Showing papers on "Transient (oscillation) published in 1975"

Power Semiconductor Circuits

Abstract: Detailed explanations suitable for self-instruction are given for the design and operation of a large variety of power supplies and converters. Provides a sound basis of theoretical knowledge while stressing practical methods, allowing the reader to apply the ideas in the text to all types of circuits. Discusses transient circuit analysis, Fourier analysis, electric machine theory, and elementary control system theory, and goes on to discuss various types of systems and their physical appearance, circuits including thyristors and the method of rating and classifying them. Individual classes of converter are examined in succeeding chapters. Numerical examples based on practical experience are included.

DYNGEN: A program for calculating steady-state and transient performance of turbojet and turbofan engines

Abstract: The DYNGEN, a digital computer program for analyzing the steady state and transient performance of turbojet and turbofan engines, is described The DYNGEN is based on earlier computer codes (SMOTE, GENENG, and GENENG 2) which are capable of calculating the steady state performance of turbojet and turbofan engines at design and off-design operating conditions The DYNGEN has the combined capabilities of GENENG and GENENG 2 for calculating steady state performance; to these the further capability for calculating transient performance was added The DYNGEN can be used to analyze one- and two-spool turbojet engines or two- and three-spool turbofan engines without modification to the basic program A modified Euler method is used by DYNGEN to solve the differential equations which model the dynamics of the engine This new method frees the programmer from having to minimize the number of equations which require iterative solution As a result, some of the approximations normally used in transient engine simulations can be eliminated This tends to produce better agreement when answers are compared with those from purely steady state simulations The modified Euler method also permits the user to specify large time steps (about 010 sec) to be used in the solution of the differential equations This saves computer execution time when long transients are run Examples of the use of the program are included, and program results are compared with those from an existing hybrid-computer simulation of a two-spool turbofan

Transient and surge protection apparatus

Abstract: Apparatus is disclosed for absorbing and dissipating the electrical energy present in voltage transients and surges occurring in a power distribution system for protecting the system and equipment connected thereto from damage due to such transients and surges. First bilateral nonlinear semiconductors having zener-type voltage breakdown characteristics and capability of essentially instantaneous breakdown for inputs exceeding a selected voltage breakdown are connected in parallel with the circuits to be protected. Such semiconductors have low energy-dissipating capability; therefore, second bilateral nonlinear semiconductors having much greater energy-dissipating capability, similar voltage breakdown characteristics, and slower response time are connected in parallel with the first semiconductors. The breakdown of the second semiconductors occurs in time to prevent the first semiconductors from being damaged from excessive dissipation. A gaseous discharge gap-type arrestor is connected essentially in parallel with the first and second semiconductors and has a selected striking voltage appropriate to the breakdown voltages of the semiconductors.Upon firing of the arrestor, the voltage is dropped to a very low value and the remaining surge energy is dissipated in the arrestor. Firing of the arrestor occurs after the breakdown of the second semiconductor in time to prevent the dissipation capability of the second semiconductor from being exceeded. The cooperative and consecutive breakdown of the three elements serves to limit the peak voltage of a surge to a safe value and dissipate the surge energy without damage to the elements, thereby preventing damage to the power distribution system and associated equipments.

A comparison of time marching schemes for the transient heat conduction equation

Abstract: This paper investigates the phenomenon of ‘noise’ which is common in most time-dependent problems. The emphasis is on the achievable accuracy that is obtained with various time-stepping algorithms and how this can be improved if noise is artificially damped to an acceptable level. A series of experiments are made where the space domain is discretized using the finite element method and the variation with time is approximated by several finite difference methods. The conclusion is reached that the Crank–Nicolson scheme with a simple averaging process is superior to the other methods investigated.

A simplified determination of transient stability regions for Lyapunov methods

Abstract: One of the major difficulties in using the Lyapunov method for on-line transient stability is the determination of the critical value of the V-function which describes the stability boundary. In one method the V critical is taken to be the minimum value of the V-function evaluated at (2n-1-1) unstable equilibrium points (u.e.p.). In this paper it is shown that an accurate determination of these points is not necessary and using the analogy of 1-mechine-infinite bus example, (2n-1-1) u.e.p.'s can be approximately obtained. Two multimachine systems (4 and 9- machine) are used as examples. The error in the stability boundary by using approximate method is shown to be acceptable. The use of Newton-Raphson method to calculate the post-fault stable equilibrium point is suggested. Also the type of mathematical model which is sufficient to represent both uniformly and non-uniformly damped multimachine systems is discussed.

On the theory of the relaxation matrix and its application to microwave transient phenomena

Abstract: The phenomenological relaxation times T1 and T2 measured in microwave transient experiments are expressed in terms of specific molecular relaxation matrix elements. Conditions for this simple T1, T2 description are also given. The system is described in terms of a kinetic equation for the density matrix, which provides a unified treatment of the microwave transient behavior, spectral line shapes, and double resonance phenomena. Spatial degeneracy of the states and m dependence of T1 and T2 are discussed in detail. The recently developed semiclassical theory of molecular collisions is then applied to obtain expressions for the relevant relaxation times.

An improved method for the digital protection of high voltage transmission lines

Abstract: This paper explores the accuracy of the digital methods for protection of high voltage transmission lines under transient fault condition on a long line and describes an improved method for future digital protection schemes. With this method it is possible to calculate R and L of high voltage transmission lines so that any number of harmonics on the current and voltage waveforms can be eliminated and it is shown to be suitable for distance protection during the first cycle of fault occurrence.

Fuel control system having an auxiliary circuit for correcting the signals generated by the pressure sensor during transient operating conditions

Abstract: A fuel control system having an auxiliary circuit for correcting the signals generated by a pressure sensor under transient operating conditions is disclosed. The circuit generates a pressure correction signal directly proportional to the first time derivative of the intake manifold pressure and inversely proportional to rotational speed of the engine which is added to the signal generated by the pressure sensor. The added signals are utilized by the electronic control unit for computing the fuel requirements of the engine to maintain a constant fuel/air ratio during steady state and transient operating conditions.

Lamp ballast circuit

Abstract: A highly efficient tuned oscillator ballast circuit especially suitable for a fluorescent lamp load includes an oscillator circuit coupled to a pulsed DC potential source and having a tuned output circuit coupled to a load circuit, to a drive circuit for the oscillator which is dependent upon current flow in the load circuit and to a rectifier and charge storage and isolation and applying network coupled to the pulsed DC potential source and providing energy thereto whenever the potential decreases below a given reference level. A transient compensating circuit to protect the oscillator components from initial or "start up" transients is also included.

Steady-State and Transient Relations: A Reply on Reswitching

Abstract: Nature of a pitfall, 41.—Substantive vindication— 43.—Deeper issue of nonsteady-state analysis, 45.

Static exciter control to improve transient stability

Abstract: In this paper a stability problem on a future power system is identified. The effect of various types of excitation controls is studied. By modification and trial, changes to the exciter which substantially improve the transient stability are developed. The improvements on this future system are demonstrated.

Sign reversals in the transient method of electrical prospecting (one‐loop version)*

Abstract: The transient electromagnetic fields observed by the MPPO-1 equipment in practice over geological structures cannot always be adequately explained by Maxwell's equation when the imaginary part of the conductivity of the rocks is neglected. If, for any reason, the conductivity of the rocks is a complex function of frequency such that the imaginary part is appreciable the model calculations must include this. This explains why some observed transient electromagnetic decay curves change sign with time.

Statistical analysis for practical circuit design

Abstract: Statistical analysis using the Monte Carlo method is shown to have significant value in the design of practical circuits. Three integrated circuit examples are described; a logic circuit with critical dc properties, a gate with stringent transient requirements, and a hybrid circuit which combines precise linear high-frequency and transient performance. Characterization and modeling problems are described in detail. A particular device family is described by deriving statistics for the parameters of a single nonlinear model, which is then used directly for dc and transient cases and can be linearized for ac applications. Parasitic elements are included for fast high-frequency applications. Complex performance criteria are derived in a post-processor in order that the results be expressed by figures of merit which are practically meaningful, such as noise immunity of a logic gate and operating margin of a digital repeater.

Transient behaviour of a twisted nematic liquid-crystal layer in an electric field

Abstract: HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. TRANSIENT BEHAVIOUR OF A TWISTED NEMATIC LIQUID-CRYSTAL LAYER IN AN ELECTRIC FIELD C. Van Doorn

Charge carrier generation, transport and trapping in amorphous poly (N-vinylcarbazole) films

Abstract: Studies on hole photoinjection in films of poly (N-vinylcarbazole) under space-charge-free conditions by the time-of-flight technique have revealed the presence of deep hole traps. The trap density is estimated to be 5–10 × 10 18 m −3 . The voltage and thickness dependence of the initial current in the space-charge-free photocurrent transient is explained in terms of the field dependence of the carrier generation and transport processes.

Aspects of dynamic stability of structures

Abstract: The dynamic nature of the transient of a structure from stability to instability is emphasized. The need to consider flutter and the paradoxical effect of mass distribution and damping on flutter loads are pointed out. A criterion is formulated for deciding upon a structure to be of the divergence type. For structures of this type, a static approach to stability is permissible. Fortunately, the majority of structures in civil engineering are of the divergence type. However, this does not exempt the civil engineer from being prepared to investigate stability by means of dynamics whenever necessary. The importance of Liapunov's direct method for stability investigations has been stressed.

Transient and steady state space-charge-limited current in CdTe

Abstract: The current response to pulsed and constant external bias is studied on wafers of semi-insulating CdTe crystals which are provided with contacts of aquadag. Space-charge-limited current (sclc) is observed. The magnitude of the large-signal turn-on transient current suggests that electrons are the injected carriers. The time constant of the current decay yields a value of the electron trapping time τ + of ∼ 10 −7 sec. Double pulse experiments provide the value of the detrapping time τ D and its activation energy E t = 0.65 eV. From these quantities, a trap concentration N t = 0.85 × 10 12 cm −3 and a trapping cross-section σ = 3.8 × 10 −13 are deduced. The results are compared with the d.c. characteristic of the devices and with data reported in the literature. Good agreement is obtained, indicating the usefulness of transient and d.c. sclc for characterizing semi-insulating materials and the injecting nature of the contacts.

Ground fault sensor

Abstract: An improved ground fault tester uses a magnetostrictive element or piezo-electric element, such as a multimorph, which changes dimensions upon being magnetized or electrically charged. The dimensional change is used to interrupt the power circuit in which the ground fault occurs. The existence of a ground fault is sensed by a sensor which supplies current to the magnetostrictive or piezo-electric element. In the case of the piezo-electric element, the charge is dissipated through a parallel discharge circuit whereby interruption of the power circuit is accomplished rapidly and is reclosed only after a time delay. Automatic time delay resetting may be easily accomplished by the addition of a single resistor and a rectifier. The dimensional change in the piezo-electric or magnetostrictive element is utilized to reset the power circuit interrupter some selected number of times and/or at reduced power whereby ground faults can be distinguished from transient disturbances on the basis of their duration rather than by analysis of their electrical characteristics.

Transient response of circular foil heat‐flux gauges to radiative fluxes

Abstract: An approximate analytical model of the transient response of a circular foil heat‐flux gauge to a step change in incident radiant heat flux is described. This model demonstrates that the sensitivity and the transient response of the gauge are significantly affected by heat flow from the foil to the center lead wire. Results obtained for the transient response to a step change in incident radiant flux from the model agree closely with experimental results from several gauges with different sensitivities. Convolution of the present model and previous exponential models of the unit step response, with a transient incident flux represented by a terminal ramp, shows that the response predicted by a previous exponential model differs significantly from that predicted by the present model.