Showing papers on "Electric power system published in 1996"
TL;DR: In this article, the authors present the present status of active filters based on state-of-the-art power electronics technology, and their future prospects and directions toward the 21st Century, including the personal views and expectations of the author.
Abstract: Attention has been paid to active filters for power conditioning which provide the following multifunctions: reactive power compensation; harmonic compensation; flicker/imbalance compensation; and voltage regulation. Active filters in a range of 50 kVA-60 MVA have been practically installed in Japan. In the near future, the term "active filters" will have a much wider meaning than it did in the 1970s. For instance, active filters intended for harmonic solutions are expanding their functions from harmonic compensation of nonlinear loads into harmonic isolation between utilities and consumers, and harmonic damping throughout power distribution systems. This paper presents the present status of active filters based on state-of-the-art power electronics technology, and their future prospects and directions toward the 21st Century, including the personal views and expectations of the author.
1,700 citations
TL;DR: In this paper, a methodology for calculation of the optimum size of a battery bank and the PV array for a standalone hybrid wind/PV power system is developed, where long term data of wind speed and irradiance recorded for every hour of the day for 30 years were used.
Abstract: In this paper, a methodology for calculation of the optimum size of a battery bank and the PV array for a standalone hybrid wind/PV power system is developed. Long term data of wind speed and irradiance recorded for every hour of the day for 30 years were used. These data were used to calculate the average power generated by a wind turbine and a PV module for every hour of a typical day in a month. A load of a typical house in Massachusetts, USA, was used as a load demand of the hybrid system. For a given load and a desired loss of power supply probability, an optimum number of batteries and PV modules was calculated based on the minimum cost of the power system.
923 citations
01 Jul 1996
TL;DR: In this article, a new method of tracing the flow of electricity in meshed electrical networks is proposed which may be applied to both real and reactive power flows, and a loss-apportioning algorithm has also been introduced which allows the break down of the total transmission loss into components to be allocated to individual loads or generators.
Abstract: Continuing trend towards deregulation and unbundling of transmission services has resulted in the need to assess what the impact of a particular generator or load is on the power system. A new method of tracing the flow of electricity in meshed electrical networks is proposed which may be applied to both real and reactive power flows. The method allows assessment of how much of the real and reactive power output from a particular station goes to a particular load. It also allows the assessment of contributions of individual generators (or loads) to individual line flows. A loss-apportioning algorithm has also been introduced which allows the break down of the total transmission loss into components to be allocated to individual loads or generators. The method can be useful in providing additional insight into power system operation and can be used to modify existing tariffs of charging for transmission loss, reactive power and transmission services.
781 citations
TL;DR: In this paper, a generalized theory of instantaneous reactive power for three-phase power systems is proposed, which is valid for sinusoidal or nonsinusoidal, balanced or unbalanced, three phase power systems with or without zero-sequence currents and/or voltages.
Abstract: A generalized theory of instantaneous reactive power for three-phase power systems is proposed in this paper. This theory gives a generalized definition of instantaneous reactive power, which is valid for sinusoidal or nonsinusoidal, balanced or unbalanced, three-phase power systems with or without zero-sequence currents and/or voltages. The properties and physical meanings of the newly defined instantaneous reactive power are discussed in detail. A three-phase harmonic distorted power system with zero-sequence components is then used as an example to show reactive power measurement and compensation using the proposed theory.
755 citations
TL;DR: In this article, the authors developed a model and a solution technique for the problem of generating electric power when demands are not certain, and provided techniques for improving the current methods used in solving the traditional unit commitment problem.
Abstract: The authors develop a model and a solution technique for the problem of generating electric power when demands are not certain. They also provide techniques for improving the current methods used in solving the traditional unit commitment problem. The solution strategy can be run in parallel due to the separable nature of the relaxation used. Numerical results indicate significant savings in the cost of operating power generating systems when the stochastic model is used instead of the deterministic model.
593 citations
TL;DR: Based on the evolutionary programming (EP) technique, the new algorithm is capable of determining the global or near global optimal dispatch solutions in the cases where the classical Lagrangian based algorithms cease to be applicable.
Abstract: This paper develops an efficient, general economic dispatch (ED) algorithm for generating units with nonsmooth fuel cost functions. Based on the evolutionary programming (EP) technique, the new algorithm is capable of determining the global or near global optimal dispatch solutions in the cases where the classical Lagrangian based algorithms cease to be applicable. Effectiveness of the new algorithm is demonstrated on two example power systems and compared to that of the dynamic programming, simulated annealing, and genetic algorithms. Practical application of the developed algorithm is additionally verified on the Taiwan power (Taipower) system. Numerical results show that the proposed EP based ED algorithm can provide accurate dispatch solutions within reasonable time for any type of fuel cost functions.
580 citations
01 May 1996
TL;DR: In this paper, a new power system stabilizer (PSS) design for damping power system oscillations focusing on inter-area modes is described, and two global signals are suggested; the tie-line active power and speed difference signals.
Abstract: This paper describes a new power system stabilizer (PSS) design for damping power system oscillations focusing on interarea modes. The input to the PSS consists of two signals. The first signal is mainly to damp the local mode in the area where PSS is located using the generator rotor speed as an input signal. The second is an additional global signal for damping interarea modes. Two global signals are suggested; the tie-line active power and speed difference signals. The choice of PSS location, input signals and tuning is based on modal analysis and frequency response information. These two signals can also be used to enhance damping of interarea modes using SVC located in the middle of the transmission circuit connecting the two oscillating groups. The effectiveness and robustness of the new design are tested on a 19-generator system having characteristics and structure similar to the Western North American grid.
523 citations
TL;DR: In this article, the authors provide comprehensive development procedures and final forms of mathematical models of a unified power flow controller (UPFC) for steady-state, transient stability and eigenvalue studies.
Abstract: This paper provides comprehensive development procedures and final forms of mathematical models of a unified power flow controller (UPFC) for steady-state, transient stability and eigenvalue studies. Based on the developed models, the impacts of control strategy, parameters and location of UPFC on power system operating conditions are discussed. The accuracy of the developed models is verified through comparing the study results with those obtained from detailed time-domain simulation using the Electromagnetic Transients Program (EMTP).
512 citations
TL;DR: In this paper, two different time-series models generated using different available wind data are used to illustrate these models, and the proposed wind models satisfy the basic statistical tests and preserve the high-order auto-correlation, seasonal property and diurnal distributions of the actual wind speed.
477 citations
TL;DR: In this article, the authors presented the concept of overall power system reliability evaluation using an educational test system, which is an important concern in today's electric utility environment, and the extended test system presented in this paper and the concepts presented assist in satisfying this requirement.
Abstract: This paper presents the concept of overall power system reliability evaluation using an educational test system. The paper extends an existing test system by developing the necessary distribution and subtransmission networks. The extended test system has all the main facilities, such as generation, switching stations, transmission, sub-transmission and radial distribution networks found in a practical system. The test system, is however, sufficiently small that students can analyze it using hand calculations or by developing small computer programs to fully understand the reliability models and evaluation techniques. Overall power system reliability evaluation is concerned with providing acceptable customer service. This is an important concern in today's electric utility environment. This should therefore be an essential element in teaching power system reliability evaluation at either the graduate or undergraduate level, The extended test system presented in this paper and the concepts presented assist in satisfying this requirement.
447 citations
TL;DR: An advanced model, based on recurrent high order neural networks, is developed for the prediction of the power output profile of a wind park, which outperforms simple methods like persistence, as well as classical methods in the literature.
Abstract: In this paper, an advanced model, based on recurrent high order neural networks, is developed for the prediction of the power output profile of a wind park. This model outperforms simple methods like persistence, as well as classical methods in the literature. The architecture of a forecasting model is optimised automatically by a new algorithm, that substitutes the usually applied trial-and-error method. Finally, the online implementation of the developed model into an advanced control system for the optimal operation and management of a real autonomous wind-diesel power system, is presented.
01 May 1996
TL;DR: In this article, the authors presented the development of an artificial neural network (ANN) based short-term load forecasting model for the Energy Control Center of the Greek Public Power Corporation (PPC), which can forecast daily load profiles with a lead time of one to seven days.
Abstract: This paper presents the development of an artificial neural network (ANN) based short-term load forecasting model for the Energy Control Center of the Greek Public Power Corporation (PPC). The model can forecast daily load profiles with a lead time of one to seven days. Attention was paid for the accurate modeling of holidays. Experiences gained during the development of the model regarding the selection of the input variables, the ANN structure, and the training data set are described in the paper. The results indicate that the load forecasting model developed provides accurate forecasts.
TL;DR: In this article, the Simplex two-phase method was used to determine coordinated relay settings for protecting a distribution network. But, the relay settings were not considered in this paper.
Abstract: An adaptive system for protecting a distribution network should determine and implement relay settings that are most appropriate for the prevailing state of the power system. This paper presents a technique for determining coordinated relay settings. The technique uses the Simplex two-phase method; Phase I determines whether the constraints selected for illustrating the conditionality between primary and back up relays are feasible, and Phase II finds the optimal relay settings. A looped distribution system, protected by directional overcurrent relays, was used for testing the technique. The tests were conducted in a laboratory environment; some results from those tests are reported in the paper.
TL;DR: In this paper, a two-layer algorithm for combined heat and power (CHP) economic dispatch is presented, which is decomposed into two subproblems: the heat dispatch and the power dispatch.
Abstract: This paper presents a new algorithm for combined heat and power (CHP) economic dispatch. The CHP economic dispatch problem is decomposed into two sub-problems: the heat dispatch; and the power dispatch. The sub-problems are connected through the heat-power feasible region constraints of cogeneration units. The connection can be interpreted by the unit heat-power feasible region constraint multipliers in the Lagrangian function, and the interpretation naturally leads to the development of a two-layer algorithm. The outer layer uses the Lagrangian relaxation technique to solve the power dispatch iteratively. In each iteration, the inner layer solves the heat dispatch with the unit heat capacities passed by the outer layer. The binding constraints of the heat dispatch are fed back to the outer layer to move the CHP economic dispatch towards a global optimal solution.
01 May 1996
TL;DR: The preliminary study shows that it is feasible to design a simple, satisfactory dynamic forecaster to predict very short-term power system load trends online and FL and NN can be good candidates for this application.
Abstract: Three practical techniques-fuzzy logic (FL), neural networks (NN), and autoregressive models-for very short-term power system load forecasting are proposed and discussed in this paper. Their performances are evaluated through a computer simulation study. The preliminary study shows that it is feasible to design a simple, satisfactory dynamic forecaster to predict very short-term power system load trends online. FL and NN can be good candidates for this application.
TL;DR: In this paper, a new formulation for power system sectionalizing device placement taking into consideration outage, maintenance and investments costs is presented, where a solution methodology based on the optimization technique of simulated annealing is proposed to determine: (i) the number of switches; and (ii) the locations of the switches.
Abstract: This paper presents a new formulation for power system sectionalizing device placement taking into consideration outage, maintenance and investments costs. The formulation of sectionalizing switches is a combinatorial constrained optimization problem with a nonlinear, nondifferentiable objective function. A solution methodology based on the optimization technique of simulated annealing, is proposed to determine: (i) the number of sectionalizing switches; and (ii) the locations of the switches. The proposed solution methodology can offer a global optimal solution for the sectionalizing device placement problem which includes the reliability, investment and maintenance costs.
TL;DR: In this article, a technique for power system fault location estimation which uses data from both ends of a transmission line and which does not require the data to be synchronized is described, which can be easily applied for offline analysis.
Abstract: A technique for power system fault location estimation which uses data from both ends of a transmission line and which does not require the data to be synchronized is described. The technique fully utilizes the advantages of digital technology and numerical relaying which are available today and can easily be applied for offline analysis. This technique allows for accurate estimation of the fault location irrespective of the fault type, fault resistance, load currents, and source impedances. Use of two-terminal data allows the algorithm to eliminate previous assumptions in fault location estimation, thus increasing the accuracy of the estimate. The described scheme does not require real-time communications, only offline post-fault analysis. The paper also presents fault analysis techniques utilizing the additional communicated information.
TL;DR: In this article, a sequential Monte Carlo simulation technique is proposed for adequacy evaluation of a generating system including WECS, taking into account the auto-correlation and fluctuating characteristics of wind speeds, the random failure of generating units and other recognized dependencies.
Abstract: A wind energy conversion system (WECS) has a different impact on the reliability performance of a generating system than does a conventional energy conversion system. This is due to the variation of wind speeds and the dependencies associated with the power output of each wind turbine generator (WTG) in a wind farm. In this paper, a sequential Monte Carlo simulation technique is proposed for adequacy evaluation of a generating system including WECS. The method is based on an hourly random simulation to mimic the operation of a generating system, taking into account the auto-correlation and fluctuating characteristics of wind speeds, the random failure of generating units and other recognized dependencies. The hourly wind speeds are simulated utilizing autoregressive and moving average time series models that are established based on the F-criterion. A small reliability test system designated as the RBTS is used to illustrate the proposed method.
TL;DR: It is indicated that one of two simple diesel dispatch strategies can, in conjunction with the frugal use of stored energy (the Frugal Discharge Strategy), be virtually as cost-effective as the Ideal Predictive Strategy.
04 Jun 1996
TL;DR: In this paper, the authors presented a new method of measurement of power system frequency, based on digital filtering and Prony's estimation method, which is more accurate than others, e.g., the measurement of angular velocity of the rotating voltage phasor.
Abstract: The main frequency is an important parameter of an electrical power system. The frequency can change over a small range due to generation-load mismatches. Some power system protection and control applications, e,g, frequency relay for load shedding, load-frequency controller, require accurate and fast estimation of the frequency. Most digital algorithms for measuring frequency have acceptable accuracy if voltage waveforms are not distorted. However, due to nonlinear devices, e,g, semiconductor rectifiers, electric arc furnaces, the voltage waveforms can include higher harmonics. The paper presents a new method of measurement of power system frequency, based on digital filtering and Prony's estimation method. Simulation results confirm, that the proposed method is more accurate than others, e,g, than the method based on the measurement of angular velocity of the rotating voltage phasor.
TL;DR: A successive linear programming methodology is presented to treat more effectively those applications where a local structure change is performed to a power system already in operation, and where the modification of the settings of already existent relays is not desirable.
Abstract: A successive linear programming methodology is presented to treat more effectively those applications where a local structure change is performed to a power system already in operation, and where the modification of the settings of already existent relays is not desirable. The dimension of the optimization problems to be solved is substantially reduced, and a sequence of small linear programming problems is stated and solved in terms of the time dial settings, until a feasible solution is reached. With the proposed technique, the number of relays of the original system to be reset is reduced substantially. It is found that there is a trade-off between the number of relays to be reset and the optimality of the settings of the relays.
TL;DR: In this article, a DC voltage-controlled static VAr compensator (SVC) using quad-series voltage-source non-PWM inverters is presented, where the primary windings of each inverter are connected in series with each other.
Abstract: This paper presents a DC voltage-controlled static VAr compensator (SVC) using quad-series voltage-source non-PWM inverters. The SVC consists of four three-phase voltage-source inverters having a common DC capacitor and four three-phase transformers, the primary windings of which are connected in series with each other. Although each inverter outputs a square wave voltage, the synthesized AC voltage of the SVC has a 24-step waveshape. This results not only in a great reduction of harmonic currents and DC voltage ripples but also in less switching and snubbing losses. This paper develops the analysis of the transient response and the resonance between the AC reactors and the DC capacitor, with the focus on practical use. Experimental results obtained from a 10-kVA laboratory system are shown to agree well with the analytical results, thus verifying the analysis and leading to the design of DC capacitance value.
TL;DR: In this paper, the authors proposed intervention by computer-based rational control schemes to reduce or eliminate the likelihood of the hidden failure of key relays in traditional relaying systems, where relays with high-vulnerability indices can be identified and their vulnerable functions and failure modes identified.
Abstract: Major blackouts are rare events, but their impact can be catastrophic. A study of significant disturbances reported by NERC in the period from 1984 through 1988 indicates that protective relays are involved in one way or another in 75 percent of major disturbances. A common scenario is that the relay has an undetected (hidden) defect that was exposed due to the conditions created by other disturbances. For example, nearby faults, overloads, or reverse power flows expose the defective relay and cause a false trip, which exacerbates the situation. Given the importance of hidden failure modes in traditional relaying systems, intervention by computer-based rational control schemes is proposed in this article. Relays with high-vulnerability indices can be identified, and their vulnerable functions and failure modes identified. Countermeasures to reduce or eliminate the likelihood of the hidden failure of key relays can be provided.
TL;DR: The concept of security regions is used to systematically and objectively compare the impact of various FACTS devices on the behaviour of power systems.
Abstract: The concept of security regions is used to systematically and objectively compare the impact of various FACTS devices on the behaviour of power systems. Scalar measures of the steady-state performance of a power system with FACTS devices are used to quantify this impact. Such measures are obtained by solving an optimal power flow within the constraints of the security region. The concept of the ideal FACTS device is introduced as a means to establish a theoretical upper bound on the performance of any realizable FACTS. Such a device is tested and compared against nonideal FACTS including the variable series reactance and the variable phase-shifter. Simulations on the IEEE 118 and 30 bus networks illustrate the above concepts.
TL;DR: In this paper, a linear adaptive neuron called Adaline is used for the estimation of harmonic components of a power system using a neural estimation algorithm that is adjusted to force the error between the actual and desired outputs to satisfy a stable difference error equation.
Abstract: The paper presents a new approach for the estimation of harmonic components of a power system using a linear adaptive neuron called Adaline. The learning parameters in the proposed neural estimation algorithm are adjusted to force the error between the actual and desired outputs to satisfy a stable difference error equation. The estimator tracks the Fourier coefficients of the signal data corrupted with noise and decaying DC components very accurately. Adaptive tracking of harmonic components of a power system can easily be done using this algorithm. Several numerical tests have been conducted for the adaptive estimation of harmonic components of power system signals mixed with noise and decaying DC components.
01 May 1996
TL;DR: In this paper, the authors describe the basic technical concepts involved in developing cost based transmission prices and introduce the concepts of transmission pricing paradigms and methodologies to better illustrate how transmission costs are transformed into transmission prices.
Abstract: In this paper, the authors describe the basic technical concepts involved in developing cost based transmission prices. They introduce the concepts of transmission pricing paradigms and methodologies to better illustrate how transmission costs are transformed into transmission prices. They also briefly discuss the role of these paradigms and methodologies in promoting "economic efficiency" which is narrowly defined in this paper. They conclude the paper with an example of the application of some of these paradigms and methodologies for pricing transmission services in Brazil.
TL;DR: In this paper, the authors proposed a Co-ordinated Secondary Voltage Control (CSVC) system, which is an automatic closed-loop system with a dynamic of a few minutes, taking into account the network conditions (topology, loads, voltage limits and the generator operating constraints).
Abstract: To achieve a better voltage-VAr control in the electric power transmission system, different facilities are used. Generators are equipped with automatic voltage regulators to cope with sudden and random voltage changes caused by natural load fluctuations or failures. Other devices like capacitors, inductors, transformers with on load tap changers are installed on the network. Faced with the evolution of the network and operating conditions, electricity utilities are more and more interested in overall and coherent control systems, automatic or not. These systems are expected to co-ordinate the actions of local facilities for a better voltage control (more stable and faster reaction) inside different areas of the network in case of greater voltage and VAr variations. They afford a better use of existing reactive resources. Also, installation of new devices can be avoided allowing economy of investment. With this in mind, EDF has designed a system called Co-ordinated Secondary Voltage Control (CSVC). It is an automatic closed loop system with a dynamic of a few minutes. It takes into account the network conditions (topology, loads), the voltage limits and the generator operating constraints. This paper presents improvements which allow the CSVC to control the voltage profile and different kinds of reactive means on a large-scale power system, Furthermore, this paper presents a solution to spread out investment costs over several years, considering a deployment gradually extended.
01 May 1996
TL;DR: In this article, the authors describe an application of an optimal power flow, solved by a direct interior point (IP) method, to restore system solvability using the P-Q load representation, where power flow unsolvability occurs when for a given set of active and reactive bus injections, the power flow equations have no real solution.
Abstract: This paper describes an application of an optimal power flow, solved by a direct interior point (IP) method, to restore system solvability. Using the P-Q load representation, power flow unsolvability occurs when, for a given set of active and reactive bus injections, the power flow equations have no real solution. The set of control actions in the IP algorithm includes rescheduling of active power of generators, adjustments on terminal voltage of generators, tap changes on LTC transformers, and as a last resort, minimum load shedding. The IP formulation allows observation of the impact of each control optimization in system solvability. Also described is a framework to calculate probabilistic indicators of solvability problems taking into account the probability of contingencies. The role of control optimization is illustrated in a real 11-bus power system and the probabilistic approach is applied to a 1600-bus power system derived from the Brazilian South/Southeast/Central West system.
31 Dec 1996
TL;DR: In this article, the electrical performance of photovoltaic modules and arrays is analyzed using outdoor measurements to provide performance parameters both at standard reporting conditions and for all operating conditions encountered by typical PV systems.
Abstract: This paper provides new test methods and analytical procedures for characterizing the electrical performance of photovoltaic modules and arrays. The methods use outdoor measurements to provide performance parameters both at standard reporting conditions and for all operating conditions encountered by typical photovoltaic systems. Improvements over previously used test methods are identified, and examples of the successful application of the methodology are provided for crystalline- and amorphous-silicon modules and arrays. This work provides an improved understanding of module and array performance characteristics, and perhaps most importantly, a straight- forward yet rigorous model for predicting array performance at all operating conditions. For the first time, the influences of solar irradiance, operating temperature, solar spectrum, solar angle-of- incidence, and temperature coefficients are all addressed in a practical way that will benefit both designers and users of photovoltaics.
TL;DR: In this paper, a robust method for identifying the leverage points of a linearized power system state estimation model is proposed. But the method is not suitable for the case of large numbers of data points and does not account for the sparsity of the Jacobian matrix.
Abstract: This paper describes a fast and robust method for identifying the leverage points of a linearized power system state estimation model. These are measurements whose projections on the space spanned by the row vectors of the weighted Jacobian matrix, the so-called factor space, do not follow the pattern of the bulk of the point cloud. In other words, their projections are outliers in the factor space. The proposed method is implemented through a new version of the projection algorithm that accounts for the sparsity of the Jacobian matrix. It assigns to each data point a projection statistic defined as the maximum of the standardized projections of the point cloud on some directions passing through the origin. Based on these projection statistics, a robustly weighted Schweppe-type GM-estimator is defined, which can be computed by a reweighted least squares algorithm. The computational efficiency and the robustness of the method are demonstrated on the IEEE-14 bus and the 118-bus systems.