Ara Bissal

Comparison of Two Ultra-Fast Actuator Concepts

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.

Electric to Mechanical Energy Conversion of Linear Ultrafast Electromechanical Actuators Based on Stroke Requirements

The operational efficiency of ultra fast actuators used as drives in high voltage direct current breakers are at best 5 %. To boost their efficiency, the design of the energizing circuit is crucial. A multi-physics finite element method (FEM) model coupled with a SPICE circuit model that is able to predict the performance of the actuator with an accuracy of at least 95 % has been developed and verified experimentally. Several variants of prototypes and models have been simulated, built, and tested. It was shown that one of the main problems leading to low efficiencies is the stroke of the drive. However, there is a possibility to increase the efficiency of the electric to mechanical energy conversion process of the studied Thomson (TC) and double sided coils (DSC) to a maximum of 54 % and 88 % respectively if their stroke is minimized. This can be done at the expense of increasing the complexity and the cost of the contact system by designing a switch with several series connected contacts that is encapsulated in a medium with a high dielectric strength. Another proposed solution is to design a current pulse with a rise time that is considerably shorter than the mechanical response time of the system. Parametric variations of capacitances and charging voltages show that the TC and the DSC can achieve efficiencies up to 15 % and 23 % respectively. Regardless of the chosen method, the DSC has a superior efficiency compared to a TC.

On the Design of Ultra-Fast Electromechanical Actuators: A Comprehensive Multi-Physical Simulation Model

In this paper, a simulation of an ultra-fast electromechanical drive was performed by using a two-dimensional axi-symmetric multi-physical finite element model. The aim of this paper is to primarily show that the following model can be used to simulate and design those actuators with good accuracy, secondly, to study the behavior and sensitivity of the system and thirdly, to demonstrate the potential of the model for industrial applications. The simulation model is coupled to a circuit and solves for the electro-magnetic, thermal, and mechanical dynamics utilizing a moving mesh. The actuator under study is composed of a spiral-shaped coil and a disk-shaped 3mm thick copper armature on top. Two numerical studies of such an actuator powered by 2640 J capacitor banks were performed. It is shown that forces up to 38 kN can be achieved in the range of 200 μs. To add credibility, a benchmark prototype was built to validate this experimentally with the use of a high speed camera and image motion analysis.

Optimal design of a medium voltage hybrid fault current limiter

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.

On the use of metal oxide varistors as a snubber circuit in solid-state breakers

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.

On the design of a linear composite magnetic damper

High-voltage direct current (HVdc) breakers are the key components in the realization of multiterminal HVdc grids. In the presence of fault current, these breakers should be able to deliver impulsive forces to swiftly open the metallic contacts. After the acceleration phase, the moving armature should be decelerated using controllable forces to avoid plastically deforming fragile components integrated in the system. In this paper, finite-element method-based simulation models, complimented with small-scale and large-scale experimental prototypes, were utilized to benchmark different damping topologies. It was found that a Halbach-based configuration can deliver a damping force that is almost two and a half times larger than its sequel. Its sequel, composed of vertically stacked oppositely oriented magnets, is easier to assemble and is also capable of generating a considerable damping force. Finally, it has been shown that both these schemes, inserted in a composite tube, have a potential to be used as dampers in HVdc breakers.

Multiphysics modeling and experimental verification of ultra-fast electro-mechanical actuators

In this paper, a multi-physics computational tool has been developed to accurately model and build high performance ultra-fast actuators. The research methodology is based on a finite element method model coupled with a circuit model. Electro- magnetic, thermal, mechanical, and algebraic equations are implemented in Comsol Multiphysics and verified with laboratory experiments of a built prototype. A simplified model is preferred as long as its underlying assumptions hold. However, in the presence of large current and force densities, nonlinearities such as deformations may occur. Such phenomena can only be captured by the use of the developed comprehensive multi-physics simulation model. Although this model is computationally demanding, it was shown to have an accuracy of at least 95% when compared with experiments.

Study of a linear Halbach passive magnetic damper

High voltage ultra-fast circuit breakers are operated with fast actuators. They are capable of generating impulsive 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. It was found that 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 which are used to create the Halbach magnet array. Finally, it is also shown that the concept provides a frictionless collision free damping demonstrating its potential to be used in fast circuit breakers.

Effect of polymer based nanocomposites on the electrical arcs in air

According to the recent developments in nanocomposites, the polymer-based nanocomposites (PNCs) show promising quality to be used for improving the operational limits of electrical switching applications like low voltage circuit breakers, switch gears, etc. Such PNCs can be made by incorporating suitable nanoparticles (NPs) into a polymeric matrix by in-situ polymerization. During the interruption of high currents, high energy plasma arcs are initiated between the two electrodes of circuit breakers. The interaction of PNCs with high energy plasma arcs generates vapors (ablation). The ablated chemical species changes the thermodynamic properties of the arcing environment which helps to quench electrical arcs effectively.1,2 During this process, some chemical species depositions and morphological changes are also observed on the surface of PNCs.

Electric to mechanical energy conversion of linear ultra-fast electro-mechanical actuators based on stroke requirements

The operational efficiency of ultra fast actuators usedas drives in high voltage direct current breakers are at best5 %. To boost their efficiency, the design of the energizing circuitis crucial. A multi-physics finite element method (FEM) modelcoupled with a SPICE circuit model that is able to predict theperformance of the actuator with an accuracy of at least 95 % hasbeen developed and verified experimentally. Several variants ofprototypes and models have been simulated, built, and tested.It was shown that one of the main problems leading to lowefficiencies is the stroke of the drive. However, there is a possibilityto increase the efficiency of the electric to mechanical energyconversion process of the studied Thomson (TC) and double sidedcoils (DSC) to a maximum of 54 % and 88 % respectively iftheir stroke is minimized. This can be done at the expense ofincreasing the complexity and the cost of the contact system bydesigning a switch with several series connected contacts that isencapsulated in a medium with a high dielectric strength. Anotherproposed solution is to design a current pulse with a rise timethat is considerably shorter than the mechanical response time ofthe system. Parametric variations of capacitances and chargingvoltages show that the TC and the DSC can achieve efficienciesup to 15 % and 23 % respectively. Regardless of the chosenmethod, the DSC has a superior efficiency compared to a TC.