bluuebunny/crossref_metadata_2025 huggingface dataset:
Some considerations on active compensation devices
Authors: Lauria D. , Tironi E.
Published: July 2010

The knowledge of the methodologies and devices bothtavoiding the disturbing injections in electrical networks and limiting the effects of disturbances existing before is a well‐known problem. In the present paper the results expected by using some active apparatuses for disturbances compensation are examined. The limits of different solutions are detected and some design elements are provided as well.
An approach to the direct analysis of transient stability
Authors: Djukanovic M. B. , Sobajic D. J. , Pao Y.‐H.
Published: July 2010

The Transient Energy Function (TEF) method has been intensely investigated over the last decade as a reliable and accurate tool for transient stability assessment of multimachine power systems. In this paper we propose the Potential Energy Boundary Surface (PEBS) based method for direct analysis of transient stability. The critical value of transient energy and the Critical Clearing Time (TCCT) are evaluated without the need for successive calculation and memorization of the system kinetic and potential energy values along the sustained fault trajectory. The method is used for determination of output features in the training phase of the neural‐net based transient security assessment. The proposed approach is tested on the well‐known ten‐generator New England test system demonstrating the validity and accuracy of obtained results.
Basic areas of research preceding design and commissioning of 1200 kV AC power transmission lines: Some key problems and solutions
Authors: Tikhodeev N. N.
Published: July 2010

In the paper is reported the experience of studies that preceded the planning, construction and operation of 1200 kV lines in Russia and Kazakhstan in the former USSR in areas peculiar to UHV power transmission, including the switching surge dielectric strength of long air gaps, selection of line insulation, profound limitation of resonance and switching overvoltages, environmental effects, corona losses of bundles with eight and more subconductors, radio interference. Both implemented and contemplated alternatives of UHV lines are discussed.
A general solution to the harmonics summation problem
Authors: Lehtonen M.
Published: July 2010

A general solution is presented for the probability density function of the amplitude of the sum of a number of harmonics from different sources. In the solution, the phase angles and amplitudes of component vectors may vary randomly in any given range. If these variation ranges are the same for all the component vectors, then ‐ in addition to them ‐ only arithmetic and geometric sums of the maximum amplitudes need to be known in order to calculate the parameters of the probability density function.
Computer‐aided calculation of the steady‐state thermal performance characteristics of low‐voltage circuit breakers
Authors: Völker F.
Published: July 2010

A discrete thermal network is given as an equivalent circuit of the steady‐state thermal performance characteristics of circuit breakers. The immediate environment of the enclosure and the feeders of the unenclosed switching device are the boundaries of the equivalent circuit, which specifically models the central phase of a three‐phase circuit breaker. Computer simulations make it possible to analyse the thermal system performance in rated service. Selected examples prove the high quality of the model and the efficiency of the described method of calculation.
Steady‐state modelling of a uniform pulse‐width modulated single‐phase AC‐to‐DC converter‐fed DC motor drive
Authors: Hamed S. A.
Published: July 2010

With the increasing availability of power transistor switches, PWM controlled rectifiers can efficiently and economically be employed in low and medium power applications of DC drive systems. In this paper, steady‐state modelling and solution of a uniform pulse‐width modulated single‐phase AC‐to‐DC converter‐fed DC motor drive is accomplished. The developed model is presented in a generalized form that is applicable irrespective of the number of pulses per supply half‐cycle. Measured and predicted parameters are shown to be very close and the model is proved to be efficient and accurate. Both continuous and discontinuous modes of operation are covered, and critical operating conditions at which the system moves from one mode to the other are thoroughly investigated. The effects of the armature inductance‐to‐resistance ratio and the chopping frequency on these critical conditions, load and line harmonics, and on the ripple contents of the armature current are also thoroughly investigated.
Solid‐liquid interface of an inductively heated metal sphere
Authors: Bex H. , Greuel K.
Published: July 2010

In this paper inductive melting in a metal sphere is investigated, whereby the temperature dependence of the sample 's most important material parameters is considered. The solid‐liquid interface in the sphere is determined in consideration of heat conduction. The melting process takes place in a vacuum with zero gravity under the influence of a homogeneous, magnetic alternating field. For the numerical solution of the heat conduction equation, homogeneous, isotropic conditions are assumed in discrete toroidal volumes. This approach simplifies, at the same time, the use of Maxwell's equations. Using the method of finite differences, the procedure yields not only the spatial location of the solid‐liquid interface but also the corresponding time and absorbed active power as a function of frequency, radius of the sphere and intensity of the exciting field. And not least, the total required melting time for melting the sphere can be determined.
Simple robust adaptive control of static VAR compensator
Authors: Machowski J. , Nelles D.
Published: July 2010

A study of power system transient stability enhancement through effective use of static VAR compensator is presented. It is shown that optimal state‐variable control can be approximately realized as a simple closed‐loop control based on locally measurable electric quantities. In order to make this regulation more effective and insensitive to the changes of the network parameters and loading condition it is proposed to use simple adaptive control with dynamic gain tuned by additional control loops. Tests done for two‐machine and multi‐machine systems have confirmed the validity and robustness of the proposed control method.
The significance of reliability indices to system planning
Authors: Wellßow W. H.
Published: July 2010

Reliability indices of power systems may have considerable uncertainties. The statistic properties of the different indices with respect to their expressiveness as decisive criteria for planning tasks are investigated. For comparing the planning variants a method being based on the probability distributions of the reliability indices is presented allowing a risk quantification. The procedure is explained by giving an example.
The rms method and its application to the evaluation of errors of instrument transformers at non‐sinusoidal waveforms
Authors: Bojna I. , Jahn P.
Published: July 2010

The paper describes a general method, the so called RMS‐value method, which allows to analyse the current, voltage and power conditions in circuits with non‐sinusoidal periodic currents and voltages, without knowledge of the content of their harmonic components. Using this method the errors of the instrument transformers, including the power measurement in circuits with non‐sinusoidal periodic currents and voltages, are defined. The suggested method is illustrated by measurements of the current transformers with specified non‐sinusoidal currents.
Novel approach to numerical equivalence investigations on synthetic circuits for circuit‐breaker testing
Authors: Witte G. , Möller K.
Published: July 2010

The paper addresses to the calculation of the interruption limit of circuit breakers in connection with equivalence studies on synthetic test circuits. After a presentation of the applied arc‐equation, a method is presented to detect the calculated interruption limit by the rate of rise of the conductance minimum as a function of the current slope. Thus, a range of decision can be defined, in order to reduce the effort for equivalence studies of synthetic test circuits.
Study of the neutral‐to‐ground voltage in a compensated power system
Authors: Leitloff V. , Pierrat L. , Feuillet R.
Published: July 2010

This paper presents an extension of the theory of compensated systems taking into account general admittances between the three phases and earth at steady‐state condition. First, an introduction to the theory and history of compensated systems is given. The influence of reactances in the voltage source and the influence of a single phase resistive earth fault on the neutral‐to‐ground voltage are studied. As an illustration of the possibilities of the extended theory, the introduction of source impedances and the detection of high‐resistive earth faults by observing the neutral‐to‐ground voltage are examined.
Inductive ultra‐wide band detection and location of partial discharges in high‐voltage cables
Authors: Wouters P. A. A. F. , Van Der Laan P. C. T. , Steennis E. F.
Published: July 2010

In medium‐ and high‐voltage cables with a helical structure of the earth screen current pulses from partial discharges travelling along the cable are observed to follow the spiralling structure. The resulting tangential current produces an axial magnetic field which can be detected by an inductive sensor without having to make any change to the cable. A specially developed inductive sensor placed around the outer sheath of an intact cable is made selectively sensitive to the high‐frequency signals (± 100 MHz) arising from the partial discharges. The discharge pulses are recorded by a fast digitizer (bandwidth of 600 MHz). In laboratory experiments partial discharges with a minimum magnitude of about 5 pCfrom electrical treeing in short, medium‐voltage cables could be detected. Location by means of transit time measurements was performed with an accuracy of about 5 cm. In one case, the polarity of the discharge signal was successfully used to locate the discharge to within 1 cm.
Adaptive algorithm for estimation of voltage phasor, frequency and rate of change of frequency
Authors: Terzija V. , Djurié M.
Published: July 2010

This paper presents results in the design of an adaptive algorithm for real‐time estimation of voltage phasor, frequency and its rate of change. The new algorithm, separated in two stages, is based on the non‐recursive “Least Error Squares Technique” (LS Technique). The estimation of the unknown parameters of the voltage signal is improved by means of an update procedure in the first stage. The update procedure is iteratively provided by the algorithm adaptation to the actual estimated frequency so that the frequency measurement range and accuracy are significantly improved and sensibility to the noise is reduced. The rate of change of frequency, estimated in the second stage using a common LS Technique, is represented by the linearly time‐dependent observation model. To demonstrate the performance of the algorithm developed, computer simulated, experimentally obtained and real‐life data records tests are presented.
Non‐linear control of induction motors via input‐output decoupling
Authors: Frick A. , Von Westerholt E. , De Fornel B.
Published: July 2010

An original two‐step input‐output decoupling approach aimed at the design of a non‐linear controller/or induction machines is described. The resulting scheme is compared to both the non‐linear control by exact linearization and the classical field‐oriented vector control. The performance of the three controllers, which are implemented in discrete time, is evaluated and compared in the framework of a realistically simulated variable speed drive. The proposed approach provides excellent flux‐speed decoupling, and it allows for a straightforward and exact limitation of the machine currents. The latter represents the major advantage to most other non‐linear control schemes, where the inaccessibility of the currents, which prevents their correct limitation, is a mayor drawback.
Performance of three‐phase fully‐controlled bridge rectifiers with non‐ideal supply feeding static active loads
Authors: Ahmed F. I. , Abdel‐Halim I. A. M. , Hassaneen K. M.
Published: July 2010

The paper presents an analysis of the performance of a three‐phase, fully‐controlled bridge rectifier feeding static active loads, when the AC supply feeding the bridge is non‐ideal. The modes of operation of the system, which depend on the overlap angle, are fully investigated. Closed‐form analytical expressions from which the performance characteristics can be obtained are derived without any approximation either in the shape of the load‐current waveforms or in the in the shape of the current during the overlap periods.
Dynamic modelling for electrical aging of a solid dielectric and partial discharges
Authors: Danikas M. G.
Published: July 2010

This “letter to the editor” deals with some aspects of the dynamic model for electrical aging in a solid dielectric presented in a recent paper by Dr. N. L. Fantana and Prof H. Böhme.
Power and current decompositions into time‐ and frequency‐domain components: analysis and comparison
Authors: Cristaldi L. , Ferrero A. , Superti Furga G.
Published: July 2010

Many 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

This 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

A 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

At 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

The 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

This 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

This 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

The 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

The 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

After 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

The 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

The 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

Flux‐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

The 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

Normally 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

The 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

The 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

Degradation 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

An 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

In 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

The 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

In 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

Adjustable 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

A 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

This 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

We 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

The 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

This 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

In 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

This 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.
Quality of residual current‐operated circuit breakers
Authors: Cantarella G. , Carrescia V. , Tommasini R.
Published: July 2010

In the last few decades, residual current‐operated circuit breakers, with (RCBO) or without integral overcurrent protection (RCCB, hereafter referred to indistinctly as “residual current devices” ‐ RCD), have assumed a fundamental importance for the electrical safety of low‐voltage systems. In accordance with IEC and CENELEC International Standards, they are a necessary protection against indirect contacts in TT systems, are recommended in TN and IT systems, and are able to prevent fires due to small earth‐fault currents. RCD with a rated residual operating current Idn ≤ 30 mA also constitute the only existing active protection against direct contacts and in the case of failure of the protective or earthing conductor. Hence, it is upon their reliability that, to a large extent, the safety of persons, of livestock and property depends in the use of low‐voltage electric power. This paper presents the results of a specific research conducted in Italy on approximately 21000 RCD installed in residential and nonresidential premises. The results of the research are analyzed in the dual intent of drawing, on a statistical basis. useful indications for improving the installation, manufacturing and testing requirements of RCD.
Generalised discrete reliability model of electromagnetic AC contactors
Authors: Ablewski Z. Wrö
Published: July 2010

In the paper discrete reliability models of AC contactors and their functional elements are presented. The models were derived from the analysis of physical and chemical processes which are observed during contactor operation. They can be used for estimation of influence of material and design parameters as well as operating conditions on contactor durability. The models presented can also be helpful in improvement of contactor design methods and in development of new durability tests which can be applied by contactor manufacturers and users.
Convergence improving minimization technique for a modified fast decoupled load flow
Authors: Berizzi A. , Silvestri A. , Zaninelli D.
Published: July 2010

This paper describes an efficient and reliable algorithm that modifies the Fast Decoupled Load Flow (FDLF) in order to overcome non‐convergence troubles in solving strongly stressed power systems. The Hartkopf's algorithm for improving the Newton‐Raphson method's convergence features in ill‐conditioned cases is taken as a basis. The proposed changes to FDLF consist fundamentally in minimizing the squared power mismatches with a second order interpolation technique. The simple modification makes it possible to establish for sure whether a case of non‐convergence is owing to numerical or to physical problems, and lets the operator evaluate the system condition correctly. Several numerical examples show the remarkable behaviour of the algorithm proposed.
A new concept of combined transformers
Authors: Poljak M. , Bojanic B. , Hafner T. , Tomasevic J.
Published: July 2010

The basic characteristics of a new concept of combined transformers consisting of an inverse current transformer and a voltage transformer with open core, are described. The results of the research and testing of impulse and AC voltage distribution, accuracy class, influence of the current transformer on the voltage transformer and vice versa are given. Thanks to its technology and simplicity, the new concept allows the commercial manufacture of combined transformers for the highest equipment voltages up to 420 kV inclusive.
Assessment of air‐density correction for practical electrode systems
Authors: Boutlendj M. , Allen N. L.
Published: July 2010

A survey is given of available data on the effects of air density upon pre‐discharges and sparkover for nonuniform field geometries under a variety of voltage waveshapes of both polarities. Semi‐empirical relationships describing the trends of the experimental data are presented. The correction methods set up by the IEC are reviewed and some emphasis has been given to the need to distinguish between the separate influences of pressure and temperature in the overall air‐density correction factors. The limits of applicability for density correction are also discussed. Finally, a generalised semi‐empirical equation taking into account the main atmospheric variations is proposed. This is shown to offer a good accuracy for the calculation of sparkover voltages over a wider density range than has been hitherto been possible.
An efficient identifier for synchronous machine dynamics
Authors: Hegazy Y. G. , Saleh K. I. , Badr M. A.
Published: July 2010

The main objective of this paper is to seek the simplest possible identification model that can simulate closely the dynamic behaviour of a synchronous generator. The successful development of such a model would be of help in devising efficient on‐line digital controllers. For this purpose, the recursive least‐squares method of identification has been used. In this respect it has been found that both a third order and a second order identifier are successful in performing this job. The remarkable finding here is the capability of such reduced models of simulating the dynamics of synchronous generators under the effect of the sub‐synchronous resonance phenomenon, where the order of the differential equations describing the system understudy is extremely high. The validity of the presented analysis and the conclusions reached are checked experimentally.
Mathematical foundations of the instantaneous power concepts: An algebraic approach
Authors: Cristaldi L. , Ferrero A.
Published: July 2010

In this paper a mathematical framework is proposed for defining the concepts of instantaneous real and instantaneous imaginary power in three‐phase systems. Up to now, the approach to the definition of these quantities has mainly been a geometrical approach, which is not generally convenient for the quantitative analysis of the electric system behaviour. The proposed framework is an algebraic approach, based on the innovative use of the hypercomplex number algebra, which is shown to be well suited to deal with three‐wire and four‐wire three‐phase systems. The relationship with the geometrical analysis proposed by Willems is discussed.
The oscillatory nature of the power in single‐ and polyphase circuits
Authors: Emanuel A. E.
Published: July 2010

This study reiterates the fact that the transfer of electric energy in AC circuits is always causing oscillations of power. It is indicated that such oscillations are supported by the energy stored in moving masses, or in the electromagnetic field, or in any type of energy storing device, such as electric batteries. Oscillations caused by an unbalanced polyphase system with purely resistive loads, or by energy storage elements, or by the integer or non‐integer harmonics injected by non‐linear loads, all of them are sustained by the same types of reservoirs of energy. This paper defines three types of oscillations and the powers associated with each type, and details the physical mechanism that controls the energy conversions that govern such oscillations.
Power theory of electrical circuits with quasi‐periodic waveforms of voltages and currents
Authors: Czarnecki L. S.
Published: July 2010

Generally known current and power equations of electrical circuits cannot be used in situations where the voltage and current waveforms are non‐periodic. The paper suggests that these equations could be applied to systems with quasi‐periodic waveforms, however, as approximate models of the power‐related phenomena. The concepts of the running RMS and complex RMS values, as well as the running active power are introduced for that purpose and applied for generalizing the current and power equations of the single‐phase and three‐phase circuits with time‐variant parameters. Fast iterative algorithms for calculating the running quantities make it possible to integrate the frequency‐domain and the time‐domain approaches into a kind of the time and frequency‐domain model of the power‐related phenomena in circuits with quasi‐periodic waveforms.
Application of running quantities for control of an adaptive hybrid compensator
Authors: Czarnecki L. S. , Chen G. , Staroszczyk Z.
Published: July 2010

A control algorithm for a hybrid compensator based on a concept of running complex RMS values of the fundamental harmonic of voltages and currents is presented in the paper. The hybrid compensator is composed of an adaptive passive balancing compensator, controlled in the frequency‐domain, and a current source, controlled in the time‐domain. The algorithm used for the compensator control is rooted in a new approach to the power theory of electrical systems with quasi‐periodic waveforms. It is based on the concept of running quantities and a forward extrapolation of the power properties of a time‐variant load. Experimental results obtained using such an algorithm for controlling a laboratory prototype of the hybrid compensator are presented in the paper.
Load‐ and line identification in multi‐phase systems: A compensation‐oriented approach
Authors: Mattavelli P. , Tenti P.
Published: July 2010

The approach presented in this paper relays on the identification of load parameters in terms of passive impedances. It is aimed to the evaluation of unbalanced and reactive currents of an n‐phase system so as to allow load compensation by means of passive components. The paper discusses also an identification method of the line parameters, from which the maximum voltage distortion caused by an individual load can be estimated: This also results in an evaluation method of the power factor, which can be used for tariffation.
On techniques for localization of sources producing distortion in three‐phase networks
Authors: Swart P. H. , van Wyk J. D. , Case M. J.
Published: July 2010

This paper extends the underlying network theory defining the direction of harmonic power in single‐phase systems to three‐phase systems. By employing symmetrical component theory for multi‐frequency systems, zero‐, positive‐ and negative‐phase sequence components may be considered separately. However, the theoretical results and the modelling show that single‐point measurements for the localization of distortion‐producing sources are not practical when these sources are distributed over the network.
An approach to the analysis of power flow with time‐variant components: The switching power
Authors: Monti A. , Riva M. , Furga G. Superti
Published: July 2010

Beginning from the previous work results, the authors present Switching Power, a new quantity very useful to comprehend energetic phenomena inside a converter. Following the definition, few theorems are presented and demonstrated, afterwards few examples are discussed to better explain the study application.
Robust control of switched power converters via sliding mode
Authors: Nicolas B. , Fadel M. , Cheron Y.
Published: July 2010

This paper presents a variable structure control approach for the output voltage regulation of switched power converters. The most outstanding feature of this control technique is its robustness towards load and line voltage disturbances. A control implementation for a basic down converter based on state‐space transformation wholly confirms this performance. An extension to inverter control results in reduced harmonic distortion in case of uncertain load characteristics. Analytical predictions are verified by experimental results.