bluuebunny/crossref_metadata_2025 huggingface dataset:
Measuring system for fast transients monitoring in gas‐insulated substations
Authors: Osmokrovic P. , Petkovic D. , Markovic O. , Kartalovic N. , Vukic D.
Published: July 2010

In this paper the results of testing and calibration of measuring systems for very fast transients (VFT) in gas‐insulated substation (GIS) are presented. The general principles for the construction of measuring systems for recording and transmission of VFT are also discussed. The paper describes in detail the constructions of four measuring probe types adjusted for VFT monitoring in 123 kV SF6‐insulated substation. The primary construction requirement was the ability to monitor VFT in 123 kV SF6‐insulated substation containing frequencies 200 MHz without distortion in both frequency and voltage domains. For the purpose of the measuring system testing and calibration an experimental facility was developed based on the computer experimental modelling technique. The verified experimental facility was then used for testing and calibration of measuring probes type. During the test, various effects on the measuring system response quality were noted with respect to the applied constructional solutions, with different kinds of dielectric material used for the low‐voltage capacitor and different diameters of the sensor probe. The obtained results are explained and the possibilities of further improvement of SF6, VFT measuring system characteristics suggested.
Use of similarity relations in the analysis of lightning‐induced transient phenomena
Authors: Frentzel R.
Published: July 2010

The Similarity Theory is an applied scientific method employed in experimental analysis. Also in the analysis of lightning protection, the Similarity Theory can be an aid, e. g. in the conversion of test results from models to full scale. Some fundamentals of the Similarity Theory were, therefore, explained in this treatise and scale laws for transient phenomena during lightning developed. These laws allow, with proper application, the construction of experimental models in which phenomena similar to those occurring in the original are reproduced. The results can then be recalculated, using the scale factor for the physical quantity, into the original configuration.
Modular secondary voltage control based on local information
Authors: Gubina F. , Curk J.
Published: July 2010

A new concept of highly decentralized secondary voltage control is presented. The concept is based on secondary voltage controllers attached to each reactive power source. The secondary controllers utilize only local information available from measurements at the generating bus and they act completely autonomously. To successfully attain information on the electrically close load bus behaviour describing their voltage profile, a group of fuzzy sets is derived based on intrinsic load node properties and statistics of their voltage deviations. They are used in the fuzzy decision process to yield new reference setting for primary voltage controllers. The tests results of proposed modular secondary control are presented for standard and non‐standard networks. The efficacy of the new concept is demonstrated.
An interactive procedure for the coordination of decoupled var/volt control in radial distribution systems
Authors: Calovic M. S. , Saric A. T.
Published: July 2010

This paper deals with mutually connected problems of reactive power compensation and voltage control in radial distribution systems. The paper presents a simple iterative procedure for optimal coordination of actions of main means for reactive compensation (shunt capacitors) and voltage control (variable turn ratio transformers), within the decoupled solution of these two subproblems. The procedure is based on the static optimization, specified as a non‐linear programming‐type problem. The paper presents the derivation of a method for the solution of specified control problems and gives an illustrative application of this method on the test example of a one‐source radial distribution system, consisting of 53 nodes and 52 branches.
Flexible approach to dynamic simulation of voltage collapse phenomenon
Authors: Rajakovic N. , Tasic D.
Published: July 2010

This paper presents the dynamic simulation of voltage collapse phenomenon in a flexible manner concerning modelling complexity. In that respect a special attention has been paid to modelling aspects of induction motor as a representative of variety of loads. A complete mathematical model used in this paper for the study of dynamic behaviour of an induction motor consists of five differential equations. This set of equations is solved by using the Runge‐Kutta method. As a parallel model a simplified approach is considered (without differential equations) reduced to algebraic network equations and the equation of motion. The effect of transformers equipped with automatic under load tap changers is also simulated. The complete model is rigorous enough in order to calculate the precise voltage‐time and P‐U curves during the induction motor start‐up procedure, while the simplified model can be used for calculation of P‐U curves only. Results from this study can be used for real‐time system control actions and for induction motor relay settings.
Extended algorithm of a fuzzy‐set based power‐system stabilizer with genetic algorithm timing
Authors: Pedram M. M. , Seifi H.
Published: July 2010

The application of fuzzy logic controllers to improve power‐system damping behaviour has received some attention in the literature during the last few years. The paper presents an approach in which besides speed and its first derivative, the second derivative is applied to the Fuzzy‐set based power‐system stabilizer (PSS), so that a three‐dimensional space with improved behaviour is formed. The parameters are then optimized by the new searching technique, the genetic algorithm. Excellent digital simulation results are demonstrated for a single machine infinite bus‐bar system.
Experimental comparison of digital control strategies in a DC servo‐drive
Authors: Dallago E. , Sassone G.
Published: July 2010

In this paper, three fixed‐parameter algorithms are studied and applied to the speed control of a DC servo‐drive. They are Proportional Integrative (PI), Pole Placement (PP), and Generalized Minimum Variance (GMV). A comparison between these algorithms is made for small‐signal step response by simulation and by obtaining experimental results. The comparison, which involves changing of some of the most important system parameters, brings out advantages and drawbacks of each algorithm when it is applied to a non‐ideal system such as the servo‐drive considered.
Stator current control for high‐speed induction machines operated from inverters with lc‐output‐filter
Authors: Rapp H. , Haag J.
Published: July 2010

Operating modern high‐speed spindles directly from an inverter often leads to intolerable disadvantages. Equipping the inverter with an LC‐outputfilter avoids these disadvantages but, on the other hand, drastically increases the system's complexity. Particularly there is no method known yet that combines an operation of high‐speed spindles via LC‐filter with high‐quality motion control. In this paper a new robust method for stator current control is introduced, which makes field‐oriented motion control easily applicable to such a system.
Suppression of torsional oscillations using thyristor‐controlled conductance in parallel to series‐capacitor segment
Authors: Wang L.
Published: July 2010

This paper presents the analyzed results of a study on the application ofthyristor‐controlled conductance in parallel to one series‐capacitor segment for suppressing sub synchronous resonance (SSR) that occurs in a series‐compensated power system. The IEEE Second Benchmark Model, systems, which has one turbine‐generator set, is taken as a standard model for this study. In order to stabilize all SSR modes in the studied system, a unified approach based on modal control theory is proposed to design a damping controller which is a dynamic output feedback compensator using shaft speed deviation of the studied generator as a feedback signal. To demonstrate the effectiveness of the proposed control scheme, frequency‐domain approach based on eigenvalue analyses and time‐domain approach based on non‐linear model simulations are performed. The simulated results show that the proposed SSR damping scheme can effectively suppress torsional oscillations of the studied system.
A diagnostic system for live electrical joints in power transmission systems
Authors: Rogler R.‐D. , Löbl H. , Schmidt J.
Published: July 2010

The resistance of an electrical joint increases depending on load current and environment until the temperature of the joint reaches a critical level, i. e. hot spots occur. To avoid such failures the joints have to be diagnosed and, if necessary, maintained. A widely applied method to inspect electrical joints is to measure the temperature rise and to compare it with empirical limit temperature rises that are assigned to several decisions. Due to unconsidered parameters this method is not sensitive enough to allow a long‐term maintenance concept. To overcome this shortcoming, the resistance of the joint has to be determined from the measured temperature. All the processes of producing, transmitting and storing power are modelled by a thermal network in which the resistance is the only unknown quantity. It can be ascertained by comparing measured and calculated temperatures. The resistance is used to determine the residual life time which depends strongly on this momentary resistance of the joint and the further load current of the line. This method will be described in a following paper.
Fault‐current limiter as an effective mean to compensate voltage dips in distribution utilities
Authors: Quaia S. , Tosato F.
Published: July 2010

The paper deals with the topic of utility power quality improvement by short‐circuit current limitation. A novel double‐tuned medium‐voltage (MV) fault‐current limiter (FCL), whose operation shows several interesting characteristics, is analyzed and discussed in the paper. A special property of this kind of FCL is the capability to quickly change its configuration in case of short circuit by either a back‐to‐back thyristor switch or a ZnO varistor. The latter solution is very attractive since it allows a significant simplification in the limiter hardware, that, in such a case, does not require any power electronic component. The above solutions are studied and compared, also through relevant computer simulation.
Application of static phase shifters on the damping of common‐mode torsional oscillations
Authors: Wang L.
Published: July 2010

A study on the application of thyristor‐controlled static phase shifters (SPS) to stabilize the common‐mode torsional oscillations occurring in a series‐capacitor compensated power system is presented in this paper. The IEEE Second Benchmark Model, system‐2, which has two non‐identical turbine‐generator sets connected to an infinite bus through a series‐capacitor compensated transmission line, is employed to investigate whether the possible unstable subsynchronous resonance (SSR) modal interactions can be suppressed by the proposed damping scheme. The torsional interactions due to one of the torsional oscillating frequencies in one machine is nearly the same as the one in another machine. In order to effectively suppress the unstable torsional modes in the studied system, a systematic approach based on modal control theory is proposed and a set of static phase‐shifter controllers (SPSC) is designed. The effectiveness of the proposed damping scheme is demonstrated by means of frequency‐domain approach based on eigenvalue analyses and time‐domain approach based on non‐linear model simulations. The simulations results show that the static phase shifters and the designed controllers can be applied to suppress common‐mode torsional interactions.
Calculation of the lifetime of electrical busbar joints
Authors: Bergmann R. , Löbl H. , Bohme H. , Großmann S.
Published: July 2010

Electrical joints can be a weak points and with it endanger the reliability of electrical power‐transmission systems. On the example of Aluminium‐to‐Aluminium and Aluminium‐to‐Copper busbar joints is shown how one can get information about the principle ageing behaviour from long‐term test. Furthermore a possibility is presented to determine limiting values for the joint resistance and to calculate the lifetime of a joint depending on the construction, conductor material and loading.
Transient behaviour of optimum‐designed three‐phase squirrel‐cage induction motors
Authors: Faiz J. , Sharifian M. B. B.
Published: July 2010

This paper describes the transient behaviour of optimum‐designed three‐phase squirrel‐cage induction motors. These motors have been designed based upon three different objective functions. They are cost, efficiency and combination of efficiency‐cost functions. Transient performance of these optimum designs and an industrial motor are compared and a suitable design for a particular fault is then introduced. A symmetrical voltage disturbance, startup and a symmetrical three‐phase short circuit are three cases considered in this investigation.
Development of power‐factor correction circuit using zero‐current switching cuk converter
Authors: Lin B.‐R. , Huang T.‐S.
Published: July 2010

A new Cuk resonant high power‐factor single‐phase AC‐to‐DC converter for the power‐factor correction is proposed in this paper, which employs zero‐current switching (ZCS) technique. Merits of the proposed converter include unity power factor, less harmonic control content, zero switching loss, simpler control stage, higher power density and unidirectional power flow. Operation principle, design analysis, small‐signal models and conditions achieving zero switching loss for the proposed converter are described. Finally, some simulation and experimental results are discussed.
The behaviour of damper cages
Authors: Fritz W. , Hyrenbach M. , Schneckmann H.‐W.
Published: July 2010

The central point of the following treatise is the investigation of the reaction mechanism of the single bars and rings of a damper cage when it is hit by the normal component of an alternating field. The reacting field of the cage is calculated by Ampere's law. The bars and rings generate positive and negative field components which are superimposed to the total reacting field. The resulting flux in a mesh is an indicator for the damping effect. The validity of the theory will be proved by measurements at a damper model in a room with constant permeability.
Algorithms of phase and current comparison protection for transmission lines
Authors: Witek B.
Published: July 2010

The paper presents a concept of a high‐speed phase/current comparison protection (PCCP) based on the digital evaluation of the differences both in phase angle and instant values of the current waveforms measured at the protected line terminals. Signal processing algorithms immune to direct current and high‐frequency components, harmonics and current transformer saturation are described. The results of faults off‐line simulations for transmission system model with frequency‐dependent parameters estimated in time domain are used for the analysis of the PCCP schemes performance during in‐zone and out‐zone faults.
Thermal stressing of power semiconductors in pulse‐controlled inverters by output currents of low fundamental frequency
Authors: Gambach H.
Published: July 2010

The range of fluctuation of the junction temperature of power semiconductors in pulse‐controlled inverters rises constantly as the fundamental frequency of the inverter output current falls. As a result, the maximum value of the junction temperature lies with low fundamental frequencies considerably above the mean value that is decisive for high fundamental frequencies. This paper takes the example of a GTO (gate‐turn‐off) pulse‐controlled inverter to explain two processes for reducing the thermal stressing of the power semiconductors at low fundamental frequencies.
Steady‐state security prediction in presence of load uncertainty
Authors: Testa A. , Menniti D. , Picardi C. , Sorrentino N.
Published: July 2010

An important problem in the Electrical Power System operation is the steady‐state security prediction. In order to take into account the load uncertainty, in this paper the authors apply a Monte‐Carlo method together with an opportune Security Index to evaluate in a preventive manner the probability to fall in insecure operating state, by determining the security index probability density function. For this aim, in a previous paper proposed by the authors, it has been possible to take advantage of an Artificial Neural Network, trained to evaluate the Security Index probability density function in presence of the optimal economical dispatching of the generation powers for the load forecast. In the present paper, a more complex scenario is considered where the security analysis can suggest to the dispatcher to determine also non‐optimal economical operating conditions to improve security. So a new, more complex, organization of the Artificial Neural Network training stage, necessary in order to obtain increased generalization capacity in the production stage, has been considered. In the first part of the paper the used security index, the Monte‐Carlo simulation and the neural network structure with its learning algorithm utilized by the authors for the particular problem are briefly recalled. Finally, a numerical application on a simple electrical test system is shown pointing out very encouraging results.
About the concept of consumed life of electrical machine windings and its application
Authors: Busch R.
Published: July 2010

In order to economize on electrical energy and materials a higher load of electrical motors is necessary. In this way it is possible that the motors operate above their rated power. Consequently, the rated temperature of the winding is exceeded and, therefore, its lifetime is shortened. For the description of the winding aging process the consumed life is an appropriate quantity. The meaning of this quantity is explained and its application is demonstrated.
On the order reduction and stability analysis of large electric machines
Authors: Toumi A. , Kamoun M. B. A.
Published: July 2010

This paper deals with the model reduction of electric machines, in order to study their steady‐state stability. The modelling of these machines is described on the base of the state‐space representation. A state‐equation form has been established, which is valid for different kinds of electric machines. The reduction condition is formulated as a non‐linear Riccati equation. In a first step, this equation is resolved under the assumption of an infinite inertia. Under such condition, the popular damping and synchronizing torque approach has been expressed in terms of the reduced model parameters. In a second step, this study is generalized taking into account the inertia, by resolving iteratively the Riccati equation. Thus, the damping and synchronizing torques in terms of inertia have been established for the first time. In order to illustrate the above results, two examples concerning the synchronous and the doubly‐fed machines are treated.
An expert‐system based power‐system restoration procedure
Authors: Seifi H. , Sedighi A.
Published: July 2010

The expert‐system restoration procedure developed in this paper employs an algorithm in which by line switchings, the downloads are restored with regard to their priorities, while any line overloads and out‐of‐limit voltages are avoided. The solutions are presented to the user in an understandable way. Computer results on the IEEE‐14‐bus system are presented.
New approach to the calculation of electrical transients, part II: Applications
Authors: Bijl N. , Van Sluis L. Der
Published: July 2010

The calculation of electrical transients in power systems is important for insulation coordination. Most of the computer programs in current use are based on the nodal admittance method. This paper describes a computer program for the calculation of electrical transients based on a new approach which enables the use of more sophisticated numerical integration routines. The program can cope with linear network elements like resistors, capacitors, reactors, voltage and current sources and with non‐linear network elements like surge arresters and arc models. The descriptions of the models and their parameters are stored in libraries separate from the main program. The user can define his own models.
Electromagnetic transient simulation studies of sinusoidal PWM unified power‐flow controllers
Authors: Song Y. H. , Liu J. Y.
Published: July 2010

This paper is concerned with the digital studies of the sinusoidal pulse‐width modulation (SPWM) unified power‐flow controller (UPFC). At first the SPWM scheme generation and the main factors affecting the functions and the control of the UPFC are discussed. Secondly, how the series part and shunt part of the SPWM UPFC are controlled and coordinated is analyzed. The paper then places the emphasis on the detailed electromagnetic transient program (EMTP) simulation of SPWM UPFC. Simulation results of SPWM UPFC regulation performance and open‐loop control are presented. The simulator is further used to investigate the operating envelope and closed‐loop control. The digital EMTP‐based simulator of SPWM UPFC implemented in this paper provides a useful tool for further research. The information presented gives a deep insight into UPFC performance.
Currents and voltages induced during earth faults in a system consisting of a transmission line and a parellel pipeline
Authors: Satsios K. J. , Labridis D. P. , Dokopoulos P. S.
Published: July 2010

A numerical procedure employing thefinite‐element method (FEM) is used in conjunction with Faraday's law, in order to predict the current in a faulted transmission line as well as the induced voltages across points on a pipeline running parallel to the faulted line and remote earth. The problem is a two‐dimensional one, be‐ cause the phase‐to‐ground fault is assumed to be outside of the parallel exposure so that the conductive in‐ terference is negligible. Therefore a two‐dimensional finite‐element mesh has been solved, that leads to the field distribution andfinally to the induced voltages. The effectof the problem “operational parameters” (mitigation wires numbec earth resistivity and overhead transmission line geometrical configuration) has been taken into account. The results lead to conclusions that may be useful to power‐system engineers.
Transient temperature rise of cable crossings
Authors: Brakelmann H. , Sahin M.
Published: July 2010

This article presents a calculation method for the transient heating of power cables in crossing configuration. By the aid of this method the current ratings can be determined taking into account the longitudinal heat flux through the metallic construction elements of the cables as well as the transient conductor temperatures for different load situations. An example will elucidate the calculation method.
Critical analysis of the concepts of instantaneous power current and of active current
Authors: Willems J. L.
Published: July 2010

This note deals with the relationship between various definitions of instantaneous power currents. From a general framework the m‐phase and the (m + l)‐conductor approaches are derived, as well as the case of unequal conductor resistances. The relationship between instantaneous, sinusoidal and time‐varying situations is also discussed.
Formal approach to multi‐phase systems
Authors: Furga G. Superti
Published: July 2010

Some formal definitions and statements about multi‐phase systems, which the three‐phase systems are particular cases of, are discussed, n‐phase elements must have one or more ordered sets ofn electrical ports. Star connection and polygonal connection are special elements. General properties of decoupling linear transformations are discussed, to fully exploit the symmetrical structure of such systems.
Separate control of power‐factor components based on phase‐locked loop
Authors: Balcells J. , González D. , Lamich M. , Aldabas E.
Published: July 2010

The power factor (PF) of a supply system can be split up in two parts: The displacement factor, due to the quadrature component of the fundamental current and the distortion factor, mainly due to harmonics in the current wave. The separate compensation of both terms has important advantages, but the controller for such separate compensation needs powerful resources to get a suitable dynamic behaviour if a frequency‐domain approach is used. This paper describes a controller based on a new method for splitting up the current wave into its fundamental component and its harmonic residue. The method uses a time‐domain approach and simplifies the closed‐loop control of power factor while giving a suitable dynamic response.
Definition of power density as a general utilization factor of electrical machines
Authors: Gutt H.‐J. , Grüner A.
Published: July 2010

Derived from the objective of developing high‐density electrical machines of new type and proceeding from the Poynting vector, the power density is defined to determine the machines' main dimensions by introducing the so‐called flux coverage as a new universally valid quantity of magnetic stress. Because very often there does not exist a well‐defined rotor volume which the formerly used utilization factor (in Germany called “Esison‐number”) could refer to, e. g. in linear motors, disk rotor motors or machines using high‐power permanent magnet or high‐temperature superconducting magnet excitation, the power density implementing the flux coverage becomes not only useful but even necessary. On the contrary to the above‐mentioned utilization factor C the power density is referred to a power‐transmitting surface, in general within a space defined by the air‐gap area. From a mathematical point of view the flux coverage can be treated like the current coverage but having the additional advantage to be independent of the winding cooling. Therefore it is a more general quantity for the design process also of new unconventional machines.
Correspondence and difference between the FBD and czarnecki current‐decomposition methods for linear loads
Authors: le Roux W. , van Wyk J. D.
Published: July 2010

The currents in a three‐phase, three‐wire system with linear load impedances, i. e. no distortion generation in the load, are decomposed by the FBD‐ and Czarnecki methods to investigate the correspondence between the two methods. The different systems used are systems with balanced loads and systems with unbalanced loads with combinations of additional inductive loads and distorted voltages. The different current components of the methods are compared to each other for balanced and unbalanced conditions. It is concluded that good correspondence can only be established in the case of a balanced three‐phase system.
Evaluation of residual network distortion during compensation according to the “instantaneous power theory”
Authors: le Roux W. , van Wyk J. D.
Published: July 2010

A theoretical evaluation is done on a three‐phase three‐wire system to show the unwanted network influence when a dynamic filter is controlled according to the “instantaneous power theory”. The evaluation is also simulated on Mathcad for various network configurations and compared to known experiments. The quantities with unwanted frequencies introduced by the compensation increase with the complexity of the systems. It is concluded that the use of this power theory for control of dynamic filters is less desirable. Two examples of rectifier systems are also given to show that the results with compensation by the “instantaneous power theory” can in some systems be worse than in others, since its effectiveness is load‐type dependent.
On the energy approach to the theory of coupled inductors
Authors: Arturi C. M.
Published: July 2010

The paper presents a revisited energy approach to the theory of a set of n coupled inductors. The hybrid constitutive relations are analyzed. It is shown that the fundamental relation expressing the energy of the system requires a minimum number of coupling terms if a set of hybrid independent variables is adopted. The hybrid independent variables also allow to represent singular systems having zero magnetizing energy or zero leakage field energy, or both, and to give a rigorous definition of the ideal transformer. Exact equivalent networks of both two‐ and three‐winding transformers are presented.
Voltage profile optimization as influenced by power‐system configuration
Authors: Abdel‐Salam M. S. , El‐Sadek M. Z. , Ibrahim A. A. , Ahmed A.
Published: July 2010

This paper extends a linear‐programming optimization‐based method proposed before for reactive‐power scheduling using generator terminal voltages and reactive powers, transformer tap‐settings and switchable reactive power sources as control variables. The system configuration following contingencies is considered ‐for the first time ‐ as an additional control variable in the optimization‐method. It is proposed to use all of the possible modifications of system configuration by opening one or nvo lines simultaneously. For this to be accurately achieved, a technique was proposed for ranking the line outages, which is based on system losses obtained by AC and/or DC load‐flow studies. The ranking agreed satisfactorily with the voltage‐reactive power index used for contingency analysis in system security studies. Voltage stability is checked before and after optimum adjustment of the control variables and proved to be better after optimum adjustment.
Computation of power systems eigenvalues using the modified nodal approach
Authors: Oswald B. R.
Published: July 2010

This paper presents a new method of forming state‐space equations of large power systems which allows to calculate their eigenvalues. The method does not require any topological tools. It is based on the extended modified nodal approach, which was presented at the IPST '97 in Seattle. The extended modified nodal approach generates a set of algebraic and state‐space equations using Kirchhoff's nodal law exclusively. Eliminating the algebraic part of these equations results in the desired state‐space equations in an explicit form.
A new space‐vector transformation for four‐conductor systems
Authors: Ferrero A. , Giuliani L. , Willems J. L.
Published: July 2010

Linear transformations are often employed in the study of three‐phase systems, since they allow for simplifying the equations describing the system behaviour. Among them, the Fortescue, Clarke and Park transformations are very widely employed. In particular, the last one leads to the formulation of the Space‐Vector theory, that is currently employed in the fields of AC machine theory, power definitions and active filtering. The greatest limitation in the use of these transformations is that they are restricted to systems with only three conductors. However, four‐conductor systems are often present in the common practice of the electric systems and the application of the Space‐ Vector theory to such systems is not as straightforward as in the case of the three‐conductor systems: a zero‐sequence quantity must be considered separately. This paper proposes a linear transformation that extends the properties of the Space‐ Vector theory to four‐conductor systems, and includes the Park transformation as a special case. The mathematical derivation of this new transformation is reported, and its application is discussed by means of some examples.
Damping circuit design for ferroresonance in floating power systems
Authors: van Craenenbroeck T. , Van Dommelen D. , Janssens N.
Published: July 2010

Practical countermeasures to prevent the occurrence of ferroresonance in floating systems are compared. Most attention is paid to the design of practical damping circuits. Existing criteria to determine the necessary ohmic load are evaluated and a new mathematical tool based on harmonic balance is presented. As the damping resistor can cause thermal overload of the voltage transformers, the use of a non‐linear damping circuit is advocated in some cases. Therefore, the proposed calculation method is extended to include the effect of non‐linear damping.
Optimal capacitor placement incorporating voltage stability and system security
Authors: Arini M. El
Published: July 2010

The purpose of this paper is to derive a systematic procedure for reactive power control to decide the optimal location and size of compensation shunt capacitors so as to improve the system voltage profile. The proposed algorithm for locating the compensators is based on the sensitivities of the reactive power flow of system lines with respect to the reactive power injection at system buses where the reactive power of shunt compensation is considered as an important strategy in controlling voltage stability. After identifying the candidate buses, the problem is formulated as linear programming problem of the minimization of the possibility of voltage collapse and improving the system voltage profile by defining fewer equations and constraints, and saving computer storage and time. A test system is selected to verify the effectiveness and to confirm the accuracy of the proposed method. We therefore conclude that the practical application of this technique would enhance the security of a power system by reducing the risk of voltage collapse.
New converter‐fed power source to increase the dynamic performance of the three‐phase electric arc furnace
Authors: Wolf A. , Thamodharan M.
Published: July 2010

The conventional three‐phase electric arc furnaces frequently cause undesired distortions in the power system, which has a low short‐circuit capacity in the form of voltage fluctuations (flicker) at the point of common coupling. This is due to the fluctuating reactive power consumption of the furnace. This paper describes a electronic‐controlled furnace transformer which enables the reactive power consumed by the furnace to be kept constant. This is made possible if the conventional power system of the three‐phase electric arc furnace is supplemented with three‐phase power controllers and a booster transformer. By regulating the (reactive) power input, these disturbances can be reduced to a minimum. This new power source was experimentally tested on a single‐phase model and the results, which are presented, are very satisfactory.
Depression following open‐heart surgery: A path model involving interleukin‐6, spiritual struggle, and hope under preoperative distress
Authors: Ai Amy L. , Pargament Kenneth I. , Appel Hoa B. , Kronfol Ziad
Published: July 2010

Faith factors (i.e., factors pertaining to religion/spirituality) have been linked with well‐being and adequate coping. Few studies have investigated negative aspects of religious coping, such as spiritual struggle. Based on the multidisciplinary literature and on previous findings, the study's analysis estimated parallel psychophysiological pathways from preoperative distress to postoperative depression in patients undergoing open heart surgery. Plasma samples for interleukin(IL)‐6 were obtained before surgery. The results showed that a link between spiritual struggle and IL‐6 mediated the indirect effects of preoperative anxiety on postoperative depression. Avoidant coping also mediated the influence of anxiety on postoperative maladjustment. Further, hope played a protective mediating role to moderate the undesirable influences of the spiritual struggle–IL‐6 link and maladaptive coping on postoperative mental health attributes. © 2010 Wiley Periodicals, Inc. J Clin Psychol 66:1–19, 2010.
The chemical denaturation of groundnut protein and fibre formation
Authors: Naismith W. E. F.
Published: July 2010

Two types of denaturing agents, (a) urea, guanidine salts and related compounds and (b) amines, have been investigated with groundnut protein for fibre formation. The considerable rise in the viscosity increment of the protein on denaturation with urea and the hydrochloride and thiocyanate of guanidine, and with bases of dissociation constant higher than 10−4, has been interpreted in terms of increased asymmetry of the protein molecules, and only where such a rise was observed could solutions of the protein with the denaturant be prepared suitable for extrusion into fibre.
The chemistry of some complex zinc and cadmium chrome pigments
Authors: Cole H. G. , le Brocq L. F.
Published: July 2010

With the help of pH curves, conditions have been found for the formation of basic double chromates of general formula R2CrO43MCrO4,M(OH)2,2H2O, where R is Na, K or NH4 and M is Zn or Cd. No NaCd compound was encountered, and the NH,Zn compound was of a different type. The decomposition of these compounds by alkali and by copious leaching with hot and cold water (KZn and KCd only) into basic zinc and cadmium compounds has been studied. Cadmium chromate and the monoxychromates of zinc and cadmium have been prepared. The identity of each compound has been characterized by equation of formation, composition, X‐ray diffraction pattern and solubility. Many of these compounds are of commercial importance as paint pigments. The NaZn, KZn, KCd and NH,Cd compounds have been prepared.
A systematic assessment of dissolved oxygen supply in a 20‐litre culture vessel
Authors: Elsworth R. , Williams V. , Harris‐Smith R.
Published: July 2010

The factors influencing aeration are discussed and, using the sulphite oxidation method of measurement, the influence of impeller diameter and speed, air rate, and air pressure on the aeration efficiency of a 20‐litre culture vessel has been determined and the power consumed by the impeller measured. Conditions are given for obtaining sulphite oxidation rates of 200–250 millimoles of O2 per litre of medium per hour which can be increased to 500–600 millimoles by raising the operating gauge pressure from zero to 1·36 atm.
Polymers from oxacyclobutanes. I. Synthesis and general properties
Authors: Farthing A. C.
Published: July 2010

A wide range of substituted oxacyclobutanes have been polymerized to give novel products, of which the polymer from 3: 3‐bis(chloromethyl)oxacyclobutane was selected for further study. Monomer syntheses, polymerization kinetics and thermodynamics, and structure—property relationships are briefly reviewed.
On the anodic polarization behaviour of aluminium
Authors: Anderson P. J. , Hocking M. E.
Published: July 2010

The behaviour of aluminium during anodic polarization in electrolytes containing anodic inhibitors and chloride ion has been examined. The existence of a critical potential of film breakdown, above which pitting corrosion occurs, has been established. The dependence of this potential on electrolyte composition shows that the anodic reactions are largely determined by competitive adsorption of anions at the film‐solution interface. Possible mechanisms by which anion adsorption may determine the anodic reactions are discussed.
Oxygen transfer in laboratory fermentersxs
Authors: Solomons G. L.
Published: July 2010

Based on the oxygen‐transfer rate as measured by the sulphite oxidation method, and using fermenters of fixed design, a series of equations was derived which enables the required power, Reynolds number and stirrer speed to be calculated for a chosen oxygen‐transfer rate. The over‐all controlling process of oxygen transfer was shown to be a function of degree of turbulence/power per unit volume.
Development of a large‐scale distillation process for purifying crude sulphur dichloride. I. Laboratory scale investigations
Authors: Rosser R. J. , Whitt F. R.
Published: July 2010

The basic principles underlying a satisfactory laboratory‐scale distillation procedure, operating at atmospheric pressure, to separate pure sulphur dichloride from a mixture with other sulphur and chlorine compounds, are recorded. The novel use of anti‐catalytic additives, such as phosphorus chlorides, to suppress decomposition during distillation at atmospheric pressures and on storage, is described.
The corrosion of aluminium
Authors: Lorking K. F. , Mayne J. E. O.
Published: July 2010

The corrosion of aluminium at room temperature has been investigated in nine decinormal solutions over the pH range 2.0–12.0. Corrosion was dependent more on the nature of the anion than on the pH of the solution.

The solubilities of hydrated and anhydrous aluminium oxide were examined and it was concluded that, except in the presence of chloride ions, corrosion was associated with the initial rate of solution of the anhydrous oxide.

Potential and anodic polarisation measurements indicated that whereas the normal anodic reaction is the formation of anhydrous oxide, in the presence of chloride, bromide and iodide ions soluble aluminium salts are formed.

It is suggested that when aluminium, carrying its air‐formed film, is immersed in a solution in the presence of oxygen, the film breaks down and a small corrosion current commences to flow. In the absence of chlorides, and similar ions, film repair can take place and the behaviour of the aluminium is controlled by the relative rates of film repair and film breakdown. In the presence of chlorides film repair does not occur and once corrosion has been initiated by film breakdown it proceeds apace. If initiation is suppressed, by saturating the solution with aluminium oxide, corrosion is inhibited.
Factors determining the ‘water requirement’ of gypsum plaster
Authors: Ridge M. J.
Published: July 2010

An investigation has been made of the relationship between the ‘water requirement’ of gypsum plaster, the surface area of the plaster determined by gas adsorption and by permeability to air, and the bulk volume. The water requirement will undoubtedly depend upon the factors determining the surface area of the plaster, i.e. the particle size and shape, but the results show that other factors exert strong effects. The water requirement of hemihydrate prepared by still methods is shown to be considerably reduced by grinding in a mortar with a pestle, which increases the surface area. In contrast to its marked effects upon the rate of setting, recalcination does not affect the water requirement. There is a pronounced correlation between the water requirement and bulk volume. It appears that the factors that determine the bulk volume also play a large part in determining the water requirement. These factors involve the condition of the surface of the particles rather than their size and shape.
Raschig synthesis of hydrazine: The stability of chloramine in the reaction solution
Authors: Jeffreys G. V. , Wharton J. T.
Published: July 2010

The effect of temperature, ammonia, ethylenediaminetetra‐acetic acid (EDTA), hydrazine, ammonium chloride and caustic soda on the stability of chloramine has been studied in a small laboratory batch reactor. It has been found that all these substances accelerate the decomposition rate and would reduce the yield of hydrazine in the Raschig synthesis if they were present in excess during the initial stage of the reaction process.
The adsorption of benzene vapour from an air stream, by beds of charcoal: I. The most efficient physical arrangement of the bed
Authors: Jones W. M.
Published: July 2010

Air is often cleaned by passing contaminated air through a granular bed of an adsorbent such as charcoal. In such a situation the rate of flow of air is fixed and there is an upper limit to the physical size of the bed and an upper limit to the resistance of the bed to air‐flow through it. The problem considered is the optimum size of granule to be used in the bed and the optimum shape of the granule, leading to the longest life‐time of the bed. An empirical answer to the problem is given for the uptake of benzene by a BCNU steam‐activated charcoal; apparatus, experiments and results used are described. The method of working and the conclusion are applicable to any vapour/solid system.
Reactivity of lime and related oxides. XVI. Sintering of lime
Authors: Glasson D. R.
Published: July 2010

Calcium carbonate samples containing known amounts of additives and impurities have been calcined in air at a series of temperatures for different lengths of time. Changes in specific surface and average crystallite size show the effect of the additives and impurities (accessory minerals in limestones and chalks) on the lime sintering.

Salt and calcium sulphate each accelerate lime sintering at between 800° and 1100°. The presence of the chloride during the carbonate decomposition affects mainly the subsequent surface activity and sintering behaviour of the lime. Added phosphates have comparatively little influence on lime sintering at 800°, 900° or 1000°. When lime separates from the decomposition of carbonato‐apatites, the phosphate recrystallises to fluor‐apatite and sinters.

Ferric oxide progressively increases lime sintering at 800°, 900°, 1000° and 1100°. Like anhydrite, its low Tammann temperature (650°) readily permits ion diffusion into lime cracks and fissures, promoting sintering. Alumina, with a higher Tammann temperature (890°), appreciably enhances lime sintering only above 1100°. The comparatively low Tammann temperature of silica (730°) does not, however, lead to greatly increased lime sintering below 1100°, probably because of formation and separation of calcium silicates with higher Tammann temperatures similar to that of alumina.
Formation of acetylene in electron‐activated cracking of liquid hydrocarbons
Authors: Brooks J. D. , Hesp W. R. , Rigby D.
Published: July 2010

By cracking pure liquid hydrocarbons such as n‐heptane, cyclohexane and benzene by means of an anomalous glow discharge in a small bench‐scale apparatus at reduced pressure (15 torr) and at flow rates of 0.5–4.0 × 10−3gmole/min and power inputs of 100–450 watts, high degrees of total conversion (up to 85% on carbon basis) and acetylene formation (up to 50%) were secured. Optimum yields of acetylene were obtained at low flow rates and medium power inputs. The major competing reaction was found to be the secondary decomposition of acetylene into carbon and hydrogen, which became intensive at high specific power inputs.

In spite of the complexity of the reactions involved, the results showed a uniform correlation between acetylene yield and current flow. The extent of the reactions was affected by the presence of diluent gases, which had the effect of varying the concentration and energy content of the electrons in the discharge. With the benzene‐hydrogen system there was also a strong chemical effect. Thermodynamic calculations indicate that the reactions proceed in part through electron‐activation, which is characterised by the specific rate of acetylene formation related to a given number of charge carriers.

The possibility of practical applications of the results is examined.
Studies in transesterification V. Molecular sieve absorbents
Authors: Haken J. K.
Published: July 2010

An improved method for preparing methacrylate esters by transesterification makes use of molecular sieves to remove the alcohol of lower boiling point as it is formed. The procedure avoids the use of a large excess of reactant methacrylate or other entraining agent and the protracted collection of methanol or ethanol azeotropes. The reaction temperature and the reaction rate are thereby increased.
Reactivity of lime and related oxides. XIX. Production of strontium oxide
Authors: Glasson D. R. , Sheppard Margaret A.
Published: July 2010

Strontium oxide has been prepared by calcining the hydroxide and the carbonate at several temperatures up to 1200°.

Strontium hydroxide sinters considerably before decomposing above 500°. There is appreciable carbonation of the oxide products by atmospheric carbon dioxide at temperatures up to 800°.

Strontium carbonate decomposes at a reasonable yield at temperatures above 1000°. The oxide products can be activated by milling, but they sinter when subsequently calcined, especially at temperatures between 800° and 1000°. Crystallite and aggregate sizes of the strontium oxide produced from the carbonate at 1000°–1200° are similar to those of lime prepared under corresponding conditions.