Dietmar Gentsch - Academia.edu (original) (raw)

Papers by Dietmar Gentsch

2018 28th International Symposium on Discharges and Electrical Insulation in Vacuum (ISDEIV), 2018

Investigations in an alternative current synthetic circuit have been performed in order to study ... more Investigations in an alternative current synthetic circuit have been performed in order to study the influence of transverse magnetic fields on the cathode spots behavior at a short gap (∼3 mm) on CuCr contacts in vacuum. The experiments were conducted with currents from a few hundreds up to several thousands Amperes (8'000 A). With no magnetic field, it was observed that the cathode spots are located within a disk, whose radius grows with current and time (diffuse arc mode). Their motion is driven by the repulsive force between the spots. When a transverse magnetic field is imposed (>10 mT), the cathode spots had two opposite behaviors. First, the cathode spots located on the periphery of the disk in the anti-Amperian direction: those cathode spots keep their individual aspect and are quickly accelerated in a retrograde motion to the edge of the contacts, as expected in the literature. The other spots, the majority, tend to gather to form a group of spots in the Amperian direction. It has been observed that the higher the magnetic field strength, the denser the group of cathode spots become. It was also found that the concentration of cathode spots influences the plasma-electrode interaction at the anode. Indeed, it appears that the current at which the anode starts to melt is shifted to lower values in the presence of a transverse magnetic field.

CIRED 2021 - The 26th International Conference and Exhibition on Electricity Distribution, 2021

L'invention concerne un disjoncteur sous vide hybride a multiples blocs (1) comprenant au moi... more L'invention concerne un disjoncteur sous vide hybride a multiples blocs (1) comprenant au moins deux blocs (2) avec au moins un composant semi-conducteur et un interrupteur sous vide (3) comprenant une chambre de commutation sous vide (4) permettant de loger une paire de contacts electriques constituee d'un contact electrique fixe (5) et d'un contact electrique mobile axial (6), qui peut etre deplace en translation pour la commutation, ledit composant semi-conducteur etant raccorde en parallele avec l'interrupteur sous vide (3).

2014 International Symposium on Discharges and Electrical Insulation in Vacuum (ISDEIV), 2014

The magnetron method is well established for the internal pressure measurement of vacuum interrup... more The magnetron method is well established for the internal pressure measurement of vacuum interrupters. Its application during the manufacturing process is essential for the determination of the vacuum quality. The evaluation of the magnetron measurement requires precise knowledge of the residual gas composition and the influence of the metallic surfaces in the vacuum interrupter due to gas binding effects. Leading manufacturers having gained wide experience applying the magnetron method do consider these influences during the production process. However, it is also possible to measure the internal pressure in a vacuum interrupter by means of the magnetron method after a considerable long time in service, e.g. close to the end of the prospective service life. As the residual gas composition in these states is not precisely known, uncertainties in the pressure measurement can arise. Experiments with common residual gases and their typical compositions, which can form inside a vacuum i...

Vivre sans electricite est difficilement imaginable. Dans le monde industrialise, pratiquement to... more Vivre sans electricite est difficilement imaginable. Dans le monde industrialise, pratiquement toutes les activites humaines sont tributaires d'une alimentation fiable et sure, alors que dans les pays en developpement, un nombre sans cesse croissant de populations profite des bienfaits de la fee electricite. La surete du reseau electrique est conditionnee par la faculte d'interrompre et d'etablir le courant, fonction vitale lors des defauts en ligne, comme les courts-circuits. Les chambres de coupure sous vide sont des composants technologiques tres repandus dans les reseaux de distribution (10-40 kV). Pour ABB, ces chambres de coupure sous vide sont une veritable "sucess story". La hausse exponentielle de la production des dernieres annees a propulse le Groupe au premier rang mondial des fabricants en 2004. Ses produits sont les plus compacts du marche et apportent la preuve que sans innovation, point de leadership technologique !

From various pressure measuring principles, only the magnetron method, using a vacuum interrupter... more From various pressure measuring principles, only the magnetron method, using a vacuum interrupter (VI) as its own gauge, was identified in previous investigations to be suited for a quantitative on-site assessment of the vacuum inside a sealed VI. The application of this pressure measuring principle, however, requires a disconnection of the vacuum circuit breaker (VCB) and thus, an electrical switching operation, influencing the internal pressure and the residual gas composition inside the VI. Due to the impact of the arcing on the high purity surfaces and the bound residual gases, the pressure measured after disconnecting the VCB can be different from the initial pressure before the VCB has been disconnected. Hence, the influence of current interruption operations on the internal pressure and consequently, on the interpretability of the result of the on-site vacuum assessment is addressed in this contribution. An experimental test setup for investigating the internal pressure in VI...

2018 28th International Symposium on Discharges and Electrical Insulation in Vacuum (ISDEIV), 2018

In the medium range of high voltage levels, switches based on vacuum have advantages such as bein... more In the medium range of high voltage levels, switches based on vacuum have advantages such as being environmentally friendly and featuring lower maintenance costs compared to switches with sulfur hexafluoride (SF6). In order to expand the operation voltage levels of vacuum circuit breakers (VCB) up to high voltages, series arrangements are promising. Using these arrangements a symmetric voltage distribution over the switching distance is one of the main challenges. External electrical fields can cause asymmetric voltage distributions, which in turn, could lead to failure of one of the series arrangements and thus trigger a complete breakdown. The most common approach, to ensure a uniform voltage distribution, is the usage of external grading capacitors. The presented research proposes a new approach for a combined external electrical field-shielding and grading, based on an additional surrounding shield arrangement in a separate vacuum chamber to compensate additional grading capacitors. As a first step, the coupling mechanisms between the shields are simulated in COMSOL Multiphysics software for a one-pole series model with open contacts under a transient lightning impulse voltage. Here the potential drift of the floating middle part of the double breaking VCB (without plasma) is most important. In a second step the arrangement is build up in a test field for lightning impulse voltage (LIV) tests. To avoid flashovers between the shields, vacuum is chosen as insulation medium. To measure the potential of the floating middle shield, different techniques are used. In additional tests the new shield arrangement is complemented with a series arrangement of vacuum interrupters to measure the dielectric strength of the series gaps with and without external disturbances. The current research gives first results for designing shields in an additional vacuum chamber surrounding the double breaking VCB.

2020 29th International Symposium on Discharges and Electrical Insulation in Vacuum (ISDEIV), 2021

Investigations of low currents vacuum arcs (< 30 A) have been performed on CuCr, Cu and W cont... more Investigations of low currents vacuum arcs (< 30 A) have been performed on CuCr, Cu and W contact materials in order to evaluate their chopping current behavior. Results show that the arc burning between CuCr contacts is relatively stable with an average lifetime of 16 ms at 7A, in the presented test set-up. On the other hand, Cu and W contacts are less stable and more predisposed to current chop. They need a larger current to sustain an arc of a similar average lifetime, with 25 A for copper and about 27 A for tungsten. For approximatively the same average arc lifetime, it was observed that the magnitude of the arc noise, i.e. the voltage fluctuations, between both Cu and W contact pairs could reach values higher than 1500 V, whereas the ones of CuCr stayed limited below 300 V. This result denotes differences that could be exploited in further studies to assess the fundamental under-lying physical process of the life and death cycle of the cathode spots.

IEEE Transactions on Dielectrics and Electrical Insulation, 2017

Vacuum interrupters (VI) are mainly built with ceramics as insulators. During the interruption pr... more Vacuum interrupters (VI) are mainly built with ceramics as insulators. During the interruption process, the ceramics are coated with metal vapor from the contact material. In a worst case scenario, an electrical bypass is formed by the metal coating on the ceramic insulators. To avoid this, dielectric shielding is used, which provides defined surfaces for vapor coatings. Different shield arrangements offer a balance between local field stress and effective protection against impact from the metal coating. In our current work, we developed an electrostatic field simulation approach using COMSOL software. The purpose was to study the impact of the deposited layers on the performance of the VI with multiple shield arrangements. The simulations were done for three different cases, using the same VI geometry. •VI without metal coating on the ceramics; •VI with metal coating on the ceramics; •E-Field distribution between the head-shield and the metal coating on the ceramics. The identification of the effect of coatings on the electric field inside a VI during lightning impulse voltage stress can help to evaluate the breakdown voltage of the whole arrangement. Therefore, we simulated the redistribution of the electric field strength over the remaining insulated shields.

PAMM, 2019

In vacuum interrupters, metal bellows permit the motion of the moving contact with up to long con... more In vacuum interrupters, metal bellows permit the motion of the moving contact with up to long contact strokes while maintaining the ultra-high vacuum seal. In contrast to most other bellows applications, the opening and closing operation of the vacuum interrupter lead to high-impulsive motions which additionally excite bellows oscillations. Future requirements of higher switching speeds and operations demand for a simulation-driven optimization of the metal bellows to increase the mechanical lifetime of the vacuum interrupter. The damaging effect of the switching operations is investigated on the bellows. A static force is axially applied on the bellows to validate the mechanical model compared with experimental results. Furthermore, a modal analysis is performed to consider the bellows as a flexible body in a multibody simulation. To account for the multiple-frequency oscillations during the switching operation, a transient simulation is carried out where the excitation of the bellows follows from a travel curve. The global hot spot of mechanical stress is identified for further lifetime evaluations by low-cycle fatigue methods.

11th International Symposium on High-Voltage Engineering (ISH 99), 1999

ABSTRACT

24th ISDEIV 2010, 2010

The dielectric behaviour of vacuum interrupters (VI) before and after switching operations has be... more The dielectric behaviour of vacuum interrupters (VI) before and after switching operations has been investigated. At first, switching operations with different intensities of load with short circuit currents at 50Hz frequency were performed. The test objects were a standard VI with a rated voltage of 12kV, a rated current of 1250A and a short circuit interruption current of 20kA. In

IEEE Transactions on Plasma Science, 2013

ABSTRACT

IEEE Transactions on Power Delivery, 2020

For interruption operations at higher voltage levels sulfur hexafluoride (SF 6) is the dominating... more For interruption operations at higher voltage levels sulfur hexafluoride (SF 6) is the dominating insulation and interruption medium. In medium to high voltage levels vacuum has advantages compared to SF 6. In order to expand the operation voltage levels of vacuum circuit breakers (VCB) two approaches are possible. The first is the enlargement of the single contact gap and second is the series arrangement. In both cases the Time-Distance-Curve of the contact travel is one factor that influences the interruption performance of VCBs. The usage of a single gap for higher voltage levels requires an increased contact distance. In dependence of different interruption operations, like short circuit-or capacitive interruption, a controlled Time-Distance-Curve could be useful. For experimental investigations a vacuum single break test setup using a brushless servo motor with a frequency converter is built. The electrical control of the drive enables parameter variations of the Time-Distance-Curve. The velocity, acceleration, deceleration and final contact gap can be adjusted as required for testing and later in field application. For fine control a mechanical simulation considering the regulation loop between frequency converter and drive as well as the mechanical components is employed. Finally, tests of the setup for interruption operations are presented.

2008 23rd International Symposium on Discharges and Electrical Insulation in Vacuum, 2008

For low and medium voltage applications the vacuum interruption principle has been well establish... more For low and medium voltage applications the vacuum interruption principle has been well established over the past 30 years. Component materials for vacuum interrupters (VI) have to be designed for very low gas content, since this characteristic determines the quality of vacuum inside the VI for at least 30 years of service or shelf life. Vacuum integrity in a "sealed for life" VI is needed and therefore gas pressure measurements on VIs are conducted during production as a quality control process. In order to limit the pressure resolution in the range of 10-7 hPa for a long period vacuum measuring systems are applied to assure the vacuum integrity (tightness) of the VI or vacuum device (VD). Those measurements are performed during production by magnetron (Penning principle) measurements on each VI/VD. In addition, some selected VIs are analyzed by means of residual gas analysis (RGA - mass spectroscopy) for further production control and improvement. This technique is used to detect residual gases, for example: gas sources, and to investigate the diffusion of gases from material into vacuum. The measurements of magnetron and RGA are analyzed and compared herein and a description of how to eliminate gas sources by selection of suitable materials for a VI/VD will be presented.

2018 28th International Symposium on Discharges and Electrical Insulation in Vacuum (ISDEIV), 2018

Investigations in an alternative current synthetic circuit have been performed in order to study ... more Investigations in an alternative current synthetic circuit have been performed in order to study the influence of transverse magnetic fields on the cathode spots behavior at a short gap (∼3 mm) on CuCr contacts in vacuum. The experiments were conducted with currents from a few hundreds up to several thousands Amperes (8'000 A). With no magnetic field, it was observed that the cathode spots are located within a disk, whose radius grows with current and time (diffuse arc mode). Their motion is driven by the repulsive force between the spots. When a transverse magnetic field is imposed (>10 mT), the cathode spots had two opposite behaviors. First, the cathode spots located on the periphery of the disk in the anti-Amperian direction: those cathode spots keep their individual aspect and are quickly accelerated in a retrograde motion to the edge of the contacts, as expected in the literature. The other spots, the majority, tend to gather to form a group of spots in the Amperian direction. It has been observed that the higher the magnetic field strength, the denser the group of cathode spots become. It was also found that the concentration of cathode spots influences the plasma-electrode interaction at the anode. Indeed, it appears that the current at which the anode starts to melt is shifted to lower values in the presence of a transverse magnetic field.

CIRED 2021 - The 26th International Conference and Exhibition on Electricity Distribution, 2021

L'invention concerne un disjoncteur sous vide hybride a multiples blocs (1) comprenant au moi... more L'invention concerne un disjoncteur sous vide hybride a multiples blocs (1) comprenant au moins deux blocs (2) avec au moins un composant semi-conducteur et un interrupteur sous vide (3) comprenant une chambre de commutation sous vide (4) permettant de loger une paire de contacts electriques constituee d'un contact electrique fixe (5) et d'un contact electrique mobile axial (6), qui peut etre deplace en translation pour la commutation, ledit composant semi-conducteur etant raccorde en parallele avec l'interrupteur sous vide (3).

2014 International Symposium on Discharges and Electrical Insulation in Vacuum (ISDEIV), 2014

The magnetron method is well established for the internal pressure measurement of vacuum interrup... more The magnetron method is well established for the internal pressure measurement of vacuum interrupters. Its application during the manufacturing process is essential for the determination of the vacuum quality. The evaluation of the magnetron measurement requires precise knowledge of the residual gas composition and the influence of the metallic surfaces in the vacuum interrupter due to gas binding effects. Leading manufacturers having gained wide experience applying the magnetron method do consider these influences during the production process. However, it is also possible to measure the internal pressure in a vacuum interrupter by means of the magnetron method after a considerable long time in service, e.g. close to the end of the prospective service life. As the residual gas composition in these states is not precisely known, uncertainties in the pressure measurement can arise. Experiments with common residual gases and their typical compositions, which can form inside a vacuum i...

Vivre sans electricite est difficilement imaginable. Dans le monde industrialise, pratiquement to... more Vivre sans electricite est difficilement imaginable. Dans le monde industrialise, pratiquement toutes les activites humaines sont tributaires d'une alimentation fiable et sure, alors que dans les pays en developpement, un nombre sans cesse croissant de populations profite des bienfaits de la fee electricite. La surete du reseau electrique est conditionnee par la faculte d'interrompre et d'etablir le courant, fonction vitale lors des defauts en ligne, comme les courts-circuits. Les chambres de coupure sous vide sont des composants technologiques tres repandus dans les reseaux de distribution (10-40 kV). Pour ABB, ces chambres de coupure sous vide sont une veritable "sucess story". La hausse exponentielle de la production des dernieres annees a propulse le Groupe au premier rang mondial des fabricants en 2004. Ses produits sont les plus compacts du marche et apportent la preuve que sans innovation, point de leadership technologique !

From various pressure measuring principles, only the magnetron method, using a vacuum interrupter... more From various pressure measuring principles, only the magnetron method, using a vacuum interrupter (VI) as its own gauge, was identified in previous investigations to be suited for a quantitative on-site assessment of the vacuum inside a sealed VI. The application of this pressure measuring principle, however, requires a disconnection of the vacuum circuit breaker (VCB) and thus, an electrical switching operation, influencing the internal pressure and the residual gas composition inside the VI. Due to the impact of the arcing on the high purity surfaces and the bound residual gases, the pressure measured after disconnecting the VCB can be different from the initial pressure before the VCB has been disconnected. Hence, the influence of current interruption operations on the internal pressure and consequently, on the interpretability of the result of the on-site vacuum assessment is addressed in this contribution. An experimental test setup for investigating the internal pressure in VI...

2018 28th International Symposium on Discharges and Electrical Insulation in Vacuum (ISDEIV), 2018

In the medium range of high voltage levels, switches based on vacuum have advantages such as bein... more In the medium range of high voltage levels, switches based on vacuum have advantages such as being environmentally friendly and featuring lower maintenance costs compared to switches with sulfur hexafluoride (SF6). In order to expand the operation voltage levels of vacuum circuit breakers (VCB) up to high voltages, series arrangements are promising. Using these arrangements a symmetric voltage distribution over the switching distance is one of the main challenges. External electrical fields can cause asymmetric voltage distributions, which in turn, could lead to failure of one of the series arrangements and thus trigger a complete breakdown. The most common approach, to ensure a uniform voltage distribution, is the usage of external grading capacitors. The presented research proposes a new approach for a combined external electrical field-shielding and grading, based on an additional surrounding shield arrangement in a separate vacuum chamber to compensate additional grading capacitors. As a first step, the coupling mechanisms between the shields are simulated in COMSOL Multiphysics software for a one-pole series model with open contacts under a transient lightning impulse voltage. Here the potential drift of the floating middle part of the double breaking VCB (without plasma) is most important. In a second step the arrangement is build up in a test field for lightning impulse voltage (LIV) tests. To avoid flashovers between the shields, vacuum is chosen as insulation medium. To measure the potential of the floating middle shield, different techniques are used. In additional tests the new shield arrangement is complemented with a series arrangement of vacuum interrupters to measure the dielectric strength of the series gaps with and without external disturbances. The current research gives first results for designing shields in an additional vacuum chamber surrounding the double breaking VCB.

2020 29th International Symposium on Discharges and Electrical Insulation in Vacuum (ISDEIV), 2021

Investigations of low currents vacuum arcs (< 30 A) have been performed on CuCr, Cu and W cont... more Investigations of low currents vacuum arcs (< 30 A) have been performed on CuCr, Cu and W contact materials in order to evaluate their chopping current behavior. Results show that the arc burning between CuCr contacts is relatively stable with an average lifetime of 16 ms at 7A, in the presented test set-up. On the other hand, Cu and W contacts are less stable and more predisposed to current chop. They need a larger current to sustain an arc of a similar average lifetime, with 25 A for copper and about 27 A for tungsten. For approximatively the same average arc lifetime, it was observed that the magnitude of the arc noise, i.e. the voltage fluctuations, between both Cu and W contact pairs could reach values higher than 1500 V, whereas the ones of CuCr stayed limited below 300 V. This result denotes differences that could be exploited in further studies to assess the fundamental under-lying physical process of the life and death cycle of the cathode spots.

IEEE Transactions on Dielectrics and Electrical Insulation, 2017

Vacuum interrupters (VI) are mainly built with ceramics as insulators. During the interruption pr... more Vacuum interrupters (VI) are mainly built with ceramics as insulators. During the interruption process, the ceramics are coated with metal vapor from the contact material. In a worst case scenario, an electrical bypass is formed by the metal coating on the ceramic insulators. To avoid this, dielectric shielding is used, which provides defined surfaces for vapor coatings. Different shield arrangements offer a balance between local field stress and effective protection against impact from the metal coating. In our current work, we developed an electrostatic field simulation approach using COMSOL software. The purpose was to study the impact of the deposited layers on the performance of the VI with multiple shield arrangements. The simulations were done for three different cases, using the same VI geometry. •VI without metal coating on the ceramics; •VI with metal coating on the ceramics; •E-Field distribution between the head-shield and the metal coating on the ceramics. The identification of the effect of coatings on the electric field inside a VI during lightning impulse voltage stress can help to evaluate the breakdown voltage of the whole arrangement. Therefore, we simulated the redistribution of the electric field strength over the remaining insulated shields.

PAMM, 2019

In vacuum interrupters, metal bellows permit the motion of the moving contact with up to long con... more In vacuum interrupters, metal bellows permit the motion of the moving contact with up to long contact strokes while maintaining the ultra-high vacuum seal. In contrast to most other bellows applications, the opening and closing operation of the vacuum interrupter lead to high-impulsive motions which additionally excite bellows oscillations. Future requirements of higher switching speeds and operations demand for a simulation-driven optimization of the metal bellows to increase the mechanical lifetime of the vacuum interrupter. The damaging effect of the switching operations is investigated on the bellows. A static force is axially applied on the bellows to validate the mechanical model compared with experimental results. Furthermore, a modal analysis is performed to consider the bellows as a flexible body in a multibody simulation. To account for the multiple-frequency oscillations during the switching operation, a transient simulation is carried out where the excitation of the bellows follows from a travel curve. The global hot spot of mechanical stress is identified for further lifetime evaluations by low-cycle fatigue methods.

11th International Symposium on High-Voltage Engineering (ISH 99), 1999

ABSTRACT

24th ISDEIV 2010, 2010

The dielectric behaviour of vacuum interrupters (VI) before and after switching operations has be... more The dielectric behaviour of vacuum interrupters (VI) before and after switching operations has been investigated. At first, switching operations with different intensities of load with short circuit currents at 50Hz frequency were performed. The test objects were a standard VI with a rated voltage of 12kV, a rated current of 1250A and a short circuit interruption current of 20kA. In

IEEE Transactions on Plasma Science, 2013

ABSTRACT

IEEE Transactions on Power Delivery, 2020

For interruption operations at higher voltage levels sulfur hexafluoride (SF 6) is the dominating... more For interruption operations at higher voltage levels sulfur hexafluoride (SF 6) is the dominating insulation and interruption medium. In medium to high voltage levels vacuum has advantages compared to SF 6. In order to expand the operation voltage levels of vacuum circuit breakers (VCB) two approaches are possible. The first is the enlargement of the single contact gap and second is the series arrangement. In both cases the Time-Distance-Curve of the contact travel is one factor that influences the interruption performance of VCBs. The usage of a single gap for higher voltage levels requires an increased contact distance. In dependence of different interruption operations, like short circuit-or capacitive interruption, a controlled Time-Distance-Curve could be useful. For experimental investigations a vacuum single break test setup using a brushless servo motor with a frequency converter is built. The electrical control of the drive enables parameter variations of the Time-Distance-Curve. The velocity, acceleration, deceleration and final contact gap can be adjusted as required for testing and later in field application. For fine control a mechanical simulation considering the regulation loop between frequency converter and drive as well as the mechanical components is employed. Finally, tests of the setup for interruption operations are presented.

2008 23rd International Symposium on Discharges and Electrical Insulation in Vacuum, 2008

For low and medium voltage applications the vacuum interruption principle has been well establish... more For low and medium voltage applications the vacuum interruption principle has been well established over the past 30 years. Component materials for vacuum interrupters (VI) have to be designed for very low gas content, since this characteristic determines the quality of vacuum inside the VI for at least 30 years of service or shelf life. Vacuum integrity in a "sealed for life" VI is needed and therefore gas pressure measurements on VIs are conducted during production as a quality control process. In order to limit the pressure resolution in the range of 10-7 hPa for a long period vacuum measuring systems are applied to assure the vacuum integrity (tightness) of the VI or vacuum device (VD). Those measurements are performed during production by magnetron (Penning principle) measurements on each VI/VD. In addition, some selected VIs are analyzed by means of residual gas analysis (RGA - mass spectroscopy) for further production control and improvement. This technique is used to detect residual gases, for example: gas sources, and to investigate the diffusion of gases from material into vacuum. The measurements of magnetron and RGA are analyzed and compared herein and a description of how to eliminate gas sources by selection of suitable materials for a VI/VD will be presented.