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Showing papers on "Power-flow study published in 1991"


Journal ArticleDOI
TL;DR: This approach is oriented toward applications in three phase distribution system operational analysis rather than planning analysis, and the solution method is the optimally ordered triangular factorization Y/sub BUS/ method (implicit Z/ sub BUS/ Gauss method) which has very good convergence characteristics on distribution problems.
Abstract: This approach is oriented toward applications in three phase distribution system operational analysis rather than planning analysis. The solution method is the optimally ordered triangular factorization Y/sub BUS/ method (implicit Z/sub BUS/ Gauss method) which not only takes advantage of the sparsity of system equations but also has very good convergence characteristics on distribution problems. Detailed component models are needed for all system components in the simulation. Utilizing the phase frame representation for all network elements, a program called Generalized Distribution Analysis Systems, with a number of features and capabilities not found in existing packages, has been developed for large-scale distribution system simulations. The system being analyzed can be balanced or unbalanced and can be a radial, network, or mixed-type distribution system. Furthermore, because the individual phase representation is employed for both system and component models, the system can comprise single, double, and three-phase systems simultaneously. >

492 citations


Journal ArticleDOI
TL;DR: Object-oriented programming techniques makes it possible to use interval arithmetic with minimal modifications to existing software, but to reduce the conservatism inherent in all interval arithmetic computations, an iterative method is used to obtain the hull of the solution set.
Abstract: Power flow analysis is the fundamental tool for the study of power systems. The data for this problem are subject to uncertainty. Interval arithmetic is used to solve the power flow problem. Interval arithmetic takes into consideration the uncertainty of the nodal information, and is able to provide strict bounds for the solutions to the problem: all possible solutions are included within the bounds given by interval arithmetic. Results are compared with those obtainable by Monte Carlo simulations and by the use of stochastic power flows. Object-oriented programming techniques makes it possible to use interval arithmetic with minimal modifications to existing software. However, to reduce the conservatism inherent in all interval arithmetic computations, an iterative method is used to obtain the hull of the solution set. >

269 citations


Book
01 Aug 1991
TL;DR: DC Power Transmission Technology Thyristor Valve Analysis of HVDC Converters Converter andHVDC System Control Converter Faults and Protection Smoothing Reactor and DC Line Reactive Power Control Harmonics and Filters Multiterminal DC Systems Component Models for the Analysis of AC/DC Systems Power Flow Analysis.
Abstract: DC Power Transmission Technology Thyristor Valve Analysis of HVDC Converters Converter and HVDC System Control Converter Faults and Protection Smoothing Reactor and DC Line Reactive Power Control Harmonics and Filters Multiterminal DC Systems Component Models for the Analysis of AC/DC Systems Power Flow Analysis in AC/DC Systems Transient Stability Analysis Dynamic Stability and Power Modulation Harmonic and Torsional Interactions Simulation of HVDC Systems Digital Dynamic Simulation of Converters and DC Systems Appendix Index.

207 citations


Journal ArticleDOI
TL;DR: In this paper, a comparison of various methods applied to feeder reconfiguration for loss minimization is presented, and it is shown that linear programming, in the form of transportation algorithms, is not suitable for real-time application to feeders, whereas heuristic approaches, although not optimal, can provide substantial savings if properly formulated and are suited for realtime implementation.
Abstract: The authors present a comparison of various methods applied to feeder reconfiguration for loss minimization. A new linear programming method using transportation techniques and a new heuristic search method are proposed for comparison with a previously developed heuristic technique which was based on an optimal load flow analysis. The methods are compared on simulations of both a small feeder distribution system, and a larger system based on a model of a public utility commission 44 kV distribution system. This study indicates that linear programming, in the form of transportation algorithms, is not suitable for real-time application to feeder reconfiguration, whereas heuristic approaches, although not optimal, can provide substantial savings if properly formulated and are suitable for real-time implementation. >

197 citations


Patent
24 Jun 1991
TL;DR: In this article, a power supply for a computer system manager is described, where the power supply has its own secondary power source operable when input power to the system manager no longer meets preset threshold values.
Abstract: A power supply for a computer system manager, wherein the power supply has its own secondary power source operable when input power to the system manager no longer meets preset threshold values. The power supply functions in one of a discrete number of power modes depending upon the amount of energy available from either the computer input power or the secondary power source. The power supply switches to one of the group of power modes to conserve secondary power when the computer input power is no longer available. The power modes are controlled by a power mode controller which selectively directs power to discrete components of the system manager as a power conservation technique. The power mode controller always energizes the random access memory of the system manager in order to maintain data integrity. Upon detecting insufficient energy within the secondary power source, the power mode controller terminates all power flow from the power supply, including power flow to the random access memory, at which point the entire system has lost all data and configuration settings.

188 citations


Journal ArticleDOI
TL;DR: The weighted least absolute value minimization method is used to solve the power system state estimation problem and resulted in considerable savings in computation times, as demonstrated by the numerical examples given for various test systems.
Abstract: The weighted least absolute value minimization method is used to solve the power system state estimation problem. The problem can be shown to be equivalent to a linear programming program and hence can be solved using the well-known Simplex method. However, a direct adaptation of the Simplex method results in an inefficient code. A fast algorithm originally suggested by I. Barrodale and F.D.K. Roberts (1973) is further improved and applied to the power system state estimation problem. The use of the algorithm resulted in considerable savings in computation times, as demonstrated by the numerical examples given for various test systems. >

101 citations


Journal ArticleDOI
TL;DR: The solution method is an iterative compensation method, which uses a single optimally ordered factorization of the bus admittance matrix, commonly used in power flow analysis, to simulate the fault condition and enables a factorized Y/sub Bus/ solution, resulting in many advantages.
Abstract: A rigid approach to short circuit analysis for large-scale distribution systems is introduced. The approach uses an individual (a-b-c) phase-based system representation, a nontrivial transformer model, and includes the contribution due to load. The method can, therefore, be applied to balanced or unbalanced, radial, network, or mixed-type distribution systems. This approach is oriented toward applications in distribution system operation analysis rather than the more typical planning-oriented analysis. The solution method is an iterative compensation method, which uses a single optimally ordered factorization of the bus admittance matrix (Y/sub Bus/), commonly used in power flow analysis, to simulate the fault condition. The use of this method in a short circuit analysis program enables a factorized Y/sub Bus/ solution, resulting in many advantages. Using a common factorization, both power flow and short circuit analyses are possible in a single execution. Since the factorization is unchanged, multiple faults of various types can be simulated in one run of the program. >

75 citations


Journal ArticleDOI
TL;DR: In this article, the feasibility of the pilot-point approach and tradeoffs involved in secondary voltage controller designs are discussed. But the authors focus on the secondary voltage control in power systems.
Abstract: Recent results are reported on a pilot-point-based secondary voltage control in power systems. Similarities and differences compared to the optimal power flow methodology are described, and theoretical background for secondary voltage controller design is reviewed. Two complementary design problem formulations are reported, together with simulations on the New England 39 bus and Bonneville Power Administration 338 bus power system models. The results show the feasibility of the pilot-point approach and reveal the nature of the tradeoffs involved in secondary voltage controller designs. >

65 citations


Journal ArticleDOI
28 Sep 1991
TL;DR: In this paper, a power flow program is developed to analyze the harmonic distortion of a power system with various types of harmonic loads, and the proposed program can be applied to solve the harmonic current flow, voltage harmonic distortion factor, resonance frequency, and current amplification factor at every bus in the system.
Abstract: A power flow program is developed to analyze the harmonic distortion of a power system with various types of harmonic loads. The proposed program can be applied to solve the harmonic current flow, voltage harmonic distortion factor, resonance frequency, and current amplification factor at every bus in the system. In this study, a large metal factory is selected for the harmonic power flow analysis. The current waveforms at every bus are measured and analyzed to determine various orders of harmonic components. These harmonic currents are used in the computer simulation to determine the harmonic voltage distortion factor at the buses of the system, and the variations of resonance impedance and amplification factor with frequencies are investigated. Finally, the program is used to calculate the harmonic load flow when the metal factory is expanded by including a new plant in the power system, and proper filters are designed to alleviate the harmonic problems. >

57 citations


Journal ArticleDOI
01 Jan 1991
TL;DR: In this paper, an efficient method for minimising real power losses and improving the voltage profile of large scale power systems is presented, which is solved through optimal adjustments of reactive power generation in the system by changing generator voltages, shunt capacitors, and tap setting of tap changing transformers.
Abstract: An efficient method for minimising real power losses and improving the voltage profile of large scale power systems is presented. The problem is solved through optimal adjustments of reactive power generation in the system by changing generator voltages, shunt capacitors, and tap setting of tap changing transformers. It is formulated in a linearised form suitable for the linear programming technique and decomposition methods. The power system planning and corresponding problems with the addition of new reactive power sources have been integrated with the operational characteristic of the system, and results have been presented. The proposed method does not require the inversion of the Jacobian matrix, and its superiority lies in the reduction of the computation time and memory space, as well as a fast convergence for the solution of large scale systems.

34 citations


Journal ArticleDOI
01 Jul 1991
TL;DR: In this paper, the authors proposed a new methodology for the combined solution of the topological identification observability analysis and bad data processing problems in power systems based on a pattern analysis approach.
Abstract: The authors propose a new methodology for the combined solution of the topological identification observability analysis and bad data processing problems in power systems. The solution is based on a pattern analysis approach. An efficient framework is suggested for solving data acquisition and processing problems, as well as joining pattern analysis and analytical procedures. Two different techniques of pattern analysis are combined to produce a classifier and an estimator with unique characteristics to deal with noisy environments. Unobservable network areas, multiple interacting bad data and bad critical measurements can be efficiently treated. The patterns required for the training process can be acquired from the SCADA system and/or from load-flow simulations. Test results are presented for the IEEE 24-busbar reliability test system. >

Proceedings ArticleDOI
22 May 1991
TL;DR: Operation problems that result from MV distribution networks with local asynchronous generation sources connected are examined and the presence of asynchronous generators imposes the adoption of a consistent bus modelization using a new bus type, the PX bus, where P is the active generated power and X is a nonlinear magnetizing reactance.
Abstract: Operation problems that result from MV distribution networks with local asynchronous generation sources connected are examined. In order to analyze steady-state operating situations, a load-flow calculation must be performed. The presence of asynchronous generators imposes the adoption of a consistent bus modelization using a new bus type, the PX bus, where P is the active generated power and X is a nonlinear magnetizing reactance. This approach introduces some modifications in the conventional load-flow algorithms, thereby increasing the total number of iterations. >

Proceedings ArticleDOI
22 May 1991
TL;DR: A fuzzy AC load flow model is presented in which fuzzy data are used to obtain possibility distributions of voltages, active and reactive flows and losses, currents, and generated powers.
Abstract: A fuzzy AC load flow model is presented in which fuzzy data are used to obtain possibility distributions of voltages, active and reactive flows and losses, currents, and generated powers. These distributions are compared with the ones obtained through a Monte Carlo based simulation in order to evaluate the errors inherent to the fuzzy AC load flow. >

Journal ArticleDOI
TL;DR: An application of vector and parallel processing to power flow outage studies on large-scale networks is presented and two algorithms are proposed and compared with the results of a program written for scalar processing.
Abstract: An application of vector and parallel processing to power flow outage studies on large-scale networks is presented. Standard sparsity programming is not well suited to the capabilities of vector and parallel computers because of the extremely short vectors processed in load flow studies. In order to improve computational efficiency, the operations required to perform both forward/backward solution and power residual calculation are gathered in the form of long FORTRAN DO loops. Two algorithms are proposed and compared with the results of a program written for scalar processing. Simulations for the outage studies on IEEE standard networks and some different configurations of the Italian and European (UCPTE) EHV systems are run on a CRAY Y-MP8/432 vector computer (and partially on a IBM 3090/200S VF). The multitasking facility of the CRAY computer is also exploited in order to shorten the wall clock time required by a complete outage simulation. >

Journal ArticleDOI
TL;DR: A review of the existing techniques for schduling the power generation in an electric power system which consists of various types of generating units is provided in this article. But the focus of this paper is on the economic aspects of power generation scheduling.
Abstract: As the size of an electric power system grows, the economic significance of power generation scheduling becomes more and more apparent. A proper schedule for the generation of electricity will also ensure the reliability of a power system and extend the operational lives of its constituent units. This paper provides a review of the existing techniques for schduling the power generation in an electric power system which consists of various types of generating units. First, power generation scheduling problem will be presented and its economic importance will be discussed. Then, the application of different techniques such as Priority Lists Scheme, Dynamic Programming, Mixed Interger Programming, Benders’ Decomposition and Lagrangian Relaxation in solving this problem will be described. Also, computational advantages and shortcomings of each technique will be discussed. Finally, our experience in advancing the state-of-art, and improving the scheduling process for a large power system will be prese...

Proceedings ArticleDOI
28 Sep 1991
TL;DR: In this article, a reverse harmonic power flow study program called HARMTRACER is proposed to trace the flow of harmonics in a radial distribution system from the point of measurement to the harmonic source or sources.
Abstract: To aid in locating the source and type of harmonics in a distribution system, a computer program called HARM TRACER has been developed. HARM TRACER is a reverse harmonic power flow study program which traces the flow of harmonics in a radial distribution system from the point of measurement to the harmonic source or sources. It does so by considering each bus of the radial distribution system one at a time and calculating the bus voltages and injected or absorbed power at all frequencies. Based on the harmonic voltages, direction of harmonic currents, and harmonic power injections, the buses that are sources of harmonics are identified. >

Proceedings ArticleDOI
13 Oct 1991
TL;DR: The authors discuss the utilization of a decision making methodology for optimal placement of volt ampere reactive (VAr) compensators in electric power systems that will help electric power system planners to select one overall reactive power installation pattern that will satisfy system performance as well as engineering and economic constraints.
Abstract: The authors discuss the utilization of a decision making methodology for optimal placement of volt ampere reactive (VAr) compensators in electric power systems. The methodology will help electric power system planners to select one overall reactive power installation pattern that will satisfy system performance as well as engineering and economic constraints. The main goal of the optimal placement of VAr compensators is the selection of specific load buses in the network which can satisfy several criteria. For the decision making process, the results of analysis of each criterion is interpreted into a verbal rating rather than using the precise numerical values. The ratings can therefore be expressed by the degree of belonging to a fuzzy set, which allows for numerical representation of ratings over a range of values. >

Journal ArticleDOI
TL;DR: In this article, an optimal centralized controller capable of tracking these changes and controlling the nonlinear elements of the power system state vector is proposed, where the primary role played by voltage control and the need to represent the dynamics of the external system are shown from simulation case studies.
Abstract: Power system multiswing transient stability during a disturbance may be substantially improved through proper control of power system bus voltages. These bus voltages are normally nonlinear functions of state variables defined for the generators and their control elements. Postfault changes in the power system may also require a power system operating point different from the prefault value. An optimal centralized controller capable of tracking these changes and controlling the nonlinear elements of the power system state vector is proposed in this paper. The primary role played by voltage control and the need to represent the dynamics of the external system are shown from the results of simulation case studies.

Journal ArticleDOI
01 Sep 1991
TL;DR: The paper presents detailed results on the performance comparisons of the investigated AC load flow techniques, i.e. fast decoupled, second-order Newton Raphson and the super-decoupled load flows.
Abstract: The paper presents detailed results on the performance comparisons of the investigated AC load flow techniques, i.e. fast decoupled, second-order Newton Raphson and the super-decoupled load flows. The results are compared on the basis of the convergence rates, iteration counts, memory requirements and the CPU times. Comparative performance evaluations of these three methods with respect to ill-conditioning networks and line-outage simulations are also investigated. Extensive performance tests have been carried out on the standard IEEE 5, 14, 24 and 57 bus test systems.

Patent
22 Jul 1991
TL;DR: In this paper, the authors proposed to realize highly efficient control by modifying the control period of a voltage-reactive power controller according to the system conditions, such as the state of the power system.
Abstract: PURPOSE: To realize highly efficient control by modifying the control period of a voltage-reactive power controller according to the system conditions. CONSTITUTION: An automatic power supply system comprising an input unit 2 for taking in information from a power system 1 as an input data, a data base 31 relevant to the facilities constituting the power system 1, a voltage.reactive power controlling/processing section 32, and a power system control means 4 is further provided with a section 33 reserving control period for each time band so that the control period for the voltage.reactive power controlling/processing section can be selected according to the state of power system. COPYRIGHT: (C)1993,JPO&Japio

Proceedings ArticleDOI
28 Sep 1991
TL;DR: In this paper, a controller based on a fuzzy logic expert system is proposed for a slip-recovery drive with two GTOs to transform it into a fully controllable inverter, which allows independent control over voltage and displacement factor.
Abstract: Conventional slip-recovery drives are plagued with a low overall power factor, due to the naturally commutated power convertor in the rotor circuit. One solution consists of adding two GTOs to the converter bridge, in order to transform it into a fully controllable inverter, which allows for independent control over voltage and displacement factor. When appropriately controlled, this converter is capable of producing reactive power in just the right amount to fully compensate the reactive power consumed by the power induction machine. Unity power displacement factor is then attainable over most of the operating range. A controller based on a fuzzy logic expert system is proposed. >

Proceedings Article
K. Suzuki1, T. Sumida1, S. Uda1, M. Shimomura, S. Tanaka 
05 Nov 1991
TL;DR: In this paper, the authors discussed the relation between a recently developed excitation system and its improved stability, and the evaluation of the system stability was performed by using a brushless exciter.
Abstract: The improvement of the power stability is now strongly required because it plays a key role for the enhancement of power supply reliability. This requirement has become particularly urgent one as power plants have expanded in their size and as their locations are getting more and more remote from populated areas. In this situation, the excitation system is also required to achieve various improvements such as smaller floor occupancy, quick response, etc. Among others, the quick response excitation system is especially of great importance, because it improves the stability of a power system and also because it is more reliable and more cost-effective than expensive reinforcement of power transmission systems. The authors discuss the relation between a recently developed excitation system and its improved stability, and the evaluation of the system stability. As a result, they reach the conclusion that in case the ceiling voltage is the same, the quick response brushless excitation system improves transient stability more effectively than the thyristor excitation system. And finally, the improvement of the power system stability by replacing a DC exciter with a brushless exciter is described as an example of the above application.

Proceedings ArticleDOI
28 Aug 1991
TL;DR: In this article, a decentralized control technique for the load-frequency control (LFC) of a single area multimachine power system is presented, where the decentralized computation is carried out both horizontally by generating a group of local decoupled optimization subproblems and vertically through the division of the coordination task into two nested optimization processes.
Abstract: This paper presents a decentralized control technique for the Load-Frequency Control (LFC) of a single area multimachine power system. This technique is evolved from a three-level hierarchical scheme which successfully converts the LFC problem into an interactive proess. The decentralized computation is carried out both horizontally by generating a group of local decoupled optimization subproblems, and vertically through the division of the coordination task into two nested optimization processes. The former ensures that the optimal local subproblems are satisfied and hence, yields the local optimum solutions. The latter takes into account system nonlinearities and interconnections art d ensures that the performance of the overall system is optimized. This paper differs from previous works in that the proposed technique is fast and simple, and permits optimality at all the levels while providing a decomposed solution. Moreover, the proposed scheme guarantees practically zero steady-state error in both frequency and tie-line power at the final time.

Proceedings ArticleDOI
10 Mar 1991
TL;DR: In this article, the authors review the power components in the time domain and show that capacitors for power factor correction should be based on an accurate method for calculating reactive power in the presence of harmonics and distortion.
Abstract: Conventional design of capacitors for power factor correction at any bus in a system is based on the fundamental component of reactive power. In case of nonsinusoidal situations the conventional method for designing these capacitors does not give the expected power factor at a certain bus due to harmonic distortion and resonance. The authors review the power components in the time domain. These components are active, reactive and residual power. The authors also show that designing capacitors for power factor correction should be based on an accurate method for calculating reactive power in the presence of harmonics and distortion. >

Journal ArticleDOI
TL;DR: In this article, the effect of single phase open conditions in stability studies accurately was shown by considering the line to be open at both ends instead of at one end only, and a method of calculating the two-port parameters, as seen from the two openings, with ground as a return node, was derived.
Abstract: The general practice in representing a power transmission line with one phase open in stability studies is to assume that the phase is open at one end only. The error involved in such a representation, especially at EHV voltages with a long line section that is not fully compensated, can be appreciable. It is shown that to represent the effect of single phase open conditions in stability studies accurately the equivalent line parameters should be calculated by considering the line to be open at both ends instead of at one end only. The exact method of representing the phase open condition in positive-sequence network simulations in stability studies is derived. A method of calculating the two-port parameters, as seen from the two openings, given the four-port parameters with ground as a return node, is derived. >

Proceedings ArticleDOI
28 Aug 1991
TL;DR: The PSS design has been modified so that the adaptive gains are selected in real time based on the operating conditions and worst case network parameters.
Abstract: A new 'Gain Scheduling Stabilizer' for interconnected power systems has been described in this paper. The design of the PSS is based on a priori information about readily available machine and excitation system parameters and 'Observation' for a certain duration of time of the network from the bus of the machine concerned to ascertain the electrodynamic coupling of the machine to rest of the network. The computational complexity of this PSS requires the use of relatively sophisticated computing system. Though, such computers are now available, they are not in common actual power plants. With this in view, the PSS design has been modified so that the adaptive gains are selected in real time based on the operating conditions and worst case network parameters. The modified PSS can be implemented using on-line computers having capabilities similar to those of ordinary PCs or even /spl mu/P systems with moderate memory and computational capabilities.

17 Sep 1991
TL;DR: In this article, the smallest singular value of the power flow Jacobian is used as a feasible measure of the voltage stability in an AC/DC system, and the method is based on power flows on a well-established steady-state model and complex system configurations can be analyzed.
Abstract: A new approach to analysing power/voltage stability in AC/DC systems is developed. The method is based on power flows on a well-established 'quasi steady-state' model and complex system configurations can be analysed. In addition to traditional measures such as the effective short circuit ratio (ESCR) and dV/dQ, the smallest singular value of the power flow Jacobian is used and found to be a feasible measure of the voltage stability. >

Proceedings Article
05 Nov 1991
TL;DR: A model that is simple and still captures the important features of the HVDC system and an appropriate control of the convertors can be used to stabilize a voltage instability in the system are presented.
Abstract: When analysing HVDC systems connected to weak AC systems it is important to have a model that is simple and still captures the important features of the system. Such a model is presented and a number of conclusions are drawn from simple arguments based on physical observations of this system. These findings are verified by a more rigorous mathematical treatment of the problem. This analysis includes both steady state and dynamic conditions. It is also demonstrated how an appropriate control of the convertors can be used to stabilize a voltage instability in the system. >

Proceedings ArticleDOI
28 Aug 1991

Proceedings ArticleDOI
07 Apr 1991
TL;DR: A detailed study of some well-known test systems clearly indicates that the new method is at least 50% more efficient than the conventional Newton-Raphson method in finding a pair of close solutions in ill-conditioned power systems.
Abstract: A complete analytical study of the invariant manifolds for the Newton-Raphson solution of the power flow equations is presented. Based on these results, a new test is developed to reduce the computational effort of finding the solutions to ill-conditioned power systems. A detailed study of some well-known test systems clearly indicates that the new method is at least 50% more efficient than the conventional Newton-Raphson method in finding a pair of close solutions in ill-conditioned power systems. >