Showing papers on "Electrical network published in 1987"

Real-time modeling of power networks

Abstract: The use of large digital computers in control centers has made it possible to track the changing conditions in the power system with a mathematical model in the computer. This real-time model can be used to assess the security of the present system as well as to check out possible control strategies. In this paper the various steps in constructing the model from the real-time measurements are described. These steps include the determination of the network topology, the estimation of the network state, and the approximate modeling of the unobservable (external) network. This paper also discusses the checks for observability and bad measurements, and the calculation of bus load forecast factors and generator penalty factors.

Hardware modeling system and method for simulating portions of electrical circuits

Abstract: A hardware modeling system 10 simulates portions of electrical circuits 16, 18 utilizing actual hardware components in the simulation. Access to these hardware modeling elements 16, 18 is provided on a shared basis to plural workstations 14. Simulation vectors for plural users may be stored discontiguously in a first memory 26 and a single user's vectors are transferred to a second memory 28 for streaming to the elements 16, 18. An optional timing analyzer and memory circuit 34 periodically samples outputs from pins of the hardware modeling elements to provide timing information on the response of such elements. High impedance testing and bus contention detection is performed on the pins of the hardware modeling elements. Clocking signals applied to the hardware modeling elements are adjustable and may be set at extremely high frequencies. A special gating circuit 292 accesses each pin of the hardware modeling elements and incorporates one or more of the above features.

Aggregation of Induction Motors for Transient Stability Load Modeling

Abstract: An investigation of several methods for aggregating induction motors is described. The accuracy of the methods is compared using frequency-domain techniques. A new method involving the use of one or two aggregate motors is described and shown to be superior to other methods.

Transient Stability Simulation by Waveform Relaxation Methods

Abstract: In this paper, a new methodology for power system dynamic response calculations is presented. The technique known as the waveform relaxation has been extensively used in transient analysis of VLSI circuits and it can take advantage of new architectures in computer systems such as parallel processors. The application in this paper is limited to swing equations of a large power system. Computational results are presented.

Disorder-Induced Nonlinear Conductivity

Abstract: We consider an electrical network of resistors in two dimensions. Each resistor has a threshold value for the potential drop below which it becomes an insulator. If the thresholds are randomly distributed, the current flowing through the total network is not proportional to the external voltage. A new nonlinear relation between current and voltage appears.

Optimal Reactive Power Allocation

Abstract: A systematic procedure is developed to locate reactive power devices in a power system based on a set of indices, that are based on overall system conditions. After identifying the desired locations, the cost of installation and number of reactive power devices, subject to any required practical and real economic constraints, are minimized. Existing controllers are fully utilized before adding any new devices. Linearized sensitivity relationships of power systems are used to obtain an objective function for minimizing the cost of installation. The constraints include the limits on dependent variables (reactive powers of the generators, load bus voltages) and control variables (generator voltages, tap positions, switchable reactive power sources). A parametric linear programming technique based on active set analysis is proposed to solve the reactive power allocation problem.

Simplified Feeder Modeling for Loadflow Calculations

Abstract: Three models of a distribution system are developed in this paper. Included are descriptions of simulation models of the diverse components of a typical distribution system. The three system models are illustrated by examples. They are applied to an actual feeder and the results are analyzed to show the advantages and disadvantages of each model. A unique method is developed for combining the discrete distributed load voltage drop solution with the discrete distributed load losses solution. The development of this combined method is in the form of a tutorial , as are the developments of the components of this method. The conclusion is reached that it is possible to reduce many complex feeders to simple models in the study of feeder voltage profiles and losses with negligible error.

Probabilistic Modeling of Power System Harmonics

Abstract: A generalized procedure to obtain the probabilistic model of power system harmonic current injection and propagation is presented. The model takes into account random variations of both the operating modes as well as the configuration of nonlinear loads connected to a distribution feeder. The method is illustrated by an example of a bus having linear as well as nonlinear loads of different types. Potential applications of the model are also discussed.

Efficient Newton-Raphson algorithm for load-flow calculation in transmission and distribution networks

Abstract: An efficient algorithm is presented for load-flow solutions in electrical power systems. The algorithm is based on the Newton-Raphson process and uses a partitioned-matrix approach to the Jacobian equation which was previously suggested for array-processor applications. It is shown that this approach is also beneficial when using conventional computer systems. The numerical method and computation techniques employed are described, and their relationship to modern computer architectures is considered. The algorithm is highly efficient for the solution of transmission networks but also has particular advantages for lower-voltage networks, and for difficult or ill conditioned load-flow problems. Computational results, obtained using minicomputer hardware, are given for a variety of networks of up to 734 nodes. The numerical method which has been developed is also applicable to other power-system problems including state estimation and dynamic simulation.

Overload protection for D.C. circuits

Abstract: Protection for D.C. electrical circuit branches against incipient overloads comprises the use of semiconductor devices known as intelligent switches. An intelligent switch comprises a main controlled conduction path whose conductivity is controlled by an external control input. The semiconductor architecture is configured to possess internal self-protection for the main controlled conduction path against incipient current and/or temperature rises exceeding the device's rating by rendering the main controlled conduction path non-conductive when such incipient conditions are sensed. The invention, recognizing that this internal self-protection attribute can be used also to provide protection for external circuit components connected to the switch in the branch, further comprises the elimination of external protective devices from the branch such that the intelligent switch itself provides the entire overload protection within the branch. The invention is especially beneficial in automotive electrical application, imparting improvements to particular specific circuits of automotive electrical systems.

Transients in Low-Voltage Supply Networks

Abstract: For nearly 28000 transients, appearing at 40 measuring places during a total measuring time of about 3400 h on low-voltage supply networks in industrial and nonindustrial areas, time-domain parameters were determined. Of about one-third of the transient disturbances, a Fourier transform yielded frequency-domain data. After a description of the automated measuring system (AMS), results of measurements are presented. A statistical evaluation of several time-and frequency-domain transient parameters proved to be possible. In additional analyses, parameters are derived which are of interest in electro-magnetic-disturbance calculations and conducted-susceptibility tests.

A Simplified Two-Terminal HVDC Model and Its Use in Direct Transient Stability Assessment

Abstract: The use of the Transient Energy Function (TEF) method in transient stability analysis is extended to include an ac/dc system with a two terminal HVDC. A simple, yet accurate, dc model which is valid for first swing transient stability studies is developed and tested. The model used includes the steady-state converter model with the static dc line representation, the fast changing dc power, and voltage dependent current order limit (VDCOL); while the dynamics of the dc internal controls are neglected. With this model, the dc operation mode is determined by an inference method, and the corresponding dc variables are computed. Using the simplified dc model, the Transient Energy Function is modified to include the effect of the two terminal HVDC. A procedure for first swing transient stability assessment of an ac/dc system is proposed and is tested on a 20-generator test system. Transient stability assessment with the new method is presented and compared with results obtained with the EPRI transient stability program.

Comparison of steady-state and dynamic models for the calculation of AC/DC system harmonics

Abstract: The steady-state and dynamic simulation models currently proposed for the derivation of AC/DC system waveforms are described. Their application to the prediction of harmonic distortion is compared with reference to accuracy, general applicability and computational efficiency. It is concluded that generally the use of an iterative steady-state algorithm provides the most accurate and efficient solution. However, such an algorithm often presents convergence problems and in such cases dynamic simulation provides the necessary back up to obtain a solution.

Ozonator power supply employing a current source inverter

Abstract: A versatile current source inverter power supply for an ozonator in which a gating control circuit controls the gating of a thyristor bridge inverter power supply in a manner in which the output current to the ozonator is controlled and regulated. The current source inverter power supply circuit includes a DC/AC thyristor bridge inverter circuit coupled at its input terminals to a direct current power source and at its output terminals to an electrical network which includes the capacitative ozonator load. The thyristor bridge inverter includes a first pair of thyristors and diodes coupled to conduct current in a first direction through the electrical network, and a second pair of thyristors and diodes coupled to conduct current in a second, opposite direction through the electrical network. The electrical network includes a step up high voltage transformer, with its primary winding coupled to the thyristor bridge inverter and its secondary winding coupled to the ozonator load. First and second commutating capacitors are connected across the first and second pairs of thyristors for commutating off the thyristors. An adjustable current pulse amplitude conrol circuit is provided for controlling the amplitude of current pulses supplied through the thyristor bridge to the ozonator load.

A Simulation Study of Intracranial Pressure Increment Using an Electrical Circuit Model of Cerebral Circulation

Abstract: An electrical circuit model of the cerebral circulation is presented. Changes of pulsatile waves of the intracranial pressure (ICP) and the cerebral blood volume (CBV) with ICP increment were investigated by simulation of the cerebral blood flow using this model. The simulation is performed by a small signal approximation using the pulsatile component. The results obtained are able to explain the phenomenon of changes in pulsatile wave of ICP with ICP increment. With regard to the CBV, the modeling results are useful for application to rheoencephalography (REG) using electrical impedance method for noninvasive ICP monitoring.

Real-time power system simulation

Abstract: This paper describes the theoretical basis and application of a simulation package for electrical generation, transmission and distribution systems. The software provides an environment for the development and testing of online analysis and control algorithms, and also has potential for application in operator training. Dynamic and algebraic models of power system elements are described which are appropriate for study time scales of up to one day. Numerical techniques are presented which obtain solutions with acceptable accuracy in real time for medium sized networks using minicomputer hardware. Typical results are given for a test network of 30 substations which illustrate the dynamic behaviour of the network under emergency conditions.

Graphics Aided Interactive Analysis of Radial Distribution Networks

Abstract: This paper presents an interactive graphics package for distribution system analysis. The radial operation of the distribution networks is exploited in order to effect a fast and accurate calculation of the power flows, the voltage drops and the power losses at the various segments of a feeder for a given set of typical load curves. The algorithms developed are based on an efficient method to store the network topology and can easily accommodate changes in the infeeding nodes and variations in the network structure due to switching operations. The interactive environment allows the user to obtain the results of his studies against the one-line diagram of the network and effect changes in it in basically diagrammatic terms. The package requires very modest computer resources and provides planning and operating engineers with a powerful tool to conduct analytical distribution system studies with ease and flexibility.

Design of Optimal Modulation Controllers for Multiarea AC/DC Systems Using Eigenvalue Sensitivities

Abstract: This paper develops a new technique for the design of optimal modulation controllers for multi-area ac/dc systems. The technique is based on optimal pole assignment using eigenvalue sensitivities. The basic feature of the proposed method is that both the diagonal and the off-diagonal elements of the weighting matrices are used for the eigenvalue assignment which results in increased design flexibility. The method is applied to the design of a modulation controller for a strongly interconnected three area ac/dc system. Dynamic simulation results presented in the paper show that the proposed modulation controller results in significant improvement of dynamic performance of the interconnected system.

Posture-correcting devices

Abstract: Improvements in posture-correcting devices include a switch, wherein the switch has one contact mounted on an elastic length of material connected to a strap and the other contact connected to an inelastic pad. In addition, the improvements include readily detachable electrical circuits so that a circuit incorporating a particular type of signalling device can be selected for use.

Circuit with memory for detecting intermittent changes in resistance, current, voltage, continuity, power interruption, light, and temperature

Abstract: Electrical circuits for detecting intermittent and continuous electrical parameters such as continuity for open or closed circuits, AC power interruption or decrease in frequency, DC power interruption, missing electrical pulses; and voltage, resistance, and current levels that are greater than or less than present high and low limits. This invention also detects temperature and light (illumination) that is greater or less than present limits. The invention has a memory and both a (variable time delayed) automatic, and a manual memory reset. It provides both visual and a defeatable audio indicators or alarms. The advantage of said invention is that it detects intermittent conditions as brief as fractions of microseconds that may occur as frequently as milliseconds apart or as infrequently as days apart; it also detects steady state conditions. The invention is embodied as individual circuits capable of detecting a single parameter or as a multi-function test circuit having the capability to detecting numerous parameters. This invention is well suited to be packaged as a hand-held test instrument or as "built in" special test or monitoring circuit.

Electromechanical lamp switching

Abstract: An electromechanical switching device connects and disconnects a second lamp means from a first circuit powering a first lamp means upon alternate powerings of the first circuit. A mechanical device switches the switching means and an electrical circuit across the first circuit has a relay to control the mechanical device.

DC System Resonance Analysis

Abstract: DC filters and dc smoothing reactors are primarily designed to meet performance requirements with regard to telephone interference levels and commutation failure frequency. Other factors, however, place constraints on the size of the dc filter capacitance and the smoothing reactor inductance. The principal constraint is the avoidance of resonance conditions on the dc side at a low order harmonic of the commutating voltage. This paper discusses the factors which must be considered when analyzing dc side resonance. Specific considerations for the Intermountain Power Project are given.

Voltage-Distortion Compensation in Electrical Plants Supplying Static Power Converters

Abstract: Voltage distortion compensation is a problem that must often be tackled in electrical plants supplying nonlinear loads, such as static power converters, both to ensure reliable behavior of apparatus sensible to harmonics and to comply with standard limits. Analysis of the compensation system constituted by harmonic filters and protection reactance is carried out, to clarify their contribution to voltage distortion factor improvement and fundamental project criteria. To this end a study of the current commutation transient, cause of voltage notches and, hence, of voltage distortion, is performed in the presence of filters, and the distortion factor is calculated by means of two separate methods. Comparison between these methods, based on voltage notches and harmonic voltage drop, respectively, and determination of the expressions for estimating the overlap angle after filter insertion allow the influence of filters on the line and the converter to be analyzed.

Computation, Measurement and Mitigation of Neutral-to-Earth Potentials on Electrical Distribution Systems

Abstract: This paper presents computer generated profiles of primary-neutral-to-earth potentials of electrical distribution systems which incorporate a variety of techniques used to mitigate neutral-to-earth potential ("stray voltage") at dairy farm facilities. Techniques available to the power supplier and power user include an Electronic Grounding System which provides voltage reduction factors of as much as 200 to 1. A new method of measuring these voltages using a computer data acquisition system which monitors every cycle of the power-frequency voltages on eight totally independent channels for extended periods is described.

Theoretical analysis of the electrical aspects of the basic electro-impulse problem in aircraft de-icing applications

Abstract: A method of modelling a system consisting of a cylindrical coil with its axis perpendicular to a metal plate of finite thickness, and a simple electrical circuit for producing a transient current in the coil, is discussed in the context of using such a system for de-icing aircraft surfaces. A transmission line model of the coil and metal plate is developed as the heart of the system model. It is shown that this transmission model is central to calculation of the coil impedance, the coil current, the magnetic fields established on the surfaces of the metal plate, and the resultant total force between the coil and the plate. FORTRAN algorithms were developed for numerical calculation of each of these quantities, and the algorithms were applied to an experimental prototype system in which these quantities had been measured. Good agreement is seen to exist between the predicted and measured results.

Efficient pole-assignment method for designing stabilisers in multimachine power systems

Abstract: An efficient pole-assignment method for designing power-system stabilisers in multimachine systems is proposed. The method fully exploits the structure of linearised power-system equations and, as a result, the amount of computations required is reduced considerably. The effectiveness of the method is demonstrated using a numerical example.