Showing papers on "Transient (oscillation) published in 1987"

Transient Stability Simulation by Waveform Relaxation Methods

Abstract: In this paper, a new methodology for power system dynamic response calculations is presented. The technique known as the waveform relaxation has been extensively used in transient analysis of VLSI circuits and it can take advantage of new architectures in computer systems such as parallel processors. The application in this paper is limited to swing equations of a large power system. Computational results are presented.

Transient photoconductivity measurements in semi‐insulating GaAs. I. An analog approach

Abstract: An experimental arrangement is described by which emission coefficient behavior associated with deep‐level traps in semi‐insulating GaAs can be surveyed, from the photoconductive transient behavior following a trap‐filling light pulse. This method, often referred to as PITS (for photoinduced transient spectroscopy) has analogies with the transient capacitance spectroscopy usable for conductive material, but some significant differences also. The necessary experimental precautions which can maximize the probability of getting reliable data are described, and illustrated by PITS results obtained with bulk semi‐insulating samples of Cr‐doped GaAs. Those results include data for five kinds of trap with activation energies from 0.3 to 0.8 eV, of which some are readily identifiable and others are not. The method described in this paper relies on analog measurement of the change in sample voltage during a specified time interval of the photoconductive decay.

Frequency Dependent Characteristics of Grounding Systems

Abstract: This paper presents models for the computation of frequency characteristics and transient response of power grounding systems. The methodology can accommodate any configuration of a grounding system comprising rectilinear conductors. The approach is based on transmission line concepts. Finite element analysis is employed to model the constituent parts of a grounding system. The grounding system is segmented into short lengths of earth embedded electrodes which are characterized as lossy transmission lines with distributed inductance, capacitance, series resistahce, resistance to earth, and mutual coupling to any other finite element of earth conductors. The parameters of the short earth embedded electrodes are computed by solution of Maxwell's equations and assuming quasi-static conditions. The paper presents a validation procedure which is based on comparison of analysis results to test results obtained at BPA. The model is applicable for transient phenomena comprising a wide range of frequencies. Results are presented which illustrate the properties of grounding systems to low as well as high frequency transients.

Induction Machine Modelling for Electromagnetic Transient Program

Abstract: A method is presented by which an accurate dynamic induction motor model may be developed from a knowledge of standard specification data for the motor. The incorporation of the model into the Electromagnetic Transients Program (EMTP) is described. Examples are given of its use in the study of the starting performance of a large induction motor and of the response of the same motor following various electrical faults.

Application of transient correlation functions to shear flow far from equilibrium

Abstract: Morriss and Evans recently developed a generalization of the Green-Kubo relations which is valid for nonequilibrium steady states far from equilibrium. This formalism relates the nonequilibrium response to transient time correlation functions which connect the nonequilibrium steady state to the equilibrium state. In the linear regime, the transient time correlation functions reduce to simple equilibrium Green-Kubo relations. The transient time correlation function method thus provides a long-sought-after fundamental relation between nonequilibrium molecular dynamics algorithms and the Green-Kubo formalism which is only valid close to equilibrium. In this paper we demonstrate the use of the transient time correlation function formalism for isothermal planar Couette flow. The results show that the nonlinear steady-state response can be calculated by integrating the appropriate transient response time correlation function. In particular, the nonlinear shear stress and pressure calculated in this way agree with the values calculated directly.

Transient analysis of charge-transfer in SC filters-gain error and distortion

Abstract: In switched-capacitor (SC) circuits, op amps often slew during the charge-transfer transient. When this happens, the charge-transfer error is no longer proportional to the input signal. The charge-transfer transient is studied in detail, taking into account the slewing behavior of the amplifiers. Analytical expressions are obtained for the charge-transfer error of an SC integrator. In switched-capacitor signal processing, the harmonic distortion can be defined as the harmonic distortion of the envelope of the sampled-data sequence. A Fourier analysis is carried out on the sampled-data sequence corrupted by the charge-transfer error due to slewing of the operational transconductance amplifiers. Analytical expressions are derived for harmonic distortions of an SC integrator. Analysis of the results shows that slew-induced harmonic distortion can be minimized by using large transconductance. It is possible to design SC filters with low power consumption and low harmonic distortion without resorting to class AB amplifiers.

A 580 kHz switching regulator using on-off control

Abstract: The analysis and design of a 580 kHz switching regulator incorporating a series-resonant converter is described. On-off control is used in the feedback loop of the regulator to achieve regulation of the output voltage. An easy-to-use graphical method of analysis of transient currents is introduced as a tool for the analysis and design of the regulator. The 40W regulator circuit which has been built shows exceptionally good transient load regulation and high efficiency.

Interpretation of transient electromagnetic soundings over three-dimensional structures for the central-loop configuration

Abstract: Summary. An assessment is made of the bias of fitting constrained layeredearth models to transient electromagnetic data obtained over 3-D structures. In this assessment we use the central-loop configuration and show that accurate estimates of the depth of burial of 3-D structures can be obtained with layered-earth model fitting. However, layered-earth interpretations are not reliable for estimating depth extents and resistivities of 3-D structures. When layered earths are used for interpretation, it is advantageous in some cases to use data based on the magnetic field instead of the voltage. A magnetic-field definition of apparent resistivity, in contrast to a definition based on the voltage, eliminates apparent-resistivity overshoots and undershoots in the data. A resistivity undershoot in the data can produce an extraneous and misleading layer in an interpretation of a 3-D resistive structure. Due to 3-D effects, apparent-resistivity soundings (magnetic field and voltage) may rise so steeply at late times that it may not be possible to fit a sounding to a reasonable layered-earth model. Truncating such a sounding, over a buried conductor, allows for a reasonable layered-earth fit and an accurate estimate of the depth to the conductor. However, the resistivity of the conductor is overestimated. Measurements of the horizontal field in the central-loop configuration can map 3-D structures, provided the sensor is located accurately at the centre of the transmitting loop. Horizontal-field calculations show that the transients peak on the flanks of a 3-D structure, but are depressed over the structure's centre. Weak transient responses flanked by two large transient responses, which are opposite in sign, locate the structure. The sign reversal is caused by a corresponding reversal in the currents that are channelled through or deflected away from conductive or resistive structures, respectively.

Modelling of transient production and decay following laser excitation of opaque materials

Abstract: The generation and decay of transient species in light-scattering materials is examined theoretically. Two limiting cases of transient distribution can be identified for which straightforward mathematical solutions are available: (a) where an exponentially falling-off concentration of transients exists beneath the sample surface and (b) where a homogeneous transient concentration (a ‘plug’) exists beneath the sample surface. Between and including these limits, the concentration profile can be calculated by a numerical iterative thin-slice approach. This method also permits calculation of the experimentally available reflectances R of the sample at the analysing wavelength. The size of the transient absorption is governed by the extinction coefficients of the initial absorber and the transient. In the case of a transient species which shows both luminescence and absorption, it is found that the emission intensity and the transient absorption at the same wavelength are proportional to each other. For a transient decaying by a unimolecular pathway, the rate constant can be obtained in case (a) from the slope of a plot of ln (1 –R)vs. time, while for case (b) ln [F(R)] must be plotted against time, where F(R) is the Kubelka–Munk function. If the decay follows a bimolecular pathway, the rate constant can be evaluated from the slope of a 1/F(R) plot vs. time only for case (b). In all other cases no straightforward method is available. Experimental data are presented and discussed for benzil microcrystals, an example of case (a) where the predicted superimposition of transient decay and phosphorescence is also observed, and for acridine adsorbed on silica gel, an example of case (b).

Two-Dimensional Transient Solutions for Crossflow Heat Exchangers With Neither Gas Mixed

Abstract: The two-dimensional transient behavior of gas-to-gas crossflow heat exchangers is investigated, solving by analytical methods the thermal balance equations in order to determine the transient distribution of temperatures in the core wall and in both the unmixed gases. Assuming large wall capacitance, the general solutions are deduced by the Laplace transform method and are presented as integrals of modified Besel functions on space and time, for a transient response with any arbitrary initial and inlet conditions, in terms of the number of transfer units, capacity rate and conductance ratio. Specializing the entrance temperature and assuming constant initial conditions, the most meaningful transient conditions (such as step, ramp, and exponential responses) have been simulated and the relevant solutions, expressed by means of either integrals or series, have been accurately computed with extremely low computational time. The temperature responses are then presented in graphic form for a wide range of the number of transfer units.

Fast, sensitive laser deflection system suitable for transient plasma analysis

Abstract: A laser deflection measurement system has been developed which is both fast (τ≊20 ns) and sensitive (δφ≊0.5 μrad). This diagnostic is capable of sensing and discriminating between electrons and neutral particles in a multicomponent plasma, and yields quantitative results. The technique allows continuous measurements in time. Construction is inexpensive and simple to field. This system is, therefore, highly competitive with traditional techniques in diagnosing the development of transient plasmas.

Method and apparatus for characterizing a radio transmitter

Abstract: A method and apparatus for identifying a radio transmitter. The transient frequency or phase history of the turn-on characteristics of a transmitter is detected and digitized. The history can be analyzed by a microprocessor operating a computer program to gather transient phase information from an unknown transmitter and to classify the transmitter in accordance with a transient characteristic.

Identification and Modelling of Load Characteristics at High Frequencies

Abstract: A simple technique for identifying the high frequency characteristics of a load feeder is presented. The method is based on applying signal processing techniques to the transient bus voltage and feeder current produced by a capacitor bank switching operation. The method was applied to identify the frequency characteristics of two 27.6 kV feeders at a substation in Ontario. Models reproducing the identified frequency characteristics were developed and their frequency behaviour is compared to those of the conventional models.

A finite element study of transient wave propagation in plates

Abstract: Studies of transient wave propagation in plates were carried out to establish a ba­ sis for the impact-echo technique as a nondestructive test for flaw detection in concrete. The surface displacements caused by stress waves generated by point impact on a plate were calculated using both the Green's function solution and the finite element method; displace­ ment waveforms obtained by the two approaches showed good agreement. Displacement and stress fields in a plate were studied using finite element analy­ sis. It was shown that transient point load applied normal to a stress-free boundary gives rise to P- and S­ "wakes" -disturbances trailing the P­ and S-waves. The displacement and stress fields in each wake resemble those in the preceding wave.

Transient photoconductivity measurements in semi-insulating GaAs II: A digital approach

Abstract: We describe an experimental setup designed to study photoconductive transients in semi‐insulating materials. The method, known as photoinduced transient spectroscopy, is based on a digital signal‐averaging technique. Although this digital method eliminates or reduces many of the experimental problems encountered when using an analog approach, several new problems arise. The method is described, and the difficulties are illustrated using data obtained from both Cr‐doped and nominally undoped samples of GaAs.

Voltage surge protector

Abstract: A device for suppressing transient surges in electrical power available from an electrical outlet is disclosed The device is adapted for mounting on a back side portion of the electrical outlet Surge protection components, such as planar varistors are disposed within an insulative housing block which forms the body of the device, and the device is physically mounted and electrically connected to the electrical outlet by mounting apparatus such as stiff metal leads

Transition of transient vertical natural-convection flows in water

Abstract: Experimental results and interpretations are given for transient natural convection adjacent to a suddenly heated flat vertical surface in quiescent water. The 1.24 m high surface resulted in laminar, transition and turbulent regimes downstream, in transients and in steady state, over a wide range of surface-energy input rates. Flows were visualized and velocity and temperature measurements made at various downstream locations, after imposing a uniform internal-energy generation rate within the very thin surface. Upflow development from quiescence to steady state was found to depend strongly on the downstream location x and imposed input heat flux. Laminar flow persisted into steady state, for short downstream distances. Further downstream, the flow became turbulent during the transient. Relaminarization at later time occurred only for lower flux inputs. Local measurements across the fluid layer show that the transient disturbances close to the leading edge of the surface are confined to within the final steady boundary layer. Downstream, they extend much further into the ambient. First disturbances always arose before the leading-edge-effect propagation estimates. The trend of data was in agreement with theory for a non-dimensional time τ < 85. For larger τ, turbulence instead terminated the one-dimensional transport regime simultaneously, at all downstream locations. This single value of τ also amounts to a single value of the non-dimensional thermal energy of the flow, ETT = 19.7. Disturbance frequency data early in the transient suggest the presence of a strongly selective amplification mechanism, very similar to that found in steady flows. The non-dimensional times at which local steady state was achieved were best correlated by a Fourier number, over a wide range of energy input conditions. Turbulence arising during the transient enhances the thermal transport significantly. Local convection coefficients then were found to be as much as 40% higher than the eventual steady values.

Design of a Modular Program for Transient Nonlinear Analysis of Large 3-D Building Structures

Abstract: This report describes the plans for the development of a computer modelling and analysis system for transient fully nonlinear seismic analysis of large buildings. The emphasis is on modelling the buildings at a "macro" level, i.e., modelling in terms of elements which correspond to structural members such as beams, shear walls. connections, and the like. It is recognized that the research needs are vast with advances required in geometric modelling, finite-element modelling, material modelling, nonlinear analysis, and interactiveadaptive user interface schemes. Further, the magnitude of the computational problem in terms of computer memory and solution time requires access to supercomputing or some parallel processing option, pref.erably with a graphical "window" for monitoring the computations. It is felt that coordination and cooperation among different research groups is essential to avoid duplication of effort and to accelerate research. Yith this objective in mind, a shareable platform or testbed computer program is proposed and is currently under initial development at Cornell University. A high degree of modularity is a central objective in the development of this program to permit expansion, porting, and modification over its useful life. One of the keys to modularity is the availability of an efficient data management system. which can manage data associated with the relationships among the different components of the building, their attributes, and the methods of manipulating the attributes.

Output hold-up circuit for a step-up voltage regulator

Abstract: An arrangement for enhancing the available energy storage capability of a hold-up energy storage element for use with the step-up or boost regulator stage of a power supply enables use of smaller hold-up storage elements, such as capacitors. The circuit stores energy at the boost regulator output and returns the energy either to the regulator input in the event of a transient line failure, or to the regulator output during a load transient. The invention provides improved transient fault tolerance by increasing the hold-up time of the storage element.

A Simplified Two-Terminal HVDC Model and Its Use in Direct Transient Stability Assessment

Abstract: The use of the Transient Energy Function (TEF) method in transient stability analysis is extended to include an ac/dc system with a two terminal HVDC. A simple, yet accurate, dc model which is valid for first swing transient stability studies is developed and tested. The model used includes the steady-state converter model with the static dc line representation, the fast changing dc power, and voltage dependent current order limit (VDCOL); while the dynamics of the dc internal controls are neglected. With this model, the dc operation mode is determined by an inference method, and the corresponding dc variables are computed. Using the simplified dc model, the Transient Energy Function is modified to include the effect of the two terminal HVDC. A procedure for first swing transient stability assessment of an ac/dc system is proposed and is tested on a 20-generator test system. Transient stability assessment with the new method is presented and compared with results obtained with the EPRI transient stability program.

Transient Tests on a Voltage-Regulated Controlled-Current PWM Converter

Abstract: The controlled-current PWM converter has the capability of delivering near sinusoidal current waveforms with unity and even leading power factors. This paper describes its transient characteristics when operated with a simple proportional feedback control to ensure regulated dc voltage output. Experimental tests show that it has fast step response and that it survives abnormal operational conditions such as brown-outs and loss of a single phase.

Transient Waves in Layered Media

Abstract: Pictorial Guide to Transient Waves and Time Symmetry. Introduction. 1. Plane Waves in Full Space. 2. Point-Source Representations and Transient Responses from an Acoustic Planar Interface. 3. Time-Symmetric Point-Source Response from a Planar Acoustic Interface. 4. Analysis of Reflection and Transmission Responses. 5. Transient Line-Source Response from a Planar Acoustic Interface. 6. Transient Plane-Wave Propagation in a Stack of Acoustic Layers. 7. Point-Source Response of a Stack of Layers. 8. Point Source within a Stack of Layers. 9. Line Source within a Stack of Layers. 10. Zero-Offset Point-Source Response: Geometrical Optics Expansion. 11. Multilayer Plane-Wave Decomposition. 12. Free Elastic Surface Point-Source Response. 13. Living in a Complex World. 14. Analytic Signals and Integral Transforms. Appendices: A. Specification of Fundamental Square-Root Function. B. Some Properties of the D-Function. C. Contribution of Inhomogeneous Waves in the Transient Weyl Integral. D. Properties of the Analytic Square-Root Potential. References. Index.

The influence of eddy currents on magnetic actuator performance

Abstract: In this letter the effects of eddy currents on the transient performance of electromagnetic actuators is discussed. It is shown that a transfer function representation, that includes a first-order model of the eddy current influence, can be obtained which is suitable for control system analysis.

A comparative analysis of thermal blood perfusion measurement techniques.

Abstract: The object of this study was to devise a unified method for comparing different thermal techniques for the estimation of blood perfusion rates and to perform a comparison for several common techniques. The approach used was to develop analytical models for the temperature response for all combinations of five power deposition geometries (spherical, one- and two-dimensional cylindrical, and one- and two-dimensional Gaussian) and three transient heating techniques (temperature pulse-decay, temperature step function, and constant-power heat-up) plus one steady-state heating technique. The transient models were used to determine the range of times (the time window) when a significant portion of the transient temperature response was due to blood perfusion. This time window was defined to begin when the difference between the conduction-only and the conduction-plus-blood flow transient temperature (or power) responses exceeded a specified value, and to end when the conduction-plus-blood flow transient temperature (or power) reached a specified fraction of its steady-state value. The results are summarized in dimensionless plots showing the size of the time windows for each of the transient perfusion estimation techniques. Several conclusions were drawn, in particular: (a) low perfusions are difficult to estimate because of the dominance of conduction, (b) large heated regions are better suited for estimation of low perfusions, (c) noninvasive heating techniques are superior because they have the potential to minimize conduction effects, and (d) none of the transient techniques appears to be clearly superior to the others.

A computer-controlled instrument for the measurement of the thermal conductivity of liquids

Abstract: A new instrument for the measurement of the thermal conductivity of liquids by the transient hot-wire method is described. The instrument has features in common with earlier versions but employs a novel technique for the determination of the transient temperature rise of the hot wire during the course of a measurement. New determinations of the thermal conductivity of toluene confirm the accuracy of the instrument to be better than 0.5%.

Transient and Harmonic Voltages Associated with Automated Capacitor Switching on Distribution Systems

Abstract: One of the functions proposed for distribution automation systems is automated capacitor switching to control power factor and voltage profile on feeder circuits. This is one of the functions being implemented as part of the Athens Automation and Control Experiment on the Athens Utilities Board (AUB) in Athens, Tennessee. A concern with automated capacitor switching is the increase in harmonic and transient voltages due to different capacitor configurations on the distribution system. A study was performed to evaluate the impact of the automated capacitor switching on the AUB distribution system. The study has identified problem areas, methods for determining the problem areas, and possible solutions. The substation capacitor banks were found to be the dominant factor in both the transient and harmonic repsonses of the distribution system. The harmonic response of the system is dominated by the parallel inductance/capacitance of the circuit comprised of the substation capacitor and equivalent source reactance at the substation. The transient analyses indicated that when the substation capacitor is energized, magnified transient voltages can occur at switched-in feeder capacitors. An evaluation of the effect of automated capacitor switching is necessary to properly design the automated capacitor switching schemes and the required arrester protection for any harmonic and/or transient overvoltage contingency.

Propagation characteristics of picosecond electrical transients on coplanar striplines

Abstract: Using a cryogenic electro‐optic sampling technique, we have studied the transient propagation characteristics of superconducting and normal indium lines in the picosecond regime. Transient dispersion effects, including increased rise time and increased pulse width, the introduction of ringing on the waveform, and a novel ‘‘pulse sharpening’’ were observed. A model that takes into consideration the effects of modal dispersion and superconducting complex conductivity was established, and an algorithm was developed that accurately describes all of the experimental findings.