bluuebunny/crossref_metadata_2025 huggingface dataset:
Analysis of the voltage harmonics of PWM voltage fed inverters using high switching frequencies and different modulation functions
Authors: Van Broeck H. Der
Published: July 2010

This paper presents different methods to determine the harmonics of pulse width modulated patterns by means of a minimum on mathematical equations. The first solution is based on a FFT algorithm and allows detailed investigations for a low frequency ratio of the PWM. The second solution consists of a single expression by which any harmonic based on a high switching frequency can be determined. It can, however, also be applied at low frequency ratios above z 15 and takes different modulation schemes into account. Starting from the pure sinusoidal PWM a third harmonic can be injected, the space vector modulation can be applied or the flat top modulation can be considered. The third approach calculates the most important harmonics of the PWM by a simple equation which can be solved without numerical help. The results of the paper are suitable for three phase PWM transistor inverters in electrical drives or in line converters.
Electric citybus with two induction motors ‐power electronics and motor control
Authors: Langheim J. , Fetz J.
Published: July 2010

After a short introduction into the project of an electrically driven citybus with two individual induction machines, this paper describes the power electronic hardware including IGBT‐inverter and on‐board supply system as well as the structure of the field‐oriented motor control. The on‐board power supply has been especially designed for this vehicle. It supplies electric loads such as board systems, measurement devices and control components. The induction machines are separately fed by two ICBT‐inverters. They are operated at a high switching frequency due to the low leakage inductance of the machines. Fast switching leads to high dU/dt‐values which may destroy the motor windings. In order to reduce the high dU/dt‐stress on the machines, an appropriate circuit has been developed and is presented. The induction machines are controlled by a field oriented control. The choice of the reference current components and the control structure assure a good dynamic performance and low machine losses. Measurements obtained in a laboratory test‐setup are presented.
Piezoelectric motors and their applications
Authors: Schöner H.‐P.
Published: July 2010

The principle of operation of piezoelectric motors is explained. Different general approaches for converting small displacements of the piezo element into continuous motion are described. The use of resonant oscillations gives relatively powerful piezoelectric motors. A short review of the historical development is given. General properties of piezoelectric motors are explained. Limiting factors for the power of piezoelectric motors are discussed in comparison to standard electromagnetic motors. The force per active area of piezoelectric motors is shown to be 30 to 100 times larger compared to small electromagnetic motors. The tilted speed/torque characteristic is explained from material properties in the motor. Other general aspects, especially with respect to the choice of materials, are discussed. This motor type will provide advantageous solutions especially for many different positioning applications.
Calculations of resistances and reactances of a single‐sided linear induction motor
Authors: Gieras J.
Published: July 2010

The equations for resistances and reactances of the equivalent circuit of a single‐sided linear induction motor with a double‐layer reaction rail (secondary) are given. The influence of the magnetic saturation due to leakage fluxes on the primary winding leakage reactance and the influence of the longitudinal end effect on the vertical branch impedance is discussed. Other effects such as the transverse edge effect, the skin effect, the non‐linearity of magnetic circuit and the primary compensating turns are also included. It is proved that the equivalent circuit gives a better accuracy than the finite element method in case of calculating the thrust and normal force of a large‐scale linear induction motor.
Contribution to the calculation of electromagnetic channels for molten metal transportation
Authors: Pesteanu O.
Published: July 2010

The paper presents the construction of a conveying channel of relatively small active power and with direct network supply of the inductor winding. By calculation of the magnetic field with the variables‐separation method, on one side, and by representation of the conveying channel as a cascade of four‐terminal networks on the other, an equivalent circuit is determined, which takes into consideration the following: the reaction of currents induced in the molten metal, in the protective plate and in the cooling tubes of the inductor, the transverse edge effects, the magnetic field decrease normally to the inductor surface, the influence of slot openings and the higher waves of the travelling magnetic field. Finally two industrial dosing channels are presented.
Apparent and reactive powers in three‐phase systems: In search of a physical meaning and a better resolution
Authors: Emanuel A. E.
Published: July 2010

This work analyzes the resolution of the apparent power in three‐phase systems defined by means of symmetrical components and using the product between an equivalent voltage [(V+)2+(V‐)2+(V0)2]1/2 and an equivalent current [(I+)2 + (I‐)2 + (I0)2]1/2. It was found that each component of such a defined apparent power S has a definite physical meaning. The results emphasize the need to separate the negative and zero sequence active power from the positive sequence power.
Current and power equations at bidirectional flow of harmonic active power in circuits with rotating machines
Authors: Czarnecki L. S.
Published: July 2010

A substantial portion of electric energy, up to two third of the amount produced, is converted into mechanical energy by various rotating machines. These are supplied mainly from three‐phase sources of a sinusoidal voltage. There are situations, however, where this voltage is strongly distorted. In recent years, progress was achieved regarding comprehension of the power phenomena in circuits with non‐sinusoidal voltages and their power factor improvement. This is due to a power theory based on the current orthogonal decomposition into the active, scattered, reactive and unbalanced current. That theory does not take into account, however, peculiar power properties of the rotating machines. This paper suggests a modification of this theory to a form that might be more suitable for describing the flow of energy between a rotating machine and a three‐phase source of non‐sinusoidal voltage.
A kalman filter‐based technique for combined digital estimation of voltage flicker and phasor in power distribution systems
Authors: Kamwa I. , Srinivasan K.
Published: July 2010

Electric power quality is of prime importance when sensitive electronic equipment is involved. One of the aspects of power quality is known as flicker level. The present paper proposes an algorithm for real‐time monitoring of voltage flicker based on the Kalman filtering technique. First a stochastic state space model of the system voltage with a linear time‐invariant transition matrix has been established, yet non‐linear in the scalar observation model. Using noisy measurements of a single‐phase voltage, an extended Kalman filter leads to instantaneous value of rms voltage and phase. Then the flicker level has been derived by appropriate filtering and statistical processing on short records of the rms voltage measurements. Simulated and actual data demonstrating the effectiveness of the overall scheme in estimating voltage phasor and flicker for a wide range of swing frequencies are presented and discussed. Among the several power system applications of the new stochastic observer considered, a remote load control concept based on the carrier amplitude modulation is shown being possible and included are test results confirming the filter capability to retrieve sequences of amplitude‐modulated bit patterns travelling through the power line to customer sites.
Microprocessor‐based speed control of DC motor fed from semiconverter supply
Authors: Zaki A. M. , El‐Sattar A. A. , Wahsh S. , Amer S.
Published: July 2010

The tremendous progress in semiconductor technology has made solid state DC motor drives suitable for many practical applications. In this work a simple method for gate control of a semiconverter circuit feeding a separately excited DC motor is presented which is used to vary the motor speed. The transient as well as steady‐state characteristic performances have been obtained theoretically using closed form solution and experimentally using digital techniques. The required firing pulses were generated digitally using a 16‐bit microprocessor system. A set‐up for the experimental system has been designed and built in the laboratory. There is excellent agreement between the computed results and those obtained from the actual set‐up.
Numerical simulation of induction heating: A finite‐element approximation
Authors: Conraths H.‐J.
Published: July 2010

A precise knowledge about the electromagnetic field, the eddy currents and the temperature distribution is necessary to optimize induction heating devices which are used to heat up thin, moving metal strips in a continuous process. As this information cannot be gained from conventional, analytical methods, a new numerical simulation method, based on a finite‐element approximation, has been developed. The coupled electrical‐thermal process is modelled by a set of partial differential equations which are discretized using the Method of Weighted Residuals (Galerkin‐Method). The temperature dependency of the electrical and thermal conductivity as well as convection and radiation at the surface of the strip are included in the mathematical model. The validity of this numerical approximation is proved by the comparison of calculated and measured temperature distributions in two test cases. Finally, a simple example shows how the new method can be used in the analysis and optimization of the induction heating system.
Short‐term load forecast by plausibility checking of announced demand: An expert‐system approach
Authors: Markovié M. L. , Fraissler W. F.
Published: July 2010

Short‐Term Load Forecast at Verbundgesellschaft (VG ‐ the Austrian Electricity Board) is presented. As the VG has only regional utilities and large industries as purchasers, classical forecast methods are not appropriate. Much more suitable is a plausibility check of a set of announced purchasers demands, for which an expert system has been developed for one to three days ahead forecasts. It has been realized with the help of a rule‐oriented expert system shell based on Prolog, and contains about 250 rules. Normal days as well as special days are considered. The prototype has been tested at the central dispatcher of the VG since autumn 1990. Results and acceptance by the users are promising.
Apparent power and power factor definitions for polyphase non‐linear loads when supply conductors present different resistances
Authors: Mayordomo J. G. , Usaola J.
Published: July 2010

A time‐domain based method of defining the apparent power is presented. It is a generalization of the De‐penbrock method to systems whose supply conductors have different resistances. The so defined apparent power can be split into orthogonal components and it is coherent with the physical meaning of the power factor.
AC/DC current source GTO converter with high power factor
Authors: Alexa D. , Pastravanu A.
Published: July 2010

The paper proposes a new pulse‐width‐modulation controlled AC/DC current source GTO converter circuit. The circuit operation and its performances are investigated. This converter has low harmonic content and does not require any reactive power from the AC power source. An active power filter with capacitive and inductive storage is used for these purposes. A linear variation and a wide control range of the DC output voltage of the converter versus relative connecting duration are also obtained. Such a converter can be efficiently used to get a static frequency converter with direct current link, which can drive an induction motor with adjustable voltage and frequency.
Current chopping phenomena in SF6 selfblast circuit breakers
Authors: Voigt G.
Published: July 2010

In SF6 selfblast circuit breakers the arc energy provides a current dependent pressure rise in the upstream volume. For successful interruptions for smaller currents a current independent gas flow is necessary. The gas flow can cause current chopping when small inductive currents are interrupted. In the present paper chopping phenomena are investigated experimentally. Arc time constants are determined by current step experiments. A two‐pole arc model is used for the simulation of the observed phenomena.
Robust excitation controller design for synchronous generators using output feedback
Authors: Papadopoulos D. P. , Bandekas D. V. , Smith J. R.
Published: July 2010

In this work an alternate systematic procedure is proposed for the control of high‐order multiple‐input multiple‐output (MIMO) linear time‐invariant open‐loop system models. The procedure forms the corresponding high‐order single‐input multiple‐output (SIMO) open‐loop model from which it obtains an adequate reduced‐order SIMO open‐loop model (all states of which are measurable and may be made to coincide with its output variables). Then an implementable controller based on the reduced‐order SIMO model, using the spectral pole‐placing algebraic control method with complete state‐feedback, is derived. The controller of the reduced‐order SIMO model is then used for controlling the original high‐order MIMO open‐loop system model. The proposed control approach was applied to a linearized 9th‐order MIMO open‐loop synchronous generator system model and yielded an implementable excitation controller, which was tested successfully in three more operating points of the over‐ and under‐excitation regions of the generator for proving its desired robustness. The four designed 9th‐order MIMO closed‐loop systems displayed remarkably improved dynamic stability characteristics.
Measuring differential inductances of asynchronous machines
Authors: Staudt V.
Published: July 2010

Asynchronous machines in traction applications are normally saturated during voltage‐controlled operation. The saturation has an influence on the differential inductances of the stator windings. The value of these differential inductances can be calculated based on a theory and measured during a pulse period of the feeding voltage‐source inverter (VSI). This paper concentrates on the measurement of differential inductances and contains only a short recapitulation of the theory. Measured values of differential inductances might be used to estimate the stator‐flux space vector of the asynchronous machine without speed measurement even at stator frequency zero as a basis for high‐performance torque control without speed measurement.
On the electrical behaviour of the polar liquid propylene carbonate: a pseudo‐ohmic current‐voltage relation
Authors: Dittrich W.
Published: July 2010

Propylene carbonate (PC) is a liquid with significant dissociation ofionizable molecules. The dissociation velocity is nearly proportional to the field strength. By this the electric current becomes almost proportional to the field strength resulting in a pseudo‐ohmic current‐voltage relation. A model is presented, which allows an interpretation of the experimental current‐time and current‐voltage dependence.
A new family of electrical insulating fluids: perfluorinated polyethers
Authors: Pompili M. , Mazzetti C. , Forster E. O.
Published: July 2010

Perfluorinated hydrocarbons, because of their chemical inertness and thermal stability, have been used for a number of years in a limited number of applications in the electrical and electronic industries. Recently, a new family of perfluorinated ethers has become commercially available. Physical properties of this new family of insulating fluids include non‐flammability, high density and a wide range of viscosities. The physical and electrical properties of two representative samples of this family have been studied in detail and compared with those of other insulating oils. The results of this study suggest that these fluids should be of considerable interest to the electrical industry, particularly in applications requiring a high degree of fire protection combined with environmental compatibility.
The mean generalized content: a conservative quantity in periodically‐forced non‐linear networks
Authors: Superti Furga G. , Pinola L.
Published: July 2010

Non‐linear networks working in periodical non‐ sinusoidal steady state are investigated. By means of a new balanced quantity, theorems and conditions are achieved about some aspects in the harmonic generation and in the power conversion at different frequencies. An extension of the concept of reactive power emerges too. A numerical example is discussed in details and relevant results are reported.
The iec 909 standard and dynamic simulation of short‐circuit currents
Authors: Castelli‐Dezza F. , Silvestri A. , Zaninelli D.
Published: July 2010

It has taken a very long time for the Standard Committees, the VDE followed by the IEC, to complete their work on a standard for the unambiguous and conventionally correct determination of the characteristic values which identify the short‐circuit current in low‐medium and high‐voltage systems. This history forms one of the reasons why the procedure employed in the IEC 909 standard, finally arrived at, is potentially oriented towards manual implementation. This procedure is based on an approximation to the method of superposition of the effects; this approximation, however, gives sufficiently accurate results thanks to the use of a number of correction factors, mainly experimental in origin. The present‐day availability of reliable and reasonably priced calculation software for the study of the dynamic behaviour of electric energy systems has suggested a comparison between the results of calculations in accordance with IEC 909 and those using a dynamic simulation dealt with under the well‐known code EMTP. The test networks chosen are precisely those (in increasing order of completeness) put forward and resolved in Appendix A to the IEC 909 standard. The comparison shows a good measure of agreement between the two methods, permitting comment on ‐ and discussion of‐ the two approaches.
Equivalent circuit for small solid‐rotor induction motors fed from a non‐sinusoidal supply
Authors: Abdel‐Halim I. A. M. , Mansour H. A. , El‐Kassas S. I. , Hamed H. G.
Published: July 2010

In this paper an equivalent circuit for small solid‐rotor induction motors is developed in which the effect of the time harmonics of the supply are taken into consideration when the supply is non‐sinusoidal. This circuit can be used to obtain directly the characteristics of the motor, such as torque speed, current speed etc., when the motor is fed from a non‐sinusoidal supply, in the same way as the characteristics of the cage motor are obtained.
Time‐frequency representations of instantaneous complex power, voltage and current space vectors
Authors: Salvatore L. , Savino M.
Published: July 2010

This paper introduces a new time‐frequency representation and analyses the time‐frequency structure of the instantaneous complex power, voltage and current space vectors, which are powerful mathematical tools to describe the behaviour of three‐phase systems under unbalanced and non‐sinusoidal conditions. Computer simulations are carried out so that the performance of the new time‐frequency representation can be verified.
Comments on “apparent and reactive powers in three‐phase systems: in search of a physical meaning and a better resolution”
Authors: Czarnecki L. S.
Published: July 2010

It is shown in this comment that it is not so obvious that the apparent power S “has a clear physical meaning “ as it is asserted in the paper “Apparent and Reactive Powers in Three‐Phase Systems: In Search of a Physical Meaning and a Better Resolution “ published by A. E. Emanuel in ETEP 3 (J993) no. I. Moreover, the author of the discussed paper misinterprets power properties of unbalanced systems. He asserts in Section 2 that, apart from the active power P, each power in systems with sinusoidal waveforms represents the amplitude of an oscillation of power. The apparent power S in unbalanced systems may be higher than the active power P, however, despite of the lack of any oscillation of instantaneous power, since the direction of energy flow may not change with the load unbalance. The unbalanced power of a resistive unbalanced load cannot occur as a consequence of power oscillation since such a load does not have any capability of energy storage.
Steady‐state analysis of three‐phase self‐excited reluctance generators
Authors: Alolah A. I.
Published: July 2010

A three‐phase reluctance machine can be made to operate as a self‐excited generator when its rotor is driven at suitable speed by an external prime mover and its excitation is provided by a capacitor bank connected to the stator terminals. The reluctance generator has almost all the advantages of its counterpart induction generator and has in addition the advantages of constant frequency operation and low core and copper losses. This paper introduces an analysis of the three‐phase self‐excited reluctance generator. The developed analysis avoids the limitations of the previous works whereby the effect of the core loss is soundly taken into consideration. The analysis is suitable for variable speed, load and excitation capacitance operations. The validity of the proposed analysis is confirmed experimentally. The effect of neglecting the core loss is also studied.
Method for distance estimation of single‐phase‐to‐ground faults in electrical distribution networks with an isolated or compensated neutral
Authors: Lehtonen M.
Published: July 2010

The paper discusses how current and voltage measurements derived from the substation can be used for single‐phase‐to‐ground fault location in medium‐voltage distribution lines. The networks considered are assumed to be radially operated with either an isolated or compensated neutral. In these networks the fundamental frequency ground fault currents usually are so small that no reasonable fault‐distance estimate can be based on them. A possible solution is the utilisation of ground‐fault initial transients. In this paper a method for ground‐fault distance estimation, based on the least squares estimation of transient parameters, is presented.
Effect of machine and balancer parameters on the pulling into step of three‐phase reluctance
Authors: Alolah A. I. , Alsalloum A. M. , Badr M. A.
Published: July 2010

The operation of three‐phase reluctance motors when fed from a single‐phase supply has been found possible through the use of an appropriate capacitor as a phase balancer. This adds more flexibility to the modes of operation of such motors. Analysis of the associated transient process of this mode of operation has not yet been dealt with in the literature. It is the main objective of this paper to present a rigorous analysis of the transient behaviour of the three‐phase reluctance motors fed from a single‐phase supply. Particular attention will be focused on the pulling‐into‐step problem as affected by different motor‐ and supply‐system parameters. The developed mathematical model is suitable also for analysing the transient behaviour of three‐phase reluctance motors under balanced operating conditions.
A knowledge‐based method for contingency evaluation
Authors: Yerima J. Y.
Published: July 2010

In this paper new algorithms for contingency evaluation and a test of their validity with respect to accuracy are presented. These algorithms are based on a quantitative knowledge established for an arbitrary network operating state. The knowledge base is acquired by quantifying the impact of all single‐branch outages on the voltage and current profile using AC load‐flow‐based techniques. The acquired knowledge base can be utilized together with the derived formulae to evaluate the impact of multiple‐branch outages. Based on these formulae a technique has been proposed for updating the knowledge base to reflect changes in network topology. The knowledge‐base updating technique is efficient and the computational requirements are small. By defining a branch‐outage dependency factor an approach is presented to quantify the accuracy level of the results of multiple‐branch outages and to identify multiple‐branch outages leading to large computational errors. Generation unit failures are modelled using branch outages.
Digital simulation of fault arcs on long‐distance compensated transmission systems with particular reference to adaptive autoreclosure
Authors: Song Y. H. , Aggarwal R. K. , Johns A. T.
Published: July 2010

There is an increasing demand for more detailed and accurate modelling of fault arcs on Extra‐High Voltage (EHV) transmission systems. This is particularly so in relation to the design and development of alternative and improved equipment such as adaptive autoreclosure schemes and new protection techniques. This paper discusses in some detail techniques that have been developed to model fault arcs more realistically, including a time‐dependent dynamic resistance model of the primary arc and significant improvements that have been made in the dynamic conducting characteristic of secondary arcs. The statistical character of the secondary arc has been sufficiently taken into account by the dynamic conducting and reignition voltage characteristics. The new techniques are then employed for the simulation of fault transients on a long‐distance compensated system. In this respect, the evaluation of shunt compensation is also outlined, because special compensation schemes are essential for reducing the secondary arc current and recovery voltage to levels commensurate with rapid extinction in long‐distance lines. The paper concludes with a study of the implications of the simulation results in respect of the design of adaptive autoreclosure schemes by identifying interesting features of the waveforms.
Transient behaviour of the EMTP‐calculation method analyzed with the Z‐tyansformation
Authors: Linnert U. , Hosemann G.
Published: July 2010

To simulate power circuits there is the difference admittance method DLV as well as the synchronised difference admittance method SDLV with factorised eigenvalues of the network branches. For all methods, deviations depending on the step size are generally unavoidable. Here, these deviations will be analysed by simple, single‐phase examples with the help of the Z‐transformation. With large step sizes, the standard DLV is falsified by oscillations, but not the SDLV. In contrast to DLV series connections of elements with SDLV does not lead to the same result as the simulation of the entire element. Nevertheless, the results achieved with SDLV3 are more precise than those with DLV.
On the calculation of ripple factor
Authors: Gluskin E.
Published: July 2010

A simple formula which connects the ripple factors of the “half‐wave” and “full‐wave” rectified functions, both obtained from the same T‐periodic function f(t) which possesses the property f(t + T/2) = ‐f(t) and is non‐negative within half the period, is presented.
Transformer model for application in load‐how analysis
Authors: Vlachogiannis J. G. , Xypteras J. , Bakirtzis A. G.
Published: July 2010

This paper gives a closed formula which expresses the variation of the leakage reactance of transformers as a function of the transformer tap position. The derivation of the formula is based on the analysis of the distortion of the leakage field as portions of the winding are cut out by means of tappings. Three cases are examined, depending on whether taps are cut out: ‐ asymmetrically at the end of a winding, ‐ at the electrical centre of a winding or ‐ symmetrically at the end of a winding. The validity of the derived model is tested by comparison with existing transformer impedance correction data. Finally, test results from the incorporation of the model in a load‐flow program are presented.
Dynamic combination of impedance calculating distance‐protection algorithms
Authors: Lönard D.
Published: July 2010

Non‐ideal input signals lead to incorrect results of distance‐protection algorithms. A method to combine several parallel algorithms will be presented, showing possibilities to mix different types of principles to achieve an improved behaviour. One example of the so called filter‐combination algorithm will be discussed. Simulations have been carried out on a PC 486, using a digital signal‐processing model. The results proof the robust behaviour of the presented method.
Linear‐programming‐based method for optimum schedule of reactive power sources in power systems
Authors: Abdel‐Salam M. M. , El‐Sadek M. Z. , Hussein A. I. , Hussein A. A.
Published: July 2010

This paper proposes a linear‐programming optimization‐based method for reactive power scheduling using generator terminal voltages and reactive outputs, transformer tap‐settings and switchable reactive power sources as control variables. Dual linear programming is applied to minimize a composite objective function consisting of the cost of the adjusted control variables and the system transmission losses. The proposed composite objective function is more economical than that of the minimum total adjustment of the control variables and calls for less adjustments of var sources to meet the desired voltage limits. The proposed method is applicable to practical transmission and distribution networks, 500 kV to 11 kV, of small and large sizes.
High‐dynamic AC machine control without speed or position sensor
Authors: Zimmermann W.
Published: July 2010

In many applications inverter‐fed A C machines with high dynamic performance are needed, but position control is not required. Conventional field‐oriented control fulfils the dynamic requirements, but usually needs a costly position or speed sensor. Simple voltage‐frequency control avoids these sensors, but will only achieve a moderate dynamic performance. For such applications a self controlled scheme based on the measured flux vector may be used. In this paper a flux phase control loop and a method of backing the flux model with an observer to improve the behaviour at low stator frequencies are described.
A step‐down frequency‐modulated zero‐current switching quasi‐resonant converter‐fed DC drive
Authors: Reddy S. Rama , Lakshmikanth A. , Raj V. Babu , Chellamuthu C.
Published: July 2010

The simulation and implementation of a step‐down frequency‐modulated zero‐current switching quasi‐resonant converter (FM‐ZCS‐QRC)fed DC drive are presented. A parallel resonant QRC is used for the speed control of a DC motor. The FM‐ZCS‐QRC‐fed DC drive is modelled and simulated. A microprocessor‐based prototype system is also implemented for controlling the drive speed and the results predicted by simulation are verified experimentally. It is found that the FM‐ZCS‐QRC‐fed DC drive has several advantages over those fed from phase‐controlled converters, DC choppers and PWM converters.
Design of a linear robust PSS for optimal damping of multimode‐oscillations
Authors: Huwer R. , Kocher P. , Nelles D. , Wache M.
Published: July 2010

There is a simple rule to design a robust linear Power‐System Stabilizer (PSS) which is optimal independent of the network structure and operation point. Only the setting of voltage regulator determines the adjusting parameters. The paper shows the behaviour of such a PSS if two different modes of power swings occur. Both are damped as quickly as possible if the load angle of the generator does not become negative or larger than 90°.
Design of a small, axial‐flux permanent‐magnet motor
Authors: van Dessel M. , Belmans R. , Hanitsch R. , Hemead E. A.
Published: July 2010

The paper deals with the design of a disc‐type motor excited by permanent magnets. The main flux is oriented in the axial direction, yielding a pan‐cake type arrangement. The outer diameter is about 45 mm, the axial length about 15 mm. After the introduction, the motor design is explained. On the basis of these general design considerations, the average flux density at no‐load in the materials is approximated using an analytical, one‐dimensional approach. An accurate analysis of the axial flux machine requires a 3D finite‐element calculation. The 3D model design needed for this, is explained. The motor characteristics (induced voltage and torque), obtained from the 3D calculation are described and compared with measurements.
EMC analysis for grounding structures in power systems
Authors: Heimbach M.
Published: July 2010

EMC analysis of power systems requires the knowledge of the dynamic behaviour of extended grounding structures during electromagnetic transients. This paper presents an approach, which permits to determine the electromagnetic field distribution in the surroundings of the grounding system. In the first part a model for linear conductors based on the transmission‐line approach is described. The second part deals with a procedure, which allows to calculate the electromagnetic field from the results of the transmission‐line representation. Both the transmission‐line model and the field calculation are implemented in the Electro‐Magnetic Transients Program (EMTP). The interfacing with the EMTP permits not only the computation of the grounding system, but also of entire power systems as the latter can be simulated by the EMTP and connected to the grounding system.
Steady‐state analysis of soft and hard‐switched DC/DC converters
Authors: Pinola L. , Rotta E. , Testa L. , Varoli V.
Published: July 2010

A methodology for the accurate steady‐state analysis of soft‐switched (quasi‐resonant) DC/DC converters is described. It consists in a two‐steps procedure: a simplified analysis provides the initial values to an iterative algorithm which improves the accuracy of the results up to the required level. Symbolic mathematics packages make it possible to apply a rigorous approach also to the high‐order networks typical of quasi‐resonant converters. The procedure is validated by comparison of its outputs to experimental results.
About an improved evaluation of results by the standardized salt‐fog procedure for composite insulators
Authors: Schmuck F. , Barsch R. , Pilling J.
Published: July 2010

Based upon long‐term experiences with accelerating ageing tests of polymeric materials and composite insulators, the authors give a contribution to an improvement of the reproducibility and results' validity of the salt‐fog procedure. The following parameters and criteria standardized are critically evaluated: the magnitude of the fog conductivity and the continuous test duration taking at least 1000 h. Using a modified Inclined‐Plane Test, the partial discharge burning time is determined as additional diagnostic value. Summarizing, a modified salt‐fog procedure and further diagnostic values are suggested.
Short‐circuit performance of a stretched transformer winding with regard to its actual mechanical characteristics
Authors: Kozlowski M. , Pewca W.
Published: July 2010

The impact of heterogeneous mechanical structure of a transformer winding: existence of the turn insulation and the inner axial cooling ducts will be shown with regard to the actual mechanical characteristics of copper and insulation materials using a newly developed calculation method. For the distribution along the coil width of the wire permanent set values of the wires will be presented and the consequences discussed. The reason for settlement of the proper limits for permissible tensile stresses in the winding will be shown also.
An example for dynamic compensation of non‐active power in the case of non‐linear active loads
Authors: Staudt V.
Published: July 2010

A lot of different definitions for active and non‐active quantities and their compensation are known in case of single‐ or polyphase systems under steady‐state conditions. In practice the load as well as the source of such a system is varying with time. This requires compensation methods which are ready to deal with dynamic conditions. In the most general case the load may be non‐linear and even change from passive to active and vice versa. This paper presents a control scheme for a series compensator (series active filter) in a single‐phase circuit which can handle a wide range of passive and active non‐linear loads under dynamic conditions. No information about the character of the source and the load is required, as long as load and source current can be controlled by appropriate voltages.
Assessment of unbalance emission level produced by loads using the apparent power components
Authors: Mayordomo J. G. , Beites L. F. , Gutierrez J. L.
Published: July 2010

This paper proposes the application of the unbalanced fundamental power as a merit figure to establish a prediction method of the voltage unbalance emission levels produced by the connection of unbalanced loads. The total apparent power, as criterion for optimal compensation, is discussed when it is applied to loads which are sensitive to voltage unbalances such as generators and motors. The analysis of these aspects is made according to recommendations for voltage unbalances.
The problem of harmonic compensators location
Authors: Mikolajuk K.
Published: July 2010

Current harmonics can be eliminated in each individual load. Such a compensation generally must be expensive. Harmonics are partly compensated between individual consumers. Therefore, the compensation of group of consumers seems to need lower cost than individual compensation. In the case of group compensation there are two possible approaches. The first approach uses compensators controlled by a current in common buses supplying a cluster of consumers. In the second approach a voltage waveform is chosen as a control data, the compensator should maintain a sinusoidal voltage. Such an approach needs not many compensators to ensure a proper quality of energy delivered. The purpose of the presented paper is to formulate the optimization problem for compensators location in power systems. It is shown that the problem leads to combinatorial optimization. The Travelling Salesman Problem and 0‐1 Knapsack Problem are related to the presented combinatorial problem, but it seems, that there is not solved the combinatorial optimization problem which is identical to the considered one.
Principal peculiarities of ceramic and composite insulators for overhead EHV/UHV power transmission lines: Electrical characteristics, performance, reliability and application areas
Authors: Tikhodeev N. N.
Published: July 2010

Areas of rational application of cap‐and‐pin and rod line insulators manufactured of various materials (porcelain, glass and polymers) are discussed in terms of ensuring high reliability and adequate performance of strings on EHV and UHV AC and DC overhead power transmission lines. It is shown that the most critical characteristics of both cap‐and‐pin and rod units are their quality in terms of annual in‐service failure rates and their polluted dielectric strength at long‐duration exposure to the operating voltage. Additional features of importance for HVDC lines are high resistivity of the dielectric and good dielectric strength of each individual unit.
Accelerated ageing tests on composite hollow insulators under DC voltages
Authors: Petruseh W. , Week K.‐H.
Published: July 2010

Investigations are reported on two specimen of silicone rubber hollow insulators at a DC voltage of‐100 kV. Leakage current measurements are performed under natural pollution conditions and with artificial wetting. On the surface of naturally polluted insulators energised with DC voltage several types of simple microbes were found, which may influence the leakage current performance. It is also shown that accelerated ageing procedures using salt fog for creating surface discharges are not representative for inland sites with a low degree of pollution. Ageing performance of non‐ceramic insulators should be checked in general with respect to the UV‐strength of the material used. Accelerated ageing tests regarding pollution performance are necessary only if the site conditions will create surface discharges on the non‐ceramic material chosen for the insulator. A test procedure, based on the IEC1000 h test, with constant discharge activity over a selected duration is proposed for further investigation. There is no advantage regarding creepage distance dimensioning of non‐ceramic insulators in comparison to porcelain insulators for sites with surface discharges under natural conditions. The use of non‐ceramic insulators for areas with very heavy or extreme pollution seems to be questionable.
A highly efficient method for optimum electrode contour determination
Authors: Kato K. , Hikita M. , Hayakawa N. , Kito Y. , Okubo H.
Published: July 2010

A new algorithm has been developed, which enables to determine an electrode contour with an optimum electric field distribution, using‐a personal computer. The algorithm is based on the charge simulation method (CSM) and uniquely determines the optimum electrode contour from electric field distribution in the whole field space. In addition, the algorithm is capable of estimating quantitatively a target of the optimum electrode contour at the initial stage of the optimization process. Consequently, the estimation of the target electrode contour proved to need minimum number of modification to reach the optimum electrode contour. The new algorithm for optimization eminently raised the convergence of iterative calculation, resulting in a particularly efficient technique for electric field optimization.
A new application of ferrite and high‐frequency signals to power system protection
Authors: Lai L. L. , Ndeh‐Che F. , Chu K. H. , Yokoyama R. , Zhao M.
Published: July 2010

This paper reports a new scheme where ferrite materials and high‐frequency signals are used to detect power system faults. The ferrite acts as a broad band dissipater. The attenuation properties of ferrite beads on high‐frequency signals is studied and are then used on a 10 m long single‐phase transmission line model to investigate their use as a primary detection device in a non‐unit protection scheme which possesses unit protection properties. The results show that the ferrite beads attenuate the high‐frequency noise quite effectively. But the picking up of high‐frequency noise has to be considered as well.
Electromagnetic spectrum radiated from gas discharges and its relation to partial‐discharge characteristics
Authors: Okubo H. , Yamashita H. , Hayakawa N. , Ueda T. , Hikita M.
Published: July 2010

Electromagnetic spectrum radiated from partial discharges (PD) andflashover occurring in air have been measured for needle‐plane electrodes. The experimental results showed that the gain of the electromagnetic wave for both PD andflashover decrease with an increase of the distance from the discharge source in the frequency range from 30 MHz to 300 MHz. The results were discussed in terms of a model assuming that electromagnetic wave radiation from a small dipole antenna simulated that from the PD source. Consequently, the distance characteristics of the signal gain proved to agree well with the theoretical calculation in the frequency range from 35 MHz to 75 MHz. An attempt was also made to separately measure the electromagnetic spectrum caused by positive and negative PD pulses, according to AC applied voltage phase. A t the same time, PD pulses were measured with a computer‐aided measuring system. The relationship between the PD statistical characteristics and the electromagnetic spectrum has been discussed.
Irreversibility of dielectric strength of vacuum interrupters after switching operations
Authors: Osmokrovic P. , Lazarevic Z.
Published: July 2010

The irreversibility of dielectric strength of commercial vacuum interrupters after a large number of consecutive switching operations is investigated in order to find out how dielectric performance of a vacuum interrupter degrades during its service life. Three types of commercially available vacuum interrupter were tested. Two of these devices were with transverse and one with axial magnetic field, all having CuCr contacts. Breakdown voltage data are measured in appropriate experiments in which type of tested interrupters and arcing conditions are varied.
Emergency assist mode of the coordinated secondary voltage control in case of voltage instability
Authors: Popovic D. S. , Gorecan Z. A.
Published: July 2010

This paper presents the performance analysis of different operation modes of the coordinated secondary voltage control in case of voltage instability. It was found that the basic pilot‐bus voltage control mode is not suitable in case of an already initiated voltage instability process, so that the new emergency assist mode of operation is proposed. Finally, the performance of the basic and the proposed emergency assist modes are studied on the test example of the power system.
The GDL data transmission experiment
Authors: Rumpel D. , Proske D. , Kempinski W. , Hummel M.
Published: July 2010

The experiment was designed to demonstrate the data transmission capabilities of a language‐oriented data system (GDL). In a realistic simulation, an unknown computer‐controlled substation was connected to a control centre. By inquiry to the substation, the control centre computer got informed on the stock of objects and the topological connections in this substation, then designed interactive diagrams for its switchyards. Finally, this substation was controlled as for switching and transformer tapping by an operator. The time required to couple the previously unknown substation to the control system amounted to 100 s.
Numerical and experimental investigations into transverse flux induction heating
Authors: Mohring J.‐U. , Leßmann H.‐J. , Mühlbauer A. , Nacke B.
Published: July 2010

Induction heating of flat metal products can be carried out using the magnetic transverse flux or the longitudinal flux. Transverse flux induction heating offers advantages particularly in the case of thin strip material. A program package is described, which enables the numerical simulation of the current and temperature distributions in transverse flux induction heating arrangements, to investigate the physical correlations. The calculation methods for the current distribution are based on the boundary element method (BEM) and those for the temperature distribution on the finite difference method (FDM). Taking into account the installation‐specific symmetries, the calculations can be carried out on generally available computers like PC or workstations. The numerical modelling and the evaluation of the results are presented using an industrial pilot plant as an example. A transverse flux laboratory model is used for the experimental verification of the electromagnetic (EM) calculation method. The temperature distribution in the strip during the passage through the industrial pilot plant is recorded with the aid of an infrared measuring system and compared with the calculation results.