Showing papers on "Transient (oscillation) published in 1989"

Optimal Excitation of Baroclinic Waves

Abstract: Development of perturbations in a baroclinic flow can arise both from exponential instability and from the transient growth of favorably configured disturbances that are not of normal mode form. The transient growth mechanism is able to account for development of neutral and damped waves as well as for an initial growth of perturbations asymptotically dominated by unstable modes at significantly greater than their asymptotic exponential rates. Unstable modes, which are the eigenfunctions of a structure equation, are discrete and typically few in number. In contrast, disturbances favorable for transient growth form a large subset of all perturbations. To assess the potential of transient growth to account for a particular phenomena it is useful to obtain from this subset the initial condition that gives the maximum development in a well-defined sense. These optimal perturbations have a role in the theory of transient development analogous to that of the normal modes in exponential instability theo...

Noise and vibration of electrical machines

Abstract: A. Generation and Elimination of Noise and Vibration. 1. Basic acoustic terms. 2. Generation process of noise and vibration in electrical machines. 3. Electromagnetic noise and causes of vibration. 4. Vibration of rotating electrical machines. 5. Generation of airborne noise in electrical machines. 6. The effect of changes in running condition on the noise of rotating electrical machines. 7. Design considerations to reduce noise and vibration of electromagnetic origin. 8. Mechanical noise and vibrations. 9. Noises of aerodynamic origin. 10. Secondary noise reducing measures. B. Experimental Investigation of Noise and Vibration Phenomena. 11. Measuring noise and vibration phenomena. 12. Measuring the steady-state vibrations of electrical machines. 13. Noise measurements on electrical machines under steady-state operating conditions. 14. Measuring transient noise phenomena. 15. Measuring techniques of transient vibroacoustic signals. 16. Indirect measuring of transient vibroacoustic signals. C. Some Practical Applications of Vibroacoustic Methods in the Testing of Rotating Electrical Machines. 17. Noise and vibration testing in practice. 18. Applying vibration measurement to assessing the technical condition of rotating machines and to scheduling their maintenance. Epilogue with economic considerations. Appendices. References. Subject Index.

Steady-state and transient analysis of self-excited induction generators

Abstract: The authors describe a method for accurately predicting the minimum value of capacitance necessary to initiate self-excitation with a stand-alone induction generator. Final steady-state self-excitation voltages and frequencies are also calculated for loaded and unloaded operations, taking into account the rotor parameter variations with the frequency. It is shown that the calculated and measured results are in strong agreement, and for the loaded generator they agree considerably more so than when constant rotor parameters are used. The theory is also extended to include the transient build up of voltage during the initiation stage of self-excitation, and the perturbations of the terminal voltage and the stator current which result from load changes. >

An improved understanding for the transient operation of the power insulated gate bipolar transistor (IGBT)

Abstract: It is shown that a nonquasi-static analysis must be used to describe the transient current and voltage waveforms of the IGBT (insulated-gate bipolar transistor). The nonquasi-static analysis is necessary because the transports of electrons and holes are coupled for the low-gain, high-level injection conditions, and because the quasi-neutral base width changes faster than the base transit speed for typical load circuit conditions. To verify that both of these nonquasi-static effects must be included, the predictions of the quasi-static and nonquasi-static models are compared with measured current and voltage switching waveforms. The comparisons are performed for different load circuit conditions and for different device base lifetimes. >

Methods and apparatus for monitoring structural members subject to transient loads

Abstract: A method and apparatus for monitoring the structural acoustic signature of a structural member in response to a transient load, corresponding to detected vibration frequencies transmitted by the structural member including the fundamental and harmonic frequencies of the structural member, to determine changes in structural integrity and to determine the nature and type of transient loads. The structural acoustic signature of the structural member in a first condition in response to a first transient load is compared to a structural acoustic signature from a second transient load whereby differences in the signatures correspond to the occurrence of changes in the elastic qualities or condition of the structural member. The signatures are preferably evaluated in the frequency domain. The nature and type of transient load can be deter­mined by evaluating the waveform shape of B struc­tural member in response to the unknown load against a history of waveform shapes corresponding to known loads. A plurality of remote structural members such as highway bridges may be monitored by a central station.

CMOS IC stuck-open-fault electrical effects and design considerations

Abstract: The authors evaluate CMOS IC stuck-open-fault electrical effects, including voltage levels, quiescent power supply current (I/sub DDQ/), transient response, and important testing considerations. The transient responses of the defective node voltage and power supply current to the high-impedance state caused by a stuck-open defect were measured to determine if the I/sub DDQ/ measurement technique could detect stuck-open faults. The measured transient response of stuck-open faults shows that this defect acts as a memory fault for normal system and tester clock periods. The data also show that detectable elevated I/sub DDQ/ can occur rapidly for some circuit designs. Elevated I/sub DDQ/ can also occur over many clock cycles as the high-impedance node associated with the stuck-open fault undergoes a drift in its voltage. The I/sub DDQ/ technique is interpreted as significantly enhancing the detection of stuck-open defects, but not guaranteeing their detection. Modifications to the circuit layout to reduce the probability of stuck-open-fault occurrence are presented. >

Derivation of stability limits using analytical sensitivity of the transient energy margin

Abstract: In recent years considerable progress has been achieved in power system transient stability assessment using the transient energy function (TEF) method. Due to continued developments and enhancements, the TEF method has matured to a stage where reliable and accurate assessment of transient stability of a power system is now possible. An inherent advantage of the TEF method is the availability of a qualitative measure of the degree of stability (or instability) in terms of the transient energy margin (?V). This is an important step toward reducing the number of transient stability runs needed to obtain transient stability loading limits or to make changes to improve the system transient behavior, when subjected to large disturbances. In this paper, a procedure is presented to obtain quantitative answers for these limits by developing an analytical approach to energy margin sensitivity. The approach consists of determining sensitivity coefficients and the development of the dynamic sensitivity equations. A first order expression for the sensitivity of the energy margin is used to determine transient stability limits for the following parameter changes: i. Generation changes ii. Load changes iii. Network changes. The proposed procedure is tested on a 17-generator equivalent of the network of the State of Iowa. The results obtained are then compared with the limits obtained by repetitive application of the TEF method.

Transient Liquid Crystal Measurement of Local Heat Transfer on a Rotating Disk With Jet Impingement

Abstract: An experimental technique has been developed for measurement of local convection heat transfer characteristics on rotating surfaces, utilizing thin liquid crystal surface coatings in a thermal transient test procedure. The encapsulated liquid crystal coatings used are sprayed directly on the test surface and their response is observed and processed during the transient with automated computer vision and data acquisition system

Prevention of transient voltage instabilities due to induction motor loads by static VAr compensators

Abstract: The application of static VAr compensators (SVC) to prevent transient voltage instability due to the presence of large induction loads at the terminals of long transmission lines is discussed. Eigenvalue analysis is used to identify the conditions for voltage instability. The analysis is supported by transient time simulations for the complete power system following large disturbances. It is found that SVC can obviate transient voltage instabilities and maintain the load voltage near its rated value. It is shown that replacing the SVC with mechanically switched capacitors may not provide stabilization owing to the time delays associated with voltage drop detection and breaker operation. >

Dynamic simulation of voltage collapse

Abstract: The problem of voltage collapse is approached by simulation of a power system using a slightly modified transient stability program. A sufficiently complex system with 39 buses and ten generators is used in the simulations. The system is stressed by progressively increasing the system load through a multiplier k. A very small change of k (order of 1%) is used as the collapse-inducing disturbance. Total system voltage collapse was observed after the disturbance. The significance of these findings and directions for future research are considered, and the applicability of real-time control is discussed. >

The TINTE Modular Code System for Computational Simulation of Transient Processes in the Primary Circuit of a Pebble-Bed High-Temperature Gas-Cooled Reactor

Abstract: The TINTE code deals with the nuclear and thermal transient behavior of a high-temperature reactor, taking into consideration the mutual feedback effects in two-dimensional r-z geometry, including ...

Single-phase sinusoidal convertor using MOSFETs

Abstract: The authors present circuit configurations of a single-phase voltage-source AC-DC convertor for applications with a small output power, in which a regenerative capability is not required In this circuit, MOSFETs are employed so that their integral reverse-conducting diodes are available for use The supply current can be sinusoidally controlled with a near unity power factor by means of current reference hysteresis control The steady-state characteristics are investigated by experiments and state-space analysis In addition, transient responses, with a PI controller using a microcomputer to keep the constant output voltage, are shown These results confirm the usefulness of the presented circuit configurations

SPICE simulation of PWM DC-DC convertor systems: voltage feedback, continuous inductor conduction mode

Abstract: A simple and straightforward method is proposed for simulating the transient and small-signal responses of open and closed-loop switch-mode DC-DC convenors. The topologyindependent method hinges on the substitution of the switched inductor, fundamental in the realisation of suchsystems, by an equivalent circuit which represents its average behaviour. This permits simulation by a general-purpose electronic circuit simulator such as SPICE. The proposed approach is demonstrated by presenting the simulation results of a boost convertor.

A transient hot-wire method for measuring the thermal conductivity of gases and liquids

Abstract: In this paper we describe a version of a transient hot-wire apparatus which employs an integrating digital voltmeter to measure the bridge out-of-balance signal. The integrating period of the voltmeter is variable and is routinely set equal to one 60-Hz power-line cycle, 16.67 ms. Use of measurement or integration periods less than an integral multiple of the power-line period results in substantially more electronic noise and a significant degradation in experimental precision. A correction to the working equation which accounts for the integration of the out-of-balance signal is also presented. The precision of the digital voltmeter used with the apparatus is ±0.1 μV, which translates into an ultimate precision of ±0.03 mK in the measured temperature rise. In practice the precision in the temperature rise is typically ±0.3 mK, which represents a moderate improvement over the precision generally obtained with transient techniques employing automatic bridge balancing schemes. Although the current apparatus is designed principally for measurements of the thermal conductivity of liquids, it can been used for gas-phase measurements, with some decrease in accuracy due to the somewhat larger heat capacity correction which must be applied to the temperature rise measurements. The operation of the instrument was verified by measuring the thermal conductivities of toluene and nitrogen. Preliminary data are presented for the new environmentally acceptable fluorocarbons such as R-134a (CF3CH2F), R-123 (CHCl2CF3), and R-141b (CCl2FCH3).

Transient thermal stress analysis of a laminated composite beam

Abstract: This paper concerns a transient thermal stress analysis of a laminated beam made of different materials in multilayers. To simplify the problem, we treat the heat conduction problem as a one-dimensional case in the direction of thickness; then we evaluate the transient temperature solution using the Laplace transform method. For the thermoelastic fields, we obtain the thermal stress distributions by using the elementary beam theory and Airy's thermal stress function method. As an example, we carry out numerical calculations for a laminated beam made of five layers and then examine the numerical results.

Human auditory evoked potentials to frequency-modulated tones.

Abstract: Three experiments evaluated steady state and transient auditory evoked potentials (EPs) to tones that were sinusoidally modulated in frequency and to tones that alternated between two frequencies with a linear ramp. The steady state responses to sinusoidal FM were small and difficult to record at both the first and second harmonics. Ramp FM evoked larger and more consistent second harmonic steady state responses than the sinusoidal FM. Only the ramp FM stimuli elicited transient EPs and these only at low modulation rates. These responses were larger to upward ramps than to downward ramps. The response to two simultaneously presented ramp FM tones differed from the sum of responses to the individual tones, indicating some interaction in the processing of the two stimuli.

Direct transient stability assessment with excitation control

Abstract: The authors extended the applicability of the transient energy function method by incorporating the exciter effects in the energy of a multimachine power system during the first swing transient. The generator was represented by the two-axis model and the exciter was represented by one gain, one time constant, and one limiter. In this study they compute the parameters of the extended transient energy function, which assumes a constant average internal EMF. The critical value of this transient energy is determined. A procedure for its use in transient stability assessment has been developed and successfully applied to fault disturbances in two test networks. >

Design of feedback control laws for switching regulators based on the bilinear large signal model

Abstract: A method for the design of a linear feedback control law for switching regulators based on the bilinear large-signal model is presented. The resulting system guarantees a satisfactory stability region in the state space, and meets the requirements of large damping on transient responses with small feedback control energy. Large-signal transient responses are simulated and compared with the results obtained by R.W. Erickson et al. (1985). The proposed method is well suited for converter topologies with more than two state variables. >

Interlaboratory comparison of radiation-induced attenuation in optical fibers. Part 3: Transient exposures

Abstract: A comparison of the losses induced in step index multimode, graded index multimode and single mode fibers by pulsed radiation exposure has been made among 12 laboratories over a period of 5 years. The recoveries of the incremental attenuations from 10{sup -9} to 10{sup 1} s are reported. Although a standard set of measurement parameters was attempted, differences between the laboratories are evident; possible origins for these are discussed. 18 refs., 18 figs., 7 tabs.

Transient stability prediction and control in real-time by QUEP

Abstract: A method for the real-time analysis and control of power system transient stability has been developed incorporating detailed machine models. The method uses a quasi-unstable equilibrium point (QUEP) energy function approach to evaluate the stability margin of a power system. The mode of disturbance that best predicts stability is determined very rapidly by a novel generating-unit-clustering procedure. Transient stability sensitivity coefficients are calculated for use in a constrained economic dispatch algorithm. Corrective action constraints are developed as simple limits on the sums of generator outputs. A theorem stating the necessary and sufficient conditions for the existence of a power-system energy function is presented. >

Rapid and Numerically Stable Simulation of One-Dimensional Transient Water Flow in Unsaturated, Layered Soils

Abstract: We present a rapid numerical solution for vertical, transient flow of water in unsaturated soil. The model is labeled the moving mean slope model (MMS model), because it uses the slope of the natural log of the hydraulic conductivity (K) versus soil-water potential (ψ) curve as a dynamic parameter. The MMS model is developed from a model for flow in homogeneous, relatively wet soils presented by Wind and von Doorne (1975). The model can simulate transient flow in homogeneous and heterogeneous soils correctly for any rang e of soil-water content. This has been validated against semianalytical solutions and solutions obtained with traditional finite-difference and finite-element models. A Courant number analysis method is presented to make direct comparisons of criteria for avoiding numerical errors for the MMS model compared with traditional finite-difference models. For coarse-textured soils, the MMS model uses about the same computer time as the traditional finite-difference and finite-element models. For soils ranging from fine-textured to medium-textured, the MMS model is one to several orders of magnitude faster than the traditional numerical models.

Fault diagnosis of gas turbine engines from transient data

Abstract: The desirability of being able to extract relevant fault diagnostic information from transient gas turbine data records is discussed. A method is outlined from estimating the effects of unmeasured fault parameters from input/output measurements. The resultant sensitivity of the technique depends on the sampling rate and the measurement noise.

Active control of transient rotordynamic vibration by optimal control methods

Abstract: Although considerable effort has been put into the study of steady state vibration control, there are few methods applicable to transient vibration control of rotorbearing systems. In this paper optimal control theory has been adopted to minimize rotor vibration due to sudden imbalance, e.g., blade loss. The system gain matrix is obtained by choosing the weighting matrices and solving the Riccati equation. Control forces are applied to the system via a feedback loop. A seven mass rotor system is simulated for illustration. A relationship between the number of sensors and the number of modes used in the optimal control model is investigated. Comparisons of responses are made for various configurations of modes, sensors, and actuators. Furthermore, spillover effect is examined by comparing results from collocated and noncollocated sensor configurations. Results show that shaft vibration is significantly attenuated in the closed loop system.

Prediction of electromagnetic field and current transients in power transmission and distribution systems

Abstract: A time-domain model is described for predicting transient bus currents, electromagnetic fields, and cable-coupling effects caused by switching actions in high-voltage substations. Having been validated against measured transient data, the model provides a basis for predicting EMI effects resulting from abnormal switching actions, such as phase-to-ground faults, which are difficult to stage for measurement. From such worst-case estimates, the adequacy of the latest standards for microprocessor-controlled substation protection can be assessed. >