Showing papers on "Transient (oscillation) published in 1979"

A Practical Method for the Direct Analysis of Transient Stability

Abstract: This paper describes the development and evaluation of an analytical method for the direct determination of transient stability. The method developed is based on the analysis of transient energy and accounts for the nature of the system disturbance as well as for the effects of transfer conductances onsystenmbehavior. It has been evaluated on a 10 generator 39 bus system and on a 20 generator 118 bus system. The method predicts critical clearing times for first swing transient stability which agree very closely with the results of simulations.

Anomalous Transient Currents in High-Density Polyethylene around 50–70°C

Abstract: Transient currents in high-density polyethylene have been investigated at various temperatures and applied fields. A distinct difference between the transient charging and discharging currents suggests that they are attributable to space charge in the sample. The charging current peak around 70°C was explained on the basis of transient SCLC theory, and the carrier mobility was estimated to be 0.5–2.0×10-10 cm2/Vsec at 70°C. Anomalous discharging currents flowing in the same direction as the charging current were observed at 50 and 70°C, and they were concluded to be caused by the injected home space charge and the partial blocking of a metalpolymer contact.

Parametric modeling of transient electromagnetic systems

Abstract: The modeling of a transient electromagnetic system as a single-input, single-output, linear, causal process is considered. Two canonical forms are discussed; one for impulse function input and the other for more general input. Expressions are derived for errors in the estimation of the model parameters caused by errors in the process data. It is shown that Prony's method is a special case of the impulse function model and that serious errors occur in attempts to apply the method in a noisy environment. It is also shown that least squares estimation of the model parameters produces biased results and that attempts to overcome this problem have led to nonlinear equation sets. Some recommendations are made concerning noise identification and filtering in order to improve results.

Apparatus for and method of detecting high impedance faults on distribution circuits with delta connected loads

Abstract: A technique for detecting high impedance faults on distribution circuits with delta connected loads is disclosed herein. This technique bases its detection on the status of the third harmonic component in each of the three-phase line currents of the distribution circuit and specifically on a predetermined minimum increase in the amplitude of any one of these components over a continuous predetermined period, whereby to discriminate between a true high impedance fault and a transient disturbance.

An Approximate Method for Probabilistic Assessment of Transient Stability

Abstract: Power-system transient-stability evaluation deals with the performance of the system when subjected to aperiodic disturbances such as faults, sudden loss of load or generation, and line switching. Under these conditions stability is lost when one or more generators fall out of synchronism with the rest of the system. Numerous disturbances can lead to system instability and the probabilities of their occurrences are quite different. Most system-design criteria require system survival under specific fault conditions in the normal system state. Systems are therefore designed with a set of severe criteria which may be extremely unlikely. In some cases the initial criteria become too expensive to maintain and they are modified or relaxed. The probabilities of occurrences of the disturbances should be included in the assessment to develop a realistic appraisal of system adequacy. Probabilistic considerations in the stability of simple single and multi-machine systems involves simulating the system dynamics during the disturbance. In large-scale systems, such a simulation can be computationally expensive. Approximate methods of stability evaluation are quite adequate in initial system planning to identify the critical areas. This paper deals with an approximate method using Lyapunov functions to obtain a transient stability risk index which is useful in initial system planning and design studies. The procedure for considering the probabilities associated with the type, location, and clearance of faults is illustrated for a simple multimachine system. The effect of system load on the risk index is also demonstrated.

Electronic properties of chalcogenide glasses and their use in xerography

Abstract: An overview of the xerographic process and the relevant physical phenomena involved in the formation of the latent image is presented. Emphasis is on the electronic properties of a-selenium but some properties of other disordered solids will be mentioned in order to amplify features general to the disordered solid state. Specifically the discussion includes a description of the Onsager mechanism of charge generation, transient dispersive transport, and recent models of defects in chalcogenide glasses.

Observations of the transient X-ray source 4U 0115+63.

Abstract: Results are presented for HEAO A-2 pointed observations and Ariel 5 A11-Sky Monitor observations of the X-ray transient 4U 0115 + 63. The transient source pulses with a period of 3.6136 s + or - 0.0004 s, has a hard spectrum typical of an X-ray binary pulsar, and has a broad iron line emission feature. A discussion of the transient behavior is given, and inferences are made concerning the nature of the X-ray source based on the pointed data.

Design studies of superconducting generators

Abstract: An Electric Power Research Institute sponsored study of superconducting, central-station turbine-generators of 300 and 1200 MVA rating has been completed at General Electric. A unique construction concept is used for the superconducting field winding. The goal of this construction is to ensure that the winding can be energized to the current and flux density predicted by the superconductor short-sample data, without the "training" instabilities frequently encountered in large coils. The remainder of the rotor components includes an aluminum radiation shield and a compound, steel-aluminum electromagnetic shield, designed to withstand short circuit electromagnetic forces. The study was focused on generator model configurations which were proportioned to have a low transient reactance, approximately 0.2 per unit. The critical clearing times calculated for these configurations were comparable to those of conventional units, the low reactance offsetting an inherently lower rotor inertia. These generator configurations are estimated to have about half the size and weight, and about half the losses of conventional units of the same rating. Transient characteristics are described, including the effect of the rotor shielding configuration on rotor damping.

Optimal reduction of multivariable systems

Abstract: A technique is presented for obtaining optimum reduced-order models for multi-input, multi-output, linear, time-invariant systems with step and other forms of input. The reduced model approximates in the sense of minimum mean square error to the transient portion of the system response, while the steady-state portion is matched exactly.

The velocity and Z dependence of the transient magnetic field in iron

Abstract: The velocity dependence of the transient magnetic field in iron has been investigated for134Ba at four initial velocities betweenv i=0.8v 0 andv i=3.6v 0 (v 0=c/137). The present work confirms the linearv-dependence found for light ions (Z≤34). Existing data on transient fields were reanalyzed assuming a general validity of the linearv-dependence. The extractedZ-dependence shows a smooth, almost linearZ-dependence for ions withZ≥12. From the present work, with the calibration of the transient field from systematics, theg-factor of the first excited 2+ state in134Ba is determined to beg=0.41(6).

Experimental Investigation of the Transient Behavior of Motorcycles

Abstract: Analytical and experimental studies of the transient and oscillatory behavior of motorcycles are reported. Three example vehicles were used. The effects of adding load, changing operating conditions, and modifying the vehicle configuration are shown. The phenomenon known as cornering weave is illustrated and interpreted.

Three Dimensional Transient Analysis of Superconducting Generators

Abstract: Techniques for the transient analysis of a superconducting alternator are described. These techniques are based upon a three dimensional analysis. This transient simulation technique is felt to be a significant improvement over previous techniques which are based upon two-dimensional or quasi two-dimensional analyses. Typical simulation results are presented.

Switching Overvoltages in Long Crossbonded Cable Systems Using the Fourier Transform

Abstract: In this paper, the chain matrix theory of multiconductor systems has been applied to the analysis of long cross-bonded cable systems. In order to highlight the power of the method, typical results of transient voltage waveforms at various points of a system comprising 20 major sections are given. Effects of resistive and inductive sources on the transient waveforms are considered.

Method and apparatus for the protection of electrical equipment from high voltage transients

Abstract: This invention provides a high voltage transient protection unit comprising a recoverable spark gap, an L-C filter, a voltage variable resistor and provision for specified ground connection of these elements; and a method of protecting electrical equipment from damage due to a high voltage transient comprising directing any transient above a predetermined minimum voltage level through a recoverable spark gap to a first grounding circuit; delaying said transient for a sufficient time to allow said spark gap to fire and filtering out through a separate grounding circuit that portion of a transient below said predetermined minimum level and above a predetermined maximum voltage level.

Switching Transients in Static Slip-Energy Recovery Drive

Abstract: This paper deals with the study of starting transients of a static slip-energy recovery drive. The non-linear equations of the system have been simulated on a digital computer and solved by the application of Runga-Kutta method. The effects of firing angle, load, system inertia and filter time constant on transient torques and speeds following a switching operation have been investigated.

Probabilistic evaluation of transient stability in a multimachine power system

Abstract: There has been continuous development of better techniques for assessing transient instability in a power system. It has also been recognised that there is a need for additional indices of transient stability which more completely reflect all the factors that influence system stability. The bulk of the work in this area is based on deterministic models. The probabilistic nature of the basic factors which affect transient-stability performance of a power system has been demonstrated in recent papers.1,4 This paper illustrates the inclusion of probabilistic considerations in transient-stability analysis of a practical power system by application to a multimachine configuration. A relatively simple multimachine system is used to demonstrate the technique of considering the probabilities associated with the type, location and clearance of faults. The approach in this paper is not restricted by the simplifying assumptions made in Reference 4. Reliability levels for different fault types and fault locations are evaluated, and the effect of variation of selected system parameters on the overall reliability of the system is investigated.

Fundamentals of Steady-State and Transient Electromagnetic Fields in Shielding Enclosures

Abstract: A simplified theory of electromagnetic shielding by enclosures with conductive and/or magnetic wails is presented. The theory is based on a simplified type of boundary condition at the enclosure walls. Theoretical results are compared with exact solutions for steady-state and transient excitation and the approximation turns out to be extremely good in all cases of practical interest. For enclosures of arbitrary shapes, the problem is formulated as a single integral equation in the unknown current in the shield. Numerical solution of the equation is discussed, as well as a possible equivalent lumped-circuit representation.

Transient-phase studies on the creatine kinase reaction. The analysis of a reaction pathway with three intermediates.

Abstract: 1. The initial formation of creatine phosphate by creatine kinase was studied in the millisecond range and the effect of temperature on the transient and steady-state phases exploited. 2. At 25 degrees C and 35 degrees C there was no transient phase. This is in agreement with the results of Gutfreund [Engelborghs, Y., Marsh, A., and Gutfreund, H. (1975) Biochem. J. 151, 47--50]. 3. At 4 degrees C the time course of creatine phosphate formation was complex and consisted of three transient phases: a lag phase, a burst phase and a steady-state phase. Based on this result a reaction scheme for creatine kinase which includes three intermediates was proposed. Despite the completeness of the time course, the extraction of estimates for the rate constants was difficult and computer simulation and iterative methods had to be resorted to. 4. Attempts were made to provide evidence for the complex enzyme.ADP.metaphosphate.creatine on the creatine kinase reaction pathway [cf. Milner-White, E.J. and Watts, D.C. (1971) Biochem. J. 122, 727--740]. Under the conditions used these attempts were unsuccessful at times down to 2.5 ms, at 4 degrees C or 35 degrees C.

The effect of non-exponential transients on the determination of deep-trap activation energies by deep-level transient spectroscopy

Abstract: The deep-level transient spectroscopy technique is now well established for the characterisation of deep traps in semiconductors. Gross errors may appear in the trap activation energy and capture cross section, however, when non-exponential capacitance transients are present. This paper describes the mechanism which gives rise to this effect and an example of its observation in experimental data. An analysis of the transient shape is found to be necessary if such errors are to be avoided.

Harmonic and transient fields on the surface of a two-layer medium

Abstract: The article deals with the behavior of the quasi-static electromagnetic (EM) fields created by currents in a two-layer medium when the source is a vertical axis circular loop. This analysis is of use for determining the depth of investigation of induction methods in mining prospecting. The relationship of the active and reactive components of the field with the geoelectrical parameters is different, depending on the range of frequencies. Unlike the case of a confined body, the low-frequency part of the spectrum is presented as a series made up of integral and fractional powers of frequency omega and also logarithmic terms of omega . The late stage of a transient process is described with a sum of terms, proportional to the inverse power of time t. These representations are useful for determining the host rock effect against which the signal from an ore body of finite extent must be detected.

Transient Surges and Motor Protection

Abstract: Steep-fronted voltage transients can damage motor windings, leading to eventual breakdown if not immediate failure Circuit switching is the most common cause of such impulses, which may occur in both high-and low-voltage systems Capacitor bank switching and the use of vacuum contactors are two examples Several common misconceptions about the surge problem in motor circuits are explored Current studies of surge phenomena, the ability of motors to withstand surges, and the likely direction of future standards are reviewed The motor user is given some suggestions for detecting the presence of transient impulses and for guarding against their harmful effects