Showing papers in "IEEE Power & Energy Magazine in 1984"

Optimal Power Flow By Newton Approach

Abstract: The classical optimal power flow problem with a nonseparable objective function can be solved by an explicit Newton approach. Efficient, robust solutions can be obtained for problems of any practical size or kind. Solution effort is approximately proportional to network size, and is relatively independent of the number of controls or binding inequalities. The key idea is a direct simultaneous solution for all of the unknowns in the Lagrangian function on each iteration. Each iteration minimizes a quadratic approximation of the Lagrangian. For any given set of binding constraints the process converges to the Kuhn-Tucker conditions in a few iterations. The challenge in algorithm development is to efficiently identify the binding inequalities.

Hierarchical Economic Dispatch for Piecewise Quadratic Cost Functions

Abstract: This paper presents a method to solve the economic power dispatch problem with piecewise quadratic cost functions. The solution approach is hierarchical, which allows for decentral i zed computations. An advantage of this approach is the capability to optimize over a greater variety of operating conditions. Traditionally, one cost function for each generator is assumed. In this formulation multiple intersecting cost functions are assumed. This method has appl ication to fossil generation units capable of burning gas and oil , as well as other problems which result in multiple intersecting cost curves for a particular unit. The results show that the solution method is practical and valid for real-time application. The motivation for this research stems from the actual operational and planning problems of a large Southwestern Utility.

Quadratically Convergent Optimal Power Flow

Abstract: A newly developed sparse implementation of an optimization method using exact second derivatives is applied to the optimal power flow problem. Four utility systems are studied using a variety of objective functions, including fuel costs, active and reactive losses, and new shunt capacitors. Systems solved range from 350 buses to 2000 buses. Comparisons are made with an older algorithm which uses an Augmented Lagrangian to demonstrate the advantages of run time and robustness of the new method. The algorithm and accompanying software represent a technological breakthrough, since they are suitable for solving systems on the order of 2000 buses and demonstrate solution speeds of 5 minutes on large mainframe computers. The method is particularly well suited to infeasible, or even divergent starting points. An option to add shunt capacitors in the event of hopeless infeasibility guarantees an optimal solution for many difficult to solve systems. An automatic scaling feature is added to correct numerical ill-conditioning resulting from series compensation or poor R/X ratios.

Power System Stabilizer Based on Adaptive Control Techniques

Abstract: Characteristics of certain adaptive control techniques are discussed in this paper with particular emphasis on their application to power systems. A modified form of one of the more promising algorithms that makes it more suitable. for power systems is developed and described. Comparative results of studies with adaptive stabilizer based on two alternate adaptive control algorithms and a conventional fixed parameter stabilizer show the improvement in response obtained with the adaptive algorithm.

Optimal Estimation Of Voltage Phasors And Frequency Deviation Using Linear And Non-Linear Kalman Filtering: Theory And Limitations

Abstract: This paper presents two techniques for optimal tracking of power system voltage phasors and frequency deviation. The first technique is based on a two-state linear Kalman filter model. The second technique is based on a three-state extended Kalman filter model. In the latter the frequency deviation is considered a third state variable and is recursively computed on-line. It is shown that the Kalman filter models are well suited for noisy measurements. The effect of sampling rate, computer burden and overall accuracy are also investigated. Finally comparison with other techniques is presented.

Steady State Analysis of Capacitor Self-Excited Induction Generators

Abstract: The paper presents a method for the steady state analysis of self-excited induction generators using balanced terminal capacitors. Operational and steady state equivalent circuits of the induction machine are employed to predict the steady state performance under different load conditions. The analytical procedure and the related computer program is described in the paper. Simulated results are presented and compared with corresponding results obtained experimentally.

Hypothesis Testing Identification: A New Method For Bad Data Analysis In Power System State Estimation

Abstract: The anomalous data identification procedures existing today in power system state estimation become problematic-if not totally unefficient-under stringent conditions, such as multiple and interacting bad data. The identification method presented in this paper attempts to alleviate these difficulties. It consists in :(i) computing measurement error estimates and using them as the random variables of concern;(ii) making decisions on the basis of a hypothesis testing which takes into account their statistical properties. Two identification techniques are then derived and further investigated and assessed by means of a realistic illustrative example. Conceptually novel, the identification methodology is thus shown to lead to practical procedures which are efficient, reliable and workable under all theoretically feasible conditions.

Synchronization of Line-Start Permanent-Magnet AC Motors

Abstract: The line-start PM (permanent magnet) motor is a very high efficiency synchronous motor designed to operate at fixed voltage and frequency from the same power supplies as induction motors. The excitation is provided partly by the magnets, which are mounted in the rotor, and partly by the line current. A squirrel cage is provided to accelerate the motor from standstill when started ``across the line.'' This paper describes the synchronizing process and the characteristics of PM motors that lead to an inherently higher starting capability than that of comparable reluctance motors. The starting performance is described with the aid of computed transient torque/speed and related trajectories. The results have been verified with reference to detailed tests on a 25-hp motor that has been described in earlier papers. Two basic configurations of PM motor are shown in Fig. 1. On the left is a four-pole arrangement with radially magnetized magnets, and on the right a six-pole arrangement with circumferentially magnetized magnets.

Analytical Modelling of Grounding Electrodes Transient Behavior

Abstract: This paper presents the results of analytical and numerical investigations to evaluate the impulse performance of grounding electrodes. Practical grounding electrodes used-for the lightning protection of power and industrigl systems are analyzed through, a comprehensive computer program developed for this purpose. The validity of the proposed methodology has been verified with various data available in the literature. Reaiistic models of grounding electrodes involve non-linear admittance elements which here are replaced with a pie% ewise-linear approach as a result of an artificial electrode segmentation.

Probabilistic Load Flow Considering Dependence Between Input Nodal Powers

Abstract: This paper presents a new method for obtaining a probabilistic load flow solution when dependence between the input nodal powers is considered. Such dependence is modeled in order to account for the criteria used to balance the system active power and also the correlation between loads due-mainly to environmental and social factors. The proposed technique is applied to a typical power system and the results discussed.

Lightning Induced Voltages on Power Lines: Theory

Abstract: Theory is presented which shows that nearby lightning return strokes can induce voltage surges of either positive or negative polarity on an overhead line depending on the location of the lightning relative to the line. The Telegraphers' Equations are solved with the return stroke vertical and horizontal electric fields as forcing functions. The hori zontal electric fields are calculated from measured or assumed vertical fields and assuned earth conductivities. For a typical return stroke, voltage waveforms are presented for a line of 500 m length and one of 5 km length for the following conditions: earth conductivities between 10-2 mhos/m and 10-5 mhos/m, earth permittivities between ??= 15 and ??= 3, and lightning ground strike points between 0.2 km and 5.0 km of the line at a variety of positions around the line. Measured voltages on a 460 m test line described in a companion paper are compared with calculated voltage waveforms derived from measured vertical electric fields, in accordance with the developed theory. Calculated waveshapes are found to be in moderately good agreement with the measurements, but calculated magnitudes are about a factor of 4 lower than measured. Possible errors in both theory and measurement are discussed. Voltage measurements reported by other investigators are, in general, consistent with the present theory

A Method to Teach the Design and Operation of a Distribution System

Abstract: The undergraduate "power option" program at New Mexico State University consists of five courses. Of these five, one is required of all electrical engineering majors, one is a "block elective" and three are senior electives. The "block elective" is a method by which an electrical engineering major must select three courses from a list of six. The list includes one course in each of the six "option" areas offered by the department. The five power courses are: 1. Electric Machinery -------- required of all majors 2. Power Transmission Lines -- "block elective" 3. Power Systems Analysis ---- senior elective 4. Distribution Systems ------ senior elective 5. Power System Protection --- senior elective

Computer-Aided Planning of Distribution Substation and Primary Feeders

Abstract: This paper presents an improved technique for optimal planning of substations and primary feeders in power distribution systems. The technique employs an accurate, time-phased cost model and incorporates a flexible planning formulation which suits detailed analysis of limited sized distribution networks as well as approximate analysis of large scale distribution networks. The cost model includes explicit time-dependent fixed and variable charges for planned facilities as well as the cost of power losses. The planning formulation incorporates user-defined constraints on voltage drop in primary feeders. Constraints on radial power flow are automatically set by the algorithm. The planning problem is solved using an advanced, sparsity-based mixed-integer linear programming code.

A New Technique for Rapid Tracking of Frequency Deviations Based on Level Crossings

Abstract: A novel frequency computation technique suitable for single or three phase voltage signals is proposed. The method is based on a generalization of the zero crossing detection to a level crossing detection. This yields several estimates of the frequency within one cycle. A composite "best estimatet" is obtained by an appropriate weighted average of these estimates. The method is insensitive to amplitude variations, unbalance and is capable of tracking small frequency deviations in as short a duration as a fraction of a cycle. The measurement scheme is particularily suitable for integration with the digital schemes for real-time monitoring control and protection of power systems.

Computer Aided Transmission Protection System Design Part I: Alcorithms

Abstract: The role of a computer-aided-design tool in assisting protection engineers is defined. In the process, we identify three computational problems for which algorithms are not readily available: network analysis to find primary/backup relay pairs, setting directional overcurrent relays and setting distance relays. Suitable algorithms for each of these tasks are presented.

Moisture Equilibrium Charts for Transformer Insulation Drying Practice

Abstract: A set of moisture equilibrium charts applicable to transformer insulation is presented. These may be used for the estimation of dryness levels in transformer insulation during the preparative and operational stages, and also during storage. A critique on the well known Piper chart is provided. Techniques to construct equilibrium curves for the combined paper-oil system from indirect measurements are outlined, and the interpretation of these curves for practical situations is discussed.

Application of a Thyristor Controlled Var Compensator for Damping Subsynchronous Oscillations in Power Systems

Abstract: This paper presents a new concept for controlling static VAr compensators (SVC) in power systems. It allows thyristor controlled VAr compensators to effectively damp subsynchronous resonance (SSR) oscillations besides controlling the system voltage. Eigenvalue analysis and digital time simulations for the IEEE SSR benchmark system are utilized to investigate the role of the main voltage regulator of the SVC in stabilizing the system and alleviating the SSR modal interactions that may be introduced by the auxiliary speed signal alone. Stability zones are identified to optimize the compensator parameters for economical application.

Lightning Induced Voltages on Power Lines: Experiment

Abstract: We present correlated measurements of the voltage induced on a power line by nearby lightning and the vertical electric field intensity from that lightning. Data are given for more than 100 first strokes and more than 200 subsequent strokes with the lightning ground strike point located by triangulation using a network of television cameras and by thunder ranging. Voltages were measured at one end of a 460 m unenergized distribution line which was open-circuited at both ends. A neutral wire was located beneath the line and was grounded at both ends. The time-domain voltaqe and vertical electric field waveforms were detected and recorded on a system having a frequency response from less than 1 Hz to over 1 MHz. Only about half of the vol tage waveforms resemble the "classical induced positive surges" described in the literature. The magnitude and polarity of the peak induced voltage is a strong function of the location of the lightning ground strike point.

Bound Estimates of the Severity of Line Outages in Power System Contingency Analysis and Ranking

Abstract: The effect of line outages on the real power flows of a system is analyzed using the DC load flow model. It is shown that the effect of the out4ge of line jk on the power flow of an arbitrary line lm can be bounded above and below by a series of progressively tighter values which in the limit correspond to the exact DC load flow solution. The calculation of these bound estimates on the contingency line flows is progressively more computationally demanding as the limits tighten, however, the simple to compute bounds, although more conservative, still serve to filter out a large portion of the non-critical contingencies. The remaining few potentially critical outages can then be ranked and analyzed through the full DC load flow.

Optimization of Number, Location, Size, Control Type, and Control Setting of Shunt Capacitors on Radial Distribution Feeders

Abstract: A new computerized method is developed for optimizing the present worth of revenue savings associated with released system capacity and power and energy loss reductions resulting from the application of fixed and switched shunt capacitors on distribution feeders The installation cost of capacitor banks is considered A multi-section, branching feeder model with non-uniform load distribution is chosen to best approximate actual conditions found on most distribution feeders Utility industry standard capacitor bank sizes and the benefits of retaining and/or modifying presently-operating feeder capacitor banks are considered Because of the practicality of its features, this method can be a useful tool for distribution engineers It is presently in use at Central Illinois Public Service Company

Non-Linear Var Optimization Using Decomposition And Coordination

Abstract: This paper introduces a new approach to solve the var optimization problem. It computes the desired optimal solution on-line and is applicable to large system deviations, without the need of an OPF. Problem non-linearities are retained. The overall problem is decomposed into subproblems which are solved separately using a suitable NLP Method. These results are then coordinated. This process is repeated until it converges to an overall optimum point.

Calculation of Lightning-Induced Voltages on Overhead Multiconductor Systems

Abstract: A computer program has been developed for numerically analyzing lightning- induced voltages on multiconductor lines. Thi. s program can be used to clarify the effects of lightning arresters and overhead ground wires on lightning-induced voltages, which has not before been possible, anid is potentiaLly of great uise in the lightning-resistant design of distribution lines. The results obtained with this numerical analysis program were compared to the results from an analog simulation using a 1:200 scale model, and found to be in good agreement, demonstrating the usefulness and validity of the program.

Critical Energy for Direct Transient Stability Assessment of a Multimachine Power System

Abstract: This paper describes a criterion for determining the critical energy used in direct transient stability assessment of a multimachine power system using the transient energy function method. This criterion provides a method by which the controlling unstable equilibrium point (u.e.p.), for the disturbance under investigation, is identified.

An Aggregate Induction Motor Model for Industrial Plants

Abstract: A technique is developed for deriving an equivalent load model to represent the dynamic and steady state effects of a system consisting of induction motors and constant impedance loads interconnected by a network Motor parameters are calculated from standard specifications, and together with network and load data are incorporated into an admittance matrix which is used to define most of the parameters of the load equivalent The inertia and running slip are chosen to minimize the error between the transient response of the system and its equivalent Step responses are calculated using a state approach Adequacy of the equivalent is validated by comparing the response of the original system and the equivalent to simulated bus voltage change, transformer outage, and remote and local balanced faults using a transient stability program

Application of Partial Discharge Testing to Hydro Generator Maintenance

Abstract: An improved partial discharge test to ascertain hydraulic generator winding condition, has been in use for the last 7 years. The test, which can be done by generating station staff without disrupting operation, has been applied to about 140 machines in eight North American utilities. Partial discharge testing is one of the main reasons Ontario Hydro has an exceptionally low winding replacement/major repair rate. Examples of results culled from thousands of tests are presented.. The use of the partial discharge test for planning winding maintenanGe and gauging the effectiveness of repairs is discussed.

Earth Resistivity Measurement Interpretation Techniques

Abstract: Earth resistivity measurement interpretation techniques developed as part of a major EPRI research project on transmission line grounding are described and discussed. The interpretation techniques include graphical curve matching and an advanced computer program (RESIST). The curve matching technique requires a set of theoretical Master Curves with which a field curve can be compared directly. Program RESIST is based on the analytical methods used in a more elaborate computer program which has been in operation for several years. For an electrode spacing of 2.5 meters or greater, satisfactory agreement is obtained between measured and computed results using both interpretation techniques.

A Comparison of 100 Percent Stator Ground Fault Protection Schemes for Generator Stator Windings

Abstract: This paper describes three different schemes for detecting single-phase-to-ground faults in 100% of the generator stator winding. The operating theory, a setting example, and field measurements are provided for each of the three schemes. A chart comparing the significant application characteristics of the three schemes is presented.

Reliability Modeling of Large Wind Farms and Associateed Electric Utility Interface Systems

Abstract: This paper is concerned with modeling the reliability characteristics in both probability and frequency of large electric utility application wind turbine generators together with their associated utility interface equipment. A computationally efficient algorithm is developed and applied to a wind farm with a special AC/DC/AC interface currently under design. The effects of various wind turbine/interface system component forced outage rates on the expected annual energy output of the farm is examined.