Showing papers on "Power-flow study published in 1995"
TL;DR: In this article, an evolutionary programming (EP) method was applied to optimal reactive power dispatch and voltage control for large-scale power systems, and the proposed method has been evaluated on the IEEE 30-bus system.
Abstract: This paper is concerned with application of evolutionary programming (EP) to optimal reactive power dispatch and voltage control of power systems. Practical implementation of the EP for global optimization problems of large-scale power systems has been considered. The proposed EP method has been evaluated on the IEEE 30-bus system. Simulation results, compared with those obtained using a conventional gradient-based optimization method, are presented to show the potential of application of the proposed method to power system economical operations. >
340 citations
TL;DR: A novel formulation of the network reconfiguration to achieve loss minimization and load balancing is given and well justified power flow and loss reduction formulae in terms of the on/off status of network switches are proposed for efficient system updating.
Abstract: Real-time applications demand fast computation, and this paper proposes an efficient algorithm for real-time network reconfiguration on large unbalanced distribution networks. A novel formulation of the network reconfiguration to achieve loss minimization and load balancing is given. To reduce computational requirements for the solution algorithm, well justified power flow and loss reduction formulae in terms of the on/off status of network switches are proposed for efficient system updating. The algorithm relies only on a few full power flow studies based on system states attained by explicit expressions using backward-forward sweeps for efficient computation of power system states at the critical system operating points. The solution algorithm runs in an amount of time linearly proportional to the number of tie switches and the number of sectionalizing switches in the system. The solution algorithm has been implemented into a software package and tested on unbalanced distribution systems including a system with 292 buses, 76 laterals, 7 transformers, 45 switches and 255 line sections under diverse system conditions.
117 citations
TL;DR: In this paper, a new approach for real-time short circuit analysis of radial and weakly meshed distribution networks is proposed, which works based on a well documented radial power flow study method, and uses a hybrid compensation method to account for loops, PV nodes, and fault currents simultaneously.
Abstract: This paper addresses a new approach for real-time short circuit analysis of radial and weakly meshed distribution networks. The approach works based on a well documented radial power flow study method, and uses a hybrid compensation method to account for loops, PV nodes, and fault currents simultaneously. The three-phase short circuit analysis, in its actual a-b-c phase representation, can be applied to balanced or unbalanced distribution systems. A distribution short circuit program which is developed based on this approach, is integrated with a three-phase power flow program to solve various types of single or simultaneous faults, including single-line to ground, three-line to ground, double-line to ground, line-to-line, and double three-line to ground faults. Results of the application of this approach to large-scale distribution networks are also reported in this paper.
115 citations
TL;DR: In this article, the authors proposed a two-stage process to find a suboptimal solution by analyzing the mesh distribution system in which all open switches are simulated to be closed and a radial distribution system is determined as an intermediate solution.
Abstract: Feeder reconfiguration for use by distribution management systems is discussed in this paper. Multiple objectives are proposed to reflect realistic operating environments while achieving all benefits from feeder reconfiguration. The multiple objectives considered are minimization of power losses, load balancing among supply transformers, minimization of the worst voltage drop, minimization of service interruption frequency, and balanced service of important customers for enhanced service reliability. The objective function containing five different objectives are optimized subject to capacity and protection device constraints. The overall solution approach is a two-stage process. In the first stage, a suboptimal solution is found by analyzing the mesh distribution system in which all open switches are simulated to be closed. Applying special power flow analyses to this mesh network, a radial distribution system is determined as an intermediate solution. In the second stage, this solution is continuously improved by the branch exchange scheme. Special topology models are also developed to accelerate the search procedure. Use of the algorithm is illustrated by numerical examples.
98 citations
01 Aug 1995
TL;DR: The application of this technique for a comprehensive instruction-level power analysis of a commercial 32-bit RISC-based embedded microcontroller and the salient results of the analysis and the basic instruction- level power model are described.
Abstract: A new approach for power analysis of microprocessors has recently been proposed (Tiwari et al 1994). The idea is to look at the power consumption in a microprocessor from the point of view of the actual software executing on the processor. The basic component of this approach is a measurement based, instruction-level power analysis technique. The technique allows for the development of an instruction-level power model for the given processor, which can be used to evaluate software in terms of the power consumption, and for exploring the optimization of software for lower power. This paper describes the application of this technique for a comprehensive instruction-level power analysis of a commercial 32-bit RISC-based embedded microcontroller. The salient results of the analysis and the basic instruction-level power model are described. Interesting observations and insights based on the results are also presented. Such an instruction-level power analysis can provide cues as to what optimizations in the micro-architecture design of the processor would lead to the most effective power savings in actual software applications. Wherever the results indicate such optimizations, they have been discussed. Furthermore, ideas for low power software design, as suggested by the results, are described in this paper as well.
73 citations
TL;DR: In this article, a /spl mu/ synthesis based control design methodology is presented to deal with the parametric uncertainties in power system modeling and the design process involves a nominal power system model with uncertainty descriptions which represent the parameter perturbation of synchronous generator around its nominal operating point.
Abstract: Linear control design system stabilizers (PSSs) require the nominal power system model to be formulated as a linear time invariant system. Power system operating conditions vary with system configurations and loading conditions and coefficients in nominal system model change in a complex manner. A /spl mu/ synthesis based control design methodology is presented in this paper to deal with the parametric uncertainties in power system modeling. The design process involves a nominal power system model with uncertainty descriptions which represent the parameter perturbation of synchronous generator around its nominal operating point The proposed excitation controller enables the power system to be stable over a wide range of power system operating conditions. Simulation results both in the frequency domain and in time domain are presented. >
68 citations
TL;DR: In this paper, a value-based automated transmission system planning model is presented and the impact of various network representations on the results of the model is discussed, where the authors use the generalized Benders decomposition algorithm with "importance sampling" used to solve the problem enables the model to estimate certain average information about scenarios or contingencies by examining only a very small fraction of all the scenarios and contingencies.
Abstract: A value-based automated transmission system planning model is presented in this paper and the impact of the various network representations on the results of the model is discussed. Value-based integrated resource planning provides a "societal cost" (utility operation and investment costs plus customer outage costs) minimizing composite generation-transmission system expansion plan. The model trades-off and compares the costs and benefits of alternative generation and transmission resources using a consistent economic and engineering criterion in order to determine an "optimal" resource expansion plan. The generalized Benders decomposition algorithm with "importance sampling" used to solve the problem enables the model to estimate certain average information about scenarios or contingencies by examining only a very small fraction of all the scenarios or contingencies. The impacts of system resources upon both real and reactive power can be analyzed when using the AC power flow equations. It is concluded that for transmission system planning where reactive power flows and voltage constraints are important, it is imperative that an AC power flow model be used. The combination of AC power flow and linearized power flow models, with linearization about the solution of the AC power flow model, was found to be a promising compromise between accuracy and computation time.
45 citations
TL;DR: In this paper, the sensitivity factor method is applied to the reactive power/voltage dispatch problem and combines it with the fast Newton-Raphson economic dispatch to solve the optimal power flow problem.
Abstract: This paper applies the sensitivity factor method to the reactive power/voltage dispatch problem and combines it with the fast Newton-Raphson economic dispatch to solve the optimal power flow problem. The advantage of this method is that it is fast and reliable. Firstly, the real power generalized generation shift distribution (GGSD) factors are used in economic dispatch to find the real power generation for every unit so that the fuel cost is minimum. During the process of solving the economic dispatch problem, the voltage magnitudes of load buses in a power system may be changed and may exceed the ranges of secure values. Therefore, reactive power sensitivity factors of bus voltage magnitudes are used to regulate the voltage magnitudes of load buses to the secure ranges. The process is repeated to find the optimal generation with all voltages staying within the secure ranges. Results show that the algorithm converges very fast. >
44 citations
01 Jan 1995
TL;DR: In this article, the BCU method for direct stability analysis of electric power systems is used to model electric machines using integral manifolds and a parallel solution of linear equations by overlapping epsilon decompositions.
Abstract: Bifurcation-theoretic issues in the control of voltage collapse.- Reduced-order modeling of electric machines using integral manifolds.- The BCU method for direct stability analysis of electric power systems: theory and applications.- New algorithms for slow coherency aggregation of large power systems.- Computational complexity results in parametric robust stability analysis with power systems applications.- Damping and resonance in a high power switching circuit.- Dynamic analysis of voltage collapse in power systems.- Exact convergence of a parallel textured algorithm for constrained economic dispatch control problems.- Variable structure regulation of power plant drum level.- Analysis of mechanisms of voltage instability in electric power systems.- Structural stability in power systems.- Power system load modeling.- Parallel solutions of linear equations by overlapping epsilon decompositions.- Insects, fish and computer-based super-agents.- Application of real-time phasor measurements in power system control.- On the dynamics of differential-algebraic systems such as the balanced large electric power system.- Robust stabilization of controls in power systems.
44 citations
Patent•
06 Sep 1995
TL;DR: In this article, a switch-mode circuit is employed which, in a first mode, transfers power from AC main to a constant voltage DC bus and in a second mode, power generated on the DC bus is fed back to the main power supply.
Abstract: A unity power factor power supply for an electric motor. A switch-mode circuit is employed which, in a first mode, transfers power from AC main to a constant voltage DC bus. In a second mode, power generated on the DC bus is fed back to the main power supply. The circuit of the invention automatically maintains the DC bus voltage constant and sets an adequate operation mode by processing the DC bus voltage signal. In both operation modes, the unity power factor and sinusoidal waveform of the AC main side are maintained.
41 citations
TL;DR: In this paper, the application of a fuzzy optimization technique to optimal power flow calculations has been presented, and the developed method has been tested on a large-scale power system and the results show that this method is promising for handling uncertain constraints in practical power systems.
Patent•
02 Jun 1995
TL;DR: In this paper, a power conservation system for use in a computer system has been proposed, which has an activity mointor and a plurality of modes of operation, and the power mode of operation in response to the activity of the computer system is controlled.
Abstract: A power conservation system for use in a computer system. The power conservation system has an activity mointor and a plurality of modes of operation. By controlling the power mode of operation in response to the activity of the computer system, the power consumption of the computer system is controlled. Coupling of circuit power and clock signals are used to control power consumption and both hardware and software components may separately or together monitor and control operation.
TL;DR: In this paper, an alternative formulation of the AC-DC load flow problem is presented, which shows that neglecting the converter transformer reactance results not only in reduced accuracy but also in less confidence in the validity of the solution.
29 Nov 1995
TL;DR: The unified power flow controller is used as a phase shifter and/or series compensator to regulate both angles and magnitude of branch voltages and EP, coupled with PQ power flow, selects the best regulation to minimize the real power loss and keep the power flows in their secure limits.
Abstract: This paper presents the use of an evolutionary programming (EP) to solve optimal power flow (OPF) problems in flexible AC transmission systems (FACTS). The unified power flow controller (UPFC) is used as a phase shifter and/or series compensator to regulate both angles and magnitude of branch voltages. EP, coupled with PQ power flow, selects the best regulation to minimize the real power loss and keep the power flows in their secure limits.
05 Apr 1995
TL;DR: The recent introduction of an accurate and flexible real-time digital simulator has made it possible to perform this study, and many others like it, in a new, more efficient manner.
Abstract: This paper reports on a recently completed evaluation study in which physical High Voltage Direct Cur-. rent (HVDC) controls were interconnected to the Real-. Time Digital Simulator (RTDS”). The sltudy was performed jointly by RTDS Technologies Inc. of Winnipeg, Canada and ABB Power Systems AB of Ludvika, Sweden,, In the past such a study could only have been performed us-. ing an analogue HVDC simulator. The recent introduction1 of an accurate and flexible real-time digital simulator has however made it possible to perform this study, rand many others like it, in a new, more efficient manner.
TL;DR: In this paper, a static frequency converter (SFC) is used to support the transition from synchronous condenser operation to turbine/governor operation in pumped-storage power plants.
Abstract: Most pumped-storage power plants have the capability to operate as synchronous condensers. As such, they can be brought online very quickly to support power system load requirements. However, one of the effects of making a rapid transition from synchronous condenser operation to turbine/governor operation is an initial reverse power flow into the machine. This reverse power flow can be very undesirable at a time when the power system is calling for load support. On weak or isolated power systems, this reverse power flow can lead to objectionable voltage and frequency dips in the power system. With the proper utilization of a static frequency converter (SFC) and its associated controls and auxiliary switchgear systems, the reverse power flow resulting from a transition from synchronous condenser operation can be eliminated. This paper describe a method by which an SFC system can be used to make this rapid load response in pumped-storage power plants without incurring a reverse power flow and to provide additional instantaneous short term power to support the grid.
05 Sep 1995
TL;DR: This paper presents a summary of algorithms that have proposed for pricing reactive power based on marginal cost pricing implemented using a modification of the optimal power flow algorithms and shows that the cost of reactive power transport is as equally significant as active power for maximum economic efficiency.
Abstract: For decades, power factor penalties have been used in providing reactive power pricing. Low power factor implies more current is flowing in the network than should be ideally with unity power factor. The extra current flow means the conduction losses in the wiring and transformers are higher than would be with higher power factor for a given load. With recent investigations, it has been shown that the practice of power factor penalties is unable to provide accurate price signals to customers. This paper presents a summary of algorithms that have proposed for pricing reactive power. The rates are based on marginal cost pricing implemented using a modification of the optimal power flow algorithms. The algorithms applied show that the cost of reactive power transport is as equally significant as active power for maximum economic efficiency.
TL;DR: The results strongly indicate that the proposed method outperforms the extended Ward method in producing equivalent models for security control and does not create an additional burden in maintaining and updating the EMS database.
Abstract: Traditional external network modeling techniques have been widely used in the power industry to produce equivalent models that are suitable for power flow analysis and security assessment applications. These techniques cannot be used to produce models for optimal power flow applications. In this paper, we present a new methodology that is suitable for security analysis and security control. The proposed method has been tested extensively under a wide variety of operating conditions using data from a large scale system. The results strongly indicate that the proposed method outperforms the extended Ward method in producing equivalent models for security control and does not create an additional burden in maintaining and updating the EMS database. >
TL;DR: In this paper, the authors proposed a method to eliminate AC harmonic currents by injecting equal-but-opposite harmonic compensating currents, which is applicable to any type of load considered a harmonic source.
Abstract: This article proposes a method to eliminate AC harmonic currents by injecting equal-but-opposite harmonic compensating currents. This method is applicable to any type of load considered a harmonic source. This article describes a system involving a hardware interface, a PC, and advanced software to measure, analyze, and report the condition of harmonics on the power system. This system is used to generate all the necessary harmonic currents for compensation. Digital simulation and experimental results from a single and three phase AC/DC converters are shown to verify the effectiveness of this technique. >
16 Oct 1995
TL;DR: In this paper, a comparative analysis of buck-boost power converters in continuous conduction and discontinuous conduction mode is presented, in order to study their performance in terms of power factor, total harmonic distortion, efficiency, semiconductor stress, volume, etc.
Abstract: AC/DC power converters are extensively used in various applications. The electronics equipment uses, as its input stage, a rectifier with a capacitor as a filter. A major problem associated with these loads are the harmonic currents injected into the power supply and low power factor. Therefore, it is highly desirable to include power factor correction schemes in such electronics equipment. A boost power converter in continuous conduction mode using the multiplier approach is commonly used as a power factor correction topology due to its excellent performance in the medium power range. Recently, power factor correction topologies derived from buck-boost power converters have been proposed, mainly because they emulate a natural resistor when operating in the discontinuous conduction mode, using a single control loop. Topologies derived from buck-boost power converters are an attractive solution in power factor correction applications in the relatively low power range. This paper presents a comparative analysis between boost power converters, in the continuous conduction mode, and Sepic and Cuk power converters, in the discontinuous conduction mode, in order to study their performance in terms of power factor, total harmonic distortion, efficiency, semiconductor stress, volume, etc.
05 Apr 1995
TL;DR: A new fuilly digital real-time transients siimulator which runs on a standard, multipurpose parallel computer, the Digital Transient Network Analyzer (DTNA), which can test a variety of equipment: protective relays, controllers, as n ~ l l ,as FAC'1'S and HVDC prototypes.
Abstract: The need for testing power system equipment (e.g. protective relays and controllers) is well kno\
to the industry. These tests are required for testing both the equipment itself and its interaction with the power system. Different solutions have been developed over the years to perform these itests, from off-real time numerical simulation to real time analog and hybrid laboratories. Onlly recently, fully digital, real-time simulators have been developed, capable of representing electromagnetic transients. We present in this paper a new fuilly digital real-time transients siimulator which runs on a standard, multipurpose parallel computer. With a time step of 50 / /s, the Digital Transient Network Analyzer (DTNA) can test a itle variety of equipment: protective relays, controllers, as n ~ l l ,as FAC'1'S and HVDC prototypes. The first prototype of the DTNA is scheduled at the end of 1095 and will model a power system of some 10 generators and 50 busses. KeywordsPower S y s teni sim u la t ion, Rea I 'li ni e I> i g i t a I 'I" A, Test of equipment, pairallel computer.
01 Jan 1995
TL;DR: The IEEE Press Power System Stability: Volumes I, 11, 111, and 111, by Edward Wilson Kimbark as discussed by the authors, is a classic reissue of the IEEE Power Systems Engineering Series.
Abstract: Power System Stability: Volumes I, 11, and 111, by Edward Wilson Kimbark. An IEEE Press Classic Reissue in the IEEE Press Power Systems Engineering Series, Paul M. Anderson, Series Editor (previously published by John Wiley & Sons, Inc.). IEEE Press: 445 Hoes Lane, Piscataway, NJ 08855-1331, (908) 5623967. Softcover in slipcased 3-vol. set, 1008 pages. IEEE Order No. PP5600, ISBN 0-7803-1 135-3.
21 Nov 1995
TL;DR: In this paper, a new method which applies a genetic algorithm to determine which sectionalizing switch to operate in order to solve the distribution system loss minimization reconfiguration problem is presented.
Abstract: Network reconfiguration in distribution systems is realized by changing the status of sectionalizing switches, and is usually done for loss reduction or for load balancing in the power system. This paper presents a new method which applies a genetic algorithm to determine which sectionalizing switch to operate in order to solve the distribution system loss minimization reconfiguration problem. In addition, the proposed method introduces a new limited life feature for performing natural selection of individuals. Simulations are carried out in order to verify the effectiveness of the proposed method. These results show that the proposed method is effective in dealing with the problems of homogeneity and genetic drift associated with the population in the initial state.
TL;DR: In this paper, a geographic information management system (GIS) is applied to perform the automated mapping and facility management (AM/FM) of power distribution systems for contingency load transfer.
Abstract: A geographic information management system (GIS) is applied to perform the automated mapping and facility management (AM/FM) of power distribution systems for contingency load transfer. Three phase load flow analysis is used to calculate the current flows of line switches by retrieving the network topology and facility attributes which have been stored in the AM/FM database. The current flows solved are then stored in the database as the attributes of line switches for load transfer analysis. When a system contingency such as a fault or overload occurs, the load transfer is then executed to find the switches to be operated by the heuristic search method while subjected to the system operation rules. By the proposed method, the network topology can be easily updated and displayed in the computers by the connectivity trace routine according to the switching operations. Since all the system facilities are stored in the AM/FM database according to the actual spatial coordinates, it provides practical information for the system operators and crews to allocate and operate the switches easily. To demonstrate the effectiveness of the integrated AM/FM system with application programs for distribution operation, a distribution system of Taiwan Power Company (Taipower) in Kaohsiung downtown area is selected for case study. It is found that contingency load transfer for distribution system operation can be enhanced significantly with the application of AM/FM systems to determine the switches to be operated and the corresponding spatial locations of the switches. >
15 May 1995
TL;DR: In this paper, a technique for studying the adequacy performance of a small area (area of interest) in a power network in which the remaining network is modeled as an adequacy equivalent is presented.
Abstract: This paper presents a technique for studying the adequacy performance of a small area (area of interest) in a power network in which the remaining network is modeled as an adequacy equivalent. This approach can be very useful for adequacy evaluation of a large practical power system, as it is sometimes necessary to perform detailed adequacy analysis of selected relatively small regions in the network. It is particularly useful when sensitivity analysis is to be conducted in the area of interest or in conducting adequacy studies of interconnected areas where one area can be replaced by an equivalent, thus reducing the size of the overall system.
Patent•
20 Dec 1995TL;DR: In this paper, a power system is stabilized and power swings are suppressed, by controlling a semiconductor switch used in a stabilizing apparatus which is provided at the power system in an applying manner adequately corresponding to its operation characteristics and function.
Abstract: In a power system wherein a plurality of power plants, load systems and power transmission components are connected to each other for increasing the power transmission capacity of the power system, the power system is stabilized and power swings are suppressed, by controlling a semiconductor switch used in a power system stabilizing apparatus which is provided at the power system in an applying manner adequately corresponding to its operation characteristics and function, in accordance with a stabilizing command signal generated by using state values (for example, voltage, current, power, frequency, phase angle) of the power system, detected by detecting circuits provided in the power system.
TL;DR: In this article, the implications of FACTS technologies for the security and reliability of the AC transmission system and discusses how the new systems fits into the existing systems for control of the power system as a whole.
TL;DR: In this article, the authors present a concept of system margin for evaluation of adequacy of a composite power system, which can be a useful index for planning a desirable power system and an efficient methodology to calculate maximum supplying capability is introduced.
Abstract: This paper presents a concept of system margin for evaluation of adequacy of a composite power system. It can be a useful index for planning a desirable power system. An efficient methodology to calculate maximum supplying capability is introduced. It uses DC load flow analysis and linear programming to obtain a solution which is approximate but accurate enough for first stage planning studies. The proposed method can evaluate the power system margin under various constraints which consist of power flow, frequency in case of system separation, synchronous stability and voltage stability. The validity and effectiveness of the developed methodology is confirmed through the simulation of a model system.
01 Nov 1995