Search Results (6)

Spacers for the HVDC GIS/GIL play an important role in mechanically supporting conductors and separating compartments. At the same time, their insulation performance affects the stability and safety of system operation. Design rules and knowledge specific to AC spacers do not apply to those of DC spacers. Considering the shape influence on the surface electric field intensity of the spacer under HVDC applied voltage, as determined in our previous work, an optimized shape of a spacer model based on finite element electric field calculations and using standard HVAC alumina filled epoxy material and two novel types of materials were studied. The simulation’s results show that the DC shape optimization of the spacers can effectively reduce the electric field magnitudes along the spacer under different temperature gradients. To verify practically these findings, this paper presents the reduced scale gas insulated prototype that was constructed, the optimized DC spacers that were fabricated and the DC testing results using SF₆-free surrounding gas: C4-Perfluoronitrile (C4-PFN, 3M^TM Novec^TM 4710)/CO₂ and Trifluoroiodomethane (CF₃I)/CO₂. The results show that the shape-optimized spacer models made of conventional HVAC filled epoxy material have successfully passed the tests up to the maximum applicable ±123 kV DC exceeding thus ±119 kV DC that corresponds to the nominal voltage ±500 kV DC of the full scale. Full article

Theoretical investigation of the scattering of electrons and positrons from the plasma etching gas trifluoroiodomethane (CF${}_3$I) is presented in the present work. The investigation is carried out by taking into account the screening correction arising from a semiclassical analysis of atomic geometrical overlapping of the scattering cross-sections calculated in the independent atom approximation. The scattering system e${}^{\pm }$-CF${}_3$I is studied through the calculations of the observable quantities, namely, absolute differential, Sherman function, total elastic and inelastic, momentum transfer, viscosity, ionization and total cross sections over the energy range 1 eV–1 MeV. Energy dependency of the differential cross section and Sherman function are also picturized in this work. A comparative study is carried out between scattering observables for electron impact with those for positron impact to get a better understanding of the interaction and dynamics of the collision process. The corresponding scattering quantities of the constituent atoms are calculated employing a complex optical model potential by solving the Dirac relativistic wave equations in the framework of partial wave analysis. The comparison of our results with the available experimental and theoretical data shows a reasonable agreement. Full article

Testing and validating the electrical insulation performance of full-size compact high-voltage direct current (HVDC) gas-insulated systems, gas-insulated transmission lines (GIL) and gas-insulated switchgears (GIS) is very costly and take long time. Therefore, a reduced scale system was designed and constructed to study thoroughly the spacer’s performance when subjected to higher electric fields under HVDC with different shapes, made of new advanced materials, and housed in new SF₆-free gas environment. Since the stationary DC electric field distribution along the spacer is controlled by spacer material conductivity and strongly depends upon its shape, this, the first part of two articles, proposes in a first step based on electric field calculations with COMSOL Multiphysics software, an optimized shape of a spacer model using a standard high-voltage alternating current (HVAC) alumina-filled epoxy material. Then, two novel types of materials were introduced and investigated: (i) modified filled epoxy material with a lower temperature-dependent conductivity than that of the standard HVAC material, which is interpreted by a lower thermal activation energy; and (ii) nonlinear resistive field grading material with a low nonlinearity coefficient, with and without the presence of a temperature gradient which occurs under operating service load. The numerical results show that, despite that the DC optimized profile of the spacer made of standard HVAC, alumina-filled epoxy is very effective in relaxing the electric field magnitudes along the spacer under uniform temperature—its distribution is significantly affected by the presence of a high temperature gradient causing the maximum electric field shifts along the spacer surface towards the earthed flange. Under this condition, the modified filled epoxy material with a weaker temperature-dependent conductivity results in a significant reduction of the electric field enhancement, representing thus a relevant key solution for HVDC GIL/GIS applications. Nonlinear resistive field grading material is also effective but seems unnecessary. The optimized DC spacer models are being fabricated for tests verification with C4-Perfluoronitrile (C4-PFN, 3M^TM Novec^TM 4710)/CO₂ and Trifluoroiodomethane (CF₃I)/CO₂ gas mixtures in the reduced scale gas-insulated test prototype. Full article

Increasing demand for an alternative insulation medium to sulphur hexafluoride (SF₆) has led to the investigation of new environmentally friendly insulation gases which could be used in high voltage equipment on the electrical power network. One such alternative, which is currently being explored by researchers, is Trifluoroiodomethane (CF₃I) which could potentially be used in a gas mixture with carbon dioxide (CO₂) as an insulation medium. In this paper an analysis of gaseous by-products detected as a result of high voltage breakdown through pure CF₃I and a CF₃I-CO₂ gas mixture across a sphere-sphere electrode arrangement is given. Gas chromatography and mass spectrometry (GCMS) is used to identify the gaseous by-products produced as a result of high voltage arcing which causes the gas between the electrodes to dissociate. Analysing these gas by-products helps to identify the long-term behaviour of the gas mixture in high voltage equipment. Full article

Sulfur hexafluoride (SF₆) shows excellent insulation performance as an insulating gas. It is suitable for various climate conditions due to its low boiling point (−64 °C). Therefore, it has been widely used in power grid equipment. However, its global warming potential (GWP) is 23,500 times higher than that of CO₂. Thus, it is imperative to find an environmentally friendly insulating gas with excellent insulation performance, lower GWP, and which is harmless to equipment and workers to replace SF₆. In this review, four possible alternatives, including perfluorocarbons, trifluoroiodomethane, perfluorinated ketones, and fluoronitrile are reviewed in terms of basic physicochemical properties, insulation properties, decomposition properties, and compatibility with metals. The influences of trace H₂O or O₂ on their insulation performances are also discussed. The insulation strengths of these insulating gases were comparable to or higher than that of SF₆. The GWPs of these insulating gases were lower than that of SF₆. Due to their relatively high boiling point, they should be used as a mixture with buffering gases with low boiling points. Based on these four characteristics, perfluorinated ketones (C₅F₁₀O and C₆F₁₂O) and fluoronitrile (C₄F₇N) could partially substitute SF₆ in some electrical equipment. Finally, some future needs and perspectives of environmentally friendly insulating gases are addressed for further studies. Full article

The growing environmental challenge of electrical energy systems has prompted a substantial increase in renewable energy generation. Such generation systems allow for significant reduction of CO₂ emissions compared with a traditional fossil fuel plant. Furthermore, several improvements in power systems network configuration and operation combined with new technologies have enabled reduction of losses and energy demand, thus contributing to reduction of CO₂ emissions. Another environmental threat identified in electrical networks is the leaking of insulating sulfur hexafluoride (SF₆) gas used in electrical gas insulated substations (GIS) and equipment. Because of its Global Warming Potential (GWP) of nearly 24,000 and its long life in the atmosphere (over 3000 years), SF₆ gas was recognized as a greenhouse gas at the 1997 COP3; since then its use and emissions in the atmosphere have been regulated by international treaties. It is expected that as soon as an alternative insulating gas is found, SF₆ use in high-voltage (HV) equipment will be banned. This paper presents an overview of the key research advances made in recent years in the quest to find eco-friendly gases to replace SF₆. The review reports the main properties of candidate gases that are being investigated; in particular, natural gases (dry air, N₂ or CO₂) and polyfluorinated gases especially Trifluoroiodomethane (CF₃I), Perfluorinated Ketones, Octafluorotetra-hydrofuran, Hydrofluoroolefin (HFOs), and Fluoronitriles are presented and their strengths and weaknesses are discussed with an emphasis on their dielectric properties (especially their dielectric strength), GWP, and boiling point with respect to the minimum operating temperature for HV power network applications. Full article