Showing papers on "Transient (oscillation) published in 1994"

Transient event detector for use in nonintrusive load monitoring systems

Abstract: The present invention provides a transient event detector for use in a nonintrusive electrical load monitoring system at a monitored site having at least one electrical load. The transient event detector includes a data acquisition portion for acquiring and storing start-up power transient pattern data associated with each electrical load being monitored; a monitor for continuously monitoring total power load pattern data at the site; and a processor for correlating the transient pattern data to the total power load pattern data in order to identify each electrical load.

Hybrid drive system

Abstract: A propulsion system includes an internal combustion engine predominantly operating in a steady-state mode and a driving engine operating in a transient mode, which act on the output shaft of a planetary gear train by first and second drive shafts. To obtain independent speed and torque values at the driven shaft, an additional transiently operating engine is provided which has a fixed r.p.m. ratio with the first drive shaft or the driven shaft of the planetary gear train. The two transient engines are configured as hydraulic engines or electric engines connected to a control device, a unit being provided for hydraulic or electric power flow between the two transient engines, which in turn is provided with an energy storage.

A simple FDTD model for transient excitation of antennas by transmission lines

Abstract: A simple FDTD model is developed for use with antennas that are fed from transmission lines. The model is especially designed for use with transient excitations, where the incident and reflected waveforms within the transmission line are of interest, and the latter is determined directly in the FDTD calculation. The model is verified for both transmission and reception of transient waveforms by comparison with measured results for a cylindrical monopole antenna with a plane reflector. >

Transient stability index from conventional time domain simulation

Abstract: This paper presents a practical and efficient method to incorporate energy analysis into conventional power system time domain transient stability simulation for producing a first swing stability index. The proposed method is a variation of the potential energy boundary source approach, utilizing a numerical transient energy function and a pseudo-fault-on trajectory starting from the dominant potential energy peak point of the postfault system trajectory. The transient stability index not only provides additional insight into the stability studies, but also has the potential of speeding up the stability limit derivation process by reducing the number of program runs. >

EMTP-based model for grounding system analysis

Abstract: EMC and lightning protection analyses of large power systems require the knowledge of the dynamic behavior of extended grounding systems. They cannot be regarded as equipotential planes, but must be treated as coupling paths for transient overvoltages. This contribution presents a model for linear earth conductors based on the transmission line approach and outlines its integration in the transients program EMTP. Validation of the presented model is achieved by comparison with field measurements and with a rigorous electromagnetic model. Overvoltages and electrical fields throughout electrical power systems can thus be computed. >

Plasma‐charging damage: A physical model

Abstract: An entirely physical model is proposed to explain a wide range of seemingly conflicting observations of plasma‐charging damage. Unlike other authors who largely ignored the role of substrate potential, we carefully track both the gate and the substrate potentials to explain the origin of the electric field developed across the thin oxide during plasma exposure. Central to this model is the fact that the surface floating potential tracks the plasma potential. Thus a nonuniform plasma drives the gate potential to a nonuniform distribution. Another important idea of this model is the continued adjustment by both the gate and the substrate of their potentials to satisfy the charge balance requirement of plasma system. The interaction between saturated ion‐current, asymmetric electron‐current, and the Fowler–Nordheim tunneling current produces a complex dynamic for the movements of the gate and the substrate potentials. This complex behavior of the gate and the substrate potential allows many of the reported observations in the literature to be explained logically. We explored three types of charging effect and their damage characteristics. They are dc effect, ac effect, and transient effect. The separation of dc and ac effect is artificial. They exist simultaneously and add to each other to cause more serious damage than by themselves. The model predicts antenna effects from all three types of charging effects. Unique to the ac antenna effect are saturation behavior, the oxide thickness ratio dependence, and the rf bias‐frequency dependence. The effect of ON/OFF transient is explored quantitatively using the concept of effective exposed substrate area. The combination of large antenna ratio and rapid turn‐off of plasma causes severe damage to gate‐oxide. Magnetic field in general will worsen the charging damage. The reason for that is explained. Plasma uniformity is the most important factor governing charging damage, but is not the only factor. Plasma uniformity extending beyond the edge of the wafer is important. Mere showing that the plasma is uniform across the most part of the wafer is misleading.

Nonlinear acoustical response of coated microbubbles in diagnostic ultrasound

Abstract: Microbubbles coated with a thin biodegradable polymer shell are used in SHU 563 A, a new kind of ultrasound contrast medium. These particles are durable linear scatterers for prolonged times at low acoustic pressure amplitudes. They will immediately rupture at higher amplitudes within the range of diagnostic ultrasound causing a transient nonlinear response termed lAcoustically Stimulated Acoustic Emissionr. Characteristics of this effect and some potential applications in novel and extraordinary sensitive conventional and Harmonic Imaging modes are discussed

Fast high-power/high-voltage switch using series-connected IGBTs with active gate-controlled voltage-balancing

Abstract: There exists an acute need for fast high-voltage solid-state switches in a broad area of applications. With the proposed method of active gate-controlled voltage balancing, fast high power/high voltage semiconductor switches with working voltages of several kilovolts using series-connected insulated gate bipolar transistors (IGBT) can be realized. Transient and static voltage balancing is tested on an experimental 3.5 kV/300 A switch with three series-connected 3rd-generation IGBTs. >

Transient electromagnetic interference in substations

Abstract: Electromagnetic interference levels on sensitive electronic equipment are quantified experimentally and theoretically in air and gas insulated substations of different voltages. Measurement techniques for recording interference voltages and currents and electric and magnetic fields are reviewed and actual interference data are summarized. Conducted and radiated interference coupling mechanisms and levels in substation control wiring are described using both measurement results and electromagnetic models validated against measurements. The nominal maximum field and control wire interference levels expected in the switchyard and inside the control house from switching operations, faults, and an average lightning strike are estimated using high frequency transient coupling models. Comparisons with standards are made and recommendations given concerning equipment shielding and surge protection. >

An energy function method for determining voltage collapse during a power system transient

Abstract: The occurrence of a voltage collapse is often described as a small-signal stability problem resulting from a bifurcation of the equilibrium load flow equations as the bus loads and generator power injections incur small changes. However, during a transient period, a voltage collapse may occur as a bifurcation of the transient load flow equations as the generator rotor angles vary. The purpose of this paper is to address voltage collapse in the general context of a transient stability problem for a differential algebraic equation (DAE) power system model. In particular, we define a stability region that guarantees both rotor angular stability and voltage stability. The stability region does not intersect the "impasse surface," the surface on which the bus voltage variables are not defined as functions of the generator rotor angles. Bifurcation theory is used along with some recent results that characterize the stability boundary for DAE models, to show that an important component of the stability boundary is formed by the trajectories that are tangent to the impasse surface at a fold bifurcation point. An energy function transient stability method is developed that uses a sustained fault trajectory to find the first point of intersection with the impasse surface and then involves solving for the (stability) limiting trajectory that is tangent to the impasse surface at this point. This new transient stability method is somewhat similar in theory to the potential energy boundary surface method. Also, this method can be extended to develop stability estimates for power system models in which the stability region is more complex, possibly constrained by line power flow limits, voltage magnitude limits, etc. >

Jet formation and jet velocity fluctuations in a flue organ pipe

Abstract: Flow visualization of the initial transient in a small recorderlike flue organ pipe is presented and the various stages of the jet formation are related to measurements of the acoustic response of the pipe. An initial acoustic signal, due to the unsteady volume flow of the jet, appears before the forming jet reaches the labium. This signal can easily be modeled using a low‐frequency approximation. The initial trajectory of the jet makes a curve towards the exterior of the pipe. Under certain conditions, the jet may even, at first, miss the labium. This effect is related to the steepness of the pressure rise in the foot of the pipe. The initial impact of the jet with the labium appears to be a crucial factor in the triggering of the transient. Moving the labium towards the exterior of the pipe, using a steep pressure rise or putting ears around the mouth increase the chance that the jet will hit the labium. This initial impact is followed by an impulsive vortex shedding at the labium and subsequently a high‐frequency varicoselike oscillation is observed on the jet. This oscillation is also observed without labium. After about three periods of the fundamental mode of the pipe, turbulence appears therefore destroying these coherent structures. Whereas the time dependency of the jet velocity dominates the first stage of the starting transient, the jet velocity fluctuations during steady‐state result in a non‐negligible damping. This loss mechanism is, for the fundamental mode of our experimental organ pipe, of the same order of magnitude as the radiation or visco‐thermal damping.

Control and 3-dimensional simulation model of temperature variations in a rapid thermal processing machine

Abstract: Temperature nonuniformity across a semiconductor wafer during both the transient and steady state of a typical rapid thermal processing (RTP) cycle has been a deterrent in using RTP in many VLSI unit processes. The present invention consists of a three-dimensional mathematical model to study the temperature variation across a wafer in an RTP oven for given lamp power settings, during both the transient and steady state of a typical thermal cycle and control a heating lamp back by a computer program. The simulation package has been written in FORTRAN, and the validity of various models have been checked by performing a series of oxidation experiments.

Transient performance of substation grounding systems subjected to lightning and similar surge currents

Abstract: The frequency and time domain performance of a typical substation grounding system subjected to a lightning strike is described and discussed. The computed scalar potentials, electric fields and magnetic fields are presented graphically as a function of spatial coordinate, as a function of time and as a function of both. First, a double exponential lightning surge current is injected into the center of a square ground grid. This same surge current is then injected at one corner of the grid. The response of the grounding system to the frequency domain electromagnetic spectrum of this signal is computed by a frequency domain electromagnetic field analysis software package. Once all the frequency responses have been computed, the temporal and spatial distributions of the electromagnetic fields inside and near the substation are obtained by an inverse Fourier transformation of all these responses. The results are compared with some well known low frequency results and to published work in this area. These results indicate that the performance of the grounding system is significantly dependent on frequency and on the point of impact of the lightning strike. >

Wave dependent compressor

Abstract: An audio compressor using interactive layered time constants to create an easy to use compressor which self adapts to the program characteristics and provides a desirable and pleasing effect over a wide range of audio program material. The audio compressor includes an adaptable filter connected between an output signal path and a control feedback signal path of a voltage control amplifier. The adaptable filter comprises a first resistor-capacitor circuit connected to the output signal path and producing a charging/discharging voltage which is more dependent on a transient peak value of the audio signals and a second resistor-capacitor circuit working under the charging/discharging voltage of the first resistor/capacitor circuit for producing a charging/discharging voltage which is more dependent on an average value of the audio signals. The second resistor-capacitor circuit is connected in series to the first resistor-capacitor circuit for providing a wave dependent control feedback signal to the control feedback signal path which feedback signal is instantaneously and continuously dependent upon both the average and the transient peak value of the audio signals.

Empirical thermal model for inverter-driven cage induction machines

Abstract: The paper describes an empirical thermal model which provides an estimate of stator- and rotor-conductor temperatures in an inverter-driven cage induction machine under both transient and steady-state conditions (of heating and cooling), and under constant and variable flux control. The model is based on a widely used thermal-torque derating for inverter-driven induction machines, and features a single frequency-dependent thermal resistance and time constant for each winding. It is easily implemented in real time for online thermal protection and compensation for winding-resistance variation. The technique is demonstrated on two 7.5 kW inverter drives to give temperature estimates to within 10 deg C for both transient and steady-state operation. This accuracy is shown to be sufficient to maintain torque output to within 0.01 p.u. in both voltage-forced and current-forced inverter drives. The model can be generalised for a wide range of machine sizes, without the need for specific physical details, by assuming that induction machines are constructed of similar materials, and have similar insulation thermal limits.

Transient analysis of lossless single-phase nonuniform transmission lines

Abstract: A new method has been developed to study the transient behavior of nonuniform transmission lines whose parameters can have any arbitrary space variation. Using the exponential line as a building block, s-domain expressions are obtained for the voltage and current at any point along the nonuniform line. An efficient numerical Laplace-transform inversion technique is then used to compute the time-domain solution. Computer simulations and comparisons with other solution methods are included. >

Rankine panel methods for transient free-surface flows

Abstract: A Rankine panel method is developed for the solution of transient wave-body interactions. In the presence of mean forward speed, the free surface and body boundary conditions are linearized about the double-body flow. The choices of space and time discretization are based on a systematic error and stability analysis. An artificial wave-absorbing beach is designed and employed over the outer portion of the free surface computational domain in order to avoid wave sloshing within the computational basin. The proposed numerical scheme is applied for the solution of flows around realistic ships with or without mean forward speed. The transient wave resistance problem is considered and the rate of convergence of the resultant forces and moments to their steady values is studies. Forced and free motion simulations are also carried out until steady-state is reached and the resulting forces and motions are compared with computations by the well established frequency domain version of the same Rankine panel method.

Detection of transiently chaotic swings in power systems using real-time phasor measurements

Abstract: In this paper, the concepts of transiently chaotic swings and windowed Lyapunov exponents in power system dynamics are described. An efficient computer method to detect a transiently chaotic swing from a set of real-time phasor measurements is presented. The method estimates the largest windowed Lyapunov exponent, /spl lambda//spl circ//sub [N/spl Delta/T]//sup 1/ as a detection index. In simulation results, it is shown that the proposed method has the potential to detect a transiently chaotic swing and the estimated /spl lambda//spl circ//sub [N/spl Delta/T]//sup 1/ can be used as an online stability index to predict multi-swing transient instability. >

Optimal simultaneous stabilization of linear single-input systems via linear state feedback control

Abstract: Simultaneous stabilization of a collection of linear time-invariant systems is considered. The aim is to develop a practical method for the design of a single feedback controller such that all the systems involved are stabilized with good transient responses. Hurwitz's necessary and sufficient conditions are used as the required set of constraints for simultaneous stability. For transient behaviour, we introduce the usual quadratic objective function as performance index for each system. Their sum is the objective function for the collection of systems and the problem is to minimize it by choosing a feedback gain vector subject to boundedness and the Hurwitz stability constraints. A computational technique is proposed for solving this problem. The results obtained give good transient behaviour. For illustration, two numerical examples are solved.

Transient performance of substation structures and associated grounding systems

Abstract: When lightning strikes an electric substation, large currents generated by the stroke flow in the above ground structures and grounding system and dissipate in the soil. The electromagnetic fields generated by such high currents may cause damage to equipment and may be dangerous to personnel working nearby. In this paper, the frequency and time domain performance of a substation subjected to a lightning strike is described and discussed. The computed scalar potentials, electric fields, and magnetic fields are presented graphically as a function of spatial coordinates. As a function of time and as a function of both. Two cases are considered. The first case examines the substation grounding system only, while the second case includes an above-ground structure as well. It is believed that the results of the second case have not been published before. A double exponential lightning surge current is injected at one corner of the substation. The response of the grounding system to the frequency domain electromagnetic spectrum of this signal is computed by a frequency domain electromagnetic field analysis software package. The temporal and spatial distributions of the electromagnetic fields inside and near the substation are obtained by an inverse Fourier transformation of all these responses. The presence of a soil with an arbitrary resistivity and permittivity is accurately taken into account. The analysis sheds some new light on the understanding of the effects which take place at the higher frequencies. >

Fast timing simulation of transient faults in digital circuits

Abstract: Transient fault simulation is an important verification activity for circuits used in critical applications since such faults account for over 80% of all system failures. This paper presents a timing level transient fault simulator that bridges the gap between electrical and gate-level transient fault simulators. A generic MOS circuit primitive and analytical solutions of node differential equations are used to perform transistor level simulation with accurate MOS-FET models. The transient fault is modeled by a piecewise quadratic injected current waveform; this retains the electrical nature of the transient fault and provides SPICE-like accuracy. Detailed comparisons with SPICE3 show the accuracy of this technique and speedups of two orders of magnitude are observed for circuits containing up to 2000 transistors. Latched error distributions of the benchmark circuits are also provided.

SH-wave scattering and propagation analyses at irregular sites by time domain BEM

Abstract: This article presents numerical computations of two-dimensional transient responses of canyons and alluvium deposits with various configurations subject to vertically and obliquely incident SH waves. The time domain boundary element method (BEM) is used for the analysis. Elementwise double integrals over space and time domains are performed analytically for the first time. The substructure formulation is used for the analysis of alluvium deposits. The validity of the present solution is examined for a semi-circular canyon and an alluvium whose frequency domain solutions are available from the past publications. In the following analyses, the transient responses are computed for specific Ricker wavelets under different angles of incidences for various site configurations. The results show that the proposed technique is reliable and therefore can be used to study the seismic response at irregular sites.