bluuebunny/crossref_metadata_2025_split huggingface dataset:
Third‐order passive load identification under non‐sinusoidal conditions
Authors: Mattavelli P. , Tenti P. 
Published: July 2007

AbstractThis paper presents an extension of the well known load identification method, valid under non‐sinusoidal conditions, which makes use of a 2nd‐order passive circuit and an auxiliary voltage or current generator. The proposed solution is similar, but uses a 3rd‐order passive circuit. This allows to identify the passive circuit components with positive or negative parameters, according to the aim of the identification (load modeling or compensation). Moreover, the proposed approach keeps the orthogonality between current/voltage components and removes the indetermination which occurs, with the 2nd‐order approach, in the case of sinusoidal operation. As an application example, the proposed approach is applied to the design of a hybrid compensation system including active and passive filtering.
A numerical approach to the design of conducting shields for extremely low frequency magnetic field reduction
Authors: Bottauscio O. , Chiarabaglio D. , Chiampi M. , Repetto M. 
Published: July 2007

AbstractA 3D hybrid finite Element (FEM) boundary Element (BEM) formulation for the analysis of thin conducting sheet has been applied to the evaluation of the efficiency of shielding systems for extremely low frequency magnetic fields. Low Voltage (LV) 3‐phase distribution systems constituted either by busbars or cables (straight or twisted disposal) have been investigated and the numerical model, validated by comparison to experiments, has been employed to find out the influence of several geometrical and supply parameters on the shielding efficiency.
Load frequency control for power system with reheat steam turbine and governor deadband non‐linearity by using neural network controller
Authors: Zeynelgil H. L. , Demirören A. , Şengör N. S. 
Published: July 2007

AbstractIn this paper, a neural network (NN) controller is presented for load‐frequency control of power system. The NN controller uses back propagation‐through‐time algorithm. In the power system, the reheat effect of the steam turbine and the effect of governor deadband non‐linearity are considered by describing function approach in the state space model. By comparing the results of simulations, the performance of the NN controller is better than conventional controller. NN controller gives a shorter settling time and eliminates the necessity of parameter estimation time required in conventional adaptive control techniques.
Energy storage by capacitors
Authors: Späth H. , Becker K.‐P. 
Published: July 2007

AbstractThe paper presents analytical calculations for a capacitor as an energy storage device, which is discharged with constant power. Calculated are the delivered energy, the energy losses, the residual energy, the voltages and the currents at the beginning and at the end of the discharging process as well as the feasible duration of this process, all in dependence on the delivered power. The per unit values of these quantities are plotted in diagrams with both linear and logarithmic scale. To clarify the fact, that different types of capacitors are adapted for different applications of energy storage, the results of these calculations are applied to aluminium electrolytic capacitors and to double layer capacitors. In addition, the different characteristics of both types are explained by their values of specific energy and specific power.
Ability of transfer function method to diagnose axial displacement of transformer windings
Authors: Rahimpour E. , Christian J. , Feser K. , Mohseni H. 
Published: July 2007

AbstractTransient currents can cause the mechanical displacement of transformer windings. The transfer function method is presented as a tool to detect this displacement. In order to be able to evaluate the measurements, the correlation between the characteristics of transfer functions and possible damages must be known. Axial displacement of transformer windings has been studied in this research. As test object a transformer with a primary winding of 31 double inverted disk (approx. 1.3 MVA, 10 kV) and a secondary winding with four layer concentric winding was used. A detailed mathematical model was developed for the test object and a comparison was carried out between measured and calculated results. To compare the sensitivity of transfer functions, five different transfer functions with different terminal conditions are simulated. It is shown that the detailed model can present the behaviour of the transformer winding in case of sound and displaced windings.
Successive expansion method of network planning applying symbolic analysis method
Authors: Škokljev I. 
Published: July 2007

AbstractThe conventional power system network successive expansion planning method is discussed in the context of the new paradigm of competitive electric power, energy and service market. In sequel, the paper presents an application of the conceptually new computer program, based on the symbolic analysis of load flows in power system networks. The network parameters and variables are defined as symbols. The symbolic analyzer which models analytically the power system DC load flows enables the sensitivity analysis of the power system to parameter and variable variations (costs, transfers, injections), a valuable tool for the expansion planning analysis. That virtue could not be found within the conventional approach, relying on compensation methods, precalculated distribution factors, and so on. This novel application sheds some light on the traditional power system network expansion planning method, as well as on its possible application within the system network expansion planning in the new environment assuming the competitive electric power market.
Steinmetz system design under unbalanced conditions
Authors: Jordi O. , Sainz L. , Chindris M. 
Published: July 2007

AbstractThis paper studies and develops general analytical expressions to obtain three‐phase current symmetrization under unbalanced voltage conditions. It proposes two procedures for this symmetrization: the application of the traditional expressions assuming symmetry conditions and the use of optimization methods based in the general analytical equations. Specifically, the paper applies and evaluates these methods to analyze the Steinmetz system design. Several graphics evaluating the error introduced by assumption of balanced voltage in the design are plotted and an example is studied to compare both procedures. In the example the necessity to apply the optimization techniques in highly unbalanced conditions is demonstrated.
Degree of insecurity estimation in a power system using functional link neural network
Authors: Singh S. N. , Srivastava K. N. 
Published: July 2007

AbstractSecure operation of power system has always been a challenge to system operators. With increasing interconnection and growing load demand, a power system, sometimes, may go into the insecure operation especially after severe contingencies. It is important to develop a technique to quantify the degree of insecurity in both planning and operational stages. This paper presents such an algorithm.The distance (Euclidean norm) in parameter space between any insecure point and closest point on feasible (secure) hypersurface is used as a measure of insecurity. Artificial Neural Network (ANN) based Functional Link Network (FLN) is proposed because ANN is very popular for complex problems. The various FLN models are evolved to estimate the degree of insecurity. The sample study is performed on an IEEE 30‐bus test system for different loading patterns and single line outage contingencies. The investigations reveal that the proposed FLN accurately estimates the degree of insecurity with least computational time compared to the existing methods.
Mixed p‐z approach for analytical analysis of an induction motor fed from space‐vector PWM voltage source inverter
Authors: Klima J. 
Published: July 2007

AbstractThis paper proposes an analytical method for calculating both the steady‐state and transient performance of an induction motor fed from the three‐phase voltage source inverter. As a modulation technique of the inverter we consider space vector modulation. The proposed method makes use of the Laplace and modified Z‐transformation of the space vectors (mixed p‐z approach) to predict current response of induction motor. From the Laplace transform of the stator voltage vector we can also derive Fourier analysis to predict the voltage harmonic spectrum. Experimental tests have been carried out confirming the validity of the analytical results.
Linear‐programming‐based method for optimum schedule of reactive power sources in integrated AC‐DC power systems
Authors: Abdel‐Salam M. , Seddik H. 
Published: July 2007

AbstractThis paper is aimed at obtaining the optimal flow of reactive power which corresponds to minimum real power losses in integrated AC‐DC power systems including one DC link. The DC power or DC current, drawn by the link at its rectifier side is introduced as a new control variable added to the normal control variables, i.e. transformer tap‐settings, generator terminal voltages and reactive‐power outputs, and switchable reactive power sources. The constraints include the reactive power limits of the generators, limits on the load bus voltages and the operating limits of the control variables. Dual linear programming is applied to minimize an objective function for system losses. Application of the proposed method on different test AC‐DC systems confirmed that less system losses is achieved with the introduction of the DC control variable.
Graphical representation of doubly‐fed induction machine operation: Consideration of stability and saturation limits
Authors: Poloujadoff M. , Kamoun M. B. A. , Toumi A. 
Published: July 2007

AbstractThis paper presents an extension of a previous work [1] which deals with the graphical representation of the steady‐state of doubly‐fed synchronous machine. The principal contribution of this work is a simple approach for the representation of circular diagram of the machine steady‐state stability limits. A particular interest has been given to the machine saturation. In this context, a simple approach is proposed in order to test the machine saturation level.
Cost‐benefit analysis of voltage sag mitigation methods in fiber extrusion plants
Authors: Didden M. , Belmans R. , D'haeseleer W. 
Published: July 2007

AbstractThe fiber extrusion process is very vulnerable to voltage sags. Being the biggest exporter of carpets in the world, Belgium has many textile fiber extrusion plants. This paper describes the importance of the voltage sag problem in such plants and possible mitigation methods. It turns out that the number of process outages due to voltage sags is less than described in other papers for other geographical grid locations. Still, there are economically attractive mitigation methods. Depending on the manufacturer of the production line, these methods get economically interesting if they mitigate between one and three outages a year. Together with a cost‐benefit analysis, this paper‐describes the methods that have already been implemented as well as possible future options.
Formation of self‐excited vibrations in wet rotor motors and their influence on the motor current
Authors: Kenull T. , Canders W. R. , Kosyna G. 
Published: July 2007

AbstractResearch on condition monitoring for sensitive or process relevant drives has gained increasing importance in the latest past. The efforts made to reduce repairing costs and downtime led to the requirement of monitoring electrical drives. When doing so an important aspect is the detection of damages in an early state. Condition monitoring can be done by using various kinds of sensors and by analyzing stationary and non‐stationary signals. In some cases the use of vibration sensors for pump and motor protection and condition monitoring is difficult due to insufficient space and difficult environmental conditions, e.g. high water pressure. Submersible motor pumps for example are commonly working in deep wells down to 1000 meters. That is why motor current analysis remains as the only reliable monitoring method for condition monitoring and damage protection of submersible motor pumps. As one of the results of a highly interdisciplinary project this paper reports how the damage of the journal bearings of a wet rotor motor can be detected by motor current analysis. The investigations are bound on experimental measurements of two different types of centrifugal pumps with wet rotor motors.
Wave propagation characteristics on cross‐bonded underground power transmission cables and sheath fault location
Authors: Wang X. H. , Song Y. H. , Ferguson C. P. 
Published: July 2007

AbstractIn this paper, a new method to locate the sheath fault on crossbonded power transmission cables is presented. This method utilises the transients generated by the fault and captured at both ends of the sections. On crossbonded power cables, there are six modes of waves travelling along the whole cable system and three are associated with the sheath. The waves travelling in mode 2 are used for fault location. The arrival times of the transients on both ends are localised by wavelet analysis. ATP simulations are used to test and validate the proposed fault location approach for typical power transmission cables.
Combined resonance phenomena due to earth wires grounding and conductor sagging effects in overhead transmission lines
Authors: Ãofaria J. A. Brand 
Published: July 2007

AbstractThe periodic discrete bonding of earth wires to ground, on the one hand, and the distributed conductor sagging between towers, on the other, are mechanisms that have been reported before to be individually responsible for abnormal high‐frequency responses of overhead power lines. In this paper we consider both effects superposed and then evaluate, as a function of the frequency, the even and odd mode propagation parameters characterizing a given transmission line section. We show that the two interacting mechanisms being combined do not annihilate each other; on the contrary, wave interference effects accumulate giving rise to broadband noticeable resonance phenomena for frequencies such that the line span gets close to one half wavelength, typically in the 400–600 kHz range.
An analytical approach for the operation of series compensators to relieve power flow congestion
Authors: Lim J.‐U. , Moon S.‐I. 
Published: July 2007

AbstractThis paper describes an analytical approach for the operation of series compensators to relieve power flow congestion. The flexible AC Transmission Systems (FACTS) devices such as thyristor‐controlled series capacitor (TCSC) and static synchronous series compensator (SSSC) can control power flow in the line by varying reactive line impedances. In the case of congestion problem at normal state or at contingency state, it is necessary for these devices to change their operating points to relieve the line flow congestion and eventually to increase the system security level. In order to find the approximate operating points, the changes in line flows for changes in control variables by series compensators are derived analytically in this paper. The derivation of these sensitivity factors is based on the DC model of power flow analysis and under the assumption that the generation dispatch is maintained. Changes in the direction and the amount of compensation can be determined according to sensitivity values derived from DC power flow model. For verification of the proposed method, intensive studies have been performed on a 10‐unit 39‐bus New England System equipped with multiple series compensators.
Power quality issues in the TRTS DC railway power networks
Authors: Wang Y. J. , Chen C. L. 
Published: July 2007

AbstractThis paper presents a study into power quality issues in the Taipei Rapid Transit System (TRTS). The effect of three‐phase voltage unbalance upon the second harmonic of the DC power network is simulated using the EMTP. Also studied are harmonic currents produced by the variable‐voltage variable‐frequency (VVVF) inverters of the motor‐cars at three different control modes, and possible series and parallel harmonic resonances resulting from the rail inductance and the filter capacitance.
Rotating field losses in HTSC hysteresis rotor
Authors: Grüner A. , Gutt H.‐J. 
Published: July 2007

AbstractNew materials such as High‐Temperature‐Super‐Conductors (HTSC) have new properties like “magnetic field penetration” ‐ as well as “flux creep” as also as “trapped field”. They will be researched by test results of several 3‐phase self‐starting HTSC‐hysteresis motors from 50 W to 1.0 kW output. The research of magnetic parameters of the superconducting rotor, for example rotational losses and complex permeability, are very important for design and analysis of the behaviour of HTSC‐motors. In the near future remanent “trapped field” induction higher than 1 T and thus higher energy density of these motors are to be expected.
Substation lightning shielding and risk assessment
Authors: Meliopoulos A. P. Sakis , Cokkinides G. J. 
Published: July 2007

AbstractElectric power installations are subject to lightnining, lightning overvoltages, and the associated risk of damage or disruption. The paper presents a probabilistic method for assessing the risk of damage and disruptions from lightning overvoltages. The proposed method has two components: (a) shielding analysis and evaluation using a probabilistic implementation of the electro‐geometric model and (b) a probabilistic assessment of lightning overvoltages at power equipment and control cables for a specific lightning shielding design. Both computational procedures are based on a 3‐D model of the entire electrical installation. Visualization techniques based on animated 3‐D graphics are used to demonstrate the computational methodology.
An econometric model of U.K. manufacturing employment using survey data on expected output
Authors: Wren‐Lewis Simon 
Published: July 2007

AbstractA model of U.K. manufacturing employment is estimated in which output expectations data are derived from Confederation of British Industry (CBI) survey information. The output expectations terms are highly significant, and equations including them encompass more traditional models that use current and lagged output. In addition, the equations also successfully predict the sharp falls in manufacturing employment that occurred after 1979. One interesting implication of these equations is that the decline in ‘cyclically adjusted’ productivity around 1975, and the subsequent improvement around 1980, can be largely explained in terms of a prolonged period of over‐optimistic output expectations by U.K. firms.
An adjustment procedure for predicting systematic risk
Authors: Bera Anil K. , Kannan Srinivasan 
Published: July 2007

AbstractThis paper looks at the currently available beta adjustment techniques and suggests a multiple root‐linear model to adjust for the regression tendency of betas. Our empirical investigate on indicates that cross‐sectional betas are not normally distributed, but their distribution tends to normal after a square‐root transformation. The evidence from the Box‐Cox regression model and the multivariate normality observed among betas after the transformation, make the functional form of our model correct. Also, we observe that the disturbance term of the multiple root‐linear model is well behaved. These findings make the ordinary least squares estimates unbiased and efficient. Finally, the mean square and extreme errors are found to be lower when our adjustment procedure is usedvis‐à‐visthe existing procedures.
Monetary anticipation and the demand for money in the U.K.: Testing rationality in the Shock‐Absorber hypothesis
Authors: Cuthbertson Keith , Taylor Mark P. 
Published: July 2007

AbstractThe Carr‐Darby shock‐absorber hypothesis that unanticipated changes in the money supply cause changes in real balances but anticipated changes have a unit impact on the price level (and therefore leave real balances unchanged) is tested using two‐step and joint estimation techniques. For the U.K., two‐step methods appear to support the shock‐absorber hypothesis, but the superior joint estimation technique decisively rejects the hypothesis, particularly the implicit rational expectations cross‐equation restrictions.
A forward looking model of the exchange rate
Authors: Hall S. G. 
Published: July 2007

AbstractThis paper outlines a simple framework for testing some of the underlying concepts which form the basis of a number of recent models of exchange rate determination. It estimates a structural exchange rate equation with explicit forward expectations using the Wickens errors‐in‐variables method. The paper finds a strong rejection of the simple open arbitrage model in favour of a more complex model.
A stock‐flow consistent macro‐econometric model of the UK economy—part I
Authors: Davis E. P. 
Published: July 2007

AbstractThis paper surveys briefly the main theoretical developments in the analysis of stock and flow integration in macro‐economics, then proceeds to use this corpus of theory as a critique of the structure of existing macro‐econometric models of the British economy. An outline is then suggested for a model which would take all of these stock‐flow effects into account, given the macro‐economic data currently available. In a following paper (Davis, 1987) we give a detailed account of estimation and simulation of such a stock‐flow consistent model.
Cliometrics, 1971–1986: A survey
Authors: Crafts N. F. R. 
Published: July 2007

AbstractThe paper selectively surveys recent quantitative work in economic history with special emphasis on research into unemployment in interwar Britain, the Habakkuk controversy, the Kuznets curve, the demographic transition and heights in history. It is shown that the field has advanced well beyond the routine applications of elementary microeconomics which characterized its early days. Considerably greater quantitative sophistication and a much wider coverage of historical issues have been notable features of this advance. It is argued that econometric methods need to be supplemented in historical work by other forms of evidence to obtain persuasive answers to historical questions.
Testing for exogeneity in limited dependent variable models using a simplified likelihood ratio statistic
Authors: Smith Richard J. 
Published: July 2007

AbstractA simple likelihood‐ratio statistic for the weak exogeneity of the continuously observed endogenous variables is presented for the limited information simultaneous equations models in which a single endogenous variable is censored. The statistic is a likelihood ratio test statistic for the exclusion of the reduced form residuals of the continuously observed endogenous variables and is asymptotically locally most powerful. The procedure is illustrated by an application to a model of female labour supply.
A stock‐flow consistent macro‐econometric model of the UK economy—part II
Authors: Davis E. P. 
Published: July 2007

AbstractThis paper is the second of a series of two which describe the estimation and simulation of a stock‐flow consistent macro‐economic model of the UK economy. The first part (Davis, 1987) surveyed the theoretical literature on stock‐adjustment dynamics, criticized existing UK forecasting models for omitting many potential stock‐flow interactions and gave an outline of the model which is constructed here. The estimation and simulation results suggest that variables encapsulating such stock‐flow effects are frequently significant in the estimation of key equations, and that their inclusion may make a sizeable difference to the simulation properties of a model.