| 1. |
- Hou, Yining, 1984-, et al.
(författare)
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Impact on voltage rise of PV generation in future swedish urban areas with high PV penetration
- 2014
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Ingår i: ENERGYCON 2014 - IEEE International Energy Conference. - : IEEE Computer Society. - 9781479924493 ; , s. 904-911
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Konferensbidrag (refereegranskat)abstract
- There have been a large amount of statements from different countries, claiming that the integration of photovoltaic generation in the distribution grids can eventually impact the power quality and pose challenges for the distribution system operator. In Sweden, the level of penetration of small scale distributed generation is still low and no such problems have been observed. This study is conducted to investigate the voltage levels in an urban distribution grid when the level of photovoltaic generation is increased. The study is done by modeling the Swedish urban area by PSCAD. The aspects of the model include network design of a real distribution grid, everyday load, photovoltaic generation based on real data, photovoltaic penetrations at different levels and considers the current regulations in Sweden. The results indicate that there are no problems with overvoltages even with a high penetration of photovoltaic generation. Instead the risk of over-current through the installed cables seems to be a greater limitation. The loading of the distribution transformers is decreased due to the mix of commercial and domestic loads in the local grid.
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| 2. |
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| 3. |
- Bissal, Ara, 1986-, et al.
(författare)
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Comparison of two Ultra-fast actuator concepts
- 2012
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Ingår i: IEEE transactions on magnetics. - : IEEE Press. - 0018-9464 .- 1941-0069. ; 48:11, s. 3315-3318
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, two different types of ultra-fast electromechanical actuators are compared using a multi-physical finite element simulation model that has been experimentally validated. They are equipped with a single-sided Thomson coil (TC) and a double-sided drive coil (DSC), respectively. The former consists of a spirally-wound flat coil with a copper armature on top, while the latter consists of two mirrored spiral coils that are connected in series. Initially, the geometry and construction of each of the actuating schemes are discussed. Subsequently, the theory behind the two force generation principles are described. Furthermore, the current, magnetic flux densities, accelerations, and induced stresses are analyzed. Moreover, mechanical loadability simulations are performed to study the impact on the requirements of the charging unit, the sensitivity of the parameters, and evaluate the degree of influence on the performance of both drives. Finally, it is confirmed that although the DSC is mechanically more complex, it has a greater efficiency than that of the TC.
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| 4. |
- Bissal, A., et al.
(författare)
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Hybrid multi-physics modeling of an ultra-fast electro-mechanical actuator
- 2015
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Ingår i: Actuators. - : MDPI AG. - 2076-0825. ; 4:4, s. 314-335
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Tidskriftsartikel (refereegranskat)abstract
- The challenges of an HVDC breaker are to generate impulsive forces in the order of hundreds of kilonewtons within fractions of a millisecond, to withstand the arising internal mechanical stresses and to transmit these forces via an electrically-insulating device to the contact system with minimum time delay. In this work, several models were developed with different levels of complexity, computation time and accuracy. Experiments were done with two mushroom-shaped armatures to validate the developed simulation models. It was concluded that although the electromagnetic force generation mechanism is highly sensitive to the mechanical response of the system, the developed first order hybrid model is able to predict the performance of the breaker with good accuracy.
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| 5. |
- Bissal, Ara, 1986-, et al.
(författare)
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Loadability and scaling aspects of Thomson based ultra-fast actuators
- 2012
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Ingår i: Actuator 2012.
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Konferensbidrag (refereegranskat)abstract
- In this paper, an ultra-fast single-sided Thomson based actuator is studied. The actuator is comprised of a flat spiral-shaped coil with a conductive armature in its proximity. This armature is mechanically loaded with a uniform mass distribution over its cross section. The energizing source consists of a capacitor bank that is discharged through the actuator coil resulting in a high magnetic pressure within fractions of a millisecond. The coil is dimensioned to withstand the temperature rise.An experimentally validated multi-physical finite element model is used to perform simulations by varying the mechanical load to explore the performance of the actuator topology. The obtained currents, induced forces, stresses, and accelerations of the armature are then analyzed in an attempt to develop scaling techniques that can predict for example velocity and efficiency. Finally, the results of the scaling techniques are presented and compared to each other.
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| 6. |
- Bissal, Ara, et al.
(författare)
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Optimal Energizing Source Design for Ultra-Fast Actuators
- 2013
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Konferensbidrag (refereegranskat)abstract
- One of the key enabling technologies for multi-terminal HVDCgrids is the existence of a breaker that can operate withina few milliseconds. A lot of research has been done to builddifferent ultra-fast drives to actuate the electric contacts ofthese breakers. What they all have in common is an operationalefficiency of at best 5 %. Capacitor banks are discharged throughspirally shaped flat coils to generate ultra-fast repulsive forces. Tooptimize the efficiency of the drive, the design of the energizingcircuit is crucial. The aim of this paper is to optimize theenergizing source and provide a deep explanation of the effectof the chosen capacitance and charging voltage for two actuatorconcepts, the Thomson coil (TC) and the double sided coil (DSC)for different stroke requirements. An experimentally validatedmulti-physics finite element method (FEM) simulation model is applied.
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| 7. |
- Corea-Araujo, Javier A., et al.
(författare)
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Optimum design of hybrid HVDC circuit breakers using a parallel genetic algorithm and a MATLAB-EMTP environment
- 2017
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Ingår i: IET Generation, Transmission & Distribution. - : INST ENGINEERING TECHNOLOGY-IET. - 1751-8687 .- 1751-8695. ; 11:12, s. 2974-2982
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Tidskriftsartikel (refereegranskat)abstract
- The optimum design of power system components is becoming a relevant topic in power system studies. Genetic algorithms (GAs) are considered as a proper approach for optimisation problems in which non-linear elements are involved. Several trends are presently leading GAs to a new level; for instance, its combination with parallel computing can facilitate the solution of problems where individual evaluations of the fitness function require an important computational effort. This study presents a procedure based on a MATLAB-EMTP application and the usage of a multicore environment for the optimum selection of hybrid high-voltage DC (HVDC) circuit breaker parameters; the goal is to obtain a transient response of the hybrid design with voltages, currents and fault clearance times within specified limits.
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| 8. |
- Edvardsson Rasmussen, Jesper, 1984-
(författare)
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Inner ear proteomics and barriers : Clinical and experimental findings
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Hearing is important in many aspects of life, including communication, assessing one’s surroundings, entertainment and social interaction. Hearing loss is common and according to the Global Burden of Disease Study, 5% of the global population require hearing rehabilitation (1). Pharmacological treatment options are limited, so understanding cellular mechanisms in the damaged inner ear is crucial for developing novel therapies.In this thesis, the human inner ear proteome in patients with sporadic vestibular schwannoma (VS) and its association with hearing loss were investigated. Ototoxic effects induced by furosemide were also examined, focusing on inner ear barrier function, furosemide sensitive Na-K-Cl co-transporter 1 (NKCC1), Fetuin-A, linked to tumour-associated hearing loss, and Pigment epithelium-derived factor (PEDF), potentially important for blood-endolymph barrier integrity.Translabyrinthine surgery on 35 patients, 32 with VS and three with meningioma, provided samples from perilymph, endolymph, endolymphatic sac tissue, VS biopsies and cerebrospinal fluid (CSF) for proteome analysis. Effects of furosemide on the inner ear barriers were studied in mice using 9.4Tesla MRI, and in guinea pigs using immunohistochemistry and mRNA in situ hybridisation focusing on NKCC1, Fetuin-A, and PEDF.Proteomic analysis revealed consistent sets of proteins in perilymph (91/315) and endolymph (545/1211). The proteomes of perilymph and CSF exhibited specific differences, with proteins unique to each fluid, thereby emphasizing the distinct origin of perilymph separate from CSF. Fetuin-A was inversely related to tumour-associated hearing loss, while patients with severe to profound hearing loss exhibited upregulation of complement factor H-related protein 2 (CFHR2).Furosemide compromised the blood-endolymph barrier, allowing gadolinium contrast into scala media. It affected NKCC1 of type II fibrocytes coinciding with the onset of hearing loss following high-dose furosemide, suggesting early disruption in potassium ion recirculation. Fetuin-A and PEDF were identified in the cochlea at protein and mRNA level. Their staining intensity increased in various cochlear subsites 120 minutes after furosemide administration, indicating their involvement in the cochlear response to the effects of furosemide.In summary, this thesis uncovered significant inter-individual variability in both the perilymph and endolymph proteome, alongside a consistent subset of proteins. Further, associations between hearing loss and proteome changes suggest inflammation as a potential mechanism for hearing degradation caused by vestibular schwannomas. Experimentally, impact of furosemide on blood-inner ear barriers were visualised in vivo and type II fibrocytes were identified as potential initial targets for NKCC1 blockade. Fetuin-A and PEDF were confirmed in several cell types in the cochlea and may increase in response to very high furosemide doses.
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| 9. |
- Magnusson, Jesper, 1984-, et al.
(författare)
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Design Aspects of a Medium Voltage Hybrid DC Breaker
- 2014
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Ingår i: 5th IEEE/PES Innovative Smart Grid Technologies Europe (ISGT EUROPE) 2014.
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Konferensbidrag (refereegranskat)abstract
- With increased demands on energy efficiency and stability, the use of direct current (DC) will have a natural place in the future smart grid. Today DC is mostly used in high voltage, high power transmission over large distances and in low voltage systems where the demands on reliability are high, e.g. data centres. New applications as wind farm collection grids and a desire to replace over-head lines with cables opens possibilities for DC distribution grids in medium voltage.The use of DC grids will require the development of DC breakers to handle fault in the grid. This paper presents the design aspects of a hybrid DC breaker for a medium voltage application. Since the hybrid topology consists of a mechanical switch as well as semiconductor components and metal oxide varistors, the design must handle trade-offs in performance and cost both for each part and also between the different components.
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| 10. |
- Magnusson, Jesper, 1984-
(författare)
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On the design of hybrid DC-breakers consisting of a mechanical switch and semiconductor devices
- 2015
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The interest of using direct current in networks for both transmission and distribution of power is increasing due to the higher efficiency compared to the alternating current used today. As no natural zero crossings exist in direct current, the interruption of fault currents becomes a challenge. Several circuit breaker topologies have been proposed to fulfill the requirements for DC grids. One such topology is the hybrid DC-breaker consisting of three parallel branches: a mechanical switch, a semiconductor branch, and a metal oxide varistor.The current interruption in the hybrid DC-breaker is made in three steps. A mechanical switch carries the nominal current with low losses during normal operation. When the breaker is tripped to interrupt the current, the mechanical switch is opened and commutates the current into the semiconductor branch. This branch will then conduct the current as the mechanical switch regains its voltage withstand. The semiconductors turn off and force the current into the varistor branch where the magnetic energy is absorbed and the current is forced to zero.This thesis is based on simulations and experiments to obtain design rules for such a DC-breaker. It has been shown that several aspects needs to be considered. Simulations are performed with several different models to obtain the requirements of each of the components in the DC-breaker.First of all, the choice of the semiconductor is important. There are a number of components available in the market, but typically they are optimized for fast switching applications like inverters rather than circuit breaker applications that only requires one single switching. Due to the high current and voltage ratings and the easy control, the IGBT seems to be the best choice among the commercially available components.Simulations on the mechanical switch show that there is an optimal combination of opening time and arc voltage of the to obtain a successful commutation into the semiconductor branch. The actuator is a key component since a relatively low increase in performance of the actuator drive circuit, significantly decreases the requirement of the other components in the DC-breaker.A significant part of the work has been put on the voltage transient during the turn-off of the semiconductor. As the current is forced into the varistor branch, the stray inductance in that loop will result in an over-voltage due to the high current derivative. A new type of snubber has been investigated using another varistor mounted close to the semiconductor. It has been shown that the function of the varistor snubber can be divided into two regions depending on the ratio between the snubber and the main varistor. If the ratio is high enough, the energy absorbed in the snubber varistor is only a few percent of the total energy.
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| 11. |
- Magnusson, Jesper, 1984-, et al.
(författare)
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On the Use of Metal Oxide Varistors as a Snubber Circuit in Solid-State Breakers
- 2013
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Ingår i: 2013 4th IEEE/PES Innovative Smart Grid Technologies Europe, ISGT Europe 2013. - : IEEE. - 9781479929849 ; , s. 6695454-
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Konferensbidrag (refereegranskat)abstract
- When solid-state switches are used in DC-breaker topologies, the turn-off operation can cause transient over-voltages that might harm the semiconductor itself. The over-voltage is caused by the combination of the very rapid current decrease of a solid-state switch and an undesired stray inductance in the parallel MOV-branch. The authors have proposed a possible solution where a smaller MOV is connected close to the solid-state switch to limit the over-voltage. This way, the over-voltage protection can be separated from the energy absorption task of the MOV. A small scale test set-up has been used to show that the peak voltage across the breaker is fully determined by the inner MOV. It is also shown that the performance can be increased by changing the U-I-characteristics of the outer MOV by adding several components in parallel.
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| 12. |
- Magnusson, Jesper, 1984-, et al.
(författare)
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Optimal design of a medium voltage hybrid fault current limiter
- 2014
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Ingår i: 2014 IEEE International Energy Conference, ENERGYCON. - : IEEE Computer Society. - 9781479924493 ; , s. 431-438
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Konferensbidrag (refereegranskat)abstract
- The connection of distributed generation increases the short circuit power which in turn might exceed the ratings of the installed circuit breakers. A solution is to limit the available short circuit power by increasing the grid impedance, but since there is a constant strive for lower losses and higher power transfer capabilities, this is not desired. The application of a fault current limiter (FCL) that can limit the current before the first peak enables a power system with high short circuit power and low short circuit current. This can increase the stability of the grid and reduce the requirements of other equipment. This work presents a simulation model to be used as an aid in the design of a hybrid FCL for a 12 kV AC system. The proposed model combines a transient analysis circuit model with an optimization module to obtain multiple sets of possible design parameters. The design is not straight forward since there is a trade-off between several of the design parameters.
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| 13. |
- Magnusson, Jesper, 1984-
(författare)
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Studies on Current Commutation in Hybrid DC-breakers
- 2017
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Compared to conventional AC-circuit breakers, a DC-breaker has to act fast and force the current down to zero. Many different DC-breaker topologies are available, and this thesis is focused on the hybrid DC-breaker comprising a mechanical switch and high power semiconductors.The main part of this thesis is focused on the current commutations in the hybrid DC-breaker. The two current commutations: from the mechanical switch to the semiconductor branch, and from the semiconductor to the metal oxide varistor, have completely different characteristics. When the mechanical switch opens, the metallic contacts separate and an electric arc is formed. As the voltage across the arc is higher than the voltage across the semiconductors, the current is pushed over to the semiconductor branch. The undesired stray inductance in the loop limits the current derivative and slows down the commutation. As the contacts keep separating, the arc voltage increases and eventually all current is conducted by the semiconductor and the arc ceases.For a hybrid DC-breaker, the worst case is a solid ground fault, as the fast rising current results in high current levels and makes the commutation from the mechanical switch to the semiconductor both difficult and slow. However, the fast rise of the current can be used to enhance the commutation by using coupled inductors in the two parallel branches. When the fault current rises in the semiconductor branch, the mutual coupling of the inductors causes the current in the mechanical switch to decrease and helps the commutation. The result is that the commutation time decreases with decreasing fault impedance, and makes the solid ground fault easier to handle.The commutation from the semiconductor to the metal oxide varistor is controlled by the turn-off of the semiconductor. When the semiconductor is turned off, it pulls the current down to zero with a rather constant current derivative regardless of the surrounding circuit and the system current is taken over by the metal oxide varistor. Hence, any inductance in the commutation loop will result in an over-voltage proportional to this inductance on top of the varistor voltage. By connecting a smaller metal oxide varistor, as a snubber, close to the semiconductor, the over-voltage can be controlled and the commutation from the snubber to the metal oxide varistor will be driven by the voltage difference between the two varistors.It is shown that for a 12 kV DC-system, a possible design of the mechanical switch in the hybrid DC-breaker comprises two contact gaps in series and opens with a velocity of 11 m/s. It has been experimentally verified that when starting the commutation at 4 kA, the commutation takes less than 700 us and is over before the switch has opened 1 mm.The thesis also contains proposed designs for an 80 kV DC-breaker that can be used as a modular solution for higher system voltages. For this higher voltage, the design will be a choice of the combination between the number of contact gaps in series and the opening velocity of the mechanical switch.
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| 14. |
- Parekh, Mrunal, 1987-, et al.
(författare)
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Arc Characteristics of Ultra-Fast Opening Switching Contacts in Hybrid Breakers
- 2021
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Ingår i: IEEE Transactions on Power Delivery. - : Institute of Electrical and Electronics Engineers (IEEE). - 0885-8977 .- 1937-4208. ; 36:5, s. 2872-2880
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Tidskriftsartikel (refereegranskat)abstract
- A mechanical switch can be used instead of a power electronic load commutation switch to reduce losses during normal power flow in standard hybrid DC breakers. The success of current commutation in such hybrid breakers depends on the arc voltage across the contacts of the mechanical switch. The behaviour of rapidly elongated arcs generated during the opening of an ultra-fast mechanical switch in the air is studied here. The voltage-current characteristics of the generated arcs are obtained for contact opening velocities of 6, 11 and 21 m/s. It is found that the arc voltage at a given current and contact separation increases with contact opening velocity. It is shown that stationary, zero-contact-velocity characteristics can not be used to accurately quantify the voltage build-up in fast elongating arcs in hybrid breakers. A best-fitting black-box the equation for the dynamic arc characteristics is presented for the tested velocities. The obtained voltage-current characteristics are used as input to simulate the current commutation process in a 12 kV hybrid DC circuit breaker case-study. Different scenarios of current commutation failure related to the arc voltage build-up are identified. It is shown that these failures scenarios can be avoided by increasing the contact opening velocity.
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| 15. |
- Parekh, Mrunal, 1987-, et al.
(författare)
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Design of a linear Halbach magnetic damper
- 2018
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Ingår i: International journal of applied electromagnetics and mechanics. - : IOS Press. - 1383-5416 .- 1875-8800. ; 59:2, s. 1-9
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Tidskriftsartikel (refereegranskat)abstract
- Ultra-fast circuit breakers are operated with fast electromagnetic actuators. They can generate a sufficient impulse force to swiftly open electrical contacts in a couple of milliseconds. Opening of the contacts with high velocities implies a need for a timely and controllable damping. An efficient damping mechanism then is crucial to attain an appropriate actuation performance and secure a long lifetime. In this paper a finite element model of a Halbach magnet array based magnetic damper and a corresponding experimental prototype is described. A parametric study is performed to understand the effect of load mass and incoming velocities. It was found that the magnetic field modulation plays an important role on the damping performance. A uniform and high radial component of the magnetic flux density is necessary in order to achieve high damping force. The radial magnetic field can be controlled via thickness and magnetization direction of the ring magnets that are used to create the Halbach magnet array.
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| 16. |
- Parekh, Mrunal, 1987-, et al.
(författare)
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Study of an Electromagnetic Damping Actuator
- 2018
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Ingår i: VDE Conference Proceedings on Actuator 18. - 9783800746750 ; , s. 475-478
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Konferensbidrag (refereegranskat)abstract
- Current commutation switches for HVDC devices are operated with Ultra-fast electromagnetic actuators. They can generate hundreds of kilo-newton force and swiftly open electrical contacts in a couple of milliseconds. An efficient damping mechanism then is crucial to attain an appropriate actuation performance and secure a long lifetime. In this article an electromagnetic Halbach damping actuator was studied. A numerical model based on FEA is used to calculate its damping constant and retardation time down to stand still velocity.
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