Supplementary Signals Research Articles

Optimum primary and supplementary signals optimizing the seismic data resolution

Often in practice, when generating seismic waves on a line, even with a wide-band source, numerous natural and technical obstacles cause a low resolution of reflection seismograms. In this case, the economy of the survey should be taken into consideration and rather than ignoring preexisting data, generating additional signal to complement the preexisting data should be tried. This paper describes how this can be done to optimize the resolution of the combined data. The new approach requires a fundamental change in the field technique such that records with different spectral characteristics (RDSC) are now generated from each source–receiver pair. These coincident records share a common reflectivity series, but differ from each other in wavelets and noise. A comprehensive theory for optimum processing (deconvolution) of any available suite of the RDSC is developed. The solution for the problem is a particular case of multichannel Wiener filtering. It can be thought of as two successive procedures. The first is optimum frequency-dependent weighted stacking of the RDSC. The second is single-channel zero-phase Wiener deconvolution filtering of the previous output. This representation enables suggested multichannel filtering to be easily implemented. The effectiveness of the method as well as its advantage over straight summing of the RDSC, followed by single-channel Wiener deconvolution filtering, are corroborated theoretically and demonstrated with field data. Furthermore, a solution is suggested for the problem to evaluate the spectrum of an optimum supplementary signal. The signal contributes to the available set of the RDSC and yields either maximum resolution with limited energy expenses or a certain desired resolution with minimum, but unrestricted energy expenses at the output of the optimum procedure. The optimum distribution of the spectral energy of a primary signal along the frequency axis is a particular case of the above problem with no preexisting data.

Superconducting magnetic energy storage controller design and stability analysis for a power system with various load characteristics

Abstract A simultaneous active power and reactive power (P–Q) control scheme of superconducting magnetic energy storage (SMES) unit is proposed to enhance the damping of a power system. In order to control the P–Q modulation to the power system, a proportional-integral (PI) controller is used to provide a supplementary damping signal. The parameters of the PI controller are determined by a systematic pole assignment method based on modal control theory. Both static load and dynamic load are included to improve the system model fidelity. Eigenvalue analysis and time-domain nonlinear simulation, using a power system incorporating a composite load, are illustrated to validate the effectiveness of the proposed PI SMES controller for the damping of the studied system over a wide range of operating conditions. The control scheme also shows that the stability margin of the power system is expanded.

Design of decentralized controllers for large power systems considering sparsity

This paper proposes a method for the design of power system controllers aimed at damping out electromechanical oscillations. It can be applied to the design of both power system stabilizers (PSSs) for synchronous generators and supplementary signals associated with other damping sources. Some attractive features of the method are: the parameters of all controllers are jointly determined, there is no restriction on the type of supplementary signals to be used, and controller structures are compatible with those nowadays employed in electric utilities. The control problem solution exploits sparsity, combining a system description which preserves a sparse structure with an adequate mathematical formulation of the optimal design approach. The resulting method is thus made applicable to large power systems. Results for two test systems, including a large 750-bus system, are presented. For both systems, settings for several power system stabilizers are simultaneously determined. The results are validated by using both eigenvalue analysis and nonlinear simulation.

Damping effects of supplementary excitation control signals on stabilizing generator oscillations

Damping effects of supplementary excitation control signals on stabilizing generator oscillations

Observation of two longitudinal and two transverse waves in a frozen porous medium

Experimental results on the transmission of elastic waves in a water-saturated sample of glass powder are presented. Both longitudinal and transverse waves are studied in a temperature range of [−30, 0 °C]. Two longitudinal and two transverse waves are detected. For a temperature of −28 °C and a frequency of 500 kHz, the measured velocities are of the order of 4000 and 2300 m/s for the two longitudinal waves and of 2400 and 1400 m/s for the two transverse waves. The two supplementary signals detected (one longitudinal and one transverse) are very unlikely the result of spurious reflections or electromagnetic coupling since such phenomena were not observed when replacing the porous sample by water. The values of the experimental velocities are in good agreement with the predictions of the extension of Biot’s theory to frozen porous media developed by Leclaire et al. [J. Acoust. Soc. Am. 96, 3753–3768 (1994)].

Fuzzy logic power system stabiliser

Using speed and power output deviations as the controller input variables, a fuzzy logic based controller (FLC) has been developed to perform the function of a power system stabiliser and to provide a supplementary signal to the excitation system of a synchronous machine. The complete range for the variation of each of the two controller inputs is represented by a 7*7 decision table, i.e. 49 rules. The FLC design steps and a procedure for tuning its parameters are described. Simulation studies for a variety of disturbances on the power system with the FLC-based power system stabiliser demonstrate its effectiveness in improving system performance.

Distinct roles for CD4 and CD8 as co-receptors in antigen receptor signalling

The co-ordinated interactions of multiple membrane molecules with the T-cell receptor for antigen (the TCR-CD3) are prerequisite for T-cell activation. In this review we consider the involvement of CD4, CD8, and CD45 on the two lymphocyte lineages. Experiments from many laboratories have provided concordant results leading to the consensus that CD4 and CD8 are functional analogues, providing similar supplementary signals to those generated through the TCR-CD3 complex on MHC class-II- and MHC class-I-restricted T cells, respectively. However, recent results demonstrate striking differences in the coreceptor functions of CD4 and CD8. These differences reflect the distinct properties of the molecules themselves, which in turn are associated with CD45 involvement in the activation of CD4 + and CD8 + T cells.

Turbine generator laboratory model tests to damp torsional oscillations with supplementary signals

The improvement of generator stability by the use of supplementary signals into the voltage regulator and governor loops using discrete-time linear optimal control theory has been studied with particular emphasis on providing better damping for torsional oscillations. A multi-inertia laboratory model equipped with data acquisition and control computers was constructed to model the shaft dynamics of a 660 MW Drax turbine-generator. It is shown that the shaft torsional phenomena can be adequately simulated on a micro-synchronous-generator at least as far as the dominant shaft torsional modes of vibration are concerned. The practical implementation of multi-mode linear quadratic Gaussian (LQG) controllers has been shown to enhance system stability and provide better damping to the lower frequency torsional modes, which are those most susceptible to excitation.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

USE OF SVD FOR POWER SYSTEM STABILIZER SIGNAL SELECTION

Abstract A detailed model of a single machine infinite busbar system is considered. The stator transients are included, the rotor is represented by four blocks, and the transmission line connecting the machine to the infinite busbar is assumed to be long with series compensation. The model exhibits three types of Hopf bifurcations in different regions in the parameter space. Two approaches based on linear algebra are used for the systematic evaluation of the effectiveness of the supplementary signals used for feedback in the excitation loop to stabilize the system. The first approach is based on using the minimum singular value of a complex matrix as a measure of observability of a mode in a signal. The second approach is based on the determination of the angle between the row vector representing the signal and the nullspace of a complex matrix (A–λI). The right singular vectors are used to find a basis for the nullspace.

Accelerating power versus electrical power as input signals to power system stabilizers

Power system stabilizers (PSSs) using electrical and accelerating power as supplementary signals are compared. The effect on terminal voltage and volt-ampere reactive, offset and damping of a simulated single-machine-infinite-bus system is investigated. The results show that the damping offered by a PSS using accelerating power and electrical power feedback is very similar even in the presence of large mechanical power disturbances. The benefits of accelerating power over electrical power as the supplementary signal to the PSS are not evident in the simulation studies considered. Considering the relative ease of measuring the electrical power signal compared to accelerating power signal, it is concluded that a PSS using electrical power as a supplementary signal is sufficient for damping rotor oscillations. Frequency response data are shown to support this point of view.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Slow-coherency based composite mode oscillatory stabilization by means of a hybrid PSS

This paper addresses the problem of the stabilization of composite mode electromechanical oscillations of generators. A Hybrid PSS of the two-level structure including of a local PSS and a global PSS is introduced. Time-scale decomposition is applied to the decoupling of the local and global stabilization problems, where determination of the global (inter area) control law is based on slow-coherency aggregation. Composite mode electromechanical rotor oscillations are observed, in practice, with weakly interconnected power systems. These oscillations are characterized by local and inter-area modes. In certain cases of operating conditions and/or network topology, the damping of these oscillatory modes may be negligible or even negative. The existing approaches to the stabilization of power system are basically in decentralized way, and the objective of the stability measures are largely concentrated on the damping improvement of local modes by means of a power system stabilizer (PSS), using only the local information. However, for those systems with poorly or negatively damped inter-area modes, applications of the locally tuned PSS cannot bring a total stabilization to the system, and the inter-area oscillations remain unaffected or possibly building-up to excessive margins. In this paper we have introduced the idea of the Hybrid PSS which is of a two-level control structure with local and global inputs, as in Fig. 1. The desired supplementary control signal for composite mode oscillations is obtained by a weighted combination of the local and global (inter-area) stabilization signals.

Coherency Based Stabilization of Hybrid Mode Oscillations of Interconnected Power System

This paper addresses the problem of the stabilization of hybrid mode oscillations associated with generator rotor dynamics. A Hybrid PSS with a two-level structure is proposed. Weighted combination of local and global control signals is used as the supplementary signal for the improvement of the both local and inter-area mode components. Time-scale decomposition is used for the decoupling of local and global control law design. Determination of global control law is based on slow-coherency aggregated model. A procedure for the identification of optimum stabilizer site based on an index of mode-input-assignment is introduced.

The design of turbine-generator optimal controllers including the effect of torsional modes of oscillation

Optimal linear control has been suggested for designing supplementary signal controllers for turbine-generators. It is shown that the design of the controller should include consideration of the torsional modes of oscillation of the rotor to obtain the best performance. The exciter voltage ceiling is shown to limit the sum of the synchronizing and damping torques. Practical designs normally require that tradeoffs be made. It is shown how advantage would be gained by using the supplementary signal. Normally fed to the speed governor controlling the main steam valve, for a second governor that would merely act on a fast interceptor valve. >

The Share Price Impact of UK CCA Disclosures

Abstract This study investigates the impact of the experimental standard, SSAP16 (Current Cost Accounting), on share returns on the London stock market. Approximately 200 companies were examined between 1980–84. The experimental design specifies current cost as a supplementary signal to historical cost and employs two main statistical tools: ordinary least squares regression and the abnormal performance metric. In addition, a number of different CCA measurements are specified in order to assess the sensitivity of the results and to ease comparison with other studies. The results suggest that CCA information has a small but significant impact on stock returns in the days up to announcement. However, CCA does not seem to be the main driving force behind long period returns. Returns in the long run are associated more closely with historical cost information than with that generated by SSAPI6.

Multimachine System Transient Stability Improvement using Transient Power System Stabilizers (TPSS)

Power system stabilizers (PSS) have been designed and installed [1,2] to improve the dynamic (smnall signal) response of multimachine systems. This paper presents the theory and test results for improving the transient (large disturbance) behaviour of a multimachine system by supplementing the conventional PSS with a transient power system stabilizer (TPSS). Each generator unit is fitted with a TPSS which, after computation, injects supplementary control signals into both the automatic voltage regulator (AVR) and speed governor control loops.

Power System Stabilizers — Analytical Techniques and Practical Criteria for Design

Abstract In recent years, the use of supplementary signals to improve dynamic stability of power systems has received wide attention. The cause of occurrence of spontaneous oscillations is difficult to Identify precisely except through simulation. The supplementary controls to the excitation system constitute the power system stabilizer (PSS). In this paper, a control theoretic viewpoint is presented, together with practical aspects of parameter setting, tuning and siting of PSS in a large-scale power system. It is critical to know which modes are being controlled. The traditional root locus, frequency response techniques can be supplemented by techniques of modern cuuLiul ihe in y such as dynamic compensator design or eigenvalue assignment technique. This is one area of power systems where control and power engineering disciplines have a lot in common. The paper reviews critically the existing literature in the area and provides Justification for the heuristic approaches of the early design of PSS. Practical guidelines are given for the tuning of PSS. Emphasis is also put on the kind of system studies that precede the actual decision to install PSS on any particular generating unit.

Noninvasive fluorine-19 NMR study of fluoropyrimidine metabolism in cell cultures of human pancreatic and colon adenocarcinoma.

Fluorine-19 NMR spectrometry was used to monitor the metabolism of two antineoplastic fluoropyrimidines, 5-fluorouracil (5FU) and 5'-deoxy-5-fluorouridine (5'dFUrd), in cell cultures of human pancreatic (Capan-1) and colon (HT-29) adenocarcinoma. The preliminary results showed, for the two tumor cell lines treated with 5FU, the presence in nonperfused cells of three signals corresponding to intracellular metabolites: 5FU, F-nucleotides and F-nucleosides. When the cells were perfused only the signals of F-nucleotides and 5FU were present. The F-nucleosides observed during the analysis of the nonperfused cells came from the conversion of F-nucleotides. During the NMR recording of Capan-1 cells at 37 degrees C the first metabolite of the catabolic pathway of 5FU, 5,6-dihydro-5-fluorouracil, occurred. At the beginning of the NMR recording of Capan-1 cells treated with 5'dFUrd, two signals corresponding to F-nucleotides and F-nucleosides (consistent with 5'dFUrd) were observed; during the analysis, a supplementary signal corresponding to 5FU appeared. Even after pretreatment with methotrexate the signal of 5FU incorporated into RNA was not detected. Our experiments, performed in attempts to observe the signal of the ternary complex between thymidylate synthetase (TS), 5-fluoro-2'-deoxyuridine-5'-monophosphate (FdUMP) and 5,10-methylene-tetrahydrofolate (5,10-CH2FH4), allowed detection in some cases of a broad signal, whose chemical shift was similar to that reported in the literature following incubation of TS with FdUMP and 5,10-CH2FH4, but our results were not always reproducible.

Speechreading supplemented with auditorily presented speech parameters.

Results are reported from two experiments in which the benefit of supplementing speechreading with auditorily presented information about the speech signal was investigated. In experiment I, speechreading was supplemented with information about the prosody of the speech signal. For ten normal-hearing subjects with no experience in speechreading, the intelligibility score for sentences increased significantly when speechreading was supplemented with information about the overall amplitude of the speech signal, information about the fundamental frequency, or both. Binary information about voicing appeared not to be a significant supplement. In experiment II, the best-scoring supplements of experiment I were compared with two supplementary signals from our previous studies, i.e., information about the sound-pressure levels in two 1-oct filter bands centered at 500 and 3160 Hz, or information about the frequencies of the first and second formants from voiced speech segments. Sentence-intelligibility scores were measured for 24 normal-hearing subjects with no experience in speechreading, and for 12 normal-hearing experienced speechreaders. For the inexperienced speechreaders, the sound-pressure levels appeared to be the best supplement (87.1% correct syllables). For the experienced speechreaders, the formant-frequency information (88.6% correct), and the fundamental-frequency plus amplitude information (86.0% correct), were equally efficient supplements as the sound-pressure information (86.1% correct). Discrimination of phonemes (both consonants and vowels) was measured for the group of 24 inexperienced speechreaders. Percentage correct responses, confusion among phonemes, and the percentage of transmitted information about different types of manner and place of articulation and about the feature voicing are presented.

Co-Ordination of Static Var Compensators With Long Distance Radial Transmission System for Damping Improvement

The capability of static var compensators to use supplementary signals for damping improvement has been studied. Damping is shown to be a function of the transmission system loading and a function of the static var compensator The study offers insights as to how static var compensators should be coordinated with respect to the transmission system. The technology under study is based on thyristor controlled reactor with switched capacitors. This paper is concerned with the capability of the static var controller to provide damping in radial long distance transmission lines. It is well known that the lack of positive damping sets a limit to the power transferable across a transmission line By use of supplementary feedback signals, the static var compensator can be made to enhance the system damping. This paper seeks to answer the following questions: 1) For a given design of the supplementary signal feedback, are there any operating regions in which negative damping is encountered? 2) What is the effect of an individual static var compensator in providing damping for a transmission system with multiple compensation systems? 3) What is the analytical model of a static var compensator which uses the thyristor controlled reactor technology? 4) How should the elements of the static var compensator be designed in conjunction with the transmission system when the objective is to improve damping? These questions are answered in the context of a radical line with equally spaced SVC stations as modelled in Fig. 1.

Co-Ordination Of Static Var Compenstors With Long Distance Radial Transmission System For Damping Improvement

The capability of static VAR compensators to use supplementary signals for damping improvements has been studied. Damping is shown to be a function of the transmission system loading and a function of the static VAR compensator. The study offers insights as to how static VAR compensators should be co-ordinated with respect to the transmission system. The technology under study is based on thyristor controlled reactor with switched capacitors. Only equal line sections are treated.