bluuebunny/crossref_metadata_2025_split huggingface dataset:
Power and current decompositions into time‐ and frequency‐domain components: analysis and comparison
Authors: Cristaldi L. , Ferrero A. , Superti Furga G. 
Published: July 2010

AbstractMany different theories can be found in the literature coping with the decomposition of powers and currents in electrical systems under non‐sinusoidal conditions. The main difference between them lies in the domain where the decomposition is obtained. This paper analyses both a time‐domain and a frequency‐domain decomposition of powers and currents in three‐phase systems and shows how the comparison between their results gives much more information than the results of a single decomposition about the load identification and the way the non‐active components of power and current can be compensated.
Actual measurements of apparent power and its components at low‐ and medium‐voltage buses
Authors: Emanuel A. E. 
Published: July 2010

AbstractThis paper presents values of apparent, active and non‐active powers measured in five single‐phase and in six three‐phase systems. The power values reported were measured directly or indirectly (computed). Different resolutions for the single‐phase apparent power are observed. For the three‐phase systems, the unbalance power and the effective apparent power are central to the presented measurements. This report is meant to help put in a practical context different definitions of non‐active powers, especially from the perspective of the utilities engineer.
Searching for a generalization of the reactive power ‐ a proposal
Authors: Superti Furga G. 
Published: July 2010

AbstractA new power‐like function, the “Mean Generalized Content”, is proposed which is useful for the study of non‐sinusoidal steady‐state conditions. Since this quantity is conservative and zero on the non‐linear resistors, it appears to be a generalization of the reactive power. The validity of the “Mean Generalized Content” is discussed in detail. Complementary formulations in the time and frequency domains and a geometrical description are given. Some criteria for exchanging reactive power between different frequencies and some properties concerning ideal passive rectifiers are deduced.
Some remarks on power theories
Authors: Sasdelli R. , Menchetti A. 
Published: July 2010

AbstractAt present, passive systems still provide cheaper and more reliable solutions for power‐factor improvement under non‐sinusoidal conditions. They consist of reactance one‐ports connected in parallel to the load, designed to minimize or annul a certain “compensable “ quantity which is defined with compensation in mind. The relevant power theory is then developed to provide the compensation strategy with a theoretical basis. This paper offers an overview of the features shared by power theories relevant to different passive compensation strategies and discusses the compensation of distorting loads supplied by finite power sources.
Measurement problems in power quality improvement
Authors: Menchetti A. , Sasdelli R. 
Published: July 2010

AbstractThe paper considers some problems involved in measurements to identify and model the distortion sources in power‐quality management. Since the usual indices, like power factor or total harmonic distortion, do not fully characterize the power quality, the measurement of a new index is proposed to qualify the energy exchange. The paper also deals with the propagation, through the Fast Fourier Transform (FFT), of random errors such as the quantization error which represents the lower limit of errors in digital measurements. Simulations have been carried out and the results are presented and discussed.
Combined time‐domain and frequency‐domain approach to hybrid compensation in unbalanced non‐sinusoidal systems
Authors: Czarnecki L. S. 
Published: July 2010

AbstractThis paper deals with improving power quality in a situation where this quality is degraded by a low‐quality load that may cause voltage asymmetry, harmonic distortion and variation of the voltage RMS value. The paper discusses a decomposition of the useless component of the supply current into a component compensated with an adaptive passive circuit, of parameters updated to varying load conditions once a cycle, and a component compensated with a continuously controlled current source. Controlling such a hybrid compensator requires that some parameters of the load, defined in the frequency domain, are measured along with instantaneous values of voltages and currents. Compensators with such a structure and control make it possible to circumvent limitations of active power filters with respect to their power rating.
On techniques for localization of sources producing distortion in electric power networks
Authors: Swart P. H. , Case M. J. , Van Wyk J. D. 
Published: July 2010

AbstractThis paper attempts to explore the underlying network theory relevant to the analysis of harmonic power direction. Balanced three‐phase networks reduced to single‐phase equivalents are considered. It is shown that the location of an harmonic source may be determined from the harmonic frequency active power direction.
Model of a highly saturated three‐phase autotransformer with tertiary winding and five‐limb core and analysis of a time‐varying short‐circuit transient
Authors: Arturi C. M. 
Published: July 2010

AbstractThe paper deals with the model of a highly saturated three‐phase autotransformer and the analysis of a power system short circuit with topological configuration changing during the transient (time‐varying configuration fault). The power system includes two power networks interconnected by a five‐limb core autotransformer rated 400 MVA, 400 kV/230 kV, with an internal tertiary delta‐connected winding. The short circuit considered here occurs on the 230 kV side and changes in sequence during the transient from line‐to‐earth short circuit to a line‐to‐line‐to‐earth short circuit to a three‐phase short circuit. This complex fault is intended to reproduce a real short circuit due to the failure of a current transformer in a transformer station which involves the two current transformers of the adjacent phases. It gives peak currents much higher than those obtained with conventional time‐invariant configuration short circuits. The proposed non‐linear circuit model of the autotransformer takes into account the actual configuration of both the core and the windings in highly saturated operations. The simulation of the transient is carried out by the ATP program.
Power factor in short‐circuit tests: determination by current zero crossings
Authors: Bottauscio O. , Crotti G. , Farina G. , Ruffino C. 
Published: July 2010

AbstractThe paper describes a method for the determination of the power factor in short‐circuit tests based on the analysis of the current behaviour. The knowledge of the first two zero‐crossing instants of the current permits the computation of the power factor with a satisfactory level of accuracy. The method can be easily adopted in short‐circuit test laboratories equipped with digital acquisition and processing systems.
Restrikes in vacuum circuit breakers within 9 s after current interruption
Authors: Bernauer Ch. , Kny E. , Rieder W. 
Published: July 2010

AbstractAfter interruption of load or short‐circuit currents in the range (peak values) of 0.8 kA to 10 kA, restrikes were recorded within 9 s after current interruption when the peak value of the recovery voltage exceeded a certain critical fraction of the 10% breakdown voltage of the cold gap, independent of the break current, the absolute value of the breakdown voltage, the contact distance and the contact erosion, but influenced by the shape of the electrodes. The frequency of the restrikes increased progressively with increasing recovery voltage related to the “cold” breakdown voltage. Three different modes of breakdown were observed in different time intervals.
Audible noise in speed‐controlled inverter‐fed medium‐sized induction motors
Authors: Muster J. , Budig P. K. , Belmans R. , Geysen W. , Sattler Ph. K. 
Published: July 2010

AbstractThe audible noise produced by three‐phase, squirrel‐cage induction motors, is caused by the space harmonics of the flux‐density distribution in the air gap of the machine. When the motor is supplied by a frequency inverter in order to control the speed, time harmonics in both current and voltage are present, yielding new components in the audible noise spectrum. In the paper, a number of motor‐inverter combinations are compared for medium‐sized induction motors (90 kW). As a reference case, the motors are supplied with a generator, delivering a variable frequency without harmonics. Theoretical explanations for the increase of the audible noise level and the additional frequency components are given.
Frequency of flashovers of clearances in low‐voltage ac power circuits due to overvoltage waves
Authors: Michel A. 
Published: July 2010

AbstractThe frequency distribution of the crest values of overvoltage waves in low voltage AC power circuits can be approximated by an exponential function. The flashover probability P of a clearance with an impulse withstand voltage Ǔst in an electrical equipment is given by P= exp (‐ α Ǔst). The annual number of flashovers of a single clearance in an unprotected house wiring system supplied by an unprotected overhead network depends upon the impulse withstand voltage, the latitude of the network, the annual number of thunderstorm days, the effective length and the height above ground of the overhead line. However, this does not mean, that every flashover triggers a dangerous power frequency follow current.
On the stator‐flux‐oriented control of a doubly‐fed synchronous machine
Authors: Masmoudi A. , Toumi A. , Kamoun M. B. A. , Poloujadoff M. 
Published: July 2010

AbstractFlux‐oriented control has given a great attention because of its high performances in AC variable speed drives. This paper deals with the implementation of the stator‐flux‐oriented control in a doubly‐fed synchronous machine (DFSM). Compensation of the control system is detailed according to DFSM parameters. It has been found that an adaptive control has to be performed when the load torque is a function of DFSM speed. Simulation works show that the DFSM is no longer an unstable machine when driven by a stator‐flux‐oriented control system. Moreover, the drive acquires a high dynamic which makes the DFSM one of the most attractive features in the slip recovery system domain.
Seismic withstand capability of high‐voltage switchgear equipment
Authors: Roder D. W. 
Published: July 2010

AbstractThe usefulness of the best‐known earthquake scales is described; the response spectrum is of major value to the engineer as evidence of seismic withstand capability. It is derived from seismograms. Based on the response spectrum, the earthquake is characterized by means of testing and/or calculation. The selection of test signals and their effect on the test specimen are discussed; a proven test procedure is demonstrated. An overview of the familiar calculation procedures is also given. The calculation tool is, particularly for complex structures, the finite‐element method. A way of working out the structural data often missing from calculation is described.
New digital distance‐protection system combining signal‐spectrum analysis and differential‐equation solution for power‐distribution systems
Authors: Hendrich Ch. , Wittmann E. 
Published: July 2010

AbstractNormally the incoming signal data for digital distance‐protection relays are distorted sinusoidal oscillations. To get a correct response, considering upper harmonics, it is necessary to fulfill a Fast Fourier Transformation (FFT) with signal analysis. To receive a fast reply time of protection relays, the use of differential‐equation solutions is demanded. A combination of spectrum analysis and differential solution is shown, which joins the advantages of considering upper harmonics and short‐grading time, using digital signal processors.
New method to control cascaded doubly‐fed machines in the state space
Authors: Krebs S. 
Published: July 2010

AbstractThe cascaded doublyfed machine consists of two separate induction machines which are interconnected by their rotor windings. This paper presents a general control structure for such machines, based on the principle of the field‐oriented control. An adjustable speed drive operating in subsynchronous mode is compared with an asynchronous machine‐drive system, and its advantages are shown. State‐space control methods are used to get a stable behaviour over a wide speed range.
Calculation of low‐frequency magnetic shielding of a substation using a two‐dimensional finite‐element method
Authors: Hasselgren L. , Hamnerius Y. 
Published: July 2010

AbstractThe power‐frequency magnetic field originating from an existing substation has been calculated using a two‐dimensional finite‐element model. With this model, the shielding effectiveness for different shielding materials and geometries has been simulated. Calculations were made using 5 mm thick shields on the ceiling and walls. The shield materials used were iron, aluminum and copper. The aluminum and copper shields gave the best average attenuation, 25 dB, while iron gave 10 dB attenuation of the magnetic flux density in the room above the substation. Studies of varying shield geometry in the substation showed that shielding of the switch‐gears, containing the high current busbars, in combination with a shield on the ceiling give a calculated attenuation of the field comparable to that of a shield on the ceiling and walls. The calculations have been compared with measurements for one shielding case.
Simulation of partial‐discharge processes and energy densities
Authors: Kurrat M. 
Published: July 2010

AbstractDegradation of insulation systems by partial discharges (PD) is well known. Although measuring systems are used to classify PD activity, only little information is available about the relationship between PD energy and degradation. Internal PD‐ respectively gas‐discharge processes in spherical voids are calculated with a simulation program. The model is two dimensional, rotational symmetric and regards the gas‐discharge processes by their transport coefficients. The calculated energy densities, which are responsible for material degradation, are discussed in detail.
Atp simulation for arc‐furnace flicker investigation
Authors: Cavallini A. , Montanari G. C. , Pitti L. , Zaninelli D. 
Published: July 2010

AbstractAn arc‐furnace model consisting of non‐linear, time‐varying resistance, realized by the Alternative Transients Program (ATP), is presented in this paper. It is shown that the model is appropriate for flicker investigation in electrical networks supplying arc furnaces, constituting a valid alternative to the linear arc modelling realized by amplitude modulation of voltage generators. Block diagram of the procedure for ATP modelling of the nonlinear, time‐varying arc resistance, dynamic voltage‐current characteristic of the furnace electric arc, voltage and current arc waveforms and characteristic curves of an arc furnace, obtained by ATP simulation, are presented, referring to circuit parameters taken from an actual plant and to a sinusoidal law for arc‐length time variation. Aflickermeter ATP simulation is realized to derive equivalent voltage‐variation values in agreement with the actual flicker measurements.
Calculation of the temperature distribution in an asynchronous machine
Authors: Xypteras J. , Maras K. , Spyrelis D. 
Published: July 2010

AbstractIn this paper the temperature distribution on the section vertical to the axis of an asynchronous machine is calculated. For the calculation the numerical method of “Control Volumes” has been used. The technique used can be easily modified to fit any kind of machine. It can also analyse transients.
Simulation of the heat‐ttansfer phenomena in electrical fuses by means of the digital computer
Authors: Sasu M. 
Published: July 2010

AbstractThe paper presents a method established by the author for solving the general heating equation, in overload regime, of the fusible elements destined to the current limiting electrical fuses, fusible elements made of silver tapes with variable section. The heating equation is a differential equation of the second order, non‐homogeneous, with parabolic‐type partial derivatives. There is presented the algorithm developed in view of numerical solving this differential equation, the mathematical model for the digital computer, as well as some computation results.
On the optimum diameter of wire for coils with fixed inductance and length
Authors: Baum E. , Beichler J. 
Published: July 2010

AbstractIn this paper an analytical relation is derived for the optimum diameter of wire used for winding coils of given inductance and winding breadth. The optimum diameter is the (frequency‐dependent) diameter, for which the ohmic loss of the coil becomes a minimum. The analysis takes into account the inductive coupling of the turns, capacitive coupling, however, is not considered.
Control of PWM AC‐to‐DC converters using state‐space and fuzzy‐methods
Authors: Krebs S. , Oelert K. 
Published: July 2010

AbstractAdjustable speed drive systems using AC‐machines are often fed by voltage‐source inverters. This paper presents a new strategy to control the line‐side converter. State‐space and fuzzy methods are combined to achieve a control system which includes control limits and the aspects of safety. Experiments with a drive system (30 kW) demonstrate the dynamic and steady‐state behaviour of the control.
Slot‐based equations and general equivalent circuit in induction motor‐analysis and control
Authors: Amin B. 
Published: July 2010

AbstractA general equivalent circuit of induction motors of any number of phases, valid for both permanent and transient conditions, is presented. This general equivalent circuit is based on the working equations which relate the slot electrical quantities such as “slot‐currents” and “slot‐voltages”. It is shown that a general set of transformations, called “slot‐based transformation”, lead to the definition of several complex quantities which constitute a generalisation of the well known concept of the space vectors. The functioning equations of induction motors, under any conditions, including the basic equations used infield‐oriented control, are derived from the loops and nodes equations written for this general equivalent circuit.
Investigations of switching operations on composite feeders
Authors: Hamza A.‐S. H. A. 
Published: July 2010

AbstractThis paper describes the switching operations and the accompanied overvoltages produced on composite feeders, when a circuit breaker closes at the peak of the applied voltage. Transformer and line‐cable feeders are considered. The studies have covered the energisation of both systems from sources ranging from the purely resistive to the purely inductive. The means of reducing such overvoltages, such as pre‐insertion resistor, surge arrester, shunt compensation, and combinations of them, are also included and the effect of system parameters and factors, such as circuit‐breaker position, source inductance, type of source, transmission‐line length, effect of arrester position for different values of source inductance and cable‐side and line‐side energisation, on initial voltage applied and accompanied overvoltages are covered. The results which are obtained, are summarized in tables and graphic forms, followed by a general conclusion.
Development of personal‐computer‐based high efficient technique for electric field optimization
Authors: Kato K. , Hikita M. , Hayakawa N. , Kito Y. , Okubo H. 
Published: July 2010

AbstractWe have already developed a personal‐computer‐based electric field calculation system combined with CAD (Computer‐Aided Design); the system is referred to as “CADEF” (CAD with Electric Field Analysis). This system utilizes a charge simulation method, and enables us to realize the automatic calculation of the electric field. This paper describes the results of the newly developed electric field optimizing process which is added to “CADEF”. To achieve a more efficient optimizing routine, we introduce a new algorithm to determine how to arrange the optimization charges into the region to be optimized; both positive and negative charges are assigned at the same time in the calculation step to enhance its convergence and the variety of electrode‐contour modification.
Space‐phasor theory? ‐ what is that for?
Authors: Stepina J. 
Published: July 2010

AbstractThe space‐phasor theory was developed about 30 years ago for solving complicated problems of space harmonics in electric machines. The main wave was naturally included but not as a reason for developing this method. Namely, the elementary equations based solely on the main wave can be put up easily in different ways. Unfortunately, all the authors who criticize the space‐phasor theory in their contributions think only in terms of the main wave and cannot understand the deeper sense of the method. The purpose of the present contribution is not repeating the comprehensive explanation but drawing the attention to the areas of the significant use of the space‐phasor theory published in many papers.
Analytical method for calculating harmonic currents of an AC/DC converter with AC filters
Authors: Sakui M. , Minamijima M. , Amei K. , Fujita H. 
Published: July 2010

AbstractThis paper proposes an analytical method for calculating the harmonic currents produced by a three‐phase bridge‐controlled rectifier with A C filters. In the proposed method, the effect of A C filters on the overlap angle are taken into account and analytical expressions for the harmonic currents on the AC side are derived. All the calculations are conducted only by algebraic calculation with high accuracy. The validity of the proposed method is demonstrated by comparison with the results of simulation method.
Thermal endurance of electrical insulating materials studied by the use of the kalman filter
Authors: Cacciari M. , Montanari G. C. , Barry C. P. 
Published: July 2010

AbstractIn this paper the Kalman‐Filter algorithm is applied to the Arrhenius life model, normally used for thermal endurance characterization of insulating materials. It is shown how this algorithm can be used to derive estimates of Temperature Index and Halving Intervals, i. e. the indices recommended by IEC216, using thermal endurance data relevant to three insulating materials or systems. Depending on scattering of the experimental points from the assumed linear model, especially of the points at the lowest temperatures, estimates performed by Kalman filter and according to IEC216 may considerably differ. Tests of the validity of the model, which are available in the Kalman procedure, show that there is a high probability that the linear model is not valid at the lowest test temperatures.
Modelling of non‐linear magnetic bearings with the help of the finite‐element method
Authors: Xiao W. , Weidemann B. 
Published: July 2010

AbstractThis paper is concerned with the modelling of magnetic bearings without premagnetization. The strongly nonlinear relationship between magnetic force, displacement of the rotor shaft, and regulating magnetomotive force should be modelled accurately. Based on an equivalent magnetic circuit, a model structure with an unknown parameter vector is established. With the help of the finite‐element method this parameter vector is determined by minimizing an error function which describes the difference between the real system and the model. The approach with the help of numerical analysing tools such as the finite‐element method shows a general way of modelling a complex system.