buildings and other electric facilities in a direct current (DC) field are indispensable in substations but vulnerable to earthquakes. A finite element model was developed to evaluate the seismic performance of a real ultra-high-voltage (UHV) DC wall bushing. The numerical results show that the maximum stress of the wall bushing during seismic activity does not satisfy the strength safety factor provisions within Chinese regulations. To improve the seismic performance of the wall bushing, an energy dissipation device composed of eight friction ring spring dampers (FRSDs) was proposed to be installed between the connection plate on which the bushing is mounted and a steel wall frame. In addition, optimum parameters of the FRSDs were researched and determined, then the seismic responses of the wall bushing with and without the FRSDs were compared to evaluate the energy dissipation effects. Full-scale shaking table tests were conducted on a wall bushing with the designed energy dissipation device. The validity of the numerical simulations and effectiveness of the proposed energy dissipation device of the wall bushing were verified by the experimental results in terms of seismic response mitigation.

Impact of Temperature on the Transient DC Field Distribution of ±1100 kV UHVDC Wall Bushing

UHV DC wall bushing is the only channel connecting the valve hall and the DC electric field in the converter station. For the epoxy - SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> gas composite insulation wall bushing, the main insulation material is the epoxy/crepe paper core and SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> gas. The transient process of establishing the DC electric field for the wall bushing is impacted by the temperature gradient. In this paper the 3-D temperature field of the wall bushing has been simulated considering the effect of heat conduction, convection and radiation. The simulation results have been confirmed using a temperature rise experiment. The transient process of the wall bushing under the actual operation condition has been simulated using the gas saturation current density method. The temperature impact on space charge density in the core, the surface charge on the interface, and the electric field distribution on the bushing is investigated. In this way a theoretical basis is developed for the optimal design of the bushing that is conductive to the safe operation of the bushing.

Temperature suppression of metal panel in electromagnetic field

PurposeThe purpose of this study is to suppress the temperature rise of high voltage wall bushing metal plate.Design/methodology/approachFirst, the authors built a model of a traditional metal plate and got the magnetic field intensity distribution by FEA tools. Optimized according to the magnetic field intensity distribution, the authors slot the traditional metal plate and embed permanent magnets in the slot. Finally, the authors got the temperature distribution diagrams of the above three cases at different current levels by FEA tools.FindingsSlotted metal plate is beneficial to suppress magnetic induction intensity, but the improvement of the magnetic induction intensity uniformity is not obvious. The method of embedding a permanent magnet in a slotted metal plate can optimize the magnitude and uniformity of the magnetic induction intensity in the metal plate. The larger the current passing through the metal plate, the better the temperature suppression effect of the slotted metal plate and the slotted metal plate embedded in the permanent magnet.Originality/valueThe effect of structural factors, slotting plate and setting permanent magnets on slots on the temperature of supporting plate is studied. The paper proposes two methods, slotting metal panels and embedding permanent magnet metal panels, to solve the problems of eddy current loss and high calorific value of the panel, which is of great significance to the safety of the grid equipment.

Study on the effect of solid products on DC surface flash-over voltage

According to statistics, solid product formed by the reaction between SF6 gas and metal electrodes at the connecting joint of ultra-high-voltage direct current (UHVDC) wall bushing is likely to adhere to the surface of insulating materials, which may seriously threaten the insulation of the bushing. Thus, studying the effect of the solid products on DC surface flash-over voltage is of great significance for evaluating the internal insulation of UHVDC wall bushing. The electrical parameters of the solid products were measured and compared with those of epoxy-impregnated composite insulating materials. The comparison result shows that there is a significant difference between them, which demonstrate that the solid products may have an impact on the DC flash-over voltage of epoxy-impregnated composite insulating materials. Furthermore, by means of the DC surface flash-over platform, the characteristic of the surface flash-over voltage of the epoxy-impregnated composite insulating materials with the solid products attached directly is analyzed. It is found that the decrease in the surface flash-over voltage is closely related to the type of solid product, gas pressure, distance between electrodes, way of attachment, etc.

Study on Surface Charge Accumulation Characteristics of Resin Impregnated Paper Wall Bushing Core Under Positive DC Voltage

As a critical component of a high-voltage direct current (HVDC) transmission system, resin impregnated paper (RIP) wall bushing has become a weak point because of its surface charge accumulation. This paper studies a model RIP wall bushing core designed by the equal capacitance method. The stationary resistive field along the gas–solid interface of the RIP wall bushing core is investigated theoretically by a gas model, which considers the non-linearly field-dependent volume conductivity. The results show that the gas conductivity along the core surface tends to be an arched distribution from the high-voltage conductor to the end shielding screen. The surface charge mainly accumulates at the turning point of the radius, which may threaten the core’s insulation. Then, the surface charge is obtained through a measurement system, where the experimental results are highly consistent with the simulation results. Considering the time constant of charge dissipation is nearly 15 min, it would be better to measure the surface charge on one axial direction of RIP wall bushing core after each voltage application. The simulation and experimental results of this paper can guide the design of a RIP wall bushing core.

Research on the deterioration process of electrical contact structure inside the ±500 kV converter transformer RIP bushings and its prediction strategy

Extra high-voltage converter transformer resin impregnated paper (RIP) bushing is used as the outlet device of the converter transformer, its safe operation is directly related to the reliability of the power system. Under the long-term effects of high current, strong mechanical stress and abrasion, the contact resistance of connection structure inside the bushing is prone to deteriorate. When the local overheating increases to a certain level, the insulation performance of bushing will decline and may lead to penetrating discharge. Therefore, it is vital to develop strategies for predicting the overheating fault of RIP bushings. In this study, firstly, one typical overheating fault of RIP bushing induced by the contact deterioration was diagnosed according to the fretting corrosive model and SF 6 decomposition process. Secondly, using the three-dimensional electromagnetic-thermal-fluid finite element method, the temperature distributions of RIP bushing under the different overheating degrees were simulated. Finally, based on the maintenance experience and simulation results, the diagnosis strategies were proposed. The diagnosis principle and prediction strategies were successfully helped to maintain the faulted RIP bushings and wall bushings before a destructive overheating accident could occur, which provide a basic reference for the fault prediction and improvements of relative standards.

Seismic Evaluation of Ultra-High Voltage Wall Bushing

A series of shaking table tests were carried out on a full-size polymer ultrahigh voltage wall bushing. In addition, a corresponding finite element model of the wall bushing was established. Four different earthquake ground motions—the El Centro, modulated Landers, Taft, and an artificial earthquake acceleration time history—were adopted in the study. Test results indicate that the safety factor of the wall bushing is less than the stipulated value of 1.67 in the Chinese code under the peak ground acceleration (PGA) of 2 × 0.4 g, where the factor 2 is used to simulate the amplification effect of the valve hall on the seismic responses of the wall bushing. Necessary slackness should be allowed for the conductors connected to the wall bushing because of the large displacement of the bushing terminals. There are relative displacements between the central conductor and polymer insulators during an earthquake. Increasing the out-of-plane stiffness of sealing plates at the terminals of the wall bushing could decrease the relative displacements. Moreover, a theoretical vibration model of the wall bushing was developed to demonstrate that the rocking effects of the installation plate and flange bottom plate have an influence on the seismic responses of the wall bushing.

Study on frequency domain dielectric spectroscopy of epoxy resin impregnated paper bushings under damp conditions

Epoxy resin impregnated paper (RIP) bushings are widely used as transformer bushings and wall bushings, but this type of bushing is easy to be dampened. In order to study the effect of moisture on the bushings' insulation performance, a test device was established to simulate the moisture absorption process in the air or N2 gas. Based on the frequency-domain dielectric spectroscopy (FDS) method, FDS curves that indicate the dielectric loss factor (tan δ) and capacitance (C) under different frequencies were tested and analysed. The results demonstrated that the FDS curve moves to the high frequency direction with the increase of the moisture content, and there exist minus tan δ and a negative peak in low-frequency band. Since the moisture content is much lower than in the air, tan δ and C under power frequency of the bushing almost unchanged in the N2 gas. However, the tan δ under 0.1 Hz increases sharply with the increase of trace moisture, and the higher moisture content, the greater increase rate. A damp diagnosis method for RIP bushings is proposed based on the FDS curves' frequency translation characteristics and tan δ variation law. Also the results can give references for RIP bushings' insulation diagnosis.

Seismic performance evaluation and improvement of ultra-high voltage wall bushing-valve hall system

To evaluate and improve the seismic performance of a ±800 kV ultra-high voltage (UHV) wall bushing-valve hall system, a finite element model of the system was established. Sixteen different earthquake ground motions were adopted in the analysis, and the critical seismic responses of the system were obtained. Moreover, a vibration theoretical model of the UHV wall bushing-valve hall system was established, and an investigation was conducted on the influence of different vibration components on the wall bushing seismic responses. The results indicate that the valve hall has an amplification effect on the seismic responses of the wall bushing and the vibration of the gable wall has a remarkable influence on the responses of the wall bushing. Two retrofitting measures were carried out on the valve hall to reduce the seismic responses of the wall bushing. It is concluded that increasing the stiffness of the gable wall could improve the seismic performance of the UHV wall bushing-valve hall system.

Research on key technologies in ±1100 kV ultra‐high voltage DC transmission

Based on completely mastering ±800 kV transmission technologies, the first ±1100 kV direct current (DC) transmission demonstration project is being constructed in China. Combining theoretical analysis and a large number of experiments, the margin of switching overvoltage in converter stations, the configuration scheme and performance of lightning arresters, the shielding angles of ground lines under different geographical conditions, and the maximum air gap of lines have been determined. The switching impulse flashover characteristics of equipotential sphere and typical rod-plane air gaps are also provided. The external insulation is designed differently for light, medium, and heavy pollution areas. For the ±1100 kV project, if the 8 × 1250 mm2 conductors are applied, the pole gap is 26 m and the height of the line is 25 m, all the electromagnetic parameters will meet the requirement of international electromagnetic standards. The key design points of ±1100 kV converter transformers, smoothing reactors, converter valves, and wall bushings are researched and the 75 mH smoothing reactors, ±1100 kV/5000 A converter valves, and ±1100 kV/5523 A wall bushings are successfully made. The optimised hierarchical connection modes and coordination control measure of the ±1100 kV project are studied and the results can provide sufficient technical support for the demonstration project.

Charge transport and accumulation around a spancer insulator for application in HVDC wall bushing

A charge transport model based on ion drift in gases of strong electron affinity has been studied in details and validated against experimental results in air and SF 6 at different pressure and voltage levels. The size of the insulators also differs significantly. The choice of the model parameters, i.e. the solid and gas material properties, is carefully examined with information from existing literature. Results show that using the selected parameters, satisfactory agreement between predicted and measured potential distribution and surface charge density along the insulator surface can be obtained. Computational results for an 1100 kV epoxy spacer for use in HVDC wall bushing show that the concept of electrical conductivity as a material property is no longer valid in strong electric field for the gas surrounding the insulator. The polarity and density of the accumulated surface charge depend on the relative largeness of the electrical conductivity of the insulator material and the effective conductivity of the gas. The nonlinear effect due to ion generation and recombination becomes significant at very high voltage. The metallic cap providing shielding to the triple junction at the high voltage end of the insulator can induce much stronger local electric field near the insulator surface, by a factor of 1.48, if its shape is not optimized against the insulator geometry.

Developed of High Voltage Bushing with New Shielding Technology for High Voltage Switch Cabinet

TGZ10A-40.5 wall bushing of high voltage switch cabinet from one company was taken as applied research object. Reference the development process of high voltage cable shielding technology, three samples were designed and produced depending on different sets of the shield system. The result show that: surfaces processed by the way that the inner (aluminum cylinder) and the outer (metal mesh ring) shielding components were coated with a semi-conductive material, made little sense to improve the withstand voltage level and reduce the partial discharge; surface processed by the way that inner shield component (aluminum cylinder) was coated with semi-conductive material, the outer shield component (metal mesh ring) was not coated with semi-conductive material, was obviously influenced the improvement of the withstand voltage level and reduction of the partial discharge, compared with traditional technology, the average start voltage of corona increased 23.8%, the average value of partial discharge dropped 27.7%.

Design and dielectric characteristics of the ±1100 kV UHVDC wall bushing in china

The ±1100 kV UHVDC wall bushing is the important power equipment in the ±1100 kV DC power transmission project of China. However, the reported literatures rarely mention its design method and the optimization of its insulation structure. In this paper, two specific designing schemes including the resin impregnated paper (RIP) condenser and the metalshielded core have been both adopted in the design of the wall bushing. Moreover, the actual operating environment and the rated parameters of the ±1100 kV UHVDC wall bushing have been analyzed in detail. Then, the nonlinear finite element method (FEM) analysis has been applied in the three-dimensional electric stress simulation of the UHVDC wall bushing. The electric field and temperature dependencies of the composite insulation used in the wall bushing have been taken into account. The E-field simulation results indicate that with the RIP condenser, the potential and electric field distribution can be much more uniform along the composite insulator of the bushing. Therefore, the compact design of the wall bushing can be obtained by this designing scheme. On the other hand, with the type of the metal-shielded core, the high E-field strength areas are mainly concentrated on the metal shield and the outer grading ring of the wall bushing. Therefore, the nonlinear FEM was applied in the structure optimization of the internal metal-shielded system used in the wall bushing. Finally, the maximum E-field strength of the wall bushing can meet the control requirement. Based on the simulation results and the optimization structure, the ±660 kV scaled prototype of the UHVDC wall bushing has been produced and passed through all the type tests according to the IEC 62199. The feasibility of the design of the ±1100 kV UHVDC wall bushing has been verified. This paper can provide the theoretical guidelines for the design, manufacture and operation of the UHVDC wall bushing.

Insulation Optimization of ±1000kV DC Wall Bushing

±UHV (Ultra-high voltage) DC (direct current) wall bushing is an important equipment of UHV DC transmission system. It plays a key role in the economic transfer, flexible allocation and safe usage of power. In this paper, the methods of improving the electric field distribution and insulation construction optimization are explored. The choice of insulation materials is discussed. Some calculations are made about how to optimize and design the capacitor core and how to optimize the parameters of grading rings. The research results would provide useful reference for further design and development of UHV DC wall bushings.

External flashovers, related insulation failures and corrective measures in converter stations of Nelson River bipole 1 and bipole 2

When Bipole 1 was placed in service in the 1970s at +450 kVdc, bushings were found to be vulnerable to external flashovers. Bipole 2 at +500 kVdc in the 1980s had bushings with increased strike distance of 1 m and creepage increased from 32.9 mm/kV to 43.6 mm/kV. This made the Bipole 2 bushings vulnerable to radial puncture under non-uniform wetting. Booster sheds were installed to greatly reduce external flashovers of porcelain bushings in both HVDC bipoles. Recently the porcelain clad, oil filled wall bushings of Bipole 1 have been replaced with oil-free composite wall bushings having silicone rubber sheds.

Electric Field Analysis with Space Charge Effects of ±1000kV DC Wall Bushing

±1000kV DC wall bushing is a complex insulation system working in different conditions, such as DC, AC and polarity reversal. No matter what kind of conditions, the space charge effects on the electric field distribution of the bushing are remarkable. A finite element model for ±1000kV DC wall bushing is established based on space charge theory, to analyze the electric field distribution in different conditions, especially when polarity reversal occurs. The research results provide useful references for the electric field analysis and insulation optimization of UHV (ultra high voltage) DC wall bushings.

Structural Optimization and Electric Field Analysis on the Insulation Structure of UHDV Wall Bushing

The insulation mechanism of UHVDC wall bushing is discussed. Design solution of the insulation structure is determined. In the solution, internal insulation includes SF6 gas-insulated and shielding structure, and external insulation is a type of composite insulating material, which is made up of epoxy FRP pipe and silicone rubber sheds. Creepage distance of external insulation and two types of shielding structures are designed in the paper. Finally two types of shielding structure are compared and optimized based on electric field simulation, and the result shows that dual-plate grounded shielding can enable the electric field strength of UHVDC wall bushing more evenly distributed.

Design of UHVDC Wall Bushing and its Electric Field Simulation

Reviewing and analyzing insulation mechanism of high voltage wall bushing, the structure of 1100kV UHVDC wall bushing and its key technical parameters are designed according to work conditions. Insulation structure and electric field of key bushing parts are simulated by ANSYS11.0. And the solution is optimized by SubProblem method based on the DC field theory. The result indicated that the parameters of designed solution could meet the needs of 1100kV UHVDC power transmission project.

Optimization design of grading ring and electrical field analysis of 800 kV UHVDC Wall wall bushing

This paper has analyzed the reason for the flashover of a typical 800 kV converting transformer bushing. The finite element method is applied to calculate the electric field and potential distribution along HV bushing as well as optimize the design of grading rings for the 800 kV UHVDC bushing. The three-dimensional (3D) model of 800kV bushing with valve hall configuration is established using ANSYS software. According to the calculation of electric field and potential distribution along the bushing without any grading ring, the joint of flange and shed and sheath has higher field intensity, and the electric field is rather unevenly distributed. Afterwards, this paper presents a method of adding a grading ring to the flange side in order to reduce the field intensity around the surface of shed & sheath. This method also optimizes the location and the configuration parameters of the grading ring, with an aim to limit the maximal electric field intensity around the metal fitting and the grading ring and obtain the optimal design of grading ring. Finally, it is verified by the 3D model that the maximal field intensity around the surface of flange, shed and sheath, and the grading ring is controlled within acceptable range, and the optimized design can be applied to the ±800 kV UHVDC power station project to reduce the occurrence probability of flashover of UHVDC bushing.

Electric field computation of ±1000 kv dc wall bushing with consideration of space charge effects

±1000 kV DC wall bushing under planning is a complex insulation system which bears the effects imposed by different working conditions. The existence of space charge distorts the electric field distribution, which might result in electric breakdown especially when polarity reversal occurs. Based on space charge theory, the amount of space charge can be calculated. A finite-element model for ±1000 kV DC wall bushing is established to analyze the electric field distribution under DC, AC and polarity reversal conditions especially considering the space charge effects. The electric field distribution with thermal stress is also calculated in this paper to incorporate the influence of the dielectric temperature gradients. The research results provide useful reference for electric field computation and further insulation optimization in developing ultra high voltage DC wall bushings. Copyright © 2013 John Wiley & Sons, Ltd.