bluuebunny/crossref_metadata_2025 huggingface dataset:
ChemInform Abstract: Synthesis, Characterization and Properties of Catalytically Grown Graphite Nanostructures
Authors: RODRIGUEZ N. M.
Published: July 2010

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Selective Conversion of Fuel‐Bound Nitrogen to N2 with Iron Nanoparticles
Authors: OHTSUKA Y.
Published: July 2010

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: A Man‐Made Element′s Brilliant Career. The History, Properties, and Applications of Technetium
Authors: ABRAM U.
Published: July 2010

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Bond Strength and Thermal Stability of Transition Metal Nitrides
Authors: TAKAHASHI M. , LAI G.‐C. , OHTA K. , KANAMARU F.
Published: July 2010

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Substitution of Ligands in Fluoro‐Acido Complexes of Nontransition Group III‐V Elements
Authors: PLAKHOTNIK V. N.
Published: July 2010

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Coordination Chemistry of Ambidentate Azole, Azomethine, and Azo Ligands
Authors: GARNOVSKII A. D.
Published: July 2010

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Platinum Nitrile Complexes
Authors: KUKUSHKIN YU. N.
Published: July 2010

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Electronic and Spatial Factors Influencing the Exchange Interaction in the Binuclear Copper(II) Complexes Based on 2,6‐Diformylphenol Bis(hydrazone)s
Authors: KOGAN V. A. , LUKOV V. V.
Published: July 2010

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Reactions of Potentially Tautomeric Methyl and Methylene Derivatives of Pyridine and Diazines with N‐Electrophiles
Authors: ZAGULYAEVA O. A. , OLEINIK I. V.
Published: July 2010

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Asymmetrized Tris(hydroxymethyl)methane and Related Synthons: Enantioselective Preparation and Synthetic Applications
Authors: BANFI L. , GUANTI G.
Published: July 2010

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Strategy‐Level Separations in Organic Synthesis: From Planning to Practice.
Authors: CURRAN D. P.
Published: July 2010

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Transition Metal Catalysis in the Baeyer—Villiger Oxidation of Ketones.
Authors: STRUKUL G.
Published: July 2010

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Use Ring‐Opening Cross‐Metathesis (ROM) to Construct Molecular Motifs.
Authors: CUNY G. D. , HAUSKE J. R.
Published: July 2010

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Rhenium‐Containing Catalysts in Reactions of Organic Compounds
Authors: RYASHENTSEVA M. A.
Published: July 2010

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Advances in the Chemical Synthesis of Brassinosteroids
Authors: KOVGANKO N. V. , ANANICH S. K.
Published: July 2010

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Cephalotaxus Alkaloids
Authors: MIAH M. A. J. , HUDLICKY T. , REED J. W.
Published: July 2010

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Alkaloids of the Aspidospermine Group
Authors: SAXTON J. E.
Published: July 2010

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Bufadienolides from Animal and Plant Sources
Authors: KRENN L. , KOPP B.
Published: July 2010

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Desymmetrization of Dienylsilanes. Stereoselective Access to Cyclitols and Carbasugars
Authors: LANDAIS Y.
Published: July 2010

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Oligonucleoside Methylphosphonates: Synthesis and Properties
Authors: MILLER P. S.
Published: July 2010

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Anomalous Regioselectivity of Elimination and a New Version of Elimination under Conditions of Phase‐Transfer Catalysis, Revealed in Terms of the General Elimination Rule
Authors: GEVORKYAN A. A. , ARAKELYAN A. S. , OBOSYAN N. G.
Published: July 2010

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Selective Reducing Agents for Commercial Pharmaceutical Production
Authors: BURKHARDT E. R.
Published: July 2010

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Calixarenes: From Chemical Curiosity to a Rich Source for Molecular Receptors
Authors: CASNATI A.
Published: July 2010

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: The Steric Course of Enzymic Hydroxylation at Primary Carbon Atoms
Authors: SHAPIRO S. , CASPI E.
Published: July 2010

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Induced Chemical Defense in Plants.
Authors: SCHROEDER F.
Published: July 2010

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Thalidomide, a Never Ending Story.
Authors: KNABE J.
Published: July 2010

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Innovation and the Rational Design of Drugs.
Authors: BOYD D. B.
Published: July 2010

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Present and Future Role of Chemical Mechanical Polishing in Wafer Bonding
Authors: GUI C. , ELWENSPOEK M. , GARDENIERS J. G. E. , LAMBECK P. V.
Published: July 2010

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Acetone Chemical Ionization Mass Spectrometry
Authors: PRABHAKAR S. , VAIRAMANI M.
Published: July 2010

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
ChemInform Abstract: Investigations of Intramolecular Hydrogen Bond by Nitrogen Magnetic Resonance Methods
Authors: SCHILF W. , STEFANIAK L.
Published: July 2010

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
Economic comparison of VSC HVDC and HVAC as transmission system for a 300 MW offshore wind farm
Authors: Van Eeckhout B. , Van Hertem D. , Reza M. , Srivastava K. , Belmans R.
Published: July 2010

Voltage source converter high voltage direct current (VSC HVDC) is a relatively new technology which allows the connection of islanded power systems. As such, it can form a connection between large‐scale future offshore wind farms and the onshore transmission grid. In this paper, the VSC HVDC solution is proposed as a promising alternative for high voltage alternating current (HVAC). The choice for a transmission technology is primarily based on economic considerations. Therefore, the economic value of VSC HVDC is investigated in this paper. VSC HVDC has important technical advantages for submarine installation compared to HVAC. The aim is to monetize these advantages in an economic comparison. Possible wind farm topology simplifications and optimizations due to the use of VSC HVDC are taken into account. Depending on the ownership of the transmission cable, the break‐even cable length, above which the HVDC option is chosen, varies. A sensitivity analysis is included in this paper. Copyright © 2009 John Wiley & Sons, Ltd.
Optimizing choppers and inverters by controlling cross currents with overlapping operation in the bridge legs
Authors: Klug Rolf‐Dieter
Published: July 2010

The paper describes a method that improves the current polarity changes of DC‐choppers and voltage source inverters and that increases the maximum output voltage by avoiding the switching dead time in the bridge legs. The resulting cross currents are controlled by an overlapping operation of the active power semiconductors. The two degrees of freedom of the bridge leg are used to contol nearly independently the load current by the modulation ratio and the cross current by the overlap ratio. Experimental results with a 4‐quadrant DC‐chopper with high switching frequency show the improvement coming from the elimination of the switching dead time problems.
Mechanical stress in high‐voltage switchgear with flexible single conductors under short‐circuit current load
Authors: Böhme H. , Golletz F. , Fiebiger C.
Published: July 2010

High‐voltage switchgear with flexible conductors can be exposed to high mecanical loads during short‐circuits. These loads are caused by the reaction of the flexible conductors to the electromagnetic force. Using the 110 kV supports as a part of a disconnector, the stress in the high voltage switchgear as shown does not respond quasi‐statically to the dynamic force in the flexible conductors which means, that the mechanical‐dynamic properties of the device determine the critical stress. Moreover, simple models well‐known in the system theory are used to describe the mechanical‐dynamic properties.
Modelling of induction motor loads in power‐system voltage stability studies
Authors: Brucoli M. , La Scala M. , Sbrizzai R. , Trovato M.
Published: July 2010

In planning an interconnected power network, it is very important to assess whether a voltage collapse occurs during a prefixed operating condition. However, it has been often found that voltage phenomena occur in a real system at a load condition different from the one predicted by simulation studies. One of the causes that makes the use of present procedures unreliable is the lack of adequate models for dynamic loads. To overcome this difficulty, the paper presents a practical approach which analyses the influence of dynamic load modelling on the voltage stability limits of interconnected power systems. Five different representations of induction motor loads are considered and the degree of accuracy of each model is investigated. Simulation studies on a sample power system clearly show that voltage stability limits can be strongly affected by the adopted representation.
Electromagnetic field above the earth's surface due to a buried three‐phase high‐voltage power‐line
Authors: Neelakanta P. S. , Lordan R. , Ungvichian V. , Wahid P. F.
Published: July 2010

A closed form formulation to calculate the quasistatic magnetic field above the earth's surface induced by an underground, three‐phase high‐voltage power‐line is derived. Computed results are compared with measured data.
Validity of narrow and broadband pd‐measurements on power transformers; pulse deformations
Authors: Kachler A. J. , Maier R. , Nieschwietz H.
Published: July 2010

Extensive investigations of partial discharge (pd) pulse winding response characteristics have revealed considerable physical insight into the mechanics of pulse transfer from within the windings to the externally accessable points of measurement. Based on the IEC charge measuring method, pd‐pulse response profiles were investigated on both, layer‐ and disc‐type transformers of different original size (25 MVA, 40 MVA and 1100 MVA) by means of internal pd‐pulse injections at geometrically and electrically differing sites. The winding design and the pd‐source locations influence significantly the externally measurable pd‐magnitude and pulse form. By no means and by neither broad band (BB) or narrow band (NB) method of detection is it possible to correlate externally measured apparent charge values with the dissipated charge at the pd‐source location. NB and BB instruments are equally applicable, with some preference to NB for pd‐measurements on power transformers.
Performance characteristics of the thyristor divert automatic voltage regulator
Authors: Abdel‐Halim M. A.
Published: July 2010

Fast response automatic voltage regulators utilizing static semi‐conductor elements are widely used in the systems of synchronous generators which are either isolated or connected to a large scale electric network. This paper presents an accurate circuit model for a rather recently used thyristor divert automatic voltage regulator, TDAVR. The tensor technique has been employed to develop a mathematical model describing the regulator. By the aid of this model, the performance and control characteristics of this regulator have been accurately determined. The effects of some different parameters of the regulator circuit upon its performance have been investigated. It is possible now to integrate this accurate circuit model with the already used circuit models of the synchronous generators and their exciters in place of the approximate transfer function model. Also, the model, being a detailed one, helps in proper design of the power and control circuit components of the studied A VR.
Theory and practice of energy measurement of non‐sinusoidal and asymmetrical currents and voltages
Authors: Gyarfas J. , Rapant S.
Published: July 2010

This paper deals with the evaluation of views on electric power and energy relations in one‐ and three‐phase systems by non‐sinusoidal currents and voltages. Pragmatic approach to the valuation of relations in the network with higher harmonics and by asymmetrical three‐phase systems are derived by means of an increased loss coefficient. Results of measurement of representative large users of electric power and the practical consequences are shown.
Appreciable cable conductor losses by axial magnetic fields?
Authors: Braun A.
Published: July 2010

This paper deals with the losses occuring in the cable conductor by the axial magnetic field, which is produced by the single copper wires of the outer shield in case of bonding both sides of the shield. A theoretical consideration determines the losses in copper‐ and aluminium conductors for commonly used frequencies depending on the shield characteristics. For an exemplary chosen cable configuration the additional losses are calculated.
Investigations on the rotary motion of internal ares in single phase sf6 ‐insulated switchgear
Authors: Munch R.
Published: July 2010

An internal arc in single phase sf6‐insulated switchgear implies the risk that the outer arc root stabilizes on a spot and punctures the enclosure after a short time. however, the burn‐through times increase considerably if a rotary motion of the arc around the centre electrode takes place. this paper presents results of experimental research on the rotary motion of fault arcs and measures influencing this movement. in addition to fundamental investigations two possibilities were worked out in order to guarantee a rotary motion at definite positions of a coaxial gis.
Method of calculating the magnetic flux density and forces in contact‐free magnetic bearings
Authors: Baatz M. , Hyrenbach M.
Published: July 2010

To mount electrical machines intended to work a very long time without maintenance, there are offered magnetic bearings. This article describes the physical fundamentals of calculating the magnetic flux density and the forces in magnetic bearings, in consideration of radial and axial displacement of the parts of the bearing, and the derived program. Subsequently the conclusions for the construction of magnetic bearings are summed up.
A new flexible electronic overload protective relay
Authors: El‐Sayed I. F.
Published: July 2010

This paper describes and implements an electronic relay scheme which protects industrial loads against overload and unbalance. The scheme works on a principle of integrating a pulse train. The strength of these pulses depends on the excess of current over the nominal value. It is shown that the presented scheme is capable of having variable overload protection characteristics. The relay design is directed to attain optimum overload protection that provides maximum use of motor and minimum waste operation time. The electronic circuit is described in details and different operating modes are studied. Experimental and analytical results are given and discussed.
Instrument for the registration of small and fast variations in the rms values of an alternating voltage
Authors: Nielsen N. H.
Published: July 2010

It is now possible to register small and fast voltage variations in the supply network by means of a recently developed measuring instrument. Within the fields of both measuring technique and automatic control technique, there is often a need for a simple apparatus capable of a fast transformation of the instantaneous difference between the RMS value of an alternating voltage and a fixed reference value into an analog output signal. With the chosen construction, the time response of the instrument allows for the measurement of the RMS of every consecutive period consisting of two successive half periods. The accuracy of the measurement is higher than the accuracy obtainable by means of a peak‐to‐peak measurement made on an oscillogram. The new instrument, which makes allowance for any distortion of the curve form, processes the signal analogically.
Thermal resistances of cables with corrugated sheaths
Authors: Brakelmann H. , Honerla J. , Rasquin W.
Published: July 2010

For corrugated cable sheaths the additional thermal resistances between the insulation respectively the screening surface and the sheath are examined. The results show that the air gap between the cable insulation and the corrugated sheath causes a considerably additional thermal resistance if the corrugated sheath is not in direct contact with the electric insulation. In case of an air gap thickness of 5 mm, this thermal resistance already comes up to that of the total electric insulation of an XLPE‐insulated extra‐high voltage cable. For such cases it is therefore advisable to supplement the IEC publication 287 accordingly.
Modelistic investigation of multi‐stress ac‐dc endurance of pet films
Authors: Gubanski S. M. , Montanari G. C.
Published: July 2010

In the paper, the results of life tests performed on polyethylene terephtalate (PET) films, subjected to electrical and thermal stresses simultaneously applied (multi‐stress), under AC and DC voltage, are presented and discussed, with a modelistic viewpoint. It is found that the AC electrical life lines at different temperatures drawn in semilog plot tend to show upward curvature at low electrical stresses, while fairly linear behavior is detected for the majority of life lines in bilog plot. Among the two sets of DC data, obtained in different laboratories, one behaves quite similarly to the AC results, i. e. provides clear threshold in semilog plot and straight lines in bilog plot, while the other gives straight life lines both in semilog and bilog plots. Life models able to fit the AC and DC data, based on both the inverse power and the exponential laws, are presented and checked by experimental results, in order to achieve the most suitable models for the explanation of the behavior of the tested insulating material. On the basis of these models, generalized probability distribution functions are derived, which can provide life percentiles at selected failure probabilities. Moreover, the temperature dependence of the life‐model parameters is investigated, to the aim of explaining the electrical life models in the range of test and extrapolation temperatures.
Capacitive loads by a voltage‐source active filter
Authors: Tuttas C.
Published: July 2010

Usually the filter current of an active filter (VSI‐type) is controlled by a two‐step controller and the disturbance (load current) is added to the control circuit. This method becomes unstable, if capacitive loads have to be compensated. It is shown in this paper, that the algorithm can be stabilized by additional filter capacitors. So the control circuit remains stable also at the compensation of capacitive loads.
Energy considerations for partial discharges in voids
Authors: Kurrat M.
Published: July 2010

Degradation of material is directly related to energy conversion. Information about the state of energy during partial discharges in voids is thus necessary to evaluate degradation of solid insulation. In this paper, measurable quantities are related to partial discharges energies. For spherical voids in polyethylene, these measurable quantities are compared with calculated ones. In conclusion, energy conversion in voids is discussed to estimate the relevance of different measurable quantities.
Electromagnetic performance comparison in electrical machines
Authors: Amin B.
Published: July 2010

The paper deals with the definition of a criterion for comparing the intrinsic electromagnetic performance of electrical machines and demonstrates its fairness and consistency. Conclusions obtained by comparing the intrinsic electromagnetic performance of different types of electrical machines versus switched reluctance machines (SRM) are given at the end of the paper.
Calculation of magnetic field of a switched reluctance motor using a microcomputer
Authors: Stiebler M. , Li R.
Published: July 2010

The paper is concerned with the determination of the magnetic field distribution and the static torque of a switched reluctance motor by means of the finite element method (FEM). In a simplified approach two different models are described, and a microcomputer is used to compute the field of an example motor. The analysis is extended to compute the static torque from the rate of change of magnetic co‐energy with respect to angular displacement; the results are compared with measurements.
Digital measurement system for high‐voltage impulse tests on transformers
Authors: Scheltinga L. , Vaessen P. T. M.
Published: July 2010

More information from test data can be obtained when digital measuring techniques are used. A description of a tailor made measurement system in use by a Dutch high‐voltage laboratory is presented. Schematic diagrams of the test setup and the measurement system are shown and the precautions taken to avoid electromagnetic compatibility (EMC) problems are described. Software facilities and their realization are described together with algorithms for waveshape determination. The use of a digital signal processor board for transfer function calculations is explained. Examples of tests with full and chopped lightning impulses are presented both in time and frequency domain.
Power measurement of periodic current and voltage by digital signal processing
Authors: Marganitz A.
Published: July 2010

For measuring the electric power the two‐pole parameters current and voltage must be picked up and processed to the power value. So the most important problem of power measurement is the processing of signals. Solutions therefor exist from all kind of signal processing techniques. Especially the digital signal processing with a signal processor shows a short measuring time, also if current and voltage are non‐sinusoidal. For this case, algorithms and measurement structures are presented for the different power terms as active power, reactive power and apparent power.
Harmonic insertion in PWM inverter drive schemes
Authors: Theocharis J. , Petridis V.
Published: July 2010

The procedure of harmonic insertion is generalized in this paper. Analytical expressions of the voltage spectra are derived. The insertion of the 3rd harmonic to the modulating signal, which is of particular interest, is considered as a special case. It is demonstrated in this case that the fundamental harmonic component of the phase and the line‐to‐line voltage is not affected by the insertion of the 3rd harmonic for sufficiently high values of the chopping ratio. However it has been shown that the higher harmonic spectrum is significantly improved as compared to the case of pure sinusoidal modulation. For different values of the fundamental component the optimal values of the amplitude of the third harmonic to be inserted have been calculated so that the distortion factor of the higher harmonic spectrum is minimized. Other cases of harmonic insertion are also considered which provide spectrum efficiency improvement. Experimental results are given which have been obtained by means of a microcomputer controlled PWM generator constructed for this purpose.
Factors affecting the discharge parameters of small positive rod‐plane gaps in atmospheric air
Authors: Pyrgioti E. , Menemenlis C.
Published: July 2010

Rod‐plane gaps below 55 cm with various terminations of the rod were tested with positive impulse voltages of various forms. The complete breakdown probability distributions as well as the histograms of the time‐to‐breakdown were deduced. The results indicate that while for gaps longer than 30 cm the specific breakdown voltage Em stabilizes around the value of approximately 4.5 kV/cm, below this length Em increases rapidly as the gap length decreases. Non‐Gaussian distributions of the breakdown voltages were detected and factors leading to non‐Gaussian distributions were investigated. The implications of a non‐Gaussian distribution of the breakdown in the design of air insulation of electrical installations of lower voltages were also examined.
Compensation effect in thermal aging investigated according to eyring and arrhenius models
Authors: David P. K. , Montanari G. C.
Published: July 2010

The study of the compensation effect applied in the domains of reaction rate constant as well as of time‐to‐failure in thermal endurance characterization of insulating materials is developed in the paper. In particular, the compensation effect is defined on the basis of both Arrhenius and Eyring relationships, and new life models are consequently derived. It is found that for the whole amount of investigated materials both models fit very well the experimental results and then are valid for material characterization.
Fast quadratic programming approach for large scale reactive power optimization
Authors: El‐Sayed M. A. H. , Abdel‐Rahman T. M. , Mansour M. O.
Published: July 2010

A fast quadratic programming approach has been developed to control the reactive power (VAR) generation in dispatching centers. The main objective of VAR control is to minimize the transmission losses taking into consideration the voltage constraints at each node of the network. The developed approach utilizes the decomposition of whole system into smaller subsystems and coordination of different subsystem solutions to obtain the optimal VAR control in the large scale systems. The smallest practical size of the decomposed subsystems is the one‐generator‐bus subsystem. The fast and non‐iterative VAR optimization of the decomposed subsystems is obtained based on considering only one active constraint at a time by solving the quadratic programming sub‐problems. The numerical test results of IEEE‐118 and 200 buses power system have indicated that the speed and accuracy of the proposed approach are adequate for real‐time applications on large‐scale systems. This approach is also applicable for large system deviations from its normal conditions and needs small memory size.
Non‐active power compensation using time‐window method
Authors: Blajszczak G.
Published: July 2010

The paper deals with simultaneous compensation of all components of non‐active power: reactive power, higher harmonics and an asymmetry in a three‐phase network. A new control method which allows to eliminate any non‐active components with considerably reduced delay time is proposed. In this paper a new configuration of a compensator power circuit is also proposed. The compensation ability of the new system was verified experimentally.
Standard data transmission protocols in process control applications
Authors: Funk G.
Published: July 2010

The paper describes a standard data transmission protocol that is widely used in telecontrol systems and in field‐bus systems for process control applications. The described standard is based on an asynchronous data transmission method that is used for character transmission in office automation systems. The described code guarantees Hamming distance 4 as protection against undetectable message errors. Furthermore, the article describes extensions of the standard code that achieve Hamming distances 6 and 8. The increased data integrity levels of the described data transmission protocols are achieved by defining product codes with single parity check codes and BCH codes and by defining special sync characters.
Computation of magnetic field in a switched reluctance motor using a quadratic hybrid biem‐eem method
Authors: Omekanda A. , Broche Ch. , Baland R.
Published: July 2010

The Switched Reluctance Motor (SRM) is a simple and robust electrical machine which is finding application over a wide speed and power range. The design optimization and reliability assurance of its behaviour require accurate prediction of the magnetic field distribution in its active regions. Numerical methods must be used to compute the magnetic field for several combinations of rotor positions and excitation current intensities. In that case, it is necessary to develop numerical techniques giving a better degree of precision to meet requirements of the electromagnetic quantities calculation.

In this paper, a numerical hybrid method coupling Boundary Integral Equation Method (BIEM) and Finite Element Method (FEM) is presented. The development of this two‐dimensional hybrid method is founded upon the nodal approximation of the magnetic vector potential. This nodal approximation exploits one‐ and two‐dimensional finite elements of Lagrange's family. The quadratic hybrid method coupling BIEM and FEM permits to take advantages of each of two numerical methods. The BIEM‐FEM method is used to calculate the magnetic flux distribution, magnetization curves, and torque in a 7.5 kW SRM prototype. It provides an accurate analysis of the magnetostatic field and gives precise values of the electromagnetic quantities.
Harmonic distortion in three‐phase inverters controlled by synchronous sigma‐delta‐modulation
Authors: Mertens A.
Published: July 2010

Several soft switching three‐phase inverters have been proposed in the literature, using a resonant AC or DC voltage link in order to reduce switching losses. This allows operation with higher switching frequencies. In these inverters, the switching instances have to be synchronized with the periodic zero crossings of the link voltage. Thus synchronous pulse modulation strategies like Sigma‐Delta‐Modulation have to be used for control. The benefit of high switching frequency has to be considered in the light of performance of the modulation scheme, which can be measured by determining the r.m.s. value of the distortion current. In this paper, this magnitude is calculated analytically for three‐phase inverters controlled by synchronous Sigma‐Delta Modulation. The derivation is based on the assumptions of constant link frequency and large ratio of link‐ to output frequency. The solutions allow to calculate the r.m.s. distortion current for any periodic shape of the link voltage including DC. Simulations show that the results hold for link‐ to output frequency ratios down to 100. The spectral performance of synchronous Sigma‐Delta‐Modulation is compared with conventional pulse width modulation.
Frequency domain analysis of brushless dc motor performance
Authors: Ackermann B. , Bolte E. , Howe D. , Jenkins M. K. , Zhu Z. Q.
Published: July 2010

The steady‐state performance of three‐phase brushless DC motors supplied from bipolar drive circuits is analysed using frequency domain techniques. The drive system model caters for arbitrary waveforms of the induced voltage, delta‐ and star‐connected windings, advanced and retarded commutation, the on‐time of each transistor within one cycle ranging from 120o to 180o (electrical degrees), transistor and diode voltage drops and an average switch resistance in the on‐state. Predictions from the analysis are compared with previously published results.
Some remarks to active and fictitious power in polyphase and single‐phase systems
Authors: Depenbrock M.
Published: July 2010

A generally applicable method to analyze the relations connecting currents, voltages, instantaneous‐, active‐, non‐active‐ and apparent power quantities is described. By introducing a special m‐conductor equivalent scheme a unified treatment of non‐sinusoidal, unbalanced polyphase systems is possible and a simple definition of unsymmetrical loads can be derived. It is explained why it is necessary to distinguish between the decomposition of quantities into components or into portions. The method includes other ones well known and approved in the past as more special cases.
An evaluation of the instantaneous calculation of load current components
Authors: Marshall D. A. , Venter F. P. , van Wyk J. D.
Published: July 2010

The development of theoretical techniques for the instantaneous calculation of load current components is evaluated. The associated instantaneous calculation of load power components is also evaluated since it is used in the calculation of the currents. The generation of these different power components with respect to compensation are pointed out. Further implementation of the instantaneous power theory is discussed. A three‐phase vector approach to the instantaneous calculation of power components is also discussed. Experimental results obtained by using the instantaneous power theory are illustrated.
Current compensation in three‐phase power systems
Authors: Willems J. L.
Published: July 2010

In this paper the compensation of reactive and unbalanced currents in three‐phase power systems is discussed. The main result proved is that in sinusoidal steady state any current which corresponds to zero total active power can be compensated by means of a reactive element; the compensation of the reactive currents and the compensation of the unbalanced currents in three‐phase power systems are special cases of this result. The explicit expression of the compensating reactances is derived and the multiplicity of the solutions is discussed. The result is illustrated on some examples.
Power factor improvement of three‐phase unbalanced loads with non‐sinusoidal supply voltage
Authors: Czarnecki L. S.
Published: July 2010

Three‐phase load asymmetry causes a useless current loading of the supply source and this loading increases even more if the supply voltage is non‐sinusoidal. This loading can be expressed quantitatively with the unbalanced current iuof RMS value ||iu||. A whole compensation of the unbalanced current iuwas proved to be possible with reactive balancing circuits, however, it may be very complex. This paper shows that a substantial minimization of the unbalanced current iumay be achieved with such a circuit, but of much lower complexity. The method suggested requires that the unbalanced admittances Anof the load for harmonic frequencies are known. A harmonic analysis that provides the complex RMS values of the phase voltages and currents harmonics in a cross‐section between the load and the source enables us to determine these admittances and design the balancing circuit. It was shown, moreover, that the reduction of the unbalanced current iucan be integrated with the reactive current irminimization.
A new method for reduction of current and voltage harmonic distortion in power systems
Authors: Mikolajuk K. , Tobola A.
Published: July 2010

The paper shows that it is possible to design such a switched 1 ‐port which ‐ excited by a sinusoidal voltage ‐draws desired current harmonics. The circuit switched twice within a period can generate odd current harmonics and the circuit switched once within a period generates even harmonics. This new kind of compensator has advantages of active filters such as good compensation characteristics. On the other hand it is easier to realize a large VA compensator based on the presented idea than to realize a high switching frequency static power compensator. Most established active and hybrid filters are based on a load current measurement. The compensator presented in the paper can be used to eliminate current distortion as well as voltage distortion. The two‐step optimization with the use of the harmonic voltage measurement allows to eliminate harmonic voltage. The results of numerical simulation and experimental results are presented.
Influence of the pulse‐width modulation control method on the performance of frequency inverter induction motor drives
Authors: Ch. Andresen E. , Haun A.
Published: July 2010

The methods of sinusoidal PWM voltage control, current hysteresis control, predictive current control and direct stator flux and torque control are briefly presented. The different operation principles are explained by block and structure diagrams. Their staiorflux and stator current trajectories are compared. The effect on the characteristic operational performance of induction squirrel cage motors is investigated. The harmonic losses of the stator and rotor winding and the torque oscillations are compared while considering the skin effect of the windings. Finally the torque response times are presented. The results are achieved by digital simulation and proved on a test stand with 22 kW induction motor and 30 kVA GTO frequency inverter.
Measures to raise brush life of modern DC machines
Authors: Binder A.
Published: July 2010

The maintenance periods of DC motors can be raised significantly if brush wear is reduced effectively. This is accomplished by improving commutation. The measures to reach this goal are: reducing the commutating inductance of the armature coils, minimizing dissymmetries of the magnetic circuit as well as the influence of the main flux on the compole flux, improving the mechanical performance of the commutators, using brushes which are insensitive to high brush current densities and avoiding harmful mechanical vibrations. By long‐time tests of several converter‐fed DC machines it is proved that brush life of typically 15000 h (at 1500 rpm) and rated current (up to 100 kW output power) may be realized nowadays as a standard.
Stabilizers enhancing the frequency regulation action of HVDC links supplying weak AC systems
Authors: Maris T. I. , Lygdis A. D. , Vovos N. A. , Giannakopoulos G. B.
Published: July 2010

Power System Stabilizers (PSS) superimposed to the basic control system of an HVDC link supplying a weak AC system, in order to enhance its frequency regulation action, are proposed. To decrease the AC voltage sensitivity at the inverter side, the basic control system of the HVDC link is proposed to operate with the rectifier under Minimum Ignition Angle (MIA) control and the inverter under Constant Current (CC) control. Inputs to the PSS are the frequency and the AC voltage deviations at the inverter side and their constant parameters are calculated using modal control technique. Detailed simulation results for a practical integrated AC/DC system are presented to evaluate the performance of the proposed control scheme.
The modern space‐phasor theory, Part II: Comparison with the generalized machine theory and the space‐vector theory
Authors: Serrano‐Iribarnegaray L.
Published: July 2010

It has been shown in the first part of this article that any transient state of a converted‐fed symmetrical machine can be represented in the Space‐Phasor Theory (SPhTh) by a very simple phasorial diagram. This second part discusses in detail why this is not possible in the Generalized Machine Theory (GMTh). It makes clear that the SPhTh and the GMTh are two complementary but different methods, based on the two existing “natural” approaches for analyzing electrical machines, according to the way in which the flux is split. Thereafter, relying on the comparison of both theories, other practical advantages which clearly support choosing the SPhTh are explained. The paper also includes a review of the Space‐Vector Theory by Kovacs and Racz which, in accordance with the work of other authors, is shown to be a modified version of the GMTh for the particular case of three‐phase machines.
Electric field calculation combined with a CAD system for the personal computer
Authors: Okubo H. , Maehara H. , Kato K. , Hikita M. , Kito Y.
Published: July 2010

A Personal‐Computer‐based CAD (PC‐CAD) system combined with the electric field analysis was developed and is referred to as “CADEF” (CAD system with Electric Field analysis). To construct such a system, both software and hardware need to be upgraded and the related conversion programs have to be developed. In the CADEF, the CAD drawings are fully utilized for the input data processing and the output expression of the electric field analysis. A Charge Simulation Method (CSM) is adopted as an analysis software. In the calculation process, singular points on the CSM such as the triple junctions are automatically recognized and processed. By introducing the expert knowledge and the experiential factors on the charge arrangements as the rules, the automatic calculation system is accomplished.