Showing papers on "Transient (oscillation) published in 2001"

Power Electronic Control in Electrical Systems

Abstract: Preface Electrical power systems - an overview Power systems engineering - fundamental concepts Transmission system compensation Power flows in compensation and control studies Power semiconductor devices and converter hardware issues Power electronic equipment Harmonic studies of power compensating plant Transient studies of FACTS and Custom Power equipment Examples, problems and exercises Appendix Bibliography Index

Transient and steady-state behavior of space charges in multilayer organic light-emitting diodes

Abstract: A numerical study of space charge effects in multilayer organic light-emitting diodes (OLEDs) is presented. The method of solving the coupled Poisson and continuity equations, previously established for single-layer polymer LEDs, has been extended to treat internal organic interfaces. In addition, we consider the transient current and electroluminescence response. We discuss the accumulation of charges at internal interfaces and their signature in the transient response as well as the electric field distribution. Comparison to experimental transient data of a typical bilayer LED based on tris(8-hydroxyquinolinato)aluminum (Alq3) is provided and good agreement is found. Our results are consistent with commonly assumed operating principles of bilayer LEDs. In particular, the assumptions that the electric field is predominantly dropped across the Alq3 layer and that the electroluminescence delay time is determined by electrons passing through Alq3 to the internal interface are self-consistently supported by ...

A Novel Approach to the Classification of the Transient Phenomena in Power Transformers Using Combined Wavelet Transform and Neural Network

Abstract: The wavelet transform is a powerful tool in the analysis of the power transformer transient phenomena because of its ability to extract information from the transient signals simultaneously in both the time and frequency domain. This paper presents a novel technique for accurate discrimination between an internal fault and a magnetizing inrush current in the power transformer by combining wavelet transforms with neural networks. The wavelet transform is firstly applied to decompose the differential current signals of the power transformer into a series of detailed wavelet components. The spectral energies of the wavelet components are calculated and then employed to train a neural network to discriminate an internal fault from the magnetizing inrush current. The simulated results presented clearly show that the proposed technique can accurately discriminate between an internal fault and a magnetizing inrush current in power transformer protection.

Global Transient Stability and Voltage Regulation for Power Systems

Abstract: Summary form only given as follows. This paper is concerned with the global control of power systems. It arises from the practical concern that transient stability and voltage regulation are both important properties of power system control, but they are ascribed to different model descriptions and relate to different stages of system operation (i.e. transient period and post-transient period respectively). Earlier control results deal with the two problems separately, or employ a switching strategy of two different kinds of controllers, which causes a discontinuity of system behavior. We design in this paper a global controller to co-ordinate the transient stabilizer and voltage regulator. The designed controller is smooth and robust with respect to different transient faults. Simulations on a single-machine infinite bus power system have demonstrated better performances compared with existing controllers.

Application of electrical capacitance tomography for measurement of gas-solids flow characteristics in a pneumatic conveying system

Abstract: Transient three-dimensional multiphase flows are a characteristic feature of many industrial processes. The experimental observations and measurements of such flows are extremely difficult, and industrial process tomography has been developed over the last decade into a reliable method for investigating these complex phenomena. Gas-solids flows, such as those in pneumatic conveying systems, exhibit many interesting features and these can be successfully investigated by using electrical capacitance tomography. This paper discusses the current state of the art in this field, advantages and limitations of the technique and required future developments. Various levels of visualization and processing of tomographic data obtained in a pilot-plant-scale pneumatic conveying system are presented. A case study outlining the principles of measuring the mass flow rate of solids in a vertical channel is shown.

An improved transmission-line model of grounding system

Abstract: This paper presents a time-domain transmission line model of grounding system, which includes the mutual electromagnetic coupling between the parts of the grounding structure and the influence of air-earth interface. The model can be used to simulate the transient behavior of the grounding system under lightning strike. The simulation results are in good agreement with that of the model based on the solution of full Maxwell's equations. The influence of different parameters, such as the soil relative permittivity /spl epsi//sub /spl tau//, the soil resistivity /spl rho/, and the conductivity and diameter of the conductor, on the transient voltage distribution of the grounding system is investigated. It shows that, among the parameters investigated here, the soil resistivity is the most important parameter that affects the transient response of bare buried conductors. The soil permittivity has very little influence on the transient response of the grounding system when the grounding system is buried in the soil with low resistivity, but have moderate influence in the soil with extremely high resistivity. The conductivity of the conductor and skin effect have practically no influence on the peak transient voltage of the grounding system. Increase in conductor diameter tends to decrease the peak transient voltage. The model presented in this paper is simple, but sufficiently accurate and can be used easily in engineering practice. Since the model is in the time domain, it could be easily coupled to the other time-domain models of nonlinear surge-protection components.

A new control for multi-phase buck converter with fast transient response

Abstract: The new high performance microprocessors require the power supply to provide high current, fast transient response, and tight voltage regulation. Interleaved multiphase synchronous buck converters have recently been adopted in the industry to meet the requirements. To achieve current sharing among the multiple phases, a new control scheme is developed to combine current mode control with V/sup 2/ control. It has the advantages of fast transient speed, inherent current shaking and easy compensation. In this paper, the principle and implementation of the new control is presented and the transient response is shown. The small signal model of multiphase converter with the new control is derived and applied in converter analysis and voltage loop compensation.

Damping of transient oscillations on the output LC filter of PWM inverters by using a virtual resistor

Abstract: This paper presents a method to damp transient oscillations on the output LC filter of PWM inverters by using a virtual resistor. A virtual resistor is an additional control algorithm that simulates the roles of a resistor in the output LC filters. Because no real resistor is used, the oscillations can be damped effectively without sacrificing the power efficiency. The implementation of the virtual resistor is determined by how the resistor is connected to the LC filter. Experimental results are included to verify the proposed method.

Design considerations on the line-side filter used in the dynamic voltage restorer

Abstract: The effects of harmonic voltages generated by the voltage source inverter within a dynamic voltage restorer can be mitigated through the use of a line-side filter. However, injudicious design of the harmonic-filtering system can degrade the power-quality-enhancement capability of the restorer. Inappropriate filter design may also result in the need for the inverter current rating to be increased significantly, The purpose of the investigation is therefore to carry out a systematic analysis of the filter design by considering first the selection of the filter-capacitor on the basis of meeting a prespecified harmonic-performance criterion. The effect of the capacitor on the inverter rating is then evaluated and the method of determining the filter capacity is presented. An example, which involves electromagnetic transient studies, is included to demonstrate the efficacy of the proposed design method.

Direct Steam Generation in Parabolic Troughs: First Results of the DISS Project

Abstract: This article presents the latest experimental results of the European DISS (DIrect Solar Steam) project. The experiments are subdivided into steady state and transient tests. The goal of the steady state tests is the investigation of the thermohydraulic phenomena of the occurring two phase flow, whereas the transient tests are needed for the controller design. The experimental results are compared to simulation studies. Implications for the plant operation will be discussed.

Nonlinear Transient Behavior of a Sliding System With Frictionally Excited Thermoelastic Instability

Abstract: A transient finite element simulation is developed for the two-dimensional thermoelastic contact problem of a stationary layer between two sliding layers, with frictional heat generation. The petrov-Galerkin algorithm is used to discretize the sliding layers because of the high Peclet numbers involved. The results in the linear, full contact regime were validated by comparison with the analytical predictions of Lee and Barber (1993). After separation occurs, there is a non-monotonic transition to a steady state with the contact regions separated by the same wavelength. During the transition, the migration speed exhibits values lower than those in either the linear regime or the final steady state. When several wavelengths are unstable, the final steady state is generally that corresponding to the longest unstable wavelength, even though other modes have more rapid growth rates in the linear regime.

Transient effects in saturated Raman amplifiers

Abstract: Transient phenomena in Raman optical amplifiers are studied. For the first time, transient effects are observed in saturated Raman amplifiers. An accurate model is developed to explain these transient effects.

On the modeling of the transient thermal behavior of semiconductor devices

Abstract: A mathematical model of the transient temperature response of integrated devices is presented which takes into account the three-dimensional (3-D) nature of heat flow and the physical structure of the device. Simple analytical relations for the transient thermal impedance and thermal time constants are derived for the first time. The impact of device geometry on the transient thermal response curve is discussed, and simple guidelines for the thermal design of solid-state devices operated in transient or pulsed regime are given.

Transient analysis of a unified power flow controller and its application to design of the DC-link capacitor

Abstract: This paper presents a transient analysis of a unified power flow controller (UPFC), and design of capacitance of the DC-link capacitor. Active power flowing out of the series device in transient states is theoretically discussed to derive what amount of electric energy the DC link capacitor absorbs or releases through the series device. As a result, it is clarified that the active power flowing out of the series device is stored in the line inductance as magnetic energy during transient states. Design of capacitance of the DC-link capacitor is also presented in this paper, based on the theoretical analysis. Experimental results obtained from a 10-kVA laboratory setup are shown to verify the analytical results.

Dynamic thermal multiport modeling of IC packages

Abstract: The dynamic thermal behavior of electronic subsystems is characterized by their dynamic compact models. These models have to be similar to the steady state models in describing the fact that the heat is usually leaving at different locations (ports), necessitating multiport description of the thermal behavior. In our paper we present a method suitable for direct generation of multiport dynamic compact thermal models from a series of thermal transient simulations or measurements. The generated RC electrical equivalent circuit model, exercised with a network simulator program provided the same transient functions as the measured ones for various boundary conditions, proving the accuracy of the method.

Separation of transient information in musical audio using multiresolution analysis techniques

Abstract: Whilst musical transients are generally acknowledged as holding much of the perceptual information within musical tones, most research in sound analysis and synthesis tends to focus on the steady state components of signals. A method is presented which separates the noisy transient information from the slowly time varying steady state components of musical audio. Improvements of using adaptive thresholding, and multiresolution analysis methods are then illustrated. It is shown that by analyzing the resulting transient information only, current onset detection algorithms can be improved considerably, especially for those instruments with noisy attack information, such as plucked or struck strings. The idea is then applied to audio processing techniques to enhance or decrease the strength of note attack information. Finally, the transient extraction algorithm (TSS) is applied to time-scaling implementation, where the transient and noise information is analyzed so that only steady state regions are stretched, yielding considerably improved results.

All-purpose and plug-in power-law detectors for transient signals

Abstract: A power-law statistic operating on discrete Fourier transform (DFT) data has emerged as a basis for a remarkably robust detector of transient signals having unknown structure, location, and strength. We offer a number of improvements to Nuttall's (1994) original power-law detector. Specifically, the power-law detector requires that its data be prenormalized and spectrally white; a constant false-alarm rate (CFAR) and self-whitening version is developed and analyzed. Further, it is noted that transient signals tend to be contiguous both in the temporal and frequency sense, and consequently, new power-law detectors in the frequency and the wavelet domains are given. The resulting detectors offer exceptional performance and are extremely easy to implement. There are no parameters to tune. They may be considered "plug-in" solutions to the transient detection problem and are "all-purpose" in that they make minimal assumptions on the structure of the transient signal, save of some degree of agglomeration of energy in time and/or frequency.

Transient stability simulation of power system including wind generator by PSCAD/EMTDC

Abstract: Induction machines are mostly used as generators in wind power stations. Since induction machines also have a stability problem, it is important to analyze the transient stability of the power system including wind power stations. This paper presents simulation analyses of transient stability of a power system including an induction generator performed by PSCAD/EMTDC.

Method of operating a hybrid electric vehicle to reduce emissions

Abstract: A method of operating a hybrid electric vehicle 10 to reduce emissions. The method utilizes the vehicle's electric motor/generator 12 to generate a negative torque during cold-start conditions, effective to increase the load on the internal combustion engine 16, thereby reducing the light-off time of the catalytic converter 28. The method also reduces emissions by utilizing the vehicle's motor/generator 12 to provide a supplemental torque to engine 16 during transient events, thereby reducing the generated mass flow and amount of untreated emissions.

Stability prediction for an electric power network

Abstract: A method, device and computer program product for the prediction of the stability of an electric power network, where the method is executed after a fault or contingency has occurred, and comprises the steps of (a) during a time interval in which the network is in a transient condition, determining for at least one load connected to the electric power network, at least one parameter describing an estimated steady state behavior of the load,(b) executing a load flow calculation for the electric power network using the least one parameter describing the estimated steady state behavior the at least one load, (c) determining, if the load flow calculation indicates stability has a solution, that a future stability of the electrical power network exists, or, if the load flow calculation indicates instability does not have a solution, that a future stability of the electrical power network does not exist.

Radiation element method for transient hyperbolic radiative transfer in plane-parallel inhomogeneous media

Abstract: In this study the radiation element method is formulated to solve transient radiative transfer with light radiation propagation effect in scattering, absorbing, and emitting media with inhomogeneous property. The accuracy of the method is verified by good agreement between the present calculations and Monte Carlo simulations. The sensitivity of the method against element size, ray emission number, and time increment size is examined. The transient effect of radiation propagation is essential in short-pulse laser radiation transport when the input pulse width is not considerably larger than the system radiation propagation time. The transient characteristics of radiative transfer are investigated in the media subject to collimated laser irradiation and/or diffuse irradiation withtemporal Gaussian and/or square profiles. The inhomogeneous profile of extinction coefficient of the medium affects strongly the transient radiative flux divergence inside the medium.

Transient Model Scenarios of Climate Changes for New Zealand

Abstract: Climate simulations from a group o f coupled atmosphere-ocean general circulation models are assessed against current climate observations for the south-west Pacific region. While the six models analysed simulated many of the broad climate features of this region satisfactorily, they all exhibited some shortcomings in their detailed validation against the current climate of the Australasian region and the observed El Nino—Southern Oscillation variability that affects this part of the globe. A simple physically-based downscaling is applied, that describes how New Zealand's orography causes the climate of a station to deviate from the large-scale background climate at the same latitude, under the influence o f west-east and south-north airflow variations. Downscaled projections o f New Zealand temperature and precipitation changes are then calculated from transient simulations o f the models, which are all forced by a very similar emissions scenario o f sulphate aerosol concentration and 1°/0 per annum compounding carbon dioxide concentration increase. Projected changes are presented for periods of 50 years ahead (1970-1999 to 2030-2049 change) and 100 years ahead (1970-1999 to 2070-2099). The models generally predict that mean temperatures will increase somewhat slower than for the Southern Hemisphere as a whole than for the globe, that precipitation will increase in the west and decrease in the east of the country, and that the prevailing westerly winds will intensify across New Zealand. However there is considerable variation between models. Most of the changes discussed are actual model projections for the transient simulation, relative to control run changes over the same period, rather than changes scaled per degree global warming as are sometimes given. These anthropogenic projections should be viewed within the context of natural decadal variability in circulation, that periodically could either augment or weaken the west-east rainfall gradient across New Zealand. Concentrations of greenhouse gases in the atmosphere are expected to continue to grow through the coming century, leading to changes in global, regional and local climate (1PCC, 1996). There is a widespread demand for predictions of these climate changes, for use i n studies o f likely impacts, negotiation o f agreements f o r constraining anthropogenic greenhouse gas emissions, and identification o f adaptation options. However, for the reasons described below, science cannot give exact predictions of how local and regional climates may change in the future. Corresponding author: Dr A. B. Mullan, NIWA, P.O. Box 14-901, Kilbirnie, Wellington, New Zealand. Emailb mullan@niwa.cri.nz 4 W e a t h e r and Climate 21 The anthropogenic greenhouse gas and aerosol emissionsl which will influence climate over the coming century respond to changes in population and economic growth, technology, energy availability and national and international policies. Even i f the emissions for the next century could be predicted precisely, there would still be scientific uncertainties in estimating the resulting greenhouse gas concentrations and global, regional and local climate changes. The 1995 assessment by the Intergovernmental Panel on Climate Change (IPCC) concluded that confidence is higher in hemispheric-tocontinental scale projections of climate change than in regional projections from climate models, where "confidence remains low" (IPCC, 1996). One solution to the dilemma of providing predictions in an uncertain world is the use o f scenarios. I n this approach, several greenhouse gas emission pathways are constructed f o r the future, based o n a range o f plausible social, economic and technological developments. For each of these scenarios, projections are then made for greenhouse gas concentrations and the resulting climate changes, based on scientific understanding and incorporating science-based uncertainty ranges. The result is a set of several different climate predictions, spanning the most l ikely future emissions pathways. Such projections are central to answering "whati f" questions about the vulnerability of environmental, economic and social systems and their ability to respond and adapt (NSSCCC, 1997). Scenarios of this type have been developed for the globe as a whole by the IPCC (e.g. Kattenberg et al., 1996). Regional scenarios are needed i n addition to these global scenarios, because changes in climate will not be geographically uniform (IPCC, 1996). The starting point for a regional scenario is usually a simulation o f climate across the whole globe with a computerised General Circulation Model (GCM, also referred to as Global Climate Model), which is driven by the radiative forcing f rom a particular greenhouse gas emission scenario, and simulates climate elements at a horizontal spacing of about 250 km. However this limited spatial resolution does not pick up the influences of topographical features (such as New Zealand's Southern Alps) which have a marked effect on local climate, and means that many smaller scale processes important to climate (such as the formation o f clouds and the resulting rainfall generation) have to be simulated in a simplified manner. Nested regional climate modelling (Kattenberg et al., 1996) is one approach to downscaling from the GCM scale to the regional or local scale. Output from a GCM drives a regional climate model (RegCM), w h i c h is run at a much higher spatial resolution (typically 40 k m horizontal resolution, bu t potentially 1 0 k m wi th a sufficiently powerful computer). The RegCM incorporates many o f the important topographical influences on climate, as well as simulating some of the important physical processes in more detail. A second approach is statistical downscaling (Kattenberg, op. cit.). This is a two-stage process, in which statistical relationships are first developed 1 Aerosols are small particles which reflect solar radiation and influence cloud properties. They derive largely from sulphate emissions and offset some of the warming caused by greenhouse gases. MuIlan, Wratt, Renwick.: Transient model scenarios o f climate changes 5 between local climate variables (such as temperature and rainfall) and larger-scale features (such as atmospheric pressure patterns and spatially averaged temperatures), using historical measurements and analyses. These relationships are then applied to the output of GCM predictions, to simulate local climate characteristics. Kidson and Thompson (1998) concluded that, for the models they studied, statistical downscaling and nested regional modelling exhibit similar levels o f skill in simulating current aspects o f the New Zealand climate. Statistical downscaling requires fewer computer resources than nested modelling, but assumes that current "downscaling" relationships will remain valid under a significantly perturbed climate. 1.1 New Zealand Climate Scenarios In 1988, the New Zealand Climate Committee o f the Royal Society o f New Zealand (RSNZ, 1988) made preliminary projections of New Zealand climate change, based on early GCM results and qualitative understanding o f relationships between regional atmospheric circulation and local climate. The only quantitative earlier scenarios (Pittock and Salinger, 1982; Salinger, 1982) were based on palaeoclimate reconstructions o r comparison of warm and cold years in the observed record. The first detailed climate change scenarios for New Zealand derived from GCM simulations were prepared by MuIlan and Renwick (1990), using a statistical downscaling approach. This work was updated over the next few years, leading to the scenarios reported in MuIlan (1994) and Whetton et al. (1996b), and was also the basis f o r early scenarios used i n the CLIMPACTS integrated climate impacts assessment model (Kenny et al, 1994). More recently, regional climate modelling has also been applied as a downscaling tool for simulating climate change over New Zealand (Renwick et al 1998, 1999). The work described in the previous paragraph was based on downscaling from equilibrium atmosphere GCM simulations, coupled to a simple slab ocean. The carbon dioxide in the model was doubled instantaneously, and the model was run until a climate equilibrium was reached under this new radiative forcing. Such GCMs generally predict a decrease in the meridional temperature gradient in the Southern Hemisphere, and a consequent decrease in the westerly f low across New Zealand. Cl imate modelling groups have now developed transient coupled atmosphere-ocean GCMs (A0GCMs) which simulate a gradual increase in greenhouse gas concentrations, and couple a more detailed simulation o f ocean circulation with their atmospheric simulations. These simulations generally predict an increase in Southern Hemisphere meridional temperature gradient (the equator warms more quickly than the southern oceans), and a consequent increase in westerlies across New Zealand (Whetton et al, 1996b). These differences arise because, in coupled models, heat is drawn down into the southern ocean, slowing the rate of surface warming. I f atmospheric greenhouse gas concentrations were to be stabilised, the coupled (transient) AOGCMs would ultimately approach an equilibrium solution that might not look all that different from the slab ocean result. While AOGCMs are more physically complete in terms of the processes they describe, there are still uncertainties 6 W e a t h e r and Climate 21 about the rate o f vertical heat transport in the ocean (e.g., England and Hirst, 1997; Power and Hirst, 1997), and in heat fluxes between atmosphere and ocean. These differences between the equilibrium and transient simulations have important consequences. The distribution of rainfall across New Zealand is strongly influenced by the interaction between airflows from a westerly quarter and the predominantly northeastsouthwest oriented mountain chains (Wratt et al., 1996). Initial work on statis

Development of a new data collection system and chamber for microbeam and laser investigations of single event phenomena

Abstract: A new target chamber and control system for temperature-based transient-IBIC and transient-LBIC measurements using the same experimental chamber is outlined. The system has been designed for both ultra-fast and relatively slow transient measurements as a function of temperature from 77 K to 450 K. The control system, implemented in the Labview environment, allows single ion scanning and transient acquisition on a set of oscilloscopes, for an array of temperatures and bias. The modularity of the system allows its use for a broad range of experiments from single event upset transient current measurements to scanning ion deep level transient spectroscopy charge transient measurements. In this paper, we describe the overall system and illustrate its potential by way of example.

An accurate fault location technique for distribution lines with tapped loads using wavelet transform

Abstract: This paper investigates the application of wavelet transform as an accurate fault location technique for power distribution lines with tapped loads. When a fault occurs, a transient wave travels from the fault point to substation busbars and load terminals. The time taken for the fault generated transient wave to arrive at busbars or load terminals depends on the distance traveled and the velocity of the travelling wave. In this paper, fault transient detectors (FTDs) based on digital wavelet transform (DWT) are installed at substation busbars and load terminals to capture the time taken for the transient to arrive and be synchronized with a Global Positioning System (GPS) clock. From the recorded time and the topological structure of the network, an accurate fault location is deduced. The fault location technique is validated by EMTP/ATP on an 11 kV distribution line with 7 tapped loads.

Application of resistor based superconducting fault current limiter to enhancement of power system transient stability

Abstract: This paper presents an application of a superconducting fault current limiter (SFCL) to enhance the power system transient stability. Resistance as the current limiting devices is used for damping the generator accelerating power. A method to evaluate an appropriate resistance is proposed. The SFCL is combined with the superconducting magnetic energy storage (SMES) for power system stabilization. As a result the capacity of SMES is significantly reduced.

Analysis of power system transients using wavelets and Prony method

Abstract: Transients resulting from switching of capacitor banks in electrical distribution systems affects power quality. The transient overvoltages can theoretically reach peak phase to earth values in the order of 2.0 p.u. High current transients can reach values to ten times the capacitor nominal current with duration of several milliseconds. Another severe operating condition is the switching on a second capacitor bank connected to the same bus. In the work, the characteristics of the transients are analyzed. The time of the beginning of a transient process is detected using a wavelet transform. The frequencies of transient components have been investigated applying the Fourier technique and the Prony model. The investigations show the advantages of the methods basing on the Prony model, over the Fourier technique. A distribution system was simulated using the EMTP software.