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Copyright of Electric Machines & Control / Dianji Yu Kongzhi Xuebao is the property of Electric Machines & Control and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The development of High Voltage Direct Current Gas-Insulated components that will be employed for the power supply of Neutral Beam Injectors, requires specific numerical tools to analyze the electric field distribution, with the purpose of supporting the engineering and operational phases.The tools must comply with the nonlinearity of the material properties of solid insulators and the transport mechanisms in the dielectric gas. Despite its high Global Warming Potential, SF6 will be considered as the baseline dielectric gas for the development of HVDC gas-insulated components to be used for the Acceleration Grid Power Supply of Neutral Beam Injectors. Attention especially to the mechanisms driving to an increase of leakage current flowing in the gas, thus giving rise to possible discharge phenomena is here placed, mainly focusing on radiation and injection regimes. The described methodologies are adopted for the numerical modeling of the 500 kV DC gas-insulated components that will be used for the power supply of the Neutral Beam Injector of the Divertor Tokamak Test facility. In particular, a conceptual design of the SF6 Transmission Line and the SF6-air bushing is conceived.

Partial dampness is the initial stage in the bushing damp process,so the effective diagnosis of partial dampness can avoid the further development of the damp. The partial damp diagnosis method of bushing based on the frequency domain spectroscopy (FDS) is proposed in this paper. Firstly,oil-paper insulation samples with different moisture content are prepared,and partial damped samples are formed through combination. Then the FDS characteristics are obtained. The results show that partial distribution of moisture leads to oil-paper insulation interfaces with different moisture content,and the interface relaxation polarization loss peak is introduced in the FDS curves. The greater the degree of partial dampness in the radial direction,the greater the amplitude of the loss peak,and it moves to the high frequency direction. The effectiveness of the diagnosis of partial dampness of bushing based on the characteristics of the interface relaxation polarization loss peak is verified by the simulation model of the transformer bushing. It shows that a new method for early fault warning and diagnosis of the transformer bushing is provided.

• Development of porcelain based100 kV feedthrough, for INTF system which is prototype of ITER DNB. • Attachment of metal flanges with porcelain using adhesive bonding. • The feedthrough is high vacuum compatible with local He leak tightness up to 1 × 10–9 mbar.l/s at room temperature. • Alumina, vespel and PEEK based feedthroughs are used for isolation among feedlines. • Vacuum barrier for3 1/8 inch RF feedlines have extensively checked for electrical fields. High Voltage Bushing (HVB) of the Indian Test Facility (INTF) of ITER Diagnostic Neutral Beam (DNB) is a porcelain-based 100 kV vacuum feedthrough. This will be used to feed the High Voltage (HV) supplies, coming from the HV deck to the Beam Source (BS) for the production of 100 kV H- beam under high vacuum, therefore, it has two major functions: 1. Isolate 100 kV feedlines from grounded vessel and 2. Forms vacuum boundary with 25 feedline penetrations of different kinds. INTF HVB has been designed with rigorous iterations of design optimization for vacuum, mechanical, and electrical requirements. After design, the development of INTF HVB required several prototyping activities to address the challenges in establishing the appropriate bonding methodology with high vacuum compatibility, handling procedure of large size (∼800 mm diameter and 530 mm height) insulator, prior assessments of tolerances due to as-built ovality in insulator and testing & qualification at various steps, to establish the implementation plan for manufacturing and assembly. As a result, techniques, based on prototyping, manifest to solve the challenges were utilized in the manufacturing, leading to the successful development of the HVB. [ABSTRACT FROM AUTHOR]

Abstract In this paper, bushing-breakdown was identified as one of the main causes of transformer failure that resulted in a fire outbreak in July 2015 at the Gadong Power Station, Brunei Darussalam. To perform the investigation, three specimens from the burnt pieces were collected, which were white ash, bushing housing ashes and solid remnants from the burnt site. Both JSM-610F FIELD Emission Scanning Electron Microscope (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) were used to obtain the electron images, and to analyze the types of elements present in the specimens. In addition, software simulations for the high voltage bushing failure were carried out using COMSOL Multiphysics Software for different oil levels, and the obtained results have been summarized. Finally, it is comprehended that fire outbreak happened due to leaking of the insulating oil in the high voltage bushing and loose tighten of the sealing part of the cable termination boxes. Highlights • In this paper, bushing-breakdown was identified through experimental, simulation and physical inspection. • For analysis, JSM-610F FIELD Emission Scanning Electron Microscope (SEM) and Energy Dispersive X-ray Spectroscopy (EDS) were used to obtain the electron images. • It is comprehended that fire outbreak happened due to leaking of the insulating oil in the high voltage bushing and loose tighten of the sealing part of the cable termination boxes. [ABSTRACT FROM AUTHOR]

The article describes a case study when the voltage collapse during lightning impulse tests of new power transformers was noticed and when the repeated tests finished with a positive result. The step-by-step process of reaching the conclusion on the basis of dissolved gas analysis (DGA) as a key method of the investigations was presented. The considerations on the possible source of the analysis showed that the Duval triangle method, used in the analysis of the concentration of gases dissolved in oil samples taken from bushings, more reliably and unambiguously than the ratio method recommended in the IEC 60599 Standard, indicated a phenomenon which was identified in the insulation structure of bushings analyzed. Additionally, the results from DGA were found to be consistent with an internal inspection of bushings, which showed a visible trace of discharge on the inside part of the epoxy housing, as a result of the lightning induced breakdown.

Porcelain bushings are universally employed for power transformers. However, non-condenser bushings are unsuitable for high voltage applications owing to their extreme non-linearity in potential and electric field distribution. High voltage insulated bushings are required to bring out the electrical energy through earthed barrier. Synthetic resin bonded paper condenser bushing (SRBP) and oil impregnated paper (OIP) bushing are commonly used bushings. These bushings have series of dielectric layers with conducting aluminum foils in between each layer to improve the distribution of electric field. The present paper discusses analysis of electric field distribution in a 145 kV OIP bushing with varying number of foils and their thickness using finite element method. Simulation results show that 9 foils, 4mm thickness each and 2mm gap between the foils is optimum for better distribution of the field. The paper also discusses the experimental verification of the field estimated through the simulation. [ABSTRACT FROM AUTHOR]

Abstract: The ITER Neutral Beam Injector (NBI) power supply system includes several non-standard components, whose ratings go beyond the present industrial practice. Two of these items, to be procured by Fusion for Energy, are: [1.] A −1MVdc air-insulated Faraday cage, called High Voltage Deck 1 (HVD1), hosting the Ion Source and Extractor Power Supplies (ISEPS) and the associated diagnostics. [2.] A −1MVdc feedthrough, called HVD1-TL Bushing, aimed at connecting the HVD1 to the gas (SF6) insulated Transmission Line (TL), containing inside its High Voltage (HV) conductor all ISEPS power and control cables coming from the HVD1 to be connected to the NBI Ion Source services. The paper deals with the status of the design of the HVD1 and HVD1-TL Bushing, focusing on insulation, mechanical and thermal issues as well as on their integration with the other components of the power supply system. In particular, the insulation issue of the integrated system has been addressed by means of an electrostatic Finite Element (FE) analysis whilst a FE thermal simulation has been carried out to assess the impact of the dissipation of the proposed design of the inner conductors (ISEPS conductors) not actively cooled. Finally, the paper describes the status of procurement strategy and execution. [Copyright &y& Elsevier]

Abstract: Superconducting electric equipments have a lot of advantages over the conventional devices such as improvements in overall efficiency, size reduction, high current carrying capability, and also environment-friendly products. Owing to these advantages, many research institutes have been tried to develop commercial superconducting devices, which could be applicable to the high voltage and high current electric networks. But up to now, most of the research works to develop commercial products were delayed because it was not easy to acquire reliable high voltage insulation properties and optimum insulation design skills considering extremely low temperature environments. Furthermore, it was difficult to determine optimum high voltage insulation level due to the lack of high voltage cryogenic dielectric test facilities. Thus, in order to establish the cryogenic dielectric technology regarding insulating design, cryogenic dielectric test skills, and to implement more reliable high voltage superconducting devices, high voltage cryogenic dielectric test facilities should be prepared for extra high voltage superconducting electric equipments. Recently, cryogenic dielectric test facilities were installed including 3m long 2m wide cryostat system with bushing, and 1.6MVA lightening impulse generators, 400kVA AC overvoltage test system in Korea. In this paper, design and installation of high voltage cryogenic dielectric test system including very big size FRP cryostat and high voltage bushing were minutely introduced. And some test results to develop high voltage bushings for liquid nitrogen cryostat in order to implement extra high voltage level bushings were illustrated. These test facilities will be fully utilized for the optimization of insulation design for extra high voltage superconducting electric equipments. [Copyright &y& Elsevier]

Abstract: In the ITER heating Neutral Beam Injector (NBI), a High Voltage air-insulated platform (named High Voltage Deck, HVD) will be installed to host the Ion Source and Extractor Power supply system and associated diagnostics referred to −1MV DC potential. All power and control cables are routed from the HVD via a feedthrough (HV bushing) to the gas insulated transmission line which feeds the Injector. The paper focuses on insulation and mechanical issues for both HVD and HV bushing which are very special components, far from the present industrial standards as far as voltage (−1MV DC) and dimensions are concerned. For this purpose, a preliminary design of the HVD has been carried out as concerns the mechanical structure and external shield. Then, the structure has been verified with a seismic analysis applying the seismic load excitation specified for the ITER construction site (Cadarache) and carrying out verifications according to relevant international standards. As regards the HV bushing design, proposals for the complex inner conductor structure and for interfaces to the HVD and transmission line are outlined; alternative installation layouts (aside or underneath the HVD) are compared from both mechanical and electrical points of view. [Copyright &y& Elsevier]

The article presents test results of a sectioned vacuum bushing with induced voltage distribution. The bushing was tested with voltage pulses with amplitudes of 24 and 90 kV. The setting of the voltage along the gradient rings was carried out using a galvanic coupling with the turns of a high-voltage pulse transformer. The presented method has allowed distributing the applied voltage between the sections with a deviation of less than 3.5% from the uniform distribution throughout the entire pulse duration (0.25 μs FWHM). The tests with 90 kV pulses were carried out at a pressure of 10−4 Тоrr. The conical design of the bushing provided a decrease in the average electric field strength in vacuum insulating gaps and a higher rate of the residual atmosphere pumping out, as compared to the traditional cylindrical design of pulse vacuum bushings. The investigated bushing can be used in designs of vacuum electron diodes of pulsed accelerating systems. • Evenly distributing voltage over the bushing throughout the entire pulse duration are required for specific practical and scientific applications of high voltage generators and particle accelerators. • The galvanic connection of the transformer turns with the insulator gradient rings has allowed to evenly distributing voltage over the bushing throughout the entire pulse duration. • The advantages of the cone bushing design over the cylindrical is experimentally demonstrated. [ABSTRACT FROM AUTHOR]

The article describes a case study when the voltage collapse during lightning impulse tests of new power transformers was noticed and when the repeated tests finished with a positive result. The step-by-step process of reaching the conclusion on the basis of dissolved gas analysis (DGA) as a key method of the investigations was presented. The considerations on the possible source of the analysis showed that the Duval triangle method, used in the analysis of the concentration of gases dissolved in oil samples taken from bushings, more reliably and unambiguously than the ratio method recommended in the IEC 60599 Standard, indicated a phenomenon which was identified in the insulation structure of bushings analyzed. Additionally, the results from DGA were found to be consistent with an internal inspection of bushings, which showed a visible trace of discharge on the inside part of the epoxy housing, as a result of the lightning induced breakdown. [ABSTRACT FROM AUTHOR]