Showing papers in "IEEE Power & Energy Magazine in 1982"
TL;DR: The methods presented in this paper are aimed to overcome numerical difficulties of closed mathematical solutions of the frequency-dependent line equations in the time domain.
Abstract: The parameters of transmission lines with ground return are highly dependent on the frequency. Accurate modelling of this frequency dependence over the entire frequency range of the signals is of essential importance for the correct simulation of electromagnetic transient conditions. Closed mathematical solutions of the frequency-dependent line equations in the time domain are very difficult. Numerical approximation techniques are thus required for practical solutions. The oscillatory nature of the problem, however, makes ordinary numerical techniques very susceptible to instability and to accuracy errors. The, methods presented in this paper are aimed to overcome these numerical difficulties.
876 citations
TL;DR: In this article, a new type fault locator has been developed, that calculates the reactance of a faulty line, with a micro-processor, using the one-terminal voltage and current data of the transmission line.
Abstract: A new type fault locator has been developed, that calculates the reactance of a faulty line, with a micro-processor, using the one-terminal voltage and current data of the transmission line. Errors caused by various factors such as load flow, fault resistance, and the unsymmetrical arrangement of the transmission line, are automatically corrected. The equipment is now under field test, and during the nine months of the field test, the equipment has operated satisfactorily.
617 citations
TL;DR: In this paper, a new concept of electricity pricing referred to as "spot pricing" is presented and a set of rates related to optimal spot prices are proposed and their applicability is discussed in view of different customer characteristics, metering, and communication costs.
Abstract: A new concept of electricity pricing referred to as "spot pricing" is presented. Spot pricing is shown to encompass and achieve more fully the objectives of load management techniques and other rate structures proposed so far. The contribution of this paper is the derivation of optimal spot prices and a discussion of and proposals on a number of implementation issues which arise when the theory of spot pricing is turned into practice. A set of rates related to optimal spot prices are proposed and their applicability is discussed in view of different customer characteristics, metering, and communication costs. The impact of spot pricing on line losses and reactive energy, the quality of supply and rationing is elaborated. Issues related to customer response, utility revenues, investments and generation deregulation are also discussed.
342 citations
TL;DR: This paper heuristically presents basic concepts and results of SMA and lays the foundations for their application to a number of problems in analysis of power system dynamics, particularly to the Dynamic Stability problem.
Abstract: Selective Modal Analysis (or SMA) is a physically motivated framework for understanding, simplifying and analyzing complicated linear time-invariant models of dynamic systems, see [1,2]. SMA can accurately and efficiently focus on selected portions of the structure and behavior of the system. the part of the model that is relevant to the dynamics of interest is singled out in a direct manner, and. the remainder of the model is collapsed in a way that leaves the selected structure and behavior Intact. The paper heuristically presents basic concepts and results of SMA and lays the foundations for their application to a number of problems in analysis of power system dynamics. The approach is illustrated with several examples, including a 60-machine model of a dynamic instability occurrence in an actual power system. A companion paper [3] elaborates on specific applications of SMA to power systems, particularly to the Dynamic Stability problem.
324 citations
TL;DR: In this paper, the authors present a load model for power system stability studies, which is qualitatively different from generator load modeling in many aspects, such as reliability of load estimates, models of different components must be combined to obtain a reasonably manageable overall system model and field measurements are not at all easy.
Abstract: Proper representation of load is important in power system stability studies, but it is a difficult task. Load modeling is qualitatively different from generator modeling in many aspects. Composition of load needs to be reliably estimated, models of different components must be combined to obtain a reasonably manageable overall system model, and field measurements are not at all easy.
314 citations
TL;DR: In this paper, the conventional Newton-Raphson power flow study has been reformulated to permit the inclusion of nonlinear loads, which give rise to harmonic signals which propagate throughout the power system.
Abstract: The conventional Newton-Raphson power flow study has been reformulated to permit the inclusion of nonlinear loads. These loads give rise to harmonic signals which propagate throughout the power system. The reformulation is based on the reduction to zero of the mismatch active power and reactive voltamperes, the imbalance current at harmonic frequencies, and the mismatch apparent Voltamperes. Conclusions on the existence of positive, negative, and zero sequence signals are made for harmonic frequencies. The harmonic power flow study formulation is illustrated for a three phase full wave bridge rectifier. A companion paper presents a discussion of the actual computer implementation and several practical examples.
256 citations
TL;DR: It is shown how SMA is well suited to meet the demanding requirements of Dynamic Stability analysis, including a 60-machine model of a dynamic instability occurrence in an actual power system.
Abstract: Selective Modal Analysis (or SMA) is a physically motivated framework for understanding, simplifying and analyzing complicated linear time-invariant (or LTI) models of dynamic systems [1,2,3]. SMA allows one to focus on any prespecified dynamic pattern of intrest in the model. In particular, One can efficiently and accurately compute the eigene values and eigenvectors of the natural modes of interest and their sensitivities, and also determine physically meaningful reduced order models containing these natural modes. SMA is particularly suitable for dealing with composite models, i.e. models consisting of several dynamic subsystems interrelated by static constraints. An introduction to the basic concepts of SMA pertinent to the applications being considered here is presented in the companion paper [3]. This paper concerns the application of SMA to the Dynamic Stability problem in electric power systems; it is shown how SMA is well suited to meet the demanding requirements of Dynamic Stability analysis. This is illustrated in [3] with examples, including a 60-machine model of a dynamic instability occurrence in an actual power system.
243 citations
TL;DR: This paper describes an interactive software tool for long term transmission system expansion planning based on the DC power-flow model that has been implemented in the transmission department of ELETROBRAS (the holding company of the Brazilian electric sector).
Abstract: This paper describes an interactive software tool for long term transmission system expansion planning. All network synthesis is based on the DC power-flow model. The ranking of new additions is based on a "least-effort" criterion that takes into account the pattern of flow distribution in the network. An automatic network synthesis algorithm can be used for static studies. The reinforcement criterion is based on the cost/benefit analysis of "least-effort paths" in the network. Disconnected buses are conveniently handled by the superposition of a dummy network with very low transmission capacity over the actual network. Sensitivity analysis is extensively used. The program has been implemented in the transmission departmentof ELETROBRAS (the holding company of the Brazilian electric sector). Three case studies are presented and discussed.
202 citations
189 citations
TL;DR: In this paper, a variation of Newton's method incorporating Gaussian elimination in such a way that the most recent infonnation is always used at each step of the algorithm; similar to what is done in the Gauss-Seidel process.
Abstract: In this paper mathematician K.M. Brown's method is used to solve load-flow problems. The method is Particularly effective for solving of ill-conditioned non- linear algebraic equations. It is a variation of Newton's method incorporating Gaussian elimination in such a way that the most recent infonnation is always used at each step of the algorithm; similar to what is done in the Gauss-Seidel process. The iteration converges locally and the convergence is quadratic in nature. A general discussion of ill-conditioning of a system of algebraic equations is given, and it is also show by the fixed-point formulation that the proposed method falls in the general category of sucessive approximation methods. Digital computer solutions by the proposed method are given for cases for which the standard load-flow methods failed to converge, namely 11-, 13- and 43-bus ill-conditioned test systems. A comparison of this method with the standard load-flow methods is also presented for the well-conditioned AEP 30-, and 57-bus systems.
188 citations
TL;DR: A preliminary computer implementation of the optimization model for large-scale unit commitment problems is able to reliably solve problems with 250 units over 12 (2-hour) time periods, and it is expected to be able to easily double these numbers.
Abstract: This paper is concerned with the solution of large-scale unit commitment problems. An optimization model has been developed for these problems that incorporates minimum up and down time constraints, demand and reserve constraints, cooling-time dependent startup-costs, and time varying shutdown costs, as well as other practical considerations. A solution methodology has been developed for the optimization model that has two unique features. First, computational requirements grow only linearly with the number of units. Second, performance of the algorithm can be shown (rigorously) to actually improve as the number of units increases. With a preliminary computer implementation of the algorithm, we have been able to reliably solve problems with 250 units over 12 (2-hour) time periods, and we expect to be able to easily double these numbers.
TL;DR: In this article, a voltage-dependent methodology for shunt-capacitor compensation of primary distribution feeders is presented, where a generalized computer-based procedure is described for optimally sizing and placing any specified number of fixed shunt capacitors while accounting for voltage variation along the feeder.
Abstract: A new voltage-dependent methodology for shunt-capacitor compensation of primary distribution feeders is presented. A generalized computer- based procedure is described for optimally sizing and placing any specified number of fixed shunt capacitors while accounting for voltage variation along the feeder. The procedure is applied to a physically-existing feeder with known P, Q loads to yield results for capacity release exactly comparable to those from an optimal power flow. The superiority of the new methodology over existing methods is demonstrated.
TL;DR: In this article, the optimal power flow problem is formulated based upon the decoupling principle well recognized in bulk power transmission loadflow, which is exploited by decomposing the OPF formulation into a P-Problem (P-?real power model) and a Q-Problem(Q-V reactive power model), which simplifies the formulation, improves computation time and permits a certain flexibility in the types of calculations desired.
Abstract: The optimal power flow problem is formulated based upon the decoupling principle well recognized in bulk power transmission loadflow. This principle is exploited by decomposing the OPF formulation into a P-Problem (P-?real power model) and a Q-Problem (Q-V reactive power model); which simplifies the formulation, improves computation time and permits a certain flexibility in the types of calculations desired (i.e., P-Problem, Q-Problem or both).
TL;DR: In this article, a control scheme to reduce the mismatch in power generation and consumption of electric power systems is developed using the variable structure systems concept, which is introduced to refine the dynamic properties of the presently used integral controller which has been originated in accordance with a steady state concept.
Abstract: A control scheme to reduce the mismatch in power generation and consumption of electric power systems is developed using the variable structure systems concept. This scheme is introduced to refine the dynamic properties of the presently used integral controller which has been originated in accordance with a steady state concept. The new controller changes its structure according to a certain logic which results in distinct advantageous properties.
TL;DR: In this paper, a new method for obtaining an estimate of the state of a power system using weighted least absolute value (WLAV) techniques is presented, where the WLAV estimator simultaneously detects and rejects bad data while obtaining an accurate estimate.
Abstract: A new method for obtaining an estimate of the state of a power system using weighted least absolute value (WLAV) techniques is presented. This paper shows how the WLAV estimator simultaneously detects and rejects bad data while obtaining an accurate estimate of the state. The test results presented show that the WLAV estimates, obtained with or without bad data present, are comparable to the estimates obtained by a weighted least squares (WLS) estimator using only good data.
TL;DR: In this paper, the torsional interaction phenomenon between the electrical and mechanical system is explained with the aid of the newly introduced complex torque coefficients ke(j?) and km(j?).
Abstract: The torsional interaction phenomenon between the electrical and mechanical system is explained with the aid of the newly introduced complex torque coefficients ke(j?) and km(j?). The frequency response ke(j?) characterizes the behaviour of the electrical system including the electrical damping with and without series capacitors, whereas km(j?) describes the mechanical system. Multiplication of these by the phasor ?, which denotes the generator rotor oscillation, yields the electrical and the mechanical torques, respectively.
TL;DR: In this article, a microcomputer-based prototype relay was constructed and installed on a typical utility feeder to detect most staged faults while not indicating a false trip during a three month demonstration.
Abstract: This paper describes work performed by Texas A&M University on the detection of high impedance faults on distribution primary conductors. Some grounded distribution primary conductors may exhibit a very low fault current such that they may not be cleared by over-current protection. These faults may persist indefinitely, possibly causing a fire hazard or a hazard to humans by contact with an energized line. The paper begins with an examination of the high impedance fault problem from the perspective of system protection. The fault detection theory is presented next. The system utilizes a fault-generated increase in the 2-10 kHz component of feeder current for fault detection. EPRI funding enabled the verification and demonstration of this fault detection concept. Measurements were made on several faulted and unfaulted feeders to develop a representative data base of signals to which a relay would be subject. Analysis of these data provided a time and frequency domain signature of these faults. A microcomputer-based prototype relay was constructed and installed on a typical utility feeder. It successfully detected most staged faults while not indicating a false trip during a three month demonstration.
Abstract: On-line steady-state security analysis requires the evaluation of the effects of a large number of possible contingencies on a power system. Almost all contingency analysis programs have had to rely on a list of selected contingencies to be studied. The brute force approach of testing all contingencies every time an evaluation of the system performance is needed, becomes prohibitive due to its computational burden. A particularly attractive technique is to utilize a fast, approximate method to select the few contingencies that actually affect the security of the power system and then analyze only these cases in more detail. The contingency ranking and selection methods presented in the literature have all ranked outage cases on the basis of transmission line overloads. This limits the usefulness of these technqiues as contingencies that cause only voltage problems are totally overlooked. This paper shows that there is little correlation between the contingencies that produce line overloads and those that result in unacceptable voltage profiles, further establishing the need for a contingency selection method that is also voltage sensitive. Such a method, using the first iteration of an AC power flow, is presented. It is shown that the method meets both the speed and accuracy requirements for on-line use.
TL;DR: In this article, the authors present an evaluation of some previously proposed and newly developed state estimation algorithms, including a constant, decoupled gain matrix and some other simplifying approximations.
Abstract: This paper presents an evaluation of some previously proposed and newly developed state estimation algorithms. One new algorithm, which employs a constant, decoupled gain matrix and certain other simplifying approximations, is shown to be clearly superior to the other methods considered; accordingly this algorithm has been chosen for use in AEP's new control center. The selected algorithm is fast, reliable and can process a measurement set consisting of line flows, bus injections and voltage magnitudes. Test results are given for several real networks and some standard IEEE test systems (having as many as 460 buses and R/X ratios ranging from 0.1 to 2). The network conditions used in the tests range from light load to severe contingencies with low voltages and large phase angles. A wide variety of practical and hypothetical measurement sets are considered.
TL;DR: In this article, a fixed charge transshipment problem formulation (FCNP) is used for distribution substation siting and radial feeder planning, where the concept of a long range horizon year is used together with a time-phased expansion process.
Abstract: The planning methodology presented in this paper is an application of recent advances in optimization techniques for distribution substation siting and radial feeder planning. The concept of a long range horizon year (target) is used together with a time-phased expansion process beginning with the base year and progressing to the target year. An optimal static horizon year design is first determined using a fixed charge transshipment problem formulation (FCNP). The FCNP solution methodology employs the branch-and- bound algorithm and includes explicit modeling of fixed charge and variable cost components for improved accu- racy. The time-phased expansion process selects substation sites and feeder routings from the horizon (or target) year plan, thus providing an orderly and coherent expansion. This method easily incorporates existing facilities in the decision process for maximum benefit. An example of an actual planning study is presented to illustrate the horizon year target system selection and the corresponding time-phased expansion patterns.
TL;DR: In this article, the dynamic and stability properties of wind turbine generators connected to power systems are discussed, as well as various schemes for torsional damping such as speed sensitive stabilizer and blade pitch control.
Abstract: This paper describes the dynamic and stability properties of wind turbine generators connected to power systems. Both synchronous and induction generators are considered. A comparison is made between wind turbines, steam, and hydro units. The unusual phenomena associated with wind turbines are emphasized. The general control requirements are discussed, as well as various schemes for torsional damping such as speed sensitive stabilizer and blade pitch control. Interaction between adjacent wind turbines in a "wind farm" is also considered.
TL;DR: In this paper, a new optimization method is applied to optimal power flow analysis, based on transforming the original problem to that of solving a sequence of linearly constrained subproblems using an augmented Lagrangian type objective function.
Abstract: A new optimization method is applied to optimal power flow analysis. The method is shown to be well suited to large scale (500 buses or more) power systems in that it is computationally efficient and is particularly effective with infeasible starting points. The optimization approach is based on transforming the original problem to that of solving a sequence of linearly constrained subproblems using an augmented Lagrangian type objective function. A fundamental feature of this algorithm (developed by Murtagh and Saunders) is that the solution converges quadratically on the nonlinear power flow constraints, rather than being forced to satisfy the constraints throughout the iterative process. To demonstrate the performance of this algorithm, a set of descent directions, which includes quasi-Newton (variable metric), conjugate directions, and steepest descent, are compared on the basis of convergence and computational effort for a 118 bus and a 600 bus power system.
TL;DR: In this article, the authors describe the derivation of mdels for three phase and single-phase N-winding transformers in the form of branch impedance or admittance matrices, which can be calculated from available test data of positive and zero sequence short-circuit and excitation tests.
Abstract: Detailed transformer representations are needed in the analysis of electromagnetic transients and in the analysis of unbalanced steady-state conditions. This paper describes the derivation of mdels for three- phase and single-phase N-winding transformers in the form of branch impedance or admittance matrices, which can be calculated from available test data of positive and zero sequence short-circuit and excitation tests. The models can be used for many types of studies as long as the frequencies are low enough so that capacitances in the transformer can be ignored. The inclusion of saturation effects is briefly discussed.
TL;DR: In this article, Nikola Tesla's works on wireless transmission of energy are studied and an attempt is made to explain Teslas physical model on the basis of which he concluded that the wireless transmission on a global scale is possible.
Abstract: Nikola Tesla, the inventorof the poly- phase-current system, is best known for his contribution regarding induction and other types of alternating-current machines. His patents and his published and unpublished notes about wireless transmission of energy are less known and, if known to some extent, they are usually wrongly interpreted. rFor many years the author studied Tesla's works on wireless transmission of energy and that what is given here is a review of relevant documents, unpublished notes and letters from the archives of the Nikola Tesla Museum in Belgrade. An attempt is made to explain Teslas physical model on the basis of which he concluded that the wireless transmission of energy onaglobal scale is possible. His model is critically examined in view of the present day knowledge of extremely low frequency propagation phenomena.
TL;DR: In this article, a new method for detecting changes in the power system frequency, by relating it to a leakage coefficient in the FFT, is presented, and the algorithm computes the deviation of the system frequency from the fundamental component and the best estimate of its rate of change, and finally trips the appropriate amounts of load at the appropriate time delays.
Abstract: A power system disturbance, or operating abnormality, can produce a severe generation and load imbalance, resulting in a rapid frequency decline. The possibility of such a disturbance has led to increased interest in the application of automatic under-frequency protection schemes to restore load/generation balance and to prevent equipment damage. In this paper a new method for detecting changes in the power system frequency, by relating it to a leakage coefficient in the FFT, is presented. The algorithm computes the deviation of the power system frequency from the fundamental component and the best estimate of its rate of change. The algorithm then predicts the percentage generation and load imbalance, and finally trips the appropriate amounts of load at the appropriate time delays.
TL;DR: A feasible, but suboptimal solution is proposed, which eliminates the usual search space problem and reduces the problem to a backward sequence of dispatch problems, with the generator limits being carefully adjusted between each time interval in the solution sequence.
Abstract: One of the recurring problems facing energy control center dispatchers each day is how to operate the system during the periods of high load pickup, such that there is sufflcient generation to follow the load pickup, while still maintaining reasonable reserve and/or regulation margin This paper shows a technical solution to this problem which can be achieved with a very efficient use of computer resources The problem is expressed as a dynamic programming scheduling problem, and a feasible, but suboptimal solution is proposed, which eliminates the usual search space problem This method reduces the problem to a backward sequence of dispatch problems, with the generator limits being carefully adjusted between each time interval in the solution sequence The paper also discusses an efficient algorithm for the solution of a reserve constrained economic dispatch, which is the static optimization technique used at each interval
TL;DR: In this paper, a method for calculating the apparent and incremental inductance of rotating machinery is presented. But the method is totally general and utilizes numerical field calculation techniques in obtaining stored energy in the magnetic circuits of such machines.
Abstract: Energy and winding current perturbations form the basis of a method for calculation of the saturated apparent and incremental inductances of rotating machinery as functions of rotor position and machine winding excitation currents. The method is totally general and utilizes numerical field calculation techniques in obtaining stored energy in the magnetic circuits of such machines. Thus, it can be applied to a wide class of machinery with practically any cross-sectional contours and number of windings. It can be used at any given set of excitations (any loads). This method was applied to the calculation of the apparent and incremental inductances of a 15 hp samarium cobalt permanent magnet synchronous machine. The necessary-numerical field soluitions were obtained by finite elements at both rated and no load conditions. The calculated inductances, at various rotor positions, were compared with those obtained during laboratory measurements and the agreement between calculated and measured values was consistently very good. The advantage of this method over the more traditional calculations of only the direct and quadrature axes inductances (or reactances, including transient and subtransient components) is that the entire n > n matrix of incremental inductances that truely govern the dynamic performance of an n winding machine can be determined regardless of the validity of a rotating d-q-o frame of reference.
TL;DR: In this article, the authors discuss application of mathematical programming decomposition techniques in a model for planning least-cost investments in generating capacity subject to reliability constraints, where the planning problem is decomposed into a set of subproblems, each representing theoperation of the set of generating units of fixed capacity in one year and a master problem, representing optimal generating capacity investments over the entire planning horizon.
Abstract: This paper discusses application of mathematical programming decomposition techniques in a model for planning least-cost investments in generating capacity subject to reliability constraints. The planning problem is decomposed into a set of subproblems, each representing theoperation of a set of generating units of fixed capacity in one year, and a master problem, representing optimal generating capacity investments over the entire planning horizon. The subproblems are solved using the probabilistic simulation procedure. The master problem is a linear program which uses Lagrange multipliers derived from the sub- problems. The solution is found by iteratively solving the master problem and the subproblems.
TL;DR: In this paper, the eLectric power flow problem is reformulated to account for harmonic signals which arise from nonLinear loads, and the problem of initialization of bus voltages (including harmonics) is considered and convergence of the algorithm is assessed from the theoretical viewpoint and from the results of actual studies.
Abstract: This is a companion paper to a paper of the same title, Part I, in which the eLectric power flow problem is reformulated to account for harmonic signals which arise from nonLinear loads. In this paper, implementation and practical applications are discussed. The problem of initialization of bus voltages (including harmonics) is considered and convergence of the algorithm is assessed from the theoretical viewpoint and from the results of actual studies. The principal content of this paper is two examples both containing nonlinear loads (rectifiers).