Papers by Keyword: Dynamic Characteristics

Abstract: One of the key factors that hinder satisfactory performance of metal oxide surge arresters (MOSAs) against the damaging effects of overvoltage transients is accurate representation of their dynamic behaviour. Therefore, this study analysed dynamic characteristics of MOSA using IEEE and Fernández-Díaz equivalent circuits with ABB MWK surge arrester used as a test case. The impulse current input to the equivalent circuits was modelled using Gaussian equation. Simulations were done and residual voltage and quenching time of the models for impulse currents inputs of 1, 5, 10 and 20 kA respectively were determined. The obtained residual voltages were compared with the manufacturer’s standard in the test arrester datasheet. Residual voltages of 115, 128, 137 and 157 kV respectively were obtained for 1, 5, 10 and 20 kA impulse currents impressed on both IEEE and Fernández-Díaz models. While 115 and 128 kV residual voltages respectively tallied with the manufacturer’s standard for 1 and 5 kA impulse currents, 137 and 157 kV residual voltages were found to exceed the standard for 10 and 20 kA impulse currents respectively. The quenching time for the voltage surge resulting from 1, 5, 10 and 20 kA currents injection on both adopted models were 0.2, 0.22, 0.225 and 0.23 ms respectively with no damping observed in the voltage response of Fernández-Díaz model unlike in the IEEE model. The study indicated that Fernández-Díaz model produced a better MOSA dynamic response for the study.

Abstract: A novel substrate of 4H-SiC bonded substrate is expected to solve issues such as decreasing the on-resistance, which has attracted much attention. Therefore, several studies have been conducted on the use of bonded substrates. In this study, we fabricated a DMOSFET on a bonded substrate and compared its static and dynamic characteristics with those on a single-crystal substrate. Consequently, the on-resistance of the DMOSFET fabricated on a bonded substrate was lower than that on a single-crystal substrate owing to the low resistivity of the polycrystalline substrate. Also, reverse recovery loss of the DMOSFET fabricated on a bonded substrate was lower than that on single-crystal substrate at high temperature due to low carrier lifetime in a drift layer. Additionally, we observed that the DMOSFET fabricated on a bonded substrate did not generate bipolar degradation despite the application of a forward-current stress of over 1500 A cm^-2. According to these results, we expected that the carrier lifetime in both drift layer and transfer layer was decreased on a bonded substrate.

Abstract: A 1.2 kV silicon carbide (SiC) SBD-wall-integrated trench metal oxide semiconductor field effect transistor (MOSFET) (SWITCH-MOS) exhibits potential for solving body-PiN-diode-related problems such as bipolar forward degradation and switching losses among relatively low breakdown voltage 1.2 kV-class SiC MOSFETs. In this study, dynamic characteristics and switching losses of the SWITCH-MOS and conventional MOSFET are compared. The results demonstrate that the SWITCH-MOS exhibits smaller turn-on and reverse recovery losses than a conventional MOSFET at high temperatures. Ruggedness performances such as short circuit and unclamped inductive switching capabilities were evaluated.

Abstract: This paper presents modelling of various gas application to modified atomic force microscope sensor in order to change its existing dynamic characteristics. This paper represents part of continuous research, which is focused on improvement of scanning speed of atomic force microscope (AFM) sensor. Subject of our research is enhancement of dynamic characteristics of Atomic force microscope sensor. Natural frequency of AFM sensor is the main factor influencing max scanning speed of atomic force microscope. In case of working range of frequencies approaches to the resonant frequency of cantilever, scanning results becoming inaccurate and unreliable. Improvement of properties of atomic force sensor made by adding additional nonlinear aerodynamic force to the AFM sensor. This force would act as additional controllable stiffness element, which allows shift resonant frequency to higher side. In this paper is presented research of additional nonlinear force behavior using different gasses as well as compressed air. Research covers factor of humidity of compressed air. Our research performed using 3D atomic microscope cantilever model in SolidWorks flow simulation software. Results of simulation delivered as dependencies of additional stiffness in the AFM sensor in all modelled cases. Finally, results presented in graphical form and conclusions are drawn.

Abstract: In this paper, the dynamic characteristics of rotor-bearing system with a labyrinth seal are investigated. The dynamic coefficients of labyrinth seal and the whirl speeds of rotor-bearing system are analyzed. The simplified rotor-bearing model consists of a rigid disk and a flexible shaft. The rotor-bearing system supported by two ball bearings, which are modeled as the spring-damper systems. A labyrinth seal supports one of the rigid disks. The perturbation approach has been applied to the governing equations of the bulk-flow model to calculate the dynamic coefficients of labyrinth seal. The Finite Element Method (FEM) is utilized to model the flexible-rotor system. The numerical results show the labyrinth seal effect on the dynamic characteristics of rotor-bearing system, which depend on a great variety of parameters such as geometry of the labyrinth seal.

Abstract: With the development of transportation, more and more long-span floating system steel truss-stiffened cable-stayed bridges have been built. Due to the non-restraint in longitudinal direction, this kind of bridges possess very superior performance in the dissipation of vibration energy. On account of the characteristics above, the paper intends to discuss the dynamic behavior of this type of bridges. Based on a real structure design, the numerical simulation procedure of the vibration has been introduced. According to a series of assumptions, the dynamic 3D FEM model of the bridge is established firstly. Thereafter, the vibration characteristics of the model are evaluated. Results show that the longitudinal stiffness is relatively small in comparison to the torsional stiffness. The 1st order mode is longitudinal floatation of girders and pylons. But overall the bridge is still rather flexible.

Abstract: Because the key factors of the dynamic performance of the machine tool are related to the characteristics of the conjoint interface, the feeding system as an important part of the machine tool, which contains typical rolling conjoint interface and fixed conjoint interface, so in order to study the dynamic performance of machine tool better, the modal analysis is carried out on the feeding system. In this paper, the finite element model simulation and test methods will be combined. First, making a finite element analysis of the feeding system to obtain its corresponding mode and frequency; Secondly, the actual modal test experiment is carried out, and the result is compared with the simulation result through the follow-up data processing; Finally, the causes of the error are analyzed, and the correctness of the method is verified.

Abstract: High temperature capability of silicon carbide (SiC) power MOSFETs is becoming more important as power electronics faces wider applications in harsh environments. In this paper, comprehensive static and dynamic parameters of 1.2 kV SiC MOSFETs have been measured up to 250°C. The electrical behaviors with the temperature have been analyzed using the basic device physics and analytical models.

Abstract: In order to break through the limitation of the width of river, depth of water, channel and etc., it is an optimal choice to construct a long-span suspension bridge. In a suspension bridge, the main cable is the major bearing member; and the use of super high strength cable wire can lighten the dead weight and obtain an economical design. 1960 Mpa cable wire is adopted by an under-construction suspension bridge, namely Ni-Zhou Channel Bridge, for the first time in China. In this paper, taking the Ni-Zhou Channel Bridge as a case-study, comparative analyses on dynamic characteristic and seismic response of long-span suspension bridge with 1960 Mpa cable wire are performed. Firstly, dynamic calculating model for Ni-Zhou Channel Bridge is built and its dynamic characteristics are studied; then by using response spectrum and time history analysis method, seismic response of Ni-Zhou Channel Bridge is investigated on the basis of design response spectrum and artificial seismic ground motions; finally, the energy dissipation performances of a seismic protection devices (viscous damper) are also discussed. The results show that long-span suspension bridge with 1960 Mpa cable wire has a longer natural vibration period; the use of viscous damper can effectively reduce the peak value of bending moment in stiffening girder. This paper can provide references for the project’s construction.

Abstract: The results of the research of vibro-acoustic signals, accompanying the processes of electrical discharge machining and pulsed laser treatment, are presented in this article. It is shown that the monitoring parameters of vibro-acoustic signals can improve the quality of management spark erosion equipment.