Showing papers on "Transient (oscillation) published in 1990"

Hybrid transient stability analysis (power systems)

Abstract: The hybrid method of power system transient stability analysis, which combines the desirable features of both the time-domain simulation technique and the direct method of transient stability analysis, is presented. The hybrid method first computes the actual system trajectory using time-domain simulation, then evaluates the transient energy function in order to derive a stability index for fast derivation of transient stability limits. Proper criteria are proposed to stop the time-domain simulation of the system trajectory to reduce CPU time, once the status of the system has been identified. The method was successfully applied to three test systems varying in size from four generators to 50 generators. The method is shown to be a potential tool for online calculation of transient stability limits. >

Analysis of HVDC converters connected to weak AC systems

Abstract: A method of analysis is presented and applied to a model system which is well established and extensively used in studies of HVDC converters connected to weak AC systems. The method is based on fundamental frequency quantities. A variety of phenomena and interactions of the AC/DC system can be analyzed, and basic understanding of the mechanisms can be gained. Some important properties of the system, such as voltage/power stability in different control modes and stability of tap changer action, are analyzed. Furthermore, they dynamics of a system consisting of a static VAr compensator (SVC) and DC converters are analyzed, and the requirements for stable operation are derived within the framework of the method of analysis presented. These results are verified by time simulation done by a transient stability program. >

Investigation of Transient Heat Transfer Coefficients in Quenching Experiments

Abstract: Methodological and experimental aspects of the estimation of transient heat transfer coefficients in quenching experiments, using inverse heat transfer methods, were addressed and investigated. Beck's method was used for the estimation of the transient heat transfer coefficient history from interior transient temperature measurements during quenching. Experiments involved plunging a high-purity copper sphere into cooling baths without boiling. The sphere was instrumented with several interior thermocouples for measuring the transient temperature response during quenching. Water and ethylene glycol were investigated. The early transient values of the heat transfer coefficient history were found to be about 100-120% higher than the values predicted using well-known empirical correlations for free convection. The later time values were in good agreement with those predicted with empirical correlations. The transient inverse technique has the capability of estimating early transients and subsequent quasi-steady-state values of heat transfer coefficient in a single transient experiment.

Method and apparatus for processing quasi-transient telemetry signals in noisy environments

Abstract: A software-controlled, external programmer for transcutaneously programming and receiving data from an implanted medical device providing enhanced discrimination and detection of pulse-interval-coded signals of interest telemetered out of the implanted medical device from undesirable transient and steady-state noise. The programmer incorporates a detector including an active mixer and a precision tuned active phase shifting network providing low level signal rectification, precise narrow bandpass filtering, and 30 decibels of amplification. At the detector, the received signal is mixed with a phase shifted version of itself to produce a detected DC component which is a function of frequency. The DC response emulates a system with a narrow 25 kHz bandpass filter operating at 175 kHz, but does not share its undesirable transient response. For signals in the reject band, the output produces a signal of the opposite polarity of the signals within the pass bands. Transient0 noise excites the receiver antenna and produces a ringing response accompanied by components above 400 kHz. The noise response of the antenna stimulates the detector to produce the intended inverted output. As the transient noise amplitude increases, the inverted response increases in amplitude driving the output level further away from the trigger level of a post-detection comparator. Similarly, any steady state noise signal in the reject band will also result in a steady state inverted response that does not trigger the comparator.

Dynamics of heating and cooling loads: models, simulation, and actual utility data

Abstract: Study of the recovery transient during cold load pick-up of heating and cooling loads is of concern in designing distribution systems and direct load control strategies. Examination of actual utility data reveals that this transient consists of two epochs. A description is given of five mathematical models which have been proposed in the literature for studying this transient, and a brief summary is given of results of computer experiments which show that the five models are mutually consistent, allowing the possibility of mixing or trading models where appropriate. Recommendations for monitoring new variable in load control programs are made. >

Estimation of fast transient overvoltage in gas-insulated substation

Abstract: The authors measured FTO (fast transient overvoltages) at various points of a commercial 550 kV gas-insulated substation (GIS) by operating energized disconnectors. Based on the results of these measurements, the possible levels of FTO at various points of the GIS and the probability of occurrence of large levels are discussed. Laboratory tests were also performed by using a recently developed 1 GHz surge sensor to check on the insignificance of high-frequency components due to short-surge impedance discontinuities such as spacers, disconnectors, and short bus branches. Waveforms calculated by rough simulation that ignored the short surge impedance discontinuities are compared with measured waveforms at the commercial substation, proving that simulated FTO levels agreed well with measured values. >

Transient bounds for adaptive control systems

Abstract: Adaptive control systems are essentially nonlinear, and mechanisms to analyze their stability and transient response typically derive from more general nonlinear theories such as small gain arguments or passivity. The authors consider how these theories may be applied to adaptive control to quantify transient response. This involves the explicit description of the constants appearing in the passivity theorem and for the small gain theorem which characterize both system gains and initial condition effects. The result is a fundamental connection between transient response bounds and uniform plant controllability, which connects initial state conditions with the input/output analysis. Applying these general theorems to adaptive control, one is able to interpret the uniform controllability condition as a persistency of excitation requirement and thereby to provide local bounds on transient response. >

Transient Analysis of Water Distribution Systems

Abstract: The pressures generated by transient (water hammer) conditions in pipe systems are frequently three or more times the value of normal operating pressures. Thus, transient pressures must be known if the size and strength of the required pipe is to be rationally selected, if surge-suppression equipment is to be logically sized, and if system operating rules are to be intelligently specified. With modern computer techniques it is possible to analyze distribution systems under a wide range of flow conditions and with relatively few restrictions. Examples are presented of the dangers of oversimplifying either the physical system or the operating conditions

Coupling of Transient Fields, Circuits, and Motion Using Finite Element Analysis

Abstract: The transient analysis of a coupled electro-mechanical system is undertaken. The system consists partly of spatial regions, which may support magnetic fields, that are modelled by finite elements. The regions may be attached to external electrical sources and circuits, and may also be capable of rigid body motion with respect to one another. A method for coupling the electric circuit transient equations, transient magnetic field finite element equations, and the transient mechanical motion equations is described. Only the external source variation is assumed to be known; all other field, circuit, and mechanical motion quantities are treated as unknowns and calculated. Equations for transient analysis of a general, 2-dimensional, planar, non-linear, voltage-excited system are derived in detail. The Galerkin formulation, time-discretization, and linearization of these equations are presented. The resulting global system of coupled electro-mechanical equations is assembled and investigated. Included are exam...

Simulation of brushless DC drives

Abstract: A simulation technique for brushless DC drive systems is presented. The operation of the inverter controller is incorporated into the equivalent circuit of the simulation model by means of state array matrices that describe the conduction patterns of each of the inverter devices. Inverter conduction voltages are included in the equivalent circuit representation because they can significantly affect overall system performance for low-voltage applications. The simulation technique is presented for steady-state, transient and fault conditions of operation of the drive system. Predictions are compared with experimental results for a low voltage prototype system.

Transient currents and torques in wound-rotor induction-motors using the finite-element method

Abstract: The authors describe a time-stepping finite-element technique for modelling transient torques and currents in a slip-ring induction motor. The method is based on a coupled fields and circuit equation approach that allows the winding inductances to be modified to account for certain three-dimensional effects. The numerical solution incorporates a moving rotor so that slotting and saturation effects can be modelled accurately. The method is verified by direct comparison with experimental results obtained from a motor subjected to a supply reconnection at speed. It is shown that the general method can be extended in a straightforward manner to accommodate cage induction motors.

Electromagnetic interference suppression device

Abstract: A multi-stage electromagnetic interference suppression circuit is disclosed which utilizes a diverter network, an impedance network and a clamping network. The diverter network includes a series combination of a varistor and a three terminal gas arrester to suppress incoming transient energy in both normal and common propagation modes. The clamping network serves to suppress any transient energy overshoot which is not suppressed by the diverter stage. Radio frequency interference is filtered by X and Y capacitors forming LC filters with an inductance in the impedance network.

Transient behaviour and self-excitation of wind-driven induction generator after its disconnection from the power grid

Abstract: The transient behavior of a wind-driven induction generator after its disconnection from the power grid is investigated. Measurements on an experimental arrangement, followed by theoretical analysis, show that self-excitation always occurs when there is torque and the generator is compensated. Over a wide range of compensation power, the self-excitation voltage does not change significantly. Suggestions for protection against self-excitation are made. >

Analog-digital simulation of transient-induced logic errors and upset susceptibility of an advanced control system

Abstract: A simulation study is described which predicts the susceptibility of an advanced control system to electrical transients resulting in logic errors, latched errors, error propagation, and digital upset. The system is based on a custom-designed microprocessor and it incorporates fault-tolerant techniques. The system under test and the method to perform the transient injection experiment are described. Results for 2100 transient injections are analyzed and classified according to charge level, type of error, and location of injection.

A new approach to determine transient generator winding and damper currents in case of internal and external faults and abnormal operation. III. Results

Abstract: For pt.II see IEEE Winter Meeting, New Orleans, LA, 1986. A novel method for analyzing the steady-state and transient currents in the stator, rotor, and damper windings of a large generator is discussed, and the application of the method to five classes of problems of practical importance is described. These are (1) internal phase-to-phase fault in a two-circuit machine; (2) 180 degrees out-of-phase synchronization; (3) three-phase short circuit at generator terminals; (4) clearing of a three-phase system fault; and (5) unbalanced steady-state negative phase sequence load of 6%. The authors show the individual damper bar currents and energies or electric power loadings for these cases and, for one example, the time variations of stator and damper winding currents. The investigation was conducted on a standard two-pole generator that was designed for 60 Hz operation and has a rating of 700 MW. >

A new efficient method for the transient simulation of three-dimensional interconnect structures

Abstract: An efficient method for the transient simulation of 3D interconnect structures has been developed. In this method, the time response is calculated in terms of a few poles of approximation in the frequency domain rather than via an ordinary time-domain integration method. An interconnect structure is represented in terms of equivalent 3D RC mesh networks and the transfer function of this linear circuit is then approximated by using a partial fraction series of a few poles. In order to facilitate the calculation of the transfer function, state equations are derived based on a nodal circuit analysis approach. The ICCG matrix solver has been successfully applied to the resultant matrices from the equations. It is shown that this method can produce transient responses one order of magnitude faster than conventional methods. >

Transient thermal study of semiconductor devices

Abstract: An analytical three-dimensional transient temperature solution of a two-layer semi-infinite plate structure with embedded heat sources is discussed. The thickness of the second layer is assumed to extend to infinity. By incorporating the method of images this solution can be used to approximate the structure with finite second-layer thickness. Exact temperature can also be obtained for the rectangular lateral boundaries by the use of the method of images. The correct derivation of the solution is verified by comparing it with the result of the steady-state temperature solution. A computer program has been written based upon the solution and the method of images. A variety of device structures have been studied. Results on the thermal risetime and the effect of the second-layer medium have been obtained. The software is particularly useful for devices operating under pulsed or switching conditions. >

Prepackaged electrical transient surge protection

Abstract: Electrical transient surge protection of electrical equipment downstream from a power source plus safeguarding of apparatus for providing such surge protection against failure at high currents or high temperature. Distributed-resistance fuse links facilitate operation of non-linear over-voltage means, such as varistors, in clipping transient voltage surges and shunting resulting currents to ground so as to protect watt-hour meters and downstream loads from electrical surges, and to safeguard such varistors from failure. Such apparatus may be located in such diverse places as a power line weatherhead, a watt-hour meter base, an adapter between a meter base and its normal mounting socket, or a utility panel having such a socket, or in a circuit-breaker panel downstream of the meter and upstream of metered loads.

Output driver with static and transient parts

Abstract: An output driver for high performance integrated circuits divided into two parts: static and transient. The static part is used to maintain the DC level. The transient part is active only during logic 0 to 1 and 1 to 0 transitions and is used only to assist the static part during such transitions.

Progress in Ultrasonic Measurements Research in 1990: Transient Sources for Acoustic Emission Work

Abstract: : Many techniques have been used by acoustic emission workers to produce rapid transient disturbances in elastic media. Techniques employing transient sources are necessary for characterizing many acoustic emission system components such as receiving transducers, transfer media, and other sources as well. Wave forms from seven types of sources were studied by performing experiments in which the source and a high fidelity receiver were mounted on opposite sides of an aluminum plate. Soundspeeds in the plate had been previously measured to provide information necessary for the calculation of the plate Green's function. In each experiment, a source was triggered and the ensuing output from the receiver was captured by a transient recorder. The force waveform of the source was calculated by convolving the inverse of the plate Green's function with the captured waveform.

Transient Current Dependent on Nematic Director Orientation

Abstract: Transient currents induced by the polarity reversal of an applied DC voltage in nematic liquid crystals have been studied experimentally and theoretically. The experimental results of transient currents in the cells with various treated substrate surfaces have been presented. In the theoretical studies, the presence of adsorbed charge layers on the substrate surfaces and a spatial distribution of carrier mobility dependent on a director orientation have been assumed. By one dimensional mobility distribution of drift sheet carrier across the cell, the carrier transport process and the generation mechanism of the transient current with or without peaks can be well understood. The experimental results on transient currents have been successfully explained from the interpretation of the different adsorbed charge ratio which is the ratio of adsorbed charges to the total amount of the charges in the cell.

Inelastic transient dynamic analysis of three‐dimensional problems by BEM

Abstract: A general direct boundary element formulation and its numerical implementation for solving transient dynamic problems of three-dimensional isotropic homogeneous or piecewise homogeneous solids involving material nonlinearities are presented. The algorithm produces accurate results for static nonlinear problems by using large time steps. When a large value of yield stress is selected, the incremental inelastic transient algorithm produces results identical to those obtained by elastodynamic analysis.

Statistical Energy Analysis for the Time-Integrated Transient Response of Vibrating Systems

Abstract: Energy relations, analogous to steady-state SEA power flow relations, are derived for the time-integrated transient response of each oscillator. These energy flow relations can be combined using statistical concepts, to obtain a set of energy balance equations for N coupled multimodal subsystems. It is shown that the time-integrated response of each subsystem can be described in terms of transient input energies and conventional SEA parameters, i.e., modal densities, loss factors and coupling loss factors. By solving the energy balance equations, the time-integrated response of each subsystem can be obtained