High Voltage Bushings Research Articles

Study on FDS characteristics of oil‐immersed paper insulation bushing under non‐uniform moisture content

Capacitive high-voltage bushing is one of the typical oil-immersed paper insulation equipment, which is an indispensable external connection component for power transformers. In order to evaluate the effectiveness of frequency domain spectroscopy (FDS) for diagnosing moisture content of oil-immersed paper insulation bushing, this article studied the frequency-domain dielectric characteristics of oil-immersed paper insulation samples and field bushing. At the same time, the basic principle of interfacial polarisation is used to analyse the samples and field bushing with non-uniform moisture content. The results show that the moisture content affects the whole frequency band of the FDS curve. When the distribution of moisture content is non-uniform, the paper with high moisture content has a great influence on the whole FDS curve of oil-immersed paper insulation. In addition, the FDS curves will show a significant loss peak. The frequency of the peak point gradually moves towards the high frequency as the non-uniformity of the moisture content distribution increases. The experimental results show that the variation law of oil-immersed paper insulation can be used to quantitatively evaluate the moisture content and moisture type of oil-paper insulation power equipment.

The Effect of a Vertical Electric Field on the Surface Flashover Characteristics of a Bushing Model

High-voltage bushings play a crucial role in energy conveyance. Their specialized electric structure makes the bushing more vulnerable to surface discharge. However, the influence of a vertical electric field on the surface flashover of bushing structures remains unclear. To investigate this mechanism, four simplified bushing samples were built and the influence of pollution, leakage length, and the electric field component vertical to the dielectric surface on flashover properties of the bushing samples were tested. It was found that the surface pollution level was the decisive factor that influenced flashover voltage. When the leakage length and form factor were the same, the pollution flashover of the bushing structure was lower than that of the post structure. It was also found that increasing the leakage length was not very effective in improving the flashover voltage of bushings when the equivalent salt deposit density (ESDD) was high. No obvious correlation was found between pollution flashover voltage and electric field stress. Furthermore, the uneven wetting flashover performance of the bushings was tested. Under this condition, the flashover voltage decreased with an increase of the electric field component vertical to the dielectric surface. In addition, the electric field distribution of the samples was calculated and the results were in accordance with the experimental results.

Analysis of distribution laws of insulation indicators of high-voltage oil-fillled bushings of hermetic and non-hermetic execution

The object of research is the distribution laws of capacitor-type insulation values that were obtained during preventive tests for both serviceable and defective high-voltage bushings of 110 kV of hermetic and non-hermetic execution. One of the most problematic areas is insufficient knowledge and lack of justification of the laws for distributing these preventive tests of insulation of bushings. In the course of the research, a comprehensive approach to the solution of the problems was used, including probability theory and statistical analysis, analysis of world experience and a logical approach. In the long term, the results are expected to be extended to the bushing of other types having similar problems in the diagnosis of the condition. The method of statistical processing of the results of periodic tests of high-voltage bushings is proposed, which allows to form arrays with homogeneous values of indicators in conditions of limited measurement information. It is established that for the bushings of hermetic and non-hermetic execution, the insulation values for both the serviceable and faulty state can be described by the Weibull distribution. It is established that the distribution densities for serviceable and faulty state of high-voltage bushings intersect, and therefore it is impossible to select the maximum permissible values of insulation parameters that would not give erroneous solutions. The maximum permissible values of the insulation indices of high-voltage oil-filled bushings are proposed using statistical methods and taking into account the most significant operational factors. It is shown that for high-voltage bushings of the same execution there is a shift in mathematical expectations, which is due to the difference in operating time and different load factors of transformers. This circumstance must be taken into account when adjusting the maximum permissible values of the insulation indices of high-voltage bushings. The use of the developed algorithms and procedures of mathematical statistics in the problems of diagnosing high-voltage bushings contribute to improving expert judgment and decision-making.

Seismic vulnerability of power transformer bushings: Complex structural dynamics and seismic amplification

While it is accepted that high voltage bushings mounted on power transformers receive amplified seismic loads due to the structural dynamics of the transformer tank, it is also the case that complex structures made from steel plates and frames often exhibit unpredictable dynamic behavior. Empirical and numerical studies have shown that many transformer designs produce bushing amplifications within the standard expected value of 2.0 times the load imposed on a rigid-mounted bushing. This 2x amplification is required for seismic testing according to IEEE (the Institute of Electrical and Electronics Engineers), and yet this same body of data has also shown that many designs impose greater dynamic amplification. This paper is a numerically-based case study of four power transformer bushing configurations. The study adds additional evidence that bushing amplifications greater than 2.0 are possible, and it demonstrates that the complexity of these systems makes generalization of design recommendations problematic.

Dynamic Interaction of High-Voltage Power Transformer Bushings, Turrets, and Tanks

High-voltage (HV) bushings are attached to a power transformer tank either directly or indirectly via turrets. Turrets are used to achieve electrical performance requirements, but their potential impact on the seismic performance of the supported bushings has not been considered. Earthquake simulator testing and finite-element analysis were used to quantify the amplification of ground shaking through tanks (220- and 500-kV) and turrets to the points of attachment of roof- and sidewall-supported bushings. Substantial amplification of motion was seen in both physical experiments and numerical simulations. Sample bracing schemes external to the transformer tank were investigated to potentially reduce the motions experienced by the bushings. Bushing tip displacements were reduced in all stiffening cases studied, but the outcomes for bending moment at the bushing-turret connection were mixed, with no change in some cases and significant reductions in others. The physical and numerical studies described in this paper make clear the importance of dynamic interaction of bushings, turrets, and the power transformer tank. The methods currently used to address the amplification of input motion from the base of a tank to the points of attachment of its bushing are inadequate. The seismic design of HV power transformer tanks and turrets should be supported by finite-element analysis of validated models to avoid dynamic interaction in the bushing-turret-tank system, to minimize seismic demand on the transformer bushings, and to minimize the risk of substation damage in earthquakes.

ELECTRIC FIELD DISTRIBUTION IN TRANSFORMER BUSHING

Nowadays, the majority of power transformer high voltage (HV) bushings are consists of condenser oil Impregnated paper (OIP) type. These types of HV bushings comprises of a dielectric layers with conductive foils within each layer. Due to this, electric field (EF) is uniformly distributed.  In this paper, finite element analysis (FEA) is used to calculate EF distribution along outer surface of 11 kV transformer bushing. The effect of different material types of the bushing on the EF distribution has also been studied. It is projected that the results will provide an improved understanding of the EF distribution on the bushing outlet. This study may also assist in scheming HV bushing which can reduce the magnitude EF in the bushing.

高压套管油流外溢的化学检测方法研究

高压套管油流外溢的化学检测方法研究

Progress on design and manufacturing of dc ultra-high voltage component for ITER NBI

Toward the 1MV power supply system for the ITER neutral beam injector consisting of various components with oil insulation, gas insulation and vacuum insulation, design and manufacturing of dc ultra-high-voltage component have been progressed. Thermal design of long transmission line up to 100m was established. In order to design the high-temperature water channel for the plasma grid at 1MV potential, the resistivity of high-purity water at 180°C was measured for the first time. With the obtained resistivity, realistic high-temperature water circulating system was designed. A high-voltage bushing to transmit multiple voltages simultaneously has been also developed through a careful experimental study on vacuum insulation characteristics with multi-gaps coaxial electrodes. With the empirical scaling the electrostatic screen was designed taking into account effect of multi-gap and expected deformation such as thermal elongation during operation. After the assembly, stable voltage holding of 240kV at each stage was confirmed in the manufactured HV bushing.

SPIDER high voltage bushings: Design, development and first experimental tests

The ITER project requires at least two Neutral Beam Injectors (NBIs), each accelerating to 1MV a 40A beam of negative deuterium ions, to deliver to the plasma a power of about 33MW for one hour as additional heating. The fulfilment of such demanding performances required the realization of the full size prototype of the negative ion source (SPIDER − Source for Production of Ion of Deuterium Extracted from RF plasma), as well as the full size prototype of the whole 1MV ITER injector (MITICA − Megavolt ITER Injector & Concept Advancement) at PRIMA, the test facility for the ITER neutral beams now under construction at the Consorzio RFX in Padua, Italy.The SPIDER plasma source- housed in a stainless steel vessel maintained in high vacuum − is polarized at 112kV (12kV extraction voltage and 100kV accelerating voltage), so that the vacuum vessel must be equipped with three large alumina feedthroughs, ring shaped insulators (820mm in diameter) necessary to supply the electric, hydraulics gas and diagnostic services to the plasma source. These insulators (bushings) belong to the most critical items in the SPIDER assembly and they required a particular effort in designing, manufacturing and testing. This paper gives an overview of the insulator design, development, manufacturing activities and presents the results of the high voltage acceptance tests.

Design and Development of CRIO based Data Acquisition and Control system for High Voltage Bushing Experiment

Experiment of Prototype High Voltage Bushing (PHVB) is an important step to validate the design of HV bushing (HVB) of DNB for its electrostatic performance. The experiment is performed considering scaled down configuration DNB HVB with similar operating parameters and maintaining comparable electric stresses. Applied voltage is restricted up to 60 kV considering it’s scaled down configuration. To automate the entire experimental process and acquiring important experimental data for post analysis, a dedicated Data Acquisition and Control System (DACS) is designed. CRIO (compact reconfigurable input output) is a rugged, small sized hardware platform which combines the power of real time processor and FPGA bus. NI CRIO is now widely used as a controller for small scale experiments. For ensuring smooth control operation of the experiment; NI CRIO was selected as the controller for DACS of PHVB. In this paper the technical details of DACS design, implementation and test results are discussed.

Overview of the design of the ITER heating neutral beam injectors

The heating neutral beam injectors (HNBs) of ITER are designed to deliver 16.7 MW of 1 MeV D0 or 0.87 MeV H0 to the ITER plasma for up to 3600 s. They will be the most powerful neutral beam (NB) injectors ever, delivering higher energy NBs to the plasma in a tokamak for longer than any previous systems have done. The design of the HNBs is based on the acceleration and neutralisation of negative ions as the efficiency of conversion of accelerated positive ions is so low at the required energy that a realistic design is not possible, whereas the neutralisation of H− and D− remains acceptable (≈56%).The design of a long pulse negative ion based injector is inherently more complicated than that of short pulse positive ion based injectors because: • negative ions are harder to create so that they can be extracted and accelerated from the ion source; • electrons can be co-extracted from the ion source along with the negative ions, and their acceleration must be minimised to maintain an acceptable overall accelerator efficiency; • negative ions are easily lost by collisions with the background gas in the accelerator; • electrons created in the extractor and accelerator can impinge on the extraction and acceleration grids, leading to high power loads on the grids; • positive ions are created in the accelerator by ionisation of the background gas by the accelerated negative ions and the positive ions are back-accelerated into the ion source creating a massive power load to the ion source; • electrons that are co-accelerated with the negative ions can exit the accelerator and deposit power on various downstream beamline components.The design of the ITER HNBs is further complicated because ITER is a nuclear installation which will generate very large fluxes of neutrons and gamma rays. Consequently all the injector components have to survive in that harsh environment. Additionally the beamline components and the NB cell, where the beams are housed, will be activated and all maintenance will have to be performed remotely.This paper describes the design of the HNB injectors, but not the associated power supplies, cooling system, cryogenic system etc, or the high voltage bushing which separates the vacuum of the beamline from the high pressure SF6 of the high voltage (1 MV) transmission line, through which the power, gas and cooling water are supplied to the beam source. Also the magnetic field reduction system is not described.

Impact analysis of the capacitive coupling sensor on bushing external insulation

Online impulse frequency response analysis (IFRA) method is proposed and developed as a new technique to detect the winding mechanical deformation of a running transformer. The preliminary application of IFRA has been realised by using the bushing capacitive coupling sensor (CCS). However, whether the installation of the sensor affects the normal operation of the transformer is still unknown. To study above problem, this study first establishes a simulation model for transformer bushing based on the finite-element method and discusses the influence of sensor installation on the electric field distribution of capacitive bushing. The simulation proves that the installation of the CCS has minimal effect on the safe operation of the bushing. Second, the bushing withstand voltage tests are conducted in a lab, which proves that the installation of CCS meet the requirement for safe operation of capacitive bushing. Finally, the CCSs are installed on running power facilities, and the long and safe running experience indicates that the bushing and related facilities are unaffected by CCSs. The simulation analysis, withstand voltage test, and field application verify that the installation of CCS would not threaten the safe operation of high-voltage bushing, laying the foundation for engineering application of IFRA.

DETERMINATION OF INSULATION PARAMETERS OF CURRENT TRANSFORMERS AT MULTIPLE MEASUREMENTS IN MONITORING SYSTEMS UNDER WORKING VOLTAGE

Features of the data processing procedures of multiple measurements of the dielectric loss tangent of the high-voltage insulation, which are based on the comparison method, were considered. Three procedures were compared: the one procedure uses an assignment of a particular standard object for comparison, and two procedures don't use assignments of the special standard objects. Expressions of methodical errors of studied procedures were obtained. Analysis and calculations, which use the obtained expressions were made. Evaluations showed that an influence of a change of the tangent of dielectric loss of one from the monitoring objects on results of estimation of the tangents of other monitoring objects is the distinctive feature of the procedures without assignment of the standard object. Errors of these procedures more than errors of the traditional procedure, with assignment of the standard object. The study demonstrated that procedures without assignment of standard objects lead to difficultly predictable methodological errors, which hinder to estimate the actual value of the loss tangent and to estimate outcomes of the monitoring, by means comparing with allowable values. Moreover, the decrease of estimations of loss tangents of all objects, as a result of occurrence of at least one the object with strongly bad parameters, hides occurrence of other unsuccessful objects with smaller deviations and makes difficult recognition of such deviations at early stages. Improvements in processing techniques which reduce earlier specified errors and reduce the amount of measurements are proposed. The study results are useful in monitoring and diagnostic of basic insulation of current transformers or high-voltage bushings.

Prototype high voltage bushing: Configuration to its operational demonstration

High Voltage Bushing (HVB) is the key component of Diagnostic Neutral Beam (DNB) system of ITER as it provides access to high voltage electrical, hydraulic, gas and diagnostic feedlines to the beam source with isolation from grounded vessel. HVB also provides primary vacuum confinement for the DNB system. Being Safety Important Class (SIC) component of ITER, it involves several configurational, technological and operational challenges. To ensure its operational performance & reliability, particularly electrostatic behavior, half scale down Prototype High Voltage Bushing (PHVB) is designed considering same design criteria of DNB HVB. Design optimization has been carried out followed by finite element (FE) analysis to obtain DNB HVB equivalent electric stress on different parts of PHVB, taking into account all design, manufacturing & space constraints. PHVB was tested up to 60kV without breakdown, which validates its design for the envisaged operation of 50kV DC. This paper presents the design of PHVB, FEA validation, manufacturing constraints, experimental layout with interfacing auxiliary systems and operational results related to functional performance.

Principle and simulation of a high voltage bushing for a repetitive electron accelerator

A cylindrical graded bushing for the electron gun of the ASTRA-M pulsed repetitive accelerator was developed and simulated. In previous tests of the cylindrical graded bushing, primary reasons of electrical breakdown and degradation of dielectric elements were determined. Computational software was used to analyze the electric fields and simulate processes in the voltage grading system of the cylindrical bushing. This enabled proper modification and correction to the insulator structure for known problems. The new bushing has a conical structure instead of cylindrical one. The voltage graduation system uses nonsymmetrical voltage dividing for equal potential distribution along the grading electrodes. The grading electrodes provide shielding of organic dielectric surfaces from accelerated electrons and ultraviolet irradiation. Transmitted energy losses of up to 10% have been estimated in the nonsymmetrical voltage divider of conical bushing by simulating of high voltage pulse of 600 kV amplitude and 400 ns duration.

On optimization of the insulation of high-voltage coaxial bushing

This paper considers ways to improve the electric strength of a high-voltage bushing by decreasing the maximum electric intensity. For a coaxial cylindrical bushing with radii r 0 and r m > r 0, which result in an insulation gap (r m –r 0) with permittivity e0, this problem is solved with the use of an additional layer of insulation. This layer, with permittivity e > e0, is limited by radii r 0 and r e < r m . A simple algorithm to calculate an optimal thickness of this layer was obtained; the algorithm minimizes the maximum intensity as a function of radii r 0 and r m and relative permittivity e/e0 > 1.582. The algorithm is also transformed into an algorithm of synthesis of the noted layer thickness providing minimum intensity E m . The optimal relative values of all the dimensions of a high-voltage bushing as a function of the layer permittivity and level of reduction in the intensity E m are given in a form that is convenient for practical use.

Development of design technique for vacuum insulation in large size multi-aperture multi-grid accelerator for nuclear fusion.

Design techniques for the vacuum insulation have been developed in order to realize a reliable voltage holding capability of multi-aperture multi-grid (MAMuG) accelerators for fusion application. In this method, the nested multi-stage configuration of the MAMuG accelerator can be uniquely designed to satisfy the target voltage within given boundary conditions. The evaluation of the voltage holding capabilities of each acceleration stages was based on the previous experimental results about the area effect and the multi-aperture effect. Since the multi-grid effect was found to be the extension of the area effect by the total facing area this time, the total voltage holding capability of the multi-stage can be estimated from that per single stage by assuming the stage with the highest electric field, the total facing area, and the total apertures. By applying these consideration, the analysis on the 3-stage MAMuG accelerator for JT-60SA agreed well with the past gap-scan experiments with an accuracy of less than 10% variation, which demonstrated the high reliability to design MAMuG accelerators and also multi-stage high voltage bushings.

Design of vacuum vessel for Indian Test Facility (INTF) for 100 keV neutral beams

The Indian Test Facility (INTF) vacuum vessel is designed to install a full-scale test set-up of Diagnostic Neutral Beam (DNB) [1] for the qualification of beam parameters and the behavior of beam-line components prior to installation and operation in ITER. Vacuum vessel is designed in cylindrical shape having length of ∼9m with diameter of ∼4.5m and has a detachable top-lid for mounting as well as removal of internal components during installation and maintenance phases. The Vessel has hemispherical dish-ends with large openings for high-voltage bushing on one side and duct on another side. Vessel is provided with openings for hydraulic, cryo, gas-feed and diagnostics. Vessel duct is composed of three segments with length ranges from 3m to 5m with diameter of ∼1.5m and one vessel at the end to house the second calorimeter.The objective of this paper is to present the design and analysis of vacuum vessel, with respect to its functional and operational requirements. The design calculations are done as per ASME-BPVC SectionVIII-Div.1 and subsequently Finite Element Analysis (FEM) method has been adopted to verify the design.

Assembly and gap management strategy for the ITER NBI vessel passive magnetic shield

The neutral beam system for ITER consists of two heating and current drive neutral ion beam injectors (HNB) and a diagnostic neutral beam (DNB) injector. The proposed physical plant layout allows a possible third HNB injector to be installed later. The HNB Passive Magnetic Shield (PMS) works in conjunction with the active compensation/correction coils to limit the magnetic field inside the Beam Line Vessel (BLV), Beam Source Vessel (BSV), High Voltage Bushing (HVB) and Transmission Line (TL) elbow to acceptable levels that do not interfere with the operation of the HNB components. This paper describes the current design of the PMS, having had only minor modifications since the preliminary design review (PDR) held in IO in April 2013, and the assembly strategy for the vessel PMS.

Inner insulation structure optimization of UHV RIP oil-SF6 bushing using electro-thermal simulation and advanced equal margin design method

The iso-margin method based on the classical analytical equations is widely used in the development of extra high voltage (EHV) bushing. Therefore, its effectiveness and feasibility have been fully validated. However, with the theoretical formula, it is difficult to evaluate the influence of stray capacitance and temperature on the internal electric stress of the ultra high voltage (UHV) bushing. It's necessary to further improve the traditional iso-margin method. Firstly, the basic principle of iso-margin method has been briefly described. After that, the E-field distribution of condenser bushing was investigated on the Finite Element Method (FEM) computing platform. Then, the mathematical model of the advanced equal margin design method was established. Furthermore, this paper presents the program flow of optimization which combines the simulation of electro-thermal coupling process and the particle swarm optimization (PSO) algorithm. The proposed methodology was applied to the design of the prototype of the UHV resin impregnated paper (RIP) oil-SF 6 bushing, which realizes the uniform axial E-field distribution of the bushing condenser. Meanwhile, the partial discharge margin between adjacent foils can be equal. Moreover, the hot-spot temperature is lower than the operation limiting temperature of the RIP material. The bushing condenser was fabricated according to the optimal structure design. The prototype of bushing has passed through all the type tests. In this paper, the FEM electro-thermal coupling simulation and the advanced equal margin design method were applied to the inner insulation structure optimization of the UHV RIP oil-SF 6 bushing. Meanwhile, the proposed methodology provides some theoretical guidelines for the future research and development of other types of bushing on the UHV level.