Showing papers on "Transient (oscillation) published in 1982"

Accuarte Modelling of Frequency-Dependent Transmission Lines in Electromagnetic Transient Simulations

Abstract: The parameters of transmission lines with ground return are highly dependent on the frequency. Accurate modelling of this frequency dependence over the entire frequency range of the signals is of essential importance for the correct simulation of electromagnetic transient conditions. Closed mathematical solutions of the frequency-dependent line equations in the time domain are very difficult. Numerical approximation techniques are thus required for practical solutions. The oscillatory nature of the problem, however, makes ordinary numerical techniques very susceptible to instability and to accuracy errors. The, methods presented in this paper are aimed to overcome these numerical difficulties.

Large-signal modelling and analysis of switching regulators

Abstract: A large-signal switching regulator model is derived, and prominent features of the transient response are determined. In particular, analytical expressions are found for the equilibrium points of the system which yield insight into the large-signal response, and computer-generated transient waveforms are obtained. As an example, a boost regulator is investigated, and is found to be stable for small signals but unstable for large transients.

A simulation model of the transient performance of a heat pump

Abstract: This paper describes a heat pump transient analysis computer program (TRPUMP). It is based upon component mathematical models in lumped parametric form. It uses first-order differential equations to describe single- and two-phase heat, mass and momentum transfer, and builds upon seven component sub-routines for the dynamic responses of electric motors, compressors, shafts, electric fans, air/refrigerant heat exchangers, accumulators, and thermostatic expansion valves. The model is capable of simulating dynamic responses of the air-to-air heat pump of the type commonly used in residential applications today. Confidence in the model's accuracy has been established by comparison of simulation results with test data taken at the NBS laboratories.

Response characteristics of coincident loop transient electromagnetic systems

Abstract: The occasional occurrence of persistent sign reversals in coincident loop transient electromagnetic (TEM) measurements stimulates an investigation of possible causes for this effect. By examining the response in the complex frequency plane near the spectrum of freely decaying current modes, it is shown that for any physically reasonable frequency‐independent distribution of electrical conductivity and magnetic permeability the voltage response to a step function driving current is of one sign only. Moreover, under the conditions mentioned above, the logarithm of the induced voltage is a decreasing convex function of time. These characteristics are retained for more general time functions of the driving current. The conservation of sign for frequency‐independent material parameters supports the assumption of IP effects as a possible mechanism for sign reversals. The latter point is illustrated by a simplified example.

Nonlinear-wave effects on fixed and floating bodies

Abstract: A numerical method for calculating the interaction of steep (nonlinear) ocean waves with large fixed or floating structures of arbitrary shape is described. The interaction is treated as a transient problem with known initial conditions corresponding to still water in the vicinity of the structure and a prescribed incident waveform approaching it. The development of the flow, together with the associated fluid forces and structural motions, are obtained by a time-stepping procedure in which the flow at each time step is calculated by an integral-equation method based on Green's theorem. A few results are presented for two reference situations and these serve to illustrate the effects of nonlinearities in the incident waves.

Multivariable variable-structure adaptive model-following control systems

Abstract: The design of multivariable adaptive model-following control systems is described using the theory of variable-structure systems (VSS). Both the model plant transient and the error response transient can be specified in advance. The discontinuous control enforces sliding motion on switching hyperplanes in the error state space, and the dynamic response is insensitive to certain parameter variations and disturbances. The design is straightforward and requires little computational effort.

Transient characteristics of a centrifugal pump during stopping period

Abstract: A theoretical and experimental study has been made on the transient characteristics of a centrifugal pump during its rapid acceleration from standstill to final speed Instantaneous rotatinal speed, flow-rate, and total pressure rise are measured for various start-up schemes Theoretical calculations for the prediction of transient characteristics are developed and compared with the corresponding experimental results As the results of this study, it becomes clear that the impulsive pressure and the lag in circulation formation around impeller vanes play predominant roles for the difference between dynamic and quasi-steady characteristics of turbopump during its starting period

The effect of near-surface superparamagnetic material on electromagnetic measurements

Abstract: The development of an instrument that enables transient electromagnetic (TEM) measurements to be made to voltage levels of 1 μV/A and less has enabled the detection of an anomalous transient response in some areas with lateritic soil cover. This anomalous transient causes apparent resistivity values derived from the measured transient decay to decrease at late delay times in areas where the known geology indicates the values should increase with delay time toward the resistivity value of the basement. The main cause of the anomalous transient has been identified as the response of superparamagnetic material in the lateritic soil cover. Both field and laboratory measurements of the voltage M induced by this transient, show a t-1 time dependence. This is the same behavior reported previously for magnetic viscosity over a longer time scale. Measurements of magnetic susceptibility of material separated magnetically from soil samples taken at areas where a residual response is measured, show that over a wide t...

Dynamic Simulation of Radially Oriented Permanent Magnet-Type Electronically Operated Synchronous Machines with Parameters Obtained from Finite Element Field Solutions

Abstract: A dynamic model for simulation of the transient interaction between radially oriented permanent magnet-type synchronous machines and their corresponding transistorized current source power conditioners is presented. Some key machine parameters used in this dynamic model were obtained from finite element field solutions. This dynamic model was used to obtain the transient interaction between a 15-hp samarium cobalt radially oriented permanent magnet electronically operated synchronous machine and its corresponding power conditioner. This machine was constructed for electric vehicle propulsion. Excellent correlation between various digitally simulated and actual test current and voltage waveforms, in various branches of the machine-conditioner network, has been achieved. These results are given. This modeling approach is applied to machines during the design stage, where the finite element modeling is the only way to obtain the necessary machine parameters for dynamic simulation. It is shown how such a combination of the computer-aided design tools can help in prevention of design mis-judgements that can prove costly to remedy once the hardware is in place. This is done through an actual design example of an additional machine being manufactured for electric propulsion applications.

The initiation of a coronal transient

Abstract: This paper analyzes the coronal transient/eruptive prominence event of 1980 August 5 observed by the Mauna Loa experiment system This event yielded data on the early development of the transient in the low corona between 12 R/sub sun/ and 22 R/sub sun/, information which was not available when earlier attempts were made to explain transient phenomena The transient's initial appearance in the form of a rising density-depleted structure, prior to the eruption of the associated prominence, can be explained as an effect of magnetic buoyancy The data indicate that this transient has a density depletion of 17% to 33% relative to an undisturbed corona which is approximately isothermal with a temperature of 15 x 10/sup 6/ K and a coronal density of 10 x 10/sup 9/ cm/sup -3/ at the base of the corona The height versus base length relationship of the evolving transient resembles, remarkably well, the theoretical predictions obtained from a quasi-static model of a margnetically buoyant loop system By matching this relationship with the theoretical model, we estimate the magnetic field at the base of the transient to be between 2 and 3 gauss It is also shown that the initial, nearly constant speed of the topmore » of the transient, 80 +- 20 km s/sup -1/, is consistent with a theoretical estimate calculated from the quasi-static model These results suggest that some transients are not initiated impulsively, the initial stage of the development being driven by a quasi-static response to a slow change in magnetic field conditions at the base of the corona« less

Transient Ground Potential Rise in Gas Insulated Substations - Experimental Studies

Abstract: The very rapid dielectric breakdown of SF6 (eg, during the operation of disconnect switches in gas-insulated substations) generates steep-fronted travelling waves which couple to the exterior enclosure surface at the air/SF6 bushings and cause transient ground potential rise. These high voltage transients, which can be in the 100 kV range, propagate from the air/SF6 termination, along a transmission line defined by the bus enclosure and the ground plane, toward the switchgear. This paper presents a theoretical and experimental investigation of the phenomenon, from which the basic mechanisms have been identified.

Instrument Fault Detection in a Pressurized Water Reactor Pressurizer

Abstract: A technique of functional redundancy (as opposed to hardware redundancy) for detecting incipient failures in process instruments is applied to a simulation of the loss-of-fluid test pressurizer. The failure detection scheme consists of a set of five Kalman filters and a logical means for combining estimated state variables with instrument signals to produce decision functions, which identify faults, as they occur, in each of five instruments. Test data from the simulated plant show that prompt detection of both bias faults and high noise faults is possible during small transient fluctuations in the pressurizer from its nominal operating state.

Analysis of Transient Electrical Torques and Shaft Torques in Induction Motors as a Result of Power Supply Disturbances

Abstract: A dynamic model for studying induction motor and power supply electromechanical interaction is presented. The electrical system is represented by conventional three-phase models. The motor-driven equipment shaft dynamics are determined by a lumped mass-torsional spring model. The electrical and torsional models are interconnected thru the motor electrical air gap torque and the speed and position of the motor rotor.

Measurement of the thermal conductivity of KNO3-NaNO3 mixtures using a transient hot-wire method with a liquid metal in a capillary probe

Abstract: The thermal conductivity of KNO3-NaNO3 mixtures was measured by a modified transient hot-wire method using liquid metal in a capillary as a heat source. The method was developed for measurements on electrically conducting liquids at high temperatures. Measurements were performed on pure NaNO3 and its three mixtures with KNO3 in the temperature range from 498 to 593 K.

Transient hot‐strip method for measuring thermal conductivity and specific heat of solids and fluids: Second order theory and approximations for short times

Abstract: The theory of the newly described transient hot‐strip method has been developed to include second order terms of the temperature dependence of the electrical resistivity of the hot strip. The theory indicates that second order terms should be included in situations where a high‐current pulse is being used. Approximate values of the coefficients for the second order terms have been determined numerically. For times appreciably less than the characteristic time, a simple approximation of the voltage variation as a function of time has been derived and tested experimentally.

Transient response of n‐channel metal‐oxide‐semiconductor field‐effect transistors during turnon at 10–25 °K

Abstract: The transient, excess source‐drain current which occurs under freeze‐out conditions when a metal‐oxide‐semiconductor field‐effect transistor (MOSFET) is switched into a conducting state is described. The major features of the observed transient response for n‐channel MOSFET’s in the temperature range 10–25 °K are explained in terms of a simple one‐dimensional model. The transient response is largely independent of both temperature (in this range) and the static current level, except for the variation of relaxation rate with temperature. The transient response waveform and the temperature dependence of the relaxation rate for n‐channel MOSFET’s differ greatly from previously reported results on p‐channel MOSFET’s.