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Power Industry Computer Application Conference, 1995. Conference Proceedings., 1995 IEEE

Date 7-12 May 1995

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  • Proceedings of Power Industry Computer Applications Conference

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  • An efficient algorithm for real-time network reconfiguration in large scale unbalanced distribution systems

    Page(s): 510 - 516
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    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 View full abstract»

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  • Multivariable control design for damping interarea oscillations of bulk power systems using a modal reduction technique

    Page(s): 175 - 182
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    A new technique for power system multivariable control design in order to raise precision and facilitate design procedures is described. The multivariable control scheme for damping improvement of power swings is based on the optimal feedback control theory, and in the design process, eigenvalues of a 2n×2n matrix for an n-th dimension state equation must be calculated in order to solve the Riccati equation. Hence, in order to apply this method to a bulk power system, the matrix size must be reduced. By using the modal reduction technique which is proposed in this paper, the matrix size can be reduced by about 75%. The multivariable control scheme is applied to a 164-machine power system. The result shows that the proposed technique enables multivariable control design for a bulk power system with simple procedures View full abstract»

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  • A preconditioned fast decoupled power flow method for contingency screening

    Page(s): 262 - 268
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    This paper proposes an efficient method for contingency screening in power systems. Contingency analysis requires substantial amounts of computational time in evaluating data for controlling generating units or power flows. In this paper, the Tchebychev iteration of an indirect method is presented for solving a set of linear equations of fast decoupled power flow (FDPF) in the contingency screening. Furthermore, the precondition technique is introduced to improve the convergence characteristics of the indirect method. The proposed method has been successfully applied to a 2107 node system View full abstract»

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  • The ongoing evolution of the Colorado Springs Utilities EMS minimizing the impact on system operation

    Page(s): 333 - 338
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    When Colorado Springs Utilities (CSU) purchased their energy management system (EMS), they envisioned a system that would provide for their needs and continue to evolve to meet future requirements. CSU also wanted to be able to keep current with the latest technology and operate their system with minimal staff. The initially purchased EMS provided a distributed architecture which allowed for the planned future expansion to 2500 (generation, transmission, and mostly distribution) RTUs and the addition of processors as required. The desire to keep the system current as new technologies became available is the basis for an ongoing collaboration between CSU and the EMS supplier, which has allowed CSU to incrementally evolve the system to meet all the functional requirements within budget constraints. The first update to the initially designed system was the replacement of the applications processor with high performance workstations, dramatically reducing the cost of maintenance and greatly improving the response time of the advanced power system Applications. At the same time proprietary interfaces were removed, moving the system to a more open architecture. The second update was the replacement of the remaining proprietary communications links and the existing proprietary full graphics display generators with RISC workstations. Major emphasis in the evolution process stressed timely development and testing of the upgrade with collaborative installation planning, which minimized the impact to ongoing operations View full abstract»

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  • Improved distribution system planning using computational evolution

    Page(s): 530 - 536
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    This paper presents a new problem solving environment that can utilize different forms of resources to approach better solutions in the distribution network planning domain. To implement this concept, a design optimization framework, named design by expectation (DBE), is developed. DBE exploits the adaptation of genetic algorithms in searching the optimal solution, and releases the strict requirements for objective functions and constraints in conventional optimization techniques. One example, street lighting design, is used to demonstrate the applicability of the proposed approach View full abstract»

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  • Multi-objective feeder reconfiguration by distribution management system

    Page(s): 517 - 522
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    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 View full abstract»

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  • Design of suboptimal H∞ excitation controllers

    Page(s): 199 - 205
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    This paper presents a method to design suboptimal robust excitation controllers based on H∞ control theory. The suboptimal controller results from additional constraints that are imposed on the standard optimal H∞ solution. Global stability constraints are incorporated into the H∞ algorithm to ensure stability of the interconnected power system under decentralized control. Furthermore, a Lyapunov-based index is used to evaluate the robustness properties of the closed loop. In order to obtain a reduced order controller, the method of balanced truncation is used. The suboptimal H∞ controllers are output feedback controllers. These controllers posses superior robustness as compared to conventional PSS and optimal H∞ controllers View full abstract»

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  • Computer aided power flow software engineering and code generation

    Page(s): 474 - 480
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    In this paper a software engineering concept is described which permits the automatic solution of a nonlinear set of network equations. The power how equation set can be seen as a defined subset of a network equation set. The automated solution process is the numerical Newton-Raphson solution process of the power flow equations where the key code parts are the numeric mismatch and the numeric Jacobian term computation. It is shown that both the Jacobian and the mismatch term source code can be automatically generated in a conventional language such as Fortran or C. Thereby one starts from a high level, symbolic language with automatic differentiation and code generation facilities. As a result of this software engineering process an efficient, very high quality Newton-Raphson solution code is generated which allows easier implementation of network equation model enhancements and easier code maintenance as compared to hand-coded Fortran or C code View full abstract»

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  • Analysis of high impedance faults using fractal techniques

    Page(s): 401 - 406
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    Phase currents and voltages in a power distribution system change with a certain degree of chaos when high impedance faults (HIFs) occur. This paper describes application of the concepts of fractal geometry to analyze chaotic properties of high impedance faults. Root-mean-square rather that instantaneous values of currents are used for characterization of temporal system behavior; this results in relatively short time-series available for analysis. An algorithm is presented for pattern recognition and detection of HIFs; it is based on techniques suited for analysis of relatively small data sets. Examples are given to illustrate the ability of this approach to discriminate between faults and other transients in a power system View full abstract»

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  • Knowledge-based behavior interface: its application to power network restoration support system

    Page(s): 299 - 305
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    The characteristics of power system restoration (its combinational aspects, use of knowledge from a wide variety of origins and of different types and number of criteria to satisfy) make it a difficult problem. As a solution, a number of research teams are considering the use of expert systems to generate restoration plans. Promising results have already been obtained. Yet most expert systems remain in the prototype stage. One reason seems to be that the study of support systems for knowledge-based behavior (unable to describe with any rule) is insufficient. This paper begins by analyzing power system restoration based on the human performance model and discusses knowledge-based behavior as a high conceptual level human performance to solve this problem with combinational aspects. The paper then reports on its applications to the trunk line power network dispatching center. Finally the paper verifies the relation between knowledge-based behavior and designed human interfaces with a power network restoration case-study View full abstract»

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  • Identification of ARMAX model for short term load forecasting: an evolutionary programming approach

    Page(s): 325 - 330
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    This paper proposes a new evolutionary programming (EP) approach to identify the autoregressive moving average with exogenous variable (ARMAX) model for one day to one week ahead hourly load demand forecasts. Typically, the surface of forecasting error function possesses multiple local minimum points. Solutions of the traditional gradient search based identification technique therefore may stall at the local optimal points which lead to an inadequate model. By simulating a natural evolutionary process, the EP algorithm offers the capability of converging towards the global extremum of a complex error surface. The developed EP based load forecasting algorithm is verified by using different types of data for the Taiwan Power (Taipower) system and substation load as well as temperature values. Numerical results indicate the proposed EP approach provides a method to simultaneously estimate the appropriate order and parameter values of the ARMAX model for diverse types of load data. Comparisons of forecasting errors are made to the traditional identification techniques View full abstract»

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  • Automated transmission line fault analysis using synchronized sampling at two ends

    Page(s): 407 - 413
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    This paper introduces a new approach to power system fault analysis using synchronized sampling. A digital fault recorder with a Global Positioning System (GPS) satellite receiver is the source of data for this approach. Fault analysis functions, such as fault detection, classification and location are implemented for a power transmission line using synchronized samples from two ends of a line. This technique can be extremely fast, selective and accurate, providing fault analysis performance that can not easily be matched by other known techniques View full abstract»

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  • The testing workstation: a universal testing framework for Hydro-Quebec's new SCADA/EMS

    Page(s): 345 - 350
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    Hydro-Quebec is in the process of renewing its energy management system (EMS) and its SCADA. Part of this work involves the introduction of a new data acquisition architecture. The proposed architecture requires that many systems now in operation be modified. This article describes a specialized testing workstation (TW) which provides all the testing capabilities needed to validate the full operation of the systems in the new communications environment. These include RTUs, other acquisition systems and even the new SCADA/EMS itself. The TW offers an extensive set of tools: communications analyzer, application data monitor, automatic and script-based simulators, allowing full testing of any system using the communications protocol of the new SCADA/EMS. The testing can be either at the communications level or at the application level. Since the TW has full database capabilities for field data, it can act both as a client (SCADA) and as a server (e.g. RTU). For Hydro-Quebec, the TW offers the advantage of standardizing the testing process used during the development of the new systems. The use of universal test equipment facilitates the integration of all systems into the new SCADA/EMS environment View full abstract»

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  • Distribution capacitor automation provides integrated control of customer voltage levels and distribution reactive power flow

    Page(s): 215 - 220
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    Southern California Edison Company's (SCE) capacitor automation project reduces overall net energy transfer from the substation to the customer while meeting system VAr requirements. The automated capacitor switching system developed by SCE uses new electronic meters to read real-time customer voltages and energy consumption. Two-way packet radios communicate this customer voltage data and capacitor status information to SCE computers, where a control algorithm determines the optimal capacitor-switching pattern, fine-tuning customer voltages to reduce energy consumption. Substation VAr data is integrated into the control scheme. Testing performed during the period January-December 1993 recorded an average reduction of 4.2 volts in customer voltages when the DCAP algorithm was not controlling switching of capacitors, compared against voltages when the DCAP algorithm was not controlling capacitor switching. SCE has implemented the system on 586 circuit capacitors (including 34 substation capacitors) on 174 circuits served from 20 substations View full abstract»

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  • A model for the planning of electric energy systems including exergetic considerations

    Page(s): 539 - 546
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    The relevance of exergetic analysis in the design of electric energy systems is demonstrated. This analysis provides a quantitative measure of the quality of energy in terms of its ability to perform work and leads to a more rational use of energy. A general and easy-to-use model, implemented in object oriented programming, is developed for the planning of electric energy systems including exergetic considerations. The model presented is applied to a space-beating study and to a regional planning case View full abstract»

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  • An application of interior point quadratic programming algorithm to power system optimization problems

    Page(s): 98 - 104
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    This paper presents a new interior point quadratic programming algorithm which can solve power system optimization problems with significantly less computational efforts. The proposed algorithm has the following two special features. First, it is based on the path-following interior point algorithm whose search direction is the Newton direction, and therefore the algorithm has quadratic convergence. In the second place, it solves directly a symmetric indefinite system and thus the algorithm avoids the formation of [AD-1AT] and as a result generates fewer fill-ins than the case of factorizing the positive definite system matrix for large scale power systems. This has brought about a profound speed-up. Since the formulae of the interior point method have been deduced more generally, the proposed algorithm can start from either a feasible (interior point) or an infeasible point (noninterior point). Numerical results on the IEEE test systems and a Japanese 344 bus system have verified that the proposed algorithm possesses enough robustness and needs significantly less solution time compared with already reported applications of the interior point method View full abstract»

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  • Development of the Intercontrol Center Communications Protocol (ICCP) [power system control]

    Page(s): 449 - 455
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    After a three-year research and development project that included a collaborative effort by EPRI and 20 electric utilities and vendors in the USA, two electric utilities conducted full-scale demonstrations of a proposed international standard, UCA compliant protocol for communicating between power system control centers. The recently developed Intercontrol Center Communications Protocol (ICCP) was implemented and tested at Western Area Power Administration's (WAPA) Loveland area office and at Ohio Edison (OE) company. A third node at the vendor, Harris Controls, allowed demonstration of routing and networking capabilities View full abstract»

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  • Training session evaluation-a system level perspective using a dispatcher training simulator

    Page(s): 107 - 114
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    Modern power systems are becoming increasingly complex to operate. Training departments need more tools to help them in the process of training operators. In addition, they also need more help in evaluating the training session. This creates an iterative process, whereby instructors can evaluate feedback and modify the training program appropriately to cover any holes identified, or identify the weaknesses of each trainee and help them perform better. The dispatcher training simulator (DTS) has already been recognized throughout the industry as one of the best tools to perform operator training. The authors have recognized that the actual philosophy of operator training will vary from utility to utility and will always be subjective in nature. However, one common factor in most training programs is the need to collect objective data which can be used to analyze trainee/training effectiveness and present this information in the form of a report. In this paper, the authors present a design and the results of a prototype implementation which will go a long way towards helping the instructor gather relevant data to evaluate the behavior of a power system during a training session. The training philosophy of a particular electric utility (Virginia Power) has been presented and the tool has been set up for it. The utilization of standard tools and methodologies in the design of this tool help in the ease of integration and usefulness of its outputs View full abstract»

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  • An algorithm for the allocation of distribution system demand and energy losses

    Page(s): 234 - 239
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    This paper describes a new approach to the evaluation of loss adjustment factors for distribution systems. Such factors are required for `use of system' and wheeling calculations and reflect the amount by which purchases of energy at entry points to the system must exceed consumption at the point of use to account for the losses which occur in between. Renewed interest in cost-reflective methods of charging for losses has resulted from the deregulation of the electricity supply industry in many parts of the world. An algorithm is described which combines the use of graph theory with readily available load flow results, to assign the losses in each line or transformer within the system to the consumers supplied by it. The resulting allocation is shown to account for the voltage level, location and consumption pattern of the consumer in a way which is economically efficient. A variety of strategies for apportioning losses between multiple consumers at a given location can be implemented. The algorithm is suitable for allocating both demand and energy losses. Results on a full size distribution network are presented, and are compared with traditional published loss adjustment factors View full abstract»

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  • Generation/transmission power system reliability evaluation by Monte Carlo simulation assuming a fuzzy load description

    Page(s): 554 - 559
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    This paper presents a Monte Carlo algorithm considering loads defined by fuzzy numbers. In this methodology states are sampled according to the probabilistic models governing the life cycle of system components while fuzzy concepts are used to model uncertainty related to future load behavior. This model can be used to evaluate generation/transmission power system reliability for long term planning studies as one uses the more adequate uncertainty models for each type of data. For each sampled state a fuzzy optimal power flow is run so that one builds its power not supplied membership function. The paper proposes new indices reflecting the integration of probabilistic models and fuzzy concepts and discusses the application of variance reduction techniques if loads are defined by fuzzy numbers. A case-study based on the IEEE 30 bus system illustrates this methodology View full abstract»

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  • A statistical approach to the calculation of harmonics in MV systems caused by dispersed LV customers

    Page(s): 221 - 227
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    Problems usually arise when predicting harmonics in public supply systems due to the varying characteristics of the loads connected. Based on comprehensive measurements, a statistical load model is set up providing the harmonic parameters of all LV systems fed by the same HV/MV feeder. Harmonic distortion in the MV system caused by the variety of stochastic LV customers is determined by a Monte Carlo simulation approach applying the load model View full abstract»

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  • Two applications of parallel processing in power system computation

    Page(s): 62 - 69
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    This paper discusses performance improvements achieved in two power system software modules through the use of parallel processing techniques. The first software module, EVARISTE outputs a voltage stability indicator for various power system situations. This module was designed for extended real-time use and is therefore required to give guaranteed response times. The second module, MEXICO, assesses power system reliability and operating costs by simulating a large number of contingencies for generation and transmission equipment. This module, used for power system planning purposes, uses a Monte-Carlo method to build the various power system states, and makes heavy demands on CPU time for running simulations. Like many power system computation packages, both software modules are well-suited to coarse-grain parallel processing. The first module was parallelized on a machine capable of integrating up to thirty-two processors. The distributed-memory machine and the second on a shared-memory machine. In this paper, the authors start by a description of the n process used in these two cases, then go on to give details on the performance levels achieved, discussing aspects of programming, parameter selection (number of situations processed, number of processors), and machine characteristics (limitations due to interprocessor communications network, for instance) View full abstract»

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  • A practical resource scheduling with OPF constraints

    Page(s): 92 - 97
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    This paper presents an efficient approach to short term power system resource scheduling based on the augmented Lagrangian relaxation method. The problem is divided into two stages, the commitment stage and the constrained economic dispatch stage. The proposed mathematical model incorporates optimal power flow (OPF) constraints in the unit commitment stage. By OPF constrains, the authors refer to the relevant active power constraints that are incorporated in the constrained economic dispatch stage (i.e. transmission capacity constraints, fuel and various regulated emission requirements). The inclusion of OPF constraints in the commitment stage will improve the feasibility of the constrained economic dispatch solution. Other unit commitment constraints such as spinning and operating reserve requirements, power balance as well as other relevant local constraints (i.e. unit ramping rates, upper and lower generation limits, minimum up and down times) are taken into account in the proposed model. As a larger number of constraints are dealt with, a more rigorous method is introduced for updating Lagrange multipliers to improve the solution convergence. A software package which addresses energy management systems requirements is developed and tested View full abstract»

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