bluuebunny/crossref_metadata_2025 huggingface dataset:
New current balancing and power factor improving scheme
Authors: Gagliardi F. , Lauria D. , Luciano A. M. , Tironi E. , Ubezio G.
Published: July 2010

This paper describes the main properties of a new scheme for current balancing and power factor improving of two unbalanced loads. The scheme employs a forced switching two‐phase inverter whose switching output voltage is achieved with PWM modulation. The proposed configuration has safe and reliable operation, permitting furthermore to minimize the harmonic interference transmitted to the network. In the first part of the paper the operating principles of the scheme are carried out and in the second one a possible control strategy is described.
Optimal re‐configuration of distribution network for loss reduction using non‐linear programming
Authors: Augugliaro A. , Dusonchet L. , Mangione S.
Published: July 2010

This paper deals with the problem of optimizing radially operated meshed networks in order to obtain the radial configuration which satisfies the condition of minimum power losses and also the technical constraints normally adopted for such systems. After reporting the state of art on distribution network reconfiguration, the mathematical approach to the solution of the normal state re‐configuration for loss reduction is presented, together with the non‐linear optimization model. In the proposed model, sectionalizing switches are simulated as variable resistances. By starting from the meshed network obtained by closing all switches optimal solution is found directly; the solution is addressed towards the radial structure by some suitable constraints. To solve the problem, a suitable non‐linear programming package is used. Finally some results referring to a hypothetical medium voltage test network are reported.
Calculation of temperatures in enclosed switchgears with regard to the closed circulation flow of gaseous dielectrics
Authors: Lippert T. , Böhme H.
Published: July 2010

In connection with the temperature calculation for enclosed gas isolated switchgears (especially in the case of constant load) problems arise at the mathematical modelling of the convective heat transmission, when the vertical temperature difference in the gas is important due to the circulating flow. In this case the model of the thermal network analogous to a simple electrical network is not applicable immediately. Therefore the convective heat flow within the switchgear will be determined by the calculation of the thermal flow field basing on the physical fundamental equations exclusively. A simple example demonstrates in which way the result of the field calculation will be inserted to the model of thermal network. For example the exact consideration of the convective flow field has significant influence on the result of the temperature calculation.
Trends in developing electrical actuators
Authors: Gutt H.‐J.
Published: July 2010

Electrical actuators are equipments for the conversion of electrical energy and signals into mechanical forces and movements. Sensors ‐ used in connection with these actuators ‐ are devices for the conversion of electromagnetic or mechanical units into electromagnetic signals. Both ‐ actuators and sensors ‐ become so intensively integrated, that the behaviour of electrical actuators is defined by the kind of sensor‐controlling (and no more by its construction). Further trends are tried to be quantified by technical development curves versus the time, the trends to higher actuator speed and its limits, to intensive cooling and high‐temperature superconductivity as well as to further permanent‐magnet materials and last not least to intelligent electrical actuator systems.
Iteration‐free calculation of the transient voltage breaking in industrial and power plants
Authors: Cupsa A.
Published: July 2010

Each switching operation in auxiliary systems causes overcurrents, which often entail large voltage breakings at the terminals of electric motors. In order to be able to forecast whether these motors will continue to run or run up, it is interesting to calculate the so‐called transient voltage breaking, i. e. to calculate the terminal voltages which occur within seconds after the short subtransient starting or changeover rush current. This paper describes an analytic method for this calculation, with the help of which the voltage breakings can be precisely determined without extensive iterations and without not allowed assumptions.
25 kW/200 khz parallel resonant converter for induction heating
Authors: Dede E. J. , González J. V. , Linares J. A. , Jordán J. , Ramírez D. , Maset E.
Published: July 2010

The features, technology and construction of a transistorized generator for induction heating operating over the 50 kHz … 200 kHz frequency range are presented. This new type of generator with 25 kW output power allows to replace the electronic tube generators in most part of their applications. The most outstanding advantages of this new generator in respect of tube generators are: more energy efficiency, extended service life, reduced size, separated mounting of heating station and generator. The generator incorporates an automatic frequency tracking system which allows to operate without any adjustments over a wide frequency range.
Damping of electromechanical swinging in drives with synchronous machines by a field current regulation
Authors: Uhlir I.
Published: July 2010

An electromechanical swinging of a synchronous machine can be damped by a parametric regulation of an exciting current in all cases when a mechanical time constant of a machine is substantially larger than an exciting current constant. The method described is based on the Ljapunov stability theory; it is effective for damping of swinging caused by mains frequency and voltage jitter and by mechanical moment fluctuation. A transfer function choice in an exciting current regulator is demonstrated as well as a real example of a synchronous machine 50 kVA/1500 rpm with a moment of inertia J = 160 kgm2, working as a no‐break stand‐by energy source. A seven times higher damping of swinging due to mains frequency jitter has been reached which initially had attained up to 50 % of nominal power. The description of the machine can be found in [1] and [2].
An analytical method for predicting current harmonics produced by an ac/dc converter under unbalanced supply voltage
Authors: Wang Y. J. , Pierrat L. , Feuillet R.
Published: July 2010

This paper proposes an analytical method for calculating both characteristic and uncharacteristic harmonic currents produced by a six‐pulse AC/DC converter under unbalanced supply voltage. The method allows the mathematical relationship between the complex unbalance factor (i. e. ratio of negative‐sequence voltage to positive‐sequence voltage) and the resulting harmonic currents (magnitudes and phases) to be found. An approximate harmonic model derived from the analysis is also proposed. Comparisons between the basic analytical model, the approximate model and the digital simulation results are given to validate the analysis.
Method for magnetizing curve identification in vector controlled induction machines
Authors: Levi E.
Published: July 2010

If an adaptive induction machine flux model is to be used for rotor flux space vector estimation in a vector controlled drive, the magnetizing curve of the machine has to be known. A desirable feature of the magnetizing curve identification algorithm is that the procedure should constitute a separate routine which can be executed during commissioning of the drive. An experimental procedure, which utilizes current regulated PWM inverter aimed for continuous operation of a vector controlled induction machine, is developed for this purpose. It relies on indirect vector control technique and makes use of a PC implemented indirect vector controller. Appropriate processing of data, obtained during measurements, enables identification of the magnetizing curve. To illustrate the accuracy of the algorithm, results of identification are verified by an existing method aimed for rotor time constant tuning in indirect vector controller.
Procedure for the optimization of sf6 circuit‐breakers
Authors: Habedank U. , Knobloch H.
Published: July 2010

The paper deals with the dimensioning of SF6 circuit‐breakers based on a computer program and short‐circuit breaking tests. The procedure leads to an optimization of the design of the circuit‐breaker taking into account the parameters gas pressure, contact motion, dimensions of the active parts and short‐circuit breaking current. Thus, the most advantageous breaker design no longer has to be determined only by empirical testing.
Influence of absolute humidity on the electrical breakdown in air
Authors: Schmid J.
Published: July 2010

One of the most important insulating gases in high‐voltage technique, the air, is varying with climatic conditions. The most important parameters are the pressure, temperature and the absolute humidity. The influence of humidity on the discharges is investigated in this report. First, the physical processes on the discharge development are discussed in respect to the influence of water vapour in air. Experimental results of the breakdown voltage with variable absolute humidity are explained with these processes. The experimental investigation was done with a rod‐plane gap of 20 cm to 100 cm distance and with different voltage wave shapes. The different influence of water vapour on different predischarge phenomena can be seen in different dependency of the breakdown voltage on the absolute humidity, for each type of predischarge dominating before breakdown.
An overview of present trends in energy management systems development
Authors: Asal H. P. , Dondi P. H. , Glavitsch H.
Published: July 2010

This paper starts with a brief overview of the situation in the electrical industry, with regards to electrical network configurations and operational Energy Management Systems. A concise description is provided of the network control levels, the transfer from electromechanical control to computer based control, and the types of centre‐centre communication involved. The electrical utilities requirements on new systems are then discussed, not as just another „new functional specification for controlling the process”︁ but from the point of view of second generation requirements on computer systems from a group of users now conversant with the application of computer techniques to their industry. This forms the background for considering the emerging trends in the field and the advantages and problems to be solved.
On the meaning of the park power components in three‐phase systems under non‐sinusoidal conditions
Authors: Ferrero A. , Morando A. P. , Ottoboni R. , Superti‐Furga G.
Published: July 2010

The definition and measurement of the power components in three‐phase systems under non‐sinusoidal conditions is becoming more and more an up‐to‐date problem. Some theories have already been proposed to face this problem, but the proposed solutions are not completely satisfactory, in particular when unsymmetrical, unbalanced systems are concerned. The study of three‐phase systems in terms of the Park transformation seems to be more attractive than other proposed methods. The present paper, after a short review of the properties of the Park transformation, discusses the physical meaning of the power components defined employing it, proposes a measuring equipment for the measurement of the defined power components and shows the results of some experimental work.
A new approach to synchronize a bidirectional DC‐to‐DC converter for contacfless power supplies
Authors: Eßer A.
Published: July 2010

After a short introduction into the field of contactless energy transmission this paper describes a new method to synchronize a bidirectional DC‐to‐DC converter. For example a contactless inductive transmission of energy for robots is introduced. The employed bidirectional DC‐to‐DC converters are used to feed a rotatable transformer. To allow regenerative braking of the robot drives a bidirectional power flow is necessary. Therefore the DC‐to‐DC converter, consisting of two full bridge inverters, has to be clocked synchronously. With the new method only one transformer is needed for bidirectional power flow without any auxiliary components for signal transmission.
Low‐order network equivalents for electromagnetic transients studies
Authors: Kizilcay M.
Published: July 2010

Network equivalents can be used to represent parts of a power system to reduce the complexity and the computation time during the simulation of electromagnetic transients. The goal is to simplify the representation while preserving the accuracy of transients in the remainder. First, equations for the subnetwork of interest are stated in the frequency domain using network admittance functions. For cases of practical interest, it is shown that these can be approximated by low‐order rational functions using an existing, proven optimization technique of control system engineering. Finally, the Electromagnetic Transients Program (EMTP) has been modified to permit the direct representation of such equivalents, which can be efficiently used for switching surge and fault studies. A detailed numerical example illustrates accuracy and efficiency of the new procedure.
Novel boost quasi‐resonant converter for high‐power applications
Authors: Gao Y.
Published: July 2010

In this paper a novel boost quasi‐resonant converter (boost QRC)for high‐power applications is presented. By using two switches in the boost QRC, the voltage and current stresses of the switches are reduced and the resonant inductor is smaller than in a simple boost resonant converter. There are altogether six operation modes of this boost QRC which are described in this paper. The voltage stress of the switches of this converter is only limited by the output voltage. Therefore the new boost QRC is favourable for high‐voltage and high‐power application. For applications with voltage obtained after rectification of 230 VAC mains a boost QRC was applied with IGBT as switches. Experimental results are presented.
An improvement of the iterative harmonic analysis method
Authors: De Martinis U. , Fantauzzi M. , Testa A.
Published: July 2010

The paper proposes an iterative method as a possible improvement of the classical power system harmonic analysis method known as IHA (Iterative Harmonic Analysis). Such improvement is indicated when convergence problems occur as consequence of supply system resonances, low short‐circuit ratios or strong interactions in the operation of non‐linear devices. The iterative method proposed is described and then some considerations on its accuracy and computational efficiency are carried out. Finally numerical experiments referring to single converter as well as multi‐converter installations are reported to show the applicability and the usefulness of the iterative method proposed.
Measurement of Arc‐root velocity of magnetically driven Arcs in switchgear
Authors: Worzyk Th. B.
Published: July 2010

The arc‐root velocity is an important parameter in switchgear devices using magnetically driven arcs for current interruption. Optical measurements of the arc movement may be difficult to accomplish without changing the switchgear device. A simple electrical method for determination of the arc‐root velocity is described in this paper. The arc‐root velocity is represented by the frequency of an electrical signal which makes the measurement highly unaffectable by the harsh electromagnetic environment usually found in switchgear subjected to power tests. The arc‐root velocity can be measured close to the current‐zero passage which is decisive for successful current interruption.
Pilot‐bus selection for secondary voltage control
Authors: Conejo A. , Gómez T. , de la Fuente J. I.
Published: July 2010

The secondary voltage control determines control device actions based on reference voltage values set at certain load buses denominated pilot buses. A key factor for the appropriate functioning of secondary voltage control schemes is the selection of the pilot buses. This paper addresses this problem taking into account system‐wide information, and different operating conditions regarding different load levels and different network topologies. The proposed approach improves previous approaches in two respects: the level of modelling detail and the computational efficiency. Two case studies based respectively on the IEEE 118‐bus system and the New England 39‐bus system are provided.
Vulcanization influence on TSD currents and wettability of room temperature vulcanized silicone rubber hv insulator coatings
Authors: Gubanski S. M. , Wang M.‐S. E.
Published: July 2010

Thermally Stimulated Depolarization (TSD) current spectra and surface wettabilities, represented by contact angles, i. e. the advancing angle and the receding angle, were measured on two types of high voltage room temperature vulcanized silicone rubber coatings during their vulcanization processes at room (25°C, 80 % RH) and elevated (70°C, 80 % RH) temperatures. Results show increases in the material hydrophobi‐cities with the vulcanization degree until their stabilized values are reached. Compared with the room temperature vulcanization, the elevated temperature speeds up stabilization processes of the contact angles and of the TSD spectra. Variations of the contact angle seem to be closely related with changes of the TSD peaks. In most of the cases, the contact‐angle increase is accompanied by either the TSD peak‐height decrease or the peak‐temperature increase.
Load modelling for harmonic flow calculations
Authors: Mombauer W. , Week K.‐H.
Published: July 2010

Derived from harmonic impedance measurements in the public distribution system two equivalent circuits, called load model, have been developed. The elements of the circuits are described by their probability distribution. The validity of the models are proved through comparison of calculation and measurement.
Dynamical model for electrical aging of a solid dielectric
Authors: Fantana N. L. , Böhme H.
Published: July 2010

In the paper the possibility to gain a qualitative insight into long‐time phenomena in dielectric materials, using a dynamical model, is investigated. It assumes a simplified micro structure of the material and a set of rules which apply iteratively. The rules describe some basic features of the aging phenomena under partial discharge. Stochastic aspects were modelled by using random number generators. Simulation was carried out for various starting microstructures regarding number, size and position of initial voids and for different applied voltages.
On‐line tuning of the rotor resistance in an inverter‐fed induction machine with direct‐self‐control
Authors: Klaes N. R.
Published: July 2010

This paper describes a simple adaptive torque‐balancing controller/or on‐line tuning the rotor‐temperature dependent rotor resistance in an inverter‐fed induction machine. The identification has been especially designed for use in drives with Direct‐Self‐Control. The basic version works well down to stator frequencies of a few Hz, even under transient conditions and without stator voltage sensors, but only with a DC‐link voltage sensor. It is shown that the basic version can be enhanced to work properly not only at locked rotor but even at stationary zero stator frequency except for no‐load operation. Then the information for tuning the rotor resistance at zero or very low stator frequencies is obtained by low‐frequency modulation of the stator flux magnitude and observation of the torque of a parameter‐sensitive observer concerning modulation frequency related oscillations, which occur only in the case of a mismatched rotor‐resistance parameter. The parameter is tuned via a simple l‐controller until the oscillations vanish. Experimental tests at a standard 66‐kW squirrel‐cage motor prove the excellent performance of the proposed method.
Reduction of machine current distortion using direct self control (dsc) for high‐power three‐level gto‐inverters
Authors: Hoffmann F. , Springmeier F.
Published: July 2010

Direct Self Control (DSC), developed for voltage‐source inverter‐fed induction motors, is an efficient and highly dynamic control method for inverters in the MW‐range with a limited switching frequency up to 200 Hz… 250 Hz, It is based on control ofstatorflux in a stator‐fixed reference frame; in the region below rated statorfrequency a two‐level torque controller adjusts the voltage directly so that no Pulse‐Width Modulation (PMW) is necessary. Three‐level inverters, which are best suited for very high voltage and high power demand, have several additional advantages compared to two‐level inverters, e. g. the pulsation of torque can be reduced as well as the machine current distortion. In this paper an improved two‐level torque control strategy for three‐level inverters with less current distortion is described and the practical results of its application based on measurements at a 22 kW experimental machine set are discussed.
Line‐side behaviour of three‐phase diode rectifiers with reactance smoothing
Authors: Grötzbach M. , Xu J.
Published: July 2010

This paper describes the line‐side behaviour of three‐phase diode rectifiers depending on AC‐ or DC‐side smoothing reactances. The special case of DC reactance only is investigated analytically by the aid of switching functions, showing basic dependencies for neglected commutation effects. The generalized case of AC‐and DC‐side reactances must be solved iteratively, whereby a significant reduction of the evaluation effort is achieved by a set of analytical equations. All results are presented in uniform diagrams to allow a comparison of both reactance locations. It results that DC‐side smoothing is advantageous with respect to the behaviour of the fundamental and 5th line‐current harmonic, whereas A C‐side reactances are leading to lower amplitudes for all other harmonics. In case of DC smoothing reactance, even small AC reactances influence the line‐side behaviour significantly.
An algorithm for the dimensioning of circuits for synthetic high‐voltage circuit‐breaker testing
Authors: Witte G.
Published: July 2010

The paper addresses to the design of high‐voltage circuits for synthetic circuit‐breaker testing. After a presentation of two different test circuits, a general cost function is defined, which has to be minimized in order to get the best combination of elements for these circuits. The applied algorithm is described in combination with a network calculation program as a method in order to automate the design of synthetic test circuits.
Space phasor or space vector?
Authors: Amin B.
Published: July 2010

This paper has for subject the comparison of the Space‐Vector concept to that of Space Phasor introduced by Prof. L. Serrano‐Iribarnegaray for the analysis of the induction motors, in general working conditions.
Increasing the efficiency of high‐speed solid‐rotor induction machines
Authors: Pyrhönen J. , Kurronen P.
Published: July 2010

Because of its simple structure a solid rotor is cheap and robust and so a very good alternative to be used in high‐speed induction motors. Traditionally the disadvantage with solid‐rotor motors has been a quite poor efficiency. This paper studies some possibilities of increasing the efficiency of a high‐speed solid‐rotor induction machine both in theory and practice.
Capacitive coupling through the shields of medium‐voltage cables
Authors: Braun A.
Published: July 2010

The shield ofmedium‐voltage‐XLPE cables is in general not a metal tube, but consists of several copper wires lying on the outer crepe paper above the insulation. This configuration allows a capacitive coupling between the cable conductor and external conductive objects. In this paper a theoretical consideration of the capacitive coupling using an analytical solution is described and the validity of the results is proofed with numerical methods. For several arrangements the quantity of the capacitive coupling is determined.
Analysis and design of a combined system of shunt passive and active filters
Authors: Caramia P. , Carpinelli G. , Gagliardi F. , Verde P.
Published: July 2010

Passive and active filters have traditionally been used to reduce harmonics in power systems. Only recently combined systems of shunt passive and active filters have been proposed in order to overcome the technical problems of passive filters and to reduce the costs of active ones. The paper tries to overcome some drawbacks of a combined filtering system (modified high‐pass filter) which appeared in literature. In particular, improvements in the system structure and in the steady‐state design methodology are proposed to obtain a filtering system with both satisfactory compensation characteristics and low costs. Finally, numerical applications are discussed considering a test case.
Numerical fault arc simulation based on power arc tests
Authors: Kizilcay M. , Koch K.‐H.
Published: July 2010

More than 200 power arc tests were carried out with original arrangements of overhead line insulators and arcing fittings for 20 kV, 110 kV and 220 kV. With an adequately modelled network, short‐circuit currents in the range of 2 kA to 12.5 kA can be realized. Analysis of the measurements shows that a typical arc voltage time function can be attributed to each insulator type and arrangement. Using the measured variables, which were digitally recorded and stored on optical media, an existing numerical arc model has been enhanced, which can be applied in an electromagnetic transients program to reproduce the dynamic and random behaviour of power arcs for any insulator arrangement, current and system voltage.
Behaviour of harmonic current vectors generated by six‐pulse ac/dc converters as function of plant parameters
Authors: Cavallini A. , Loggini M. , Montanari G. C.
Published: July 2010

In the paper an investigation on the behavior of six‐pulse AC/DC converters is presented, with the aim of studying the influence of plant and load parameters on harmonic currents injected by converters in A C networks. By means of a piece‐wise linear approach, the analytical solution of steady‐state currents is achieved and AC current waveform is built up. In this way, several cases with different plant parameters can be processed in reasonable computer times, and indication on plant‐parameters optimization is achieved. Comparisons are made with the approximate method, often employed to evaluate AC harmonic current amplitudes, and considered the “worst‐case” to this purpose, which resorts to Fourier series decomposition of a rectangular AC‐current waveshape.
Four‐level dc to dc converter for high‐voltage applications
Authors: Schülting L. , Posluszny M. , Platek T.
Published: July 2010

The motivation of different developments concerning multi‐level converter has two origins. In high‐power applications this technique enables among others low harmonic distortions. In addition the voltage stress of the semiconductor devices can be reduced in high‐voltage applications. This article describes a theoretical analysis, design considerations for the active and passive elements and a control method of a four‐level DC to DC converter for high‐voltage applications. The calculations and the control method are compared with measurements made in the laboratory.
Magnetic saturation in rotor‐flux‐oriented induction motor drives: operating regimes, consequences and open‐loop compensation
Authors: Levi E.
Published: July 2010

Parameter variation effects infield‐oriented induction machines can cause significant performance deterioration. Magnetic saturation of the main flux path is one of the sources of parameter variations, caused by non‐linear nature of the magnetizing curve. The paper at first discusses operating regimes of a rotor‐flux‐oriented machine which lead to operation with variable main flux in the machine. These are shown to be operation with variable stator d‐axis current command during forced excitation and in field‐weakening region, and operation with variable q‐axis current command during rapid speed changes when cross‐saturation effect causes variable main flux operation. Actual effects of variable saturation level on performance of the drive are assessed by simulation. Modified rotor flux estimation schemes are then derived, which enable instantaneous open‐loop adaptation to actual saturation degree in the machine. The proposed adaptive rotor‐flux estimators are verified by simulation and some experimental results are included as well. As the saturated induction machine representation is based on the current state‐space model, while the modified rotor‐flux estimator relies on the flux state‐space model, the performed simulation study shows that current state‐space model and flux state‐space model, although considerably different in their appearance, account for the main flux saturation in basically the same way.
Method of the air‐gap electromagnetic torque identification for a current‐fed ac drive system
Authors: Kulski† Z. H.
Published: July 2010

This paper presents a simple method of determining the air‐gap electromagnetic torque for the current‐fed induction motor. The identification procedure uses the measurement and processing the electrical terminal values of the inverter without participation of the drive motor parameters. This method uses the current‐oriented component of the air‐gap magnetic flux and the input current of the inverter. The identification of the inverter output phase in the non‐conducting state has made it possible to use the motor working windings for a direct measurement of the stator source voltage. The method which has been explained enables the standardization of the procedure of signal processing for a wide class of converter drive systems with the A C motors. The effectiveness of this identification procedure is illustrated by the laboratory test results.
A techno‐economic design study of high‐temperature superconducting power transmission cables
Authors: Ashworth S. P. , Metra P. , Slaughter R. J.
Published: July 2010

The results of a comprehensive techno‐economic design study of power transmission cables utilising High‐Temperature Superconductors are presented. A cable design is described, based upon superconductors operating at liquid nitrogen temperatures. The dimensions and operating parameters of an optimized underground cable are calculated. Based on this design the manufacture, installation, losses and operating costs of an AC High‐Temperature Superconducting (HTSC) Cable are estimated and compared with conventional underground cables for a new power link. Significant conclusions of the study are: for transmitted powers greater than I GVA the HTSC cable transmission costs become the same as for conventional cables when the superconductor critical current density exceeds 200 kA/cm' at liquid nitrogen temperature; the HTSC‐based cable is capable of transmitting up to seven times as much power (to 700 MVA at 66 kV) as a conventional cable in a 150 mm fixed diameter duct at the same transmission cost.
Optimal compensator currents for the reduction of the harmonic distortion in networks part 1: analytic solution
Authors: Dai X. , Gretsch R.
Published: July 2010

Fast harmonic compensators have been developed and will come into practical use in power systems for the reduction of harmonic currents exchanged between an installation and the feeding network or for the reduction of the voltage distortion at a single node, e. g. a central bus. In order to reduce the harmonic voltage level of an entire network a special strategy is necessary to optimize the compensator current injected into the node. The optimization problem consists in finding the minimum of the proper objective function, which can be defined e. g. as the quadratic sum of the harmonic voltages at all network nodes or of the harmonic currents in all network branches. In addition constraints such as the rated compensator current or/and the limitation of nodal harmonic voltages have to be observed. The proposed solution considers stepwise (I) a single compensator for only a single harmonic order, (II) a single compensator for multiple harmonic orders, and (III) several compensators spread over a system for a single or multiple harmonic orders. The analytic solution, in the first step under at maximum one constraint, is presented in this paper. The validity of this method has been verified by the simulating computation for a real simplified 20 kV distribution system.
Optimal compensator currents for the reduction of the harmonic distortion in networks part 2: graphic solution
Authors: Dai X. , Gretsch R.
Published: July 2010

A graphic method to optimize the compensator current which is injected into a network node in order to reduce the harmonic distortion of the network, for the single‐order harmonic problem, is presented. This method is suitable to find out whether a solution of the optimization problem, even under multiple constraints, exists and, in this case, gives the approximate optimum. Since this graphic solution is easily executed by computer, it seems to be an attractive and practicable technique. Its validity and simplicity has been verified by the simulating computation for a real simplified 20 kV distribution system.
Vulcanization influence on tsd currents and wettability of room temperature vulcanized silicone rubber hv insulator coatings
Authors: Danikas M. G. , Gubanski M.
Published: July 2010

This paper deals with the Thermally Stimulated Depolarization (TSD) current and contact angle measurements on Room Temperature Vulcanized (RTV) silicone rubber High‐Voltage (HV) insulator coatings taken recently by Dr. S. M. Gubanski and Dr. M.‐S. E. Wang.
Instantaneous sinusoidal and harmonic active and deactive currents in three‐phase power systems
Authors: Willems J. L.
Published: July 2010

In this contribution a new decomposition of sinusoidal three‐phase currents is proposed. The main feature is that it leads to the compensation of non‐active currents partly by elements without energy storage and partly by means of linear elements with energy storage (inductors and capacitors). The proposed decomposition is compared with existing procedures, such as those developed by Akagi‐Nabae and by Czarnecki. The possible generalization of this concept to distorted voltages and currents is discussed.
Measurement aspects of the voltage distortion compensation
Authors: Mikolajuk K. , Staroszczyk Z.
Published: July 2010

A complete solution of the compensator controller, allowing to eliminate voltage distortion in power system is presented. The two‐step circuit identification procedure based on the interpolating “Fast Fourier Transformation “ (FFT) has been successfully used to damp the 3rd, 5th and 7th harmonic by 60 dB at selected buses. Interpolating, flat‐top and coherent sampling methods, when used to 10 bit A/D converted (noised) signals, have been compared and simulated. It is shown that the shortest signal record requested to perform step calculations is of only one voltage period when a modified windowed coherent sampling method is used. The proposed method is tolerant to the coherency mistuning, so easy to implement even if a very simple hardware frequency multiplier is used to generate the sampling signal. A background to the presented solutions is given, allowing easily to solve similar compensating problems with different constraints.
Comments on “apparent power ‐ a misleading quantity in the non‐sinusoidal power theory: are all non‐sinusoidal power theories doomed to fail?”
Authors: Czarnecki L. S.
Published: July 2010

It is shown in this comment that recent development in the power theory of systems with non‐sinusoidal waveforms contradicts the conclusions presented in the paper “Apparent Power ‐ a Misleading Quantity in the Non‐Sinusoidal Power Theory: Are all Non‐Sinusoidal Power Theories Doomed to Fail? “ published by P. S. Filipski in ETEP 3(1993), no. J,pp. 21‐26. That paper deforms the history of the power theory development and its present state. Moreover, the notion of ‘power theory’ should not be associated with a particular power equation, but be comprehended as a knowledge base on power properties of electric circuits, revealed with various approaches. The comment discusses also the notion of ‘apparentpower’ as a conventional quantity.
Evaluation of instantaneous power terms in multi‐phase systems: techniques and application to power‐conditioning equipment
Authors: Rossetto L. , Tenti P.
Published: July 2010

This paper presents a general control method that fully utilizes the inherent capability of AC‐fed PWM converters to compensate for reactive and harmonic currents absorbed by other loads. For this purpose, suitable definitions of instantaneous active and reactive current and power terms are introduced. Simulated results demonstrate the capabilities of the proposed compensation method, which can also be implemented in existing systems, as only modifications of the control section are needed.
Parallel‐in‐time method based on shifted‐picard iterations for power system ty‐ansient stability analysis
Authors: Brucoli M. , De Roma A. , La Scala M. , Trovato M.
Published: July 2010

The transient stability analysis is the most time‐consuming computer simulation in power system studies. For this reason, in recent years, parallel processing has been applied for implementing on‐line time‐domain simulations of power system transient behaviour. As is well known, the problem of power system transient simulation consists, basically, in the solution of an initial value problem for a mixed set of Ordinary Differential Equations (ODE) and algebraic equations. The objective of this paper is to present an algorithm based on Shifted‐Picard dynamic iterations, which solves the above mentioned set of non‐linear Differential Algebraic Equations (DAE) by the iterative solution of a linear set of DAE. This feature is important because the time behaviour of the linear set of differential equations can be obtained by the solution of an integral. In this case, a multiprocessor parallel‐in‐time implementation of such algorithms is possible because each processor is devoted to the evaluation of the required variables relative to each time step. Moreover, parallelism‐in‐time allows multigrid techniques to be implemented in a natural way. Test results on realistic‐sized power systems are presented.
Electromagnetism, short‐circuit forces and strains in elbow sections of phase‐isolated, metal‐enclosed generator busbars
Authors: Knopf R. , Cupsa A.
Published: July 2010

The electromagnetic relationships (currents, field and current distribution, forces) in three‐dimensional right‐angle arrangements are determined using numerical processes. As a next stage, the short‐circuit strength is investigated with due regard given to the non‐linear material properties. The three‐dimensional calculations required for the field variables and the mechanical loads are then obtained using finite element methods. The individual influencing factors are discussed on the basis of the calculation variants. It is shown that a non‐linear, time‐dependent calculation is required for high loads. The processes presented can be used to calculate steady‐state and transient states in cables and gas‐insulated transmission routes.
Training the restoration of electricity supply systems in the netherlands
Authors: Van Ommeren P. , Van Son P. , Rumpel D. , Litzinger A.
Published: July 2010

Using a stand‐alone training simulator developed at the Gerhard‐Mercator‐ University Duisburg/Germany, a sequence of training seminars was staged in cooperation between KEMA‐ECC, the Power Systems Institute of the University, and with support of the Dutch Electricity Generating Board (Sep). A group of twelve utility operators of Sep and the different regional transport and production companies attended each seminar, with the aim of getting experience on the performance of their systems under the adverse conditions of network‐restoration. For that aim, the simulator models the Dutch 380 kV/220 kV transmission grid and eight connected subtransmission networks on 150 kV and 110 kV.
An effort to find near‐optimal bandpass filter characteristics for use in partial discharge measurements
Authors: Satish L. , Zaengl W. S.
Published: July 2010

Quantification of apparent charge is the primary goal of most Partial Discharge (PD) measuring systems and is achieved by the quasi‐integration method using bandpass filters. Past investigations have shown that commercially available PD detectors incorporate widely varying bandpass filter characteristics and so the final results obtained from two different PD measuring systems for similar input conditions were completely different. The authors feel that traceability in PD measurements can be brought about if a uniform bandpass filter characteristic can be found which may be considered as optimal for conventional applications. It so happens that even concerned international standards do not specify any such characteristics. In this short contribution, simulation studies are carried out in an attempt to find the optimal bandpass filter characteristics which yield minimum integration errors and possess short pulse resolution times.
Wettability and thermally stimulated depolarisation current spectra of naturally aged silicone rubber insulators
Authors: Wankowicz J. G. , Gubanski S. M.
Published: July 2010

Investigations are reported on high‐ and low‐temperature vulcanized silicone rubber composite insulators that were exposed to service for three, nine and eleven years under industrial or marine pollution conditions. Wetting angles and thermally stimulated depolarization (TSD) current spectra were measured. Microscopic observations of selected insulator surfaces were carried out as well. The prolonged services cause gradual and inhomogeneous losses of hydrophobicity on surfaces and inside of insulator housing materials. It is shown that there exists a correlation between the measured TSD current spectra and the wettability changes. In addition, the spectra also allow to predict an ability to support a process of hydrophobicity recovery at a housing surface. It seems that TSD measurements may be applied as a complementary test method during performance assessment of silicone rubber composite insulators.
A novel isolated, compensated darlington base‐drive configuration
Authors: Enslin J. H. R.
Published: July 2010

This paper will introduce a new isolated version of the compensated base drive for high‐power bipolar transistor switches. A unique pulse transformer is used to drive a high‐power bipolar transistor by means of a compensated Darlington pair. This Darlington pair consists of an insulated gate bipolar driving transistor (IGBT) and a high‐current single bipolar transistor. In high‐efficient, high‐power bridge applications of high‐current switches, the saturation voltage should be ultra‐low, which implies a high‐power bipolar transistor in deep saturation. This isolated base‐drive circuit is described and evaluated in these applications.
Definition and measurement of the earth resistance of an electrode covering a large area
Authors: Corbellini G. , Corbellini U.
Published: July 2010

The measurement of the earth resistance of an electrode by means of an auxiliary current electrode is affected by a systematic error with respect to the theoretical value, measured picking up the current at an infinite distance, due to the interaction between the two electrodes. The error increases with the ratio of the size of the test electrode to its distance from the auxiliary electrode. This paper suggests a method for the correction of the systematic error when the usual simplifying assumptions are made. The method itself is based on the replacement of the actual electric field, generated during the measurement, by the ideal electric field produced by punctiform electrodes. Its use allows the measurement of the earth resistance even with very short distances between the auxiliary electrode and the test electrode, taking into account the equivalent hemispherical electrodes.
Performance of a three‐phase induction motor fed from a non‐ideal single‐phase supply
Authors: Abdel‐Halim I. A. M. , Slama M. M. , Hamed H. G.
Published: July 2010

The effect of supply reactance on the performance of a three‐phase induction motor fed from a non‐ideal single‐phase supply, using a capacitor phase converter, is investigated. Equations for predicting the performance of the motor are derived, with the effect of the single‐phase supply reactance taken into consideration. Star‐and delta‐connected motors are considered in deriving the performance equations. Computed results for the motor‐performance characteristics obtained when the motor is fed from a non‐ideal single‐phase supply are compared with those obtained when the motor is fed from a non‐ideal three‐phase balanced supply having the same supply reactance as that of the single‐phase supply.
Critical review of the scientific background underlying the generalized machine theory and correlation theorems in the space‐phasor theory
Authors: Serrano‐Iribarnegaray L.
Published: July 2010

Steady‐state studies in electrical machines are based, since Steinmetz's work, on the use of time phasors on the one hand and on dividing the total flux into common and leakage flux on the other. Transients studies, however, developed many years later, have lacked analytical tools analogous to the time phasors, and have been carried out resolving the flux into self and mutual flux (Generalized Machine Theory). This paper analyzes the arguments supporting this change of focus and concludes that Steinmetz 's approach can also be extended very successfully to transients analysis, replacing the time phasors by space phasors. This results in the modern Space‐Phasor Theory, whose advantages become especially clear when using the new and powerful physical interpretation of the current and voltage phasors as well as the correlation theorems. These theorems show in what a simple and direct way the space phasors (that symbolize internal quantities) can be related to the machine external quantities during any steady or transient state.
A parameter‐identification‐based diagnosis for detecting static air‐gap eccentricity
Authors: Bradatsch T. , Filbert D.
Published: July 2010

A new method for predicting static eccentricity in an induction machine with a non‐uniform air gap is described. This procedure is based on a suitable system mode I for which the model parameters have to be identified. Under certain conditions, the mathematical model of the machine leads to an equation depending on speed, voltage, current and their derivatives. The parameters of the machine can be identified by a least‐square algorithm. The basic concept of the identification method is that the mathematical parameters will be influenced by the static eccentricity because a non‐uniform air gap will increase the inductance in all three phases of the machine. Practical results of air‐gap eccentricity detection of a low‐power motor are presented.
Contribution to iron‐loss evaluation in electrical machines
Authors: Amin B.
Published: July 2010

This paper will show that a simple formulation, similar to that used for the evaluation of the copper loss, can be used to calculate the iron loss of an electrical machine. The analytical method used in the present contribution for evaluating the iron loss of almost all types of electrical machines remains valid for any periodic, quarter‐wave symmetry‐applied voltage waveform. Accurate direct measurements of iron loss concerning five types of industrial electrical machines are presented and analyzed. These data concern two field‐excited and one permanent magnet‐excited DC commutator motors, a high‐speed, 400 Hz, induction motor used in the aeronautical industry and a permanent magnet (PM) synchronous motor used in robotics. These measurements come to support the validity of the proposed formulation and to check each specific aspect of the presented analysis.