LC
L.A. Chmura
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3 records found
1
Conference paper
(2020)
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Lukasz Chmura, Adeep Santosh, Paul van Nes, Radek Heller, Armando Rodrigo Mor, Mohamad Ghaffarian Niasar, Dennis Bergsma
Constantly growing amount of renewables and storage installed in the power system results in an increased interest in the power transfer under Direct Current (DC), especially in the low and medium voltage (LV and MV) networks. This is valid for both already existing as well as for newly installed cable systems. Although there is virtually no experience with MV DC networks and accessories, it is widely known that the electric stress distribution within insulation is different for AC and DC voltage. Liquid filled joints utilize an insulating liquid to fill the inner volume of the joint. A moisture sensitive, silicone based liquid can be taken as one of the examples. Beside all dielectric and thermal properties, such liquid has a property of hardening when getting in contact with moisture. By measurements of such material, it has been confirmed that the dielectric permittivity for solid and liquid state is of the same value. Thus the hardening process does not have influence on the field distribution under AC stress. However, the resistivity of the material changes when the hardening starts. This in turn, has an influence on the field distribution under DC. In order to investigate the criticality of liquid-solid interfaces, the DC breakdown testing was performed. More specifically, the testing focused on the interface being normal and tangential with respect the electric field. The literature states that the interface of two different insulating materials is an electrically weak spot. In our experiments, the contrary has been observed. The interface between liquid-solid silicone materials is at least as strong as the liquid form of the dielectric. In the current contribution, we will also discuss the implication of the mentioned findings on the feasibility of utilizing a silicone liquid filled AC MV joint under DC stress
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Constantly growing amount of renewables and storage installed in the power system results in an increased interest in the power transfer under Direct Current (DC), especially in the low and medium voltage (LV and MV) networks. This is valid for both already existing as well as for newly installed cable systems. Although there is virtually no experience with MV DC networks and accessories, it is widely known that the electric stress distribution within insulation is different for AC and DC voltage. Liquid filled joints utilize an insulating liquid to fill the inner volume of the joint. A moisture sensitive, silicone based liquid can be taken as one of the examples. Beside all dielectric and thermal properties, such liquid has a property of hardening when getting in contact with moisture. By measurements of such material, it has been confirmed that the dielectric permittivity for solid and liquid state is of the same value. Thus the hardening process does not have influence on the field distribution under AC stress. However, the resistivity of the material changes when the hardening starts. This in turn, has an influence on the field distribution under DC. In order to investigate the criticality of liquid-solid interfaces, the DC breakdown testing was performed. More specifically, the testing focused on the interface being normal and tangential with respect the electric field. The literature states that the interface of two different insulating materials is an electrically weak spot. In our experiments, the contrary has been observed. The interface between liquid-solid silicone materials is at least as strong as the liquid form of the dielectric. In the current contribution, we will also discuss the implication of the mentioned findings on the feasibility of utilizing a silicone liquid filled AC MV joint under DC stress
In recent years, the architecture of the power system has been the subject of a major change. The commonly known structure with centralized generation and one directional power flow, gives gradually the place to the new concept of the power network where both the energy generators and consumers are distributed. Particularly, the continuously increasing environmental concerns as well as the legal regulations result in a widespread installation of renewables. In addition, storage devices are incorporated in the network in order to cope with sudden increase of the generated energy. To facilitate the energy flow from the renewables towards the power network, the proper voltage level is maintained by means of transmission controllers. Such controllers consist of high frequency switching elements and the operation of such devices introduces high frequency harmonics that are propagated in the vicinity of the installed controller. On the one hand, a high content of harmonics is an emerging issue for the power network. On the other hand, some researches show the deleterious effect of high frequency signals on the reliability of electrical insulation. Finally, for many years, the harmonic content was not considered neither during the design nor the component’s testing phase. In our paper, we will firstly review the published researches regarding the influence of harmonics on the reliability of cables, terminations and transformers. Further on, an approach to model the influence of high frequency on the electric field and temperature distribution in two types of medium voltage cable termination, will be made. 1 INTRODUCTION
...
In recent years, the architecture of the power system has been the subject of a major change. The commonly known structure with centralized generation and one directional power flow, gives gradually the place to the new concept of the power network where both the energy generators and consumers are distributed. Particularly, the continuously increasing environmental concerns as well as the legal regulations result in a widespread installation of renewables. In addition, storage devices are incorporated in the network in order to cope with sudden increase of the generated energy. To facilitate the energy flow from the renewables towards the power network, the proper voltage level is maintained by means of transmission controllers. Such controllers consist of high frequency switching elements and the operation of such devices introduces high frequency harmonics that are propagated in the vicinity of the installed controller. On the one hand, a high content of harmonics is an emerging issue for the power network. On the other hand, some researches show the deleterious effect of high frequency signals on the reliability of electrical insulation. Finally, for many years, the harmonic content was not considered neither during the design nor the component’s testing phase. In our paper, we will firstly review the published researches regarding the influence of harmonics on the reliability of cables, terminations and transformers. Further on, an approach to model the influence of high frequency on the electric field and temperature distribution in two types of medium voltage cable termination, will be made. 1 INTRODUCTION
Original and pyrometamorphical altered Bentheimer sandstone
Petrophysical properties, surface and dielectric behavior
Bentheimer sandstone is a quartz-rich permeable hard sedimentary rock used for core flooding experiments. When fired to stabilize clays (subjected to high temperatures), pyrometamorphical phase changes induce texture and pore framework alteration. As a consequence the new dielectric response may influence wettability. The literature regarding pyrometamorphical behavior during and after thermal treatment is ambiguous, so we evaluate desirable effects (fixation of clay minerals) and undesirable effects (dielectric surface changes) in the matrix. Porosity, permeability, surface charge, specific surface area and dielectric respond were measured before and after firing of samples up to View the MathML source∼1000°C under oxidizing and non-oxidizing conditions. The matrix properties were determined using X-ray diffraction and X-ray fluorescence, scanning electron microscope imaging, and thermomechanical-, and thermogravimetric analysis with differential scanning calorimetry.
Firing causes dehydration, dehydroxylation and irreversible transformation of original clays, organic matter, and carbonates to glass, oxides and feldspars. During heating quartz transfers from α- to β -quartz and back during cooling. This changes the grain volumes and consequently reduces the matrix integrity. The sandstone has a slight porosity and permeability increase (∼5%∼5%). Further, a shift in the point of zero charge toward a higher pH may result in wettability alteration from strongly water-wet to oil-wet. Additionally, a decrease in the permittivity value and marginal dispersion of the dielectric constant (∼5%∼5%) between the high and the low frequencies was observed. Due to firing and related dispersion of the iron oxides within the matrix framework, Bentheimer sandstone becomes a weaker insulator.
...
Firing causes dehydration, dehydroxylation and irreversible transformation of original clays, organic matter, and carbonates to glass, oxides and feldspars. During heating quartz transfers from α- to β -quartz and back during cooling. This changes the grain volumes and consequently reduces the matrix integrity. The sandstone has a slight porosity and permeability increase (∼5%∼5%). Further, a shift in the point of zero charge toward a higher pH may result in wettability alteration from strongly water-wet to oil-wet. Additionally, a decrease in the permittivity value and marginal dispersion of the dielectric constant (∼5%∼5%) between the high and the low frequencies was observed. Due to firing and related dispersion of the iron oxides within the matrix framework, Bentheimer sandstone becomes a weaker insulator.
...
Bentheimer sandstone is a quartz-rich permeable hard sedimentary rock used for core flooding experiments. When fired to stabilize clays (subjected to high temperatures), pyrometamorphical phase changes induce texture and pore framework alteration. As a consequence the new dielectric response may influence wettability. The literature regarding pyrometamorphical behavior during and after thermal treatment is ambiguous, so we evaluate desirable effects (fixation of clay minerals) and undesirable effects (dielectric surface changes) in the matrix. Porosity, permeability, surface charge, specific surface area and dielectric respond were measured before and after firing of samples up to View the MathML source∼1000°C under oxidizing and non-oxidizing conditions. The matrix properties were determined using X-ray diffraction and X-ray fluorescence, scanning electron microscope imaging, and thermomechanical-, and thermogravimetric analysis with differential scanning calorimetry.
Firing causes dehydration, dehydroxylation and irreversible transformation of original clays, organic matter, and carbonates to glass, oxides and feldspars. During heating quartz transfers from α- to β -quartz and back during cooling. This changes the grain volumes and consequently reduces the matrix integrity. The sandstone has a slight porosity and permeability increase (∼5%∼5%). Further, a shift in the point of zero charge toward a higher pH may result in wettability alteration from strongly water-wet to oil-wet. Additionally, a decrease in the permittivity value and marginal dispersion of the dielectric constant (∼5%∼5%) between the high and the low frequencies was observed. Due to firing and related dispersion of the iron oxides within the matrix framework, Bentheimer sandstone becomes a weaker insulator.
Firing causes dehydration, dehydroxylation and irreversible transformation of original clays, organic matter, and carbonates to glass, oxides and feldspars. During heating quartz transfers from α- to β -quartz and back during cooling. This changes the grain volumes and consequently reduces the matrix integrity. The sandstone has a slight porosity and permeability increase (∼5%∼5%). Further, a shift in the point of zero charge toward a higher pH may result in wettability alteration from strongly water-wet to oil-wet. Additionally, a decrease in the permittivity value and marginal dispersion of the dielectric constant (∼5%∼5%) between the high and the low frequencies was observed. Due to firing and related dispersion of the iron oxides within the matrix framework, Bentheimer sandstone becomes a weaker insulator.