Showing papers on "Electrical network published in 1992"

Voltage Stability Evaluation Using Modal Analysis

Abstract: The authors discuss the voltage stability analysis of large power systems by using a modal analysis technique. The method computes, using a steady-state system model, a specified number of the smallest eigenvalues and the associated eigenvectors of a reduced Jacobian matrix. The eigenvalues, each of which is associated with a mode of voltage/reactive power variation, provide a relative measure of proximity to voltage instability. The eigenvectors are used to describe the mode shape and to provide information about the network elements and generators which participate in each mode. A simultaneous iteration method, which is well suited to applications involving large power systems, is used for selective calculation of appropriate eigenvalues. Results obtained using a 3700 bus test system are presented illustrating the applicability of the approach. >

Circuit models for three-dimensional geometries including dielectrics

Abstract: The partial element equivalent circuit (PEEC) approach has proved useful for modeling many different electromagnetic problems. The technique can be viewed as an approach for the electrical circuit modeling for arbitrary 3-D geometries. Recently, the authors extended the method to include retardation with the rPEEC models. So far the dielectrics have been taken into account only in an approximate way. In this work, they generalize the technique to include arbitrary homogeneous dielectric regions. The new circuit models are applied in the frequency as well as the time domain. The time solution allows the modeling of VLSI systems which involve interconnects as well as nonlinear transistor circuits. >

Neural network for estimation of harmonic components in a power system

Abstract: The paper presents a novel approach to the estimation of harmonics in the power system. The proposed method uses the optimisation neural network theory and its implementation in an analogue form. As is proven in the paper, this formulation, and its practical implementation, leads to the correct solution of the problem in real time. The solution presented is inexpensive and suitable for use with the solid state compensating systems to improve the quality of delivered energy.

Analysis and design of a series voltage unbalance compensator based on a three-phase VSI operating with unbalanced switching functions

Abstract: Voltage unbalance in AC supply systems is typically corrected by means of a shunt connected thyristor-controlled static VAr compensator. This approach has the disadvantage of slow response, harmonic injection into the AC system, and the requirement for large passive components. The proposed system consists of a three-phase PWM voltage source inverter, connected in series with the line through a three-phase transformer. The unbalance compensation is achieved by canceling the negative sequence component of the line-to-line voltages of the source. It is also shown that by having the inverter operate with unbalanced switching functions, it is possible to balance the load voltage and to control the amplitude of the positive sequence component in order to perform load voltage regulation. A complete mathematical description of the method is presented, demonstrating that the compensation can be achieved with low kVA inverters and low harmonic injection. Implementation procedures, design equations, and a design example are also included in order to illustrate the proposed method. Experimental results of a 1.5 kVA laboratory prototype system confirm the feasibility of the technique. >

Apparatus for combining audio and visual indicia

Abstract: An electronic book comprising a plurality of leaves, each leaf comprising pages of printed material bound at one edge to form a spine, with electrical circuits formed in each leaf. A common electronic circuit such as a speech generator and/or controller cooperates with the electrical circuits on each of the various pages, connected to the electrical circuits in the leaves through conductive paths through the spine of the book. The electrical circuits in the leaves include electrical elements such as switches, and sensory output devices (e.g., thermochromic devices, light emitting diodes, thermo-olfactory devices, electrochromic devices, and the like). The electrical elements are associated with particular portions of the printed material so that the particular portions can be selectively highlighted or emphasized (e.g., designated by actuation of a visual or olfactory device and/or text read). A particularly advantageous switch structure formed integral to the page employing standard printing techniques, the bonding of LEDs directly into the printed circuit, and various advantageous methods of construction of the book are also disclosed.

A dynamic model for the electrical characteristics of fluorescent lamps

Abstract: A model for the electrical behavior of fluorescent lamps at standard line frequency (50 Hz or 60 Hz) and at high frequency (20 kHz-50 kHz). The model is based on the following three relationships: the lamp's V-I characteristic at high frequency; the lamp's DC V-I characteristic; and the dynamic relationship between these two modes of operation. The first two are readily measured using simple lab setups, and the third is assumed linear and first order. The model is empirical, and its parameters do not correlate with physical lamp characteristics such as lamp length, diameter, or gas pressure. Most aspects of lamp operation, including operation at high frequency, line frequency, and DC, have been successfully modeled. The model was used with a numerical circuit simulator to model fluorescent lamp operation in electrical circuits. >

A new approach for noise simulation in transient analysis

Abstract: A novel technique to simulate noise is presented. Simulation of noise, which is traditionally done in the AC analysis, is shown to be also possible in the transient analysis. The proposed technique has been implemented in the electrical simulator ELDO, which therefore becomes the first simulator able to compute noise regardless of the kind of analysis. The method includes noise sources in the time domain, and the spectrum characteristics of these sources are related to new noise models available whatever the bias conditions of the components. This new technique could be applied to all electrical circuits but its usefulness is shown especially for sensitive analog sampling circuits where the knowledge of their accuracy is of high importance. >

Calculation of the induced effects due to a lightning stroke

Abstract: A method for computing the effects of a direct lightning stroke on the protection system of an industrial building is presented. The proposed method is based on a 'circuit-approach'. The lightning protection system and the 'victim' circuits are simulated by means of an equivalent electrical network formed by resistances, inductances and capacitances, having all the branches coupled together. The lightning stroke is simulated by means of an ideal current source characterised by a pulse waveshape. Propagation phenomena are considered and the ionisation phenomena in the soil are taken into account by a nonlinear current-dependent electrical model, function of the electrode's shape and the ground resistivity. Two distinct points of impact of the lightning stroke to the protection system are considered. An analysis, in the frequency and in the time domain, of effects such as step voltages of EMF induced on power cables, coaxial cables, and loops is performed. >

Arrangement to correct the linear and nonlinear transfer behavior or electro-acoustical transducers

Abstract: This invention regards an arrangement to correct the linear and nonlinear transfer behavior of electro-acoustical transducers, consisting of an electro-acoustical transducer, a distortion-reduction network connected to its input terminals, and a support system to fit the distortion-reduction network to the transducer. The distortion-reduction network shows nonlinear transfer characteristics obtained from modelling the transducer and thus changes the electrical signal such that the nonlinear effects of the network compensate for the nonlinear behavior of connected transducer. The result is an overall system with reduced distortion and improved linear transfer behavior. A fitting technique and system is used to change the parameters of the electrical network automatically to fit the actual transfer characteristics of the distortion reduction system to the transducer. Several mechanisms, unique to each transducer, are responsible for generation of nonlinear distortion.

Design model for electrical distribution systems considering renewable, conventional and energy storage units

Abstract: A new model to solve the design problem of integrated electrical distribution systems is presented, considering special modelling for the load, different sources — conventional, renewable and energy storage — as well as connection lines. The resulting formulation is a linear programming problem, which is solved by a standard optimisation package. The advantages of this ‘distributional approach’ to the design problem of integrated distribution systems can be clearly seen from the results of the case study. The model determines the optimal size and site of all types of power supply units and connection lines. The same model can also be easily extended for the solution of the distribution expansion planning problem, when the planning period is divided into multiple subsequent stages.

Finite element simulation of electrical motors fed by current inverters

Abstract: A method of examining electric machines coupled to static converters represented by a finite-element and a circuit type model is presented. This technique, based on a step-by-step process with respect to time for the simultaneous solution of the electrical circuit and electromagnetic field equations, is used for the working analysis of two permanent-magnet motors fed by a load commutated current inverter. The calculation and experimental results are compared in order to validate the proposed method. >

Simulating the dynamic electro-thermal behavior of power electronic circuits and systems

Abstract: A methodology is presented for simulating the dynamic electrothermal behavior of power electronic circuits and systems. In the approach described, the simulator simultaneously solves for the temperature distribution within the semiconductor devices, packages, and heat sinks (thermal network) along with the currents and voltages within the electrical network. The thermal network is then coupled to the electrical network through the electrothermal models for the semiconductor devices. >

Review of the design and performance features of HVDC systems connected to low short circuit ratio AC systems

Abstract: The design and performance features of ten high-voltage DC systems are discussed. All of these systems were connected to AC systems that were relatively weak compared to the rating of the DC system. Six of these systems were back-to-back, two were overhead lines, and two were undersea cable connections. AC and DC system interaction problems and how they are addressed in the design and specification of each of these systems are described. >

Modeling the circulation with three-terminal electrical networks containing special nonlinear capacitors

Abstract: Development, first of analog and later of digital computers, as well as algorithms for analysis of electrical circuits, stimulated the use of electrical circuits for modeling the circulation. The networks used as building blocks for electrical models can provide accurate representation of the hydrodynamic equations relating the inflow and outflow of individual segments of the circulation. These networks, however, can contain connections in which voltages and currents have no analogues in the circulation. Problems arise because (a) electrical current must flow in closed loops, whereas no such constraints exist for hydraulic models; and (b) electrical capacitors have a number of characteristics that are not analogous to those of hydraulic compliant chambers. Disregarding these differences can lead to erroneous results and misinterpretation of phenomena. To ensure against these errors, we introduce an imaginary electrical element, the nonlinear residual-charge capacitor (NRCC), with characteristics equivalent to those of a compliant chamber. If one uses appropriate circuit connections and incorporates the residual-charge capacitor, then all voltages and currents in the model are proper analogues of pressures and flows in the circulation. It is shown that the capacitive current represents the rate of change of volume of blood inside the vessel, as well as the rate of the corresponding displacement of volume of the surrounding tissue.

New model for single-unit representation of induction motor loads, including skin effect, for power-system transient stability studies

Abstract: The paper investigates the dynamic representation of a group of induction motors by one or more equivalent motors for power system transient stability studies. Considering the fact that large induction motors constitute a large proportion of the total system load, and that the skin-effect has a very strong effect on the performance of these machines, this effect is therefore included in the model. To enable the skin effect (deep bar effect) to be included, the stator and the rotor windings leakage reactances are separated and the core losses are ignored; and the equivalent machine is represented by seven electrical parameters instead of the conventional five parameters. A clear procedure is described on how to obtain the unknown electrical and the mechanical parameters of the equivalent machine. An efficient grouping (homogeneity) criteria is proposed to obtain subgroups in the case of a diversified group of induction machines connected to the same bus and a power system subjected to disturbances of various types. The accuracy of the equivalent model is verified by simulating its response to different types of disturbances and comparing the results with the sum of the responses of the individual machines. Excellent agreement is obtained between the response of the model and the sum of the responses of the individual machines.

Comparison of test circuits for high-voltage circuit breakers by numerical calculations with arc models

Abstract: The authors use a physical arc model to compare the switching behaviors of circuit breakers in a direct and two synthetic test circuits with a computer program. It was found that not only the shape of the transient recovery voltage, but also the topology of the electrical network that supplies the transient recovery voltage after current interruption is of importance in terms of the interrupting capability of SF/sub 6/ and air-blast circuit breakers. >

Conjugate gradient method in computer-aided circuit design

Abstract: The present invention relates to an improved method for computer-aided electrical circuit simulation which combines circuit partitioning, modified nodal formulation and conjugate-gradient solution method to efficiently analyze large electrical circuit networks. Circuit partitioning is used to create sub-circuits which isolate the passive elements of the electrical circuit. Modified nodal formulation is used to formulate matrices representative of the resultant sub-circuits. All matrices resulting from the sub-circuits containing only passive elements will be positive-definite symmetric and are efficiently solved using conjugate gradient method. Conjugate-gradient method is known to be an extremely efficient method for solving matrices of this type.

Capability chart for electrical power systems

Abstract: An extension of the concept of the load supplying capability of an electrical power system is proposed, which involves drawing a capability chart. The method for obtaining such a chart is based on an optimisation model, which is repeatedly solved to obtain the points for the chart. The uncertainties which affect the nodal load forecasts are taken into account. The application of the method to a test system is described. The chart is drawn for different system configurations as is required in planning studies that aim at obtaining the maximum power which can be effectively supplied to the loads.

Incorporation of a DC-link in a composite system adequacy assessment-DC system modelling

Abstract: Direct current (DC) links are finding increasing use throughout the world in the form of long-distance transmission and asynchronous interconnections. System reliability studies of a composite generation and transmission system containing a DC link involve modelling and evaluation of the reliability of the DC transmission line and performance of an overall composite system study with the DC link forming an integral part. The paper illustrates a technique for DC system reliability analysis using the contingency enumeration approach. A key element in this system reliability analysis is the creation of the reliability diagram from the single line diagram. A digital computer program was developed to evaluate the probability of failure, frequency of failure, and the mean duration of the possible performance levels for a DC link. The procedure and program were tested on a model DC system, and the results are presented to illustrate a proposed technique.

A method for reducing transient torsional stresses of turbine-generator shaft segments

Abstract: The author presents a method for reducing transient torsional stresses of steam turbine-generators in series-capacitor-compensated power systems, which are equipped with ZnO varistor schemes. The fundamental concept is to reduce the coupling between the electrical network and the shaft system with respect to the troublesome torsional frequency. The electrical network and the rotating shaft system are coupled through the generator air-gap torque. This coupling can be attenuated by unbalancing the network with respect to the phenomenon of torsional oscillations. This is achieved by setting the protective voltage levels of the three phases of a three-phase series capacitor at unequal values. The technical feasibility of the proposed method is demonstrated on a test system, using the BPA Electromagnetic Transients Program (EMTP) as the study tool. The impact of the proposed countermeasure on the transient torques of the system, as a result of different disturbances, is demonstrated. The limitations of the proposed method are discussed. >

A modular approach to the design of neural networks for fault diagnosis in power systems

Abstract: A modular approach to the design of neural networks for fault diagnosis in electrical networks of real size is described. Modularization is strictly based on functional criteria, rather than the usual topological criteria. This approach allows elimination of the problems inherent in this kind of application, which are large amounts of information to be processed, a high degree of uncertainty in the data, changes in the topological features, and sources of uncertainty. The most important characteristics of the model are the simplicity of the modules, the replicability of the training results, easy adaptation to topological changes, and high scalability. It allows for parallel implementation. A portion of a real distribution electrical network has been simulated. >

Fuse-programming circuit

Abstract: A fuse programming circuit having reduced energy consumption is coupled between a first potential and a second potential for providing a programmable voltage level at an output node. The electrical circuit has a fuse element having a first terminal coupled to the output node and a second terminal coupled to the first potential. The electrical circuit also has means for providing a path for passing electrical charge between the second potential and the output node, which the path between the second potential and the output node has substantially infinite resistance when the electrical charge is being transferred.

Thermodynamic and stochastic theory of electrical circuits.

Abstract: We begin the development of a thermodynamic and stochastic theory of electrical circuits approaching nonequilibrium stationary states containing linear or nonlinear capacitors, resistors, and inductors We restrict ourselves to circuits with only point attractors The theory centers around a function {phi}, and we show that: (1) it is the macroscopic driving force to a stationary state, (2) it is a global Liapunov function, (3) it provides necessary and sufficient conditions for the existence and stability of stationary states, (4) its time derivative is a component of the total dissipation, (5) it is an excess work of moving the circuit away from the stationary state, and (6) it determines a stationary probability distribution of a Fokker-Planck equation The generalization from linear to nonlinear circuits is made with the concept of an instantaneous mapping from the nonlinear circuit to a thermodynamically and kinetically equivalent linear circuit A translation of chemical to electrical networks holds at the thermodynamic but not stochastic level of description

Incorporation of a DC-link in a composite system adequacy assessment-composite system analysis

Abstract: The paper illustrates a procedure for adequacy evaluation of a composite generation and transmission system containing a direct current (DC) link. The transportation model option of the composite reliability (COMREL) program, developed at the University of Saskatchewan, is used to evaluate the composite system adequacy indices. The IEEE Reliability Test System (RTS) is augmented by adding a DC link and is used as the test system. The composite system load point and the overall system indices are calculated to quantify the adequacy of the composite system. The basic COMREL program was modified to accept a remote generation source connected to a composite system through a DC link. The analysis involves the construction of a generating capacity model at the remote bus and the movement of each generating capacity state through the DC line contingency state, without violating the carrying capability of the transmission line state or the generator state capability restriction. This type of analysis can be used to evaluate the benefits associated with design changes and capital expenditures in the DC facility. The paper presents the techniques employed for the composite system study and the results obtained for the modified RTS.

A theoretical approach to the question of biological effects of low frequency fields

Abstract: A human body in the vicinity of an overhead cable is subject to two kinds of electrical effects, inductive and capacitive, which together are responsible for tiny currents. Recent concerns about possible biological effects of such currents have made their accurate computation necessary. The author address the mathematical modeling that has to precede such computations. By an asymptotic analysis of the full set of Maxwell's equations (displacement currents not neglected), which takes into account the smallness of the electrical permittivity and the large penetration depth, the author arrives at a standard conduction problem, to which both kinds of effect contribute source terms: inductive effects give a right-hand side, and capacitive effects give a nonhomogeneous boundary condition. Numerical results are displayed. >

Fast measurement of real and reactive power in three-phase circuits

Abstract: A review of the well known two-wattmeter method for measuring real power is given, emphasising its advantages in responding immediately to changes in real power flows and eliminating the double-frequency term. The usual technique for determining reactive power is described, showing the presence of a DC term plus the troublesome double-frequency term. Theory is developed for determining reactive power flow that eliminates the double-frequency term and produces an instantly responding DC term only. Five measurement techniques are shown to be possible, three of which are of practical value. Whereas two of the five methods require a neutral connection for voltage measurement, the methods selected for practical realisation require line voltages only. The applicability of the chosen techniques to include the two-wattmeter method of real power measurement is described. An optimal choice of the techniques is suggested, based on minimal use of electronic components and longevity of calibration. A series of experimental results comparing the various techniques of fast reactive power measurement is presented, confirming the theory and showing some practical limitations to elimination of the double-frequency term.

Two-circuit power supply for vehicles

Abstract: A two-circuit power supply circuit for vehicles is proposed, in particular for vehicles having a two-circuit electrical brake system. The circuit contains a starter battery (1) and a supplementary battery (2) which each supply an electrical circuit. The two batteries (1, 2) can be charged by a rotary current generator (5) with power diodes (12) and exciter diodes (13). The charging of the supplementary battery (2) takes place via a line (14) running from the exciter diodes (13). Connected upstream of the supplementary battery there is also a monitoring module (11) which contains a charge current limiter, a charge monitor and a time delay element.