This paper presents the overall results of a residential customer survey conducted in service areas of MidAmerican Energy Company, a midwest utility. A similar survey was conducted concurrently in the industrial, commercial and institutional sectors and the survey results are presented in a companion paper. The results of this study are compared with the results of other studies performed in the high cost areas of the United States east and west coasts. This is the first ever study of this nature performed for the residential customers in the United States midwest region. Methodological differences in the study design compared to coastal surveys are discussed. Customer survey costing techniques can be categorized into three main groups: contingent valuation techniques, direct costing techniques and indirect costing techniques. Most customer surveys conducted by different organizations in the last two decades used a combination of all three techniques. The selection of a technique is mainly dependent on the type of customer being surveyed. In this MidAmerican study, contingent valuation techniques and an indirect costing technique have been used, as most consequences of power outages to residential users are related to inconvenience or disruption of housekeeping and leisure activities that are intangible in nature. The major contribution of this paper is that particulars of midwest residential customers compared to residential customers of coastal utilities are noted and customer responses on power quality issues that are important to customers are summarized.
This paper addresses the problem introduced by the slack bus in load flow solutions with uncertain nodal powers. While balancing powers in the system the slack bus will also absorb all uncertainty. The results obtained are of no practical interest unless realistic constraints are imposed on slack power production/consumption. Two methods of dealing with these constraints are investigated suitable for implementation within the recently developed boundary load flow.
This paper deals with the application of wavelet transforms for the detection, classification and location of faults on transmission lines. A global positioning system synchronizing clock is used to sample three phase voltage and current signals at both the ends of the transmission line over a moving window length of half cycle. The current signals are analyzed with Bior2.2 wavelet to obtain detail coefficients of single decompositions. Fault indices are calculated based on the sum of local and remote end detail coefficients, and compared with threshold values to detect and classify the faults. For estimation of fault location feed forward artificial neural networks are employed, which make use of third level approximate decompositions of the voltages and currents of local end obtained with Bior4.4 wavelet. Two types of neural networks are proposed, one for locating phase faults and the other for ground faults. The proposed algorithm is tested for different locations and types of faults as well as for various incidence angles and fault impedances. The algorithm is proved to be efficient and effective in detecting, classifying and locating faults.
This article presents a multi-objective framework for transmission expansion planning (TEP) with steady state voltage security consideration using AC optimal power flow (AC-OPF) within a market environment. The objectives are to minimize the investment costs (IC), operation costs (OC), load shedding cost (LSC) and also to maximize the voltage stability margin (VSM). A multi-objective mathematical programming (MMP) is formulated and the ε-constraint method is used to solve the problem. The proposed model has been applied to the well-known IEEE 24-bus Reliability Test System. The detailed results from the case study have been presented and discussed. Results are efficient and show the capability and the effectiveness of the proposed algorithm.
In this paper, a simple maximum power point tracking (MPPT) method for series-connected DC-DC converter module of photovoltaic power conditioning systems (PCS) is proposed. This approach enables maximum power point (MPP) tracking control with the converter's output voltage information instead of calculating solar array power, which significantly simplifies the sensor network by removing current sensor. Furthermore, there is no multiplication process in the P&O algorithm to track the maximum power point because the power calculation is replaced by output voltage sensing. This simple MPPT control strategy can reduce the cost and size, and can be utilized with a low performance / low cost controller. For verification of the proposed control strategy, Zigbee (Xbee-pro) wireless communications and DSP's Series Communications Interface are utilized. Also series-connected hardware prototype with multiple photovoltaic modules was built and tested.
Since privatisation, the major electricity generating companies in
Scotland (Hydro-Electric and Scottish Power) have had the opportunity to
sell their energy in three distinct ways: directly to their customers;
on a pre-arranged basis to the energy pool administered by the National
Grid Company (NGC); on spot to each other. It is with this final aspect
of energy trading that this paper is concerned. A computer-based
decision support system is described which is designed to assist trading
engineers to maximise the economic return available from trading hydro
We consider a class of discrete-time nonlinear systems for which the control design is based on singular perturbation and sliding-mode techniques. A. discrete time observer is designed to estimate the non measurable states required In the control law. The proposed controller observer scheme is applied to a synchronous generator. Simulations shows the performance of the controller-observer scheme
This paper presents the transient behavior of a single-phase self-excited induction generator (SEIG) supplying a dynamic load i.e. induction motor. The generator consists of a three-phase star connected induction machine with three capacitors and a single-phase induction motor load. The dynamic models of the SEIG and the motor load have been developed based on stationary reference frame d-q axes theory and the equations of excitation capacitors are described by three-phase abc model. Heavy transients occur during the switching of induction motor and the system becomes unstable. The use of damping resistors across series capacitors is proposed to damp out the transients for the stable operation. Using the damping resistors, the motor can be started up successfully. Simulated results have been compared with the experimental results for unsuccessful starting without damping resistances and successful starting with damping resistances to validate the developed model.
This paper gives a comparison of various performance indices and criteria used in power system stability analysis. The focus is on stability criteria based on direct methods (i.e., Lyapunov stability criteria). The comparison is made by first recasting the performance indices, and their underlying system models, in a unified notation and then identifying all the salient features of the mathematical models. Both classical and structure preserving system models are considered.
This paper contributes to the understanding of how bus and area prices are affected by losses and congestion. Recent papers have described area pricing to include bus prices that are equal within in a price area or zone. According to present Norwegian practice, the bus prices within a price area differ by an amount that is due to losses. We use a full AC optimal power flow model to illustrate this. Moreover, we demonstrate that the combined effect of transmission congestion and losses may yield a substantial change in individual bus and area prices compared with a situation with no congestion or losses.
This paper examines the integration of new sources of renewable energy into the power systems in Europe-challenges and possible solutions, application of wind power prediction tools for power system operation, new tasks that create new solutions for communication in distribution systems, wind power in Greece, integration of dispersed generation in Denmark, EdF and distributed energy resources in France, and new renewable sources in Italy, The paper also examines the European Commission Technology Platform's vision paper on Electricity Networks of the Future that was published in January 2006. In this respect, drivers towards smart grids, grids today, and key challenges for smart grids of the future are critically assessed
A nonlinear robust receding-horizon control is designed and applied to fifth-order model of induction motor in cascade structure. The control uses only measurement of the rotor speed and stator currents. The rotor flux is estimated by Kalman filter. The controller is based on a finite horizon continuous time minimization of the predicted tracking errors and no online optimization is needed. An integral action is incorporated in external loop to increase the robustness with respect to unknown time-varying load torque. The proposed nonlinear controller permits to achieve asymptotic speed and flux tracking in presence of the unknown load torque and resistances variations. In addition, it assures asymptotic decoupling of the speed and flux subsystems. The controller is applied, via simulation, to a benchmark example.
Distribution automation is considered a necessity for providing better power service in a more competitive environment. When new automatic functions are included in a distribution management system (DMS), loadings of the data links in the supervisory control and data acquisition (SCADA) system will become very heavy. In order to maintain a proper performance, system upgrade or migration will need to be considered. Two wide area network (WAN) architectures for a Taiwan Power Company's regional DMS are investigated. The WAN modeling presented in this paper is aimed to verify whether the hardware design could accommodate the communications load and to avoid overpaying for network equipments. Simulation results indicate that, to cover feeder automation functions, a WAN with distributed processing capability would provide better SCADA performance than an extension of the old centralized system.
This paper describes a method for the analysis of electromagnetic transients in multiphase transmission networks using the Numerical Laplace Transform. The proposed procedure is based on the superposition principle and is applied to switching and non-linear elements modeling. Switching operations are modeled as initial condition problems by means of injected current sources. In the case of non-linear elements, a piece-wise linear approximation is made, which reduces the problem to a sequence of switching operations. Several applications and comparisons with results obtained with the EMTDC and ATP programs are presented.
Prediction of peak electric loads in Japan up to year 2020 is discussed using the artificial neural networks (ANNs). In this study, total system load forecast reflecting current and future trends is carried out for nine power companies in Japan. Two ANNs, a three-layered back-propagation and a recurrent neural network, were designed and tested for the purpose. Predictions were done for target years 1999, 2000, 2005, 2010, 2015, and 2020, respectively. Two case studies, preservation of the status and structure reform, were also tested for predicting the loads of years 2010 and 2020. Unlike short-term load forecasting, long-term load forecasting is mainly affected by economical factors rather than weather conditions. This study focuses on economical data that seem to influence long-term electric load demands. Here, 10 factors are selected as inputs for the proposed ANNs: (1) gross national product, (2) gross domestic product, (3) population, (4) number of households, (5) number of air-conditioners, (6) amount of CO2 pollution, (7) index of industrial production, (8) oil price, (9) energy consumption, and (10) electricity price. The data used are: actual yearly, incremental growth rate from the previous year, and both together (actual and incremental growth rate from the previous year). As a result, the demands for 2010 and 2020 are predicted to be 225.779 and 249.617 GW, respectively (preservation of the status). With structure reform, the demands for 2010 and 2020 are predicted to be 219.259 and 244.508 GW.
The electric power industry in Japan is now carrying out a nation-wide research and development programme for the effective application of power electronics technologies to the bulk transmission network and interconnected power systems for the 21st century. The programme will continue for eight years funded by ten power utilities and subsidy from the national government. The research and development programme specifically consists of the following three study projects: AC high-voltage/large-current transmission (feasibility study on enhancement measures for AC transmission capability, and verification test of their effectiveness using a power system simulator); multi-terminal HVDC transmission (feasibility study on multi-terminal HVDC transmission, and development and verification test of a prototype control/protection device); high performance AC/DC converter (development of a partial model for a 300 MW self-commutated converter, and field test of the developed partial model).
In this paper a new method based on discrete wavelet transform and correlation coefficient is presented for digital differential protection. The algorithm includes offline and online operations. In offline operation, discrete wavelet transform is used to decompose typical three-phase differential currents for inrush current. Then an index is defined and computed. The index is based on the sum of the energy of detail coefficients at level 5 of three-phase differential currents at each half cycle. The online operation consists of capturing the three-phase differential currents using 10 kHz sampling rate, decomposing it by db1. Finally, the inrush current and internal fault is detected based on correlation coefficients of the computed index of pre-stored typical inrush current and a recorded indistinct signal. The effectiveness of the approach is tested using numerous inrush and internal fault currents. Simulations are used to confirm the aptness and the capability of the proposed method to discriminate inrush current from internal fault.
Modern transmission systems require adapting old networks to new schemes with major operation flexibility. Frequently, the new operation states may lead the equipment out of the design conditions. This paper shows switching transient studies, carried out over an old system, to improve its performance. The disconnection of one section of the system, due to power flow requirements, produce resonance between two parallel lines. A transient network analyzer was used to study the system of two unbalanced-coupled 500 kV lines, saturable reactors, transformers and series capacitors. Main problems and results have been included.
Forecasting the daily peak load is important for secure and profitable operation of modern power utilities. Machine learning techniques including neural networks have been used for this purpose. This paper proposes the alternative modeling approach of abductive networks, which offers simpler and more automated model synthesis. Resulting analytical input–output models automatically select influential inputs, give better insight and explanations, and allow comparison with other empirical models. Developed using peak load and extreme temperature data for 5 years and evaluated on the sixth year, a model forecasts next-day peak loads with an overall mean absolute percentage error (MAPE) of 2.50%, outperforming neural network models and flat forecasting for the same data. Two methods are described for forecasting daily peak loads up to 1 week ahead through iterative use of the next-day model or using seven dedicated models. Effects of varying model complexity are considered, and simplified analytical expressions are derived for the peak load. Proposals are made for further improving the forecasting accuracy.
This paper presents computer simulation results for the torsional interaction between a turbine generator and HV DC transmission link. An eigenvalue search technique is used to simulate torsional modes of oscillation of the turbine generator by varying the regulator parameters, the DC converter control modes, the generator reactive loading, the short-circuit ratio and damping angle of the AC system, the AC filter capacitance, etc. The design of a proportional and integral type damping controller is attempted by shifting the unstable poles to desired locations using local DC link feedback signals. The controller is found to be effective for damping out both mechanical and electrical disturbances, including a three-phase short-circuit on the converter terminal.
This paper presents the development of a Kalman filter (KF) based control scheme to improve the dynamic performance of a parallel AC/DC transmission system. The control algorithm is based on proportional-integral (PI) feedback control of thyristor firing angles in the AC/DC and DC/AC converters using KF estimates of system parameters as inputs. The work has two motivations. First, to avoid a control scheme designed by trial-and-error only, since the physical consequences of catastrophic control loss in power systems makes such approaches difficult. Second, to include physically important effects often left out of models for such systems as a mathematical convenience. Such factors include, AC line interactions, the coupling of the generator controller to the HVDC controller, reactive power effects caused by thyristor operation, frequency dependent transmission line and noise effects. PSCAD/EMTDC based simulations are presented and discussed for a number of contingencies, and conclusions drawn for future work.
A static synchronous compensator (STATCOM) may be equipped with several controllers to perform multiple control functions. However, in this paper, a study case of negative interactions between STATCOM AC and DC control is reported, which indicates that the conventional arrangement of multiple controllers for STATCOM various control functions may not always be appropriate. Hence, it is suggested that the multiple control functions of the STATCOM are implemented by a single multivariable controller, which is designed by treating the STATCOM installed in a power system as a multi-input multi-output control system. In this paper, an example is demonstrated, where a single two-variable controller is successfully designed to perform both STATCOM AC and DC voltage control function.
HVDC transmission systems can overcome some limitations inherent with AC transmission systems such as transmission over long distances and transmission via cables. One aspect of importance is the improvement in stability achieved with AC–DC transmission systems. In this paper, a methodology for the optimal Proportional Integral Derivative (PID) controller design using the Modified Genetic Algorithm (MGA) is proposed to improve the transient stability of AC–DC transmission systems after faults. This study consists of the formulation of the load flow calculation, basic controls on HVDC transmission systems, a mathematical model selection for stability analysis and a supplementary signal control by an optimal PID controller using the MGA. The proposed method is verified using computer simulation. The results show that the application of MGA-PID controller in AC–DC transmission systems will improve the transient stability. The PID controller design using the MGA method is shown to be advantageous when applied for the AC–DC transmission systems.
This paper presents the development of mathematical model representations of variable series capacitors and static phase shifters which are also known as Flexible AC Transmission Systems (FACTS) in power system economic dispatch. The objective of this research is to find the optimal locations of FACTS devices for improved economic dispatch. The proposed approach is based on the decomposition-coordination method and the network compensation technique. Taking advantage of accumulated experience in power system optimization and the existence of the Optimal Power Flow (OPF) software, the software development cost for implementing the proposed algorithm is reduced. In this paper, digital simulation studies on small power systems under different network parameters, with and without FACTS devices, were conducted. The purpose of the simulation studies was to assess the effectiveness of the proposed algorithm in minimizing the operating cost and enhancing the system performance. The results of the simulation studies and the proposed algorithm will be presented and discussed in detail in this paper.
In this paper, the modulation strategies are developed for single-phase ac/ac matrix converters. These are named positive, negative and combined switching strategies. Reduction of low order input and output currents harmonics with sinusoidal output voltages is achieved using the proposed switching strategies. There are no low frequency harmonics in the output voltage, as well. Furthermore, total harmonic distortion (THD) is reduced significantly. Using the combined switching strategy, the symmetrical output voltage and current can be achieved. The converter with the proposed switching strategies has been modeled and simulated by PSCAD software. The simulation results have a good agreement with measurement results.
Occluded gaseous cavities within the insulating materials are potential sources of electrical trees which can lead to continuous deterioration and breakdown of materials. To determine the suitability of use and to acquire the data for the dimensioning of electrical insulation systems breakdown voltage of insulators should be determined. In this paper, fuzzy logic (FL) method is used to model breakdown voltages of White Minilex Paper samples based on experimental data generated in the laboratory. Different models are proposed with different shapes of the membership functions for the FL under both dc and ac voltage conditions. The cavities are created artificially with different dimensions. Low values of mean absolute errors of the estimated breakdown voltage of the test data show the effectiveness of such models.
This paper is concerned with the control of a parallel AC/DC power systems using low-order models derived directly from test data. Experimental data are obtained by applying a pseudo random binary sequences (PRBS) signal to the excitation system and one DC converter terminal of a laboratory system and resursive least-squares based system identification, premised on the exciter and DC current order as reference inputs, is implemented. The models so obtained have been successfully used for AC/DC power system controller design.
A computer simulation method for predicting the dynamic responses of a marine power system containing both AC and DC subsystems is proposed. The method has two important features. First, it allows modelling of system components in modular form and representation of network relations by utilising Kirchhoff's current law, hence providing flexibility in model building and testing. The second feature is its ability to simulate the performance of DC machines and convertors in a combined AC/DC system. A description of the method and its application to a practical marine power system are given. The simulation results are verified practically by comparing them with a manufacturer's supplied experimental data.
This paper presents a rigorous method of determining the commutating voltage and the commutation reactance, both of which play significant roles in the analysis of AC/DC power systems under unbalanced AC conditions. An accurate but simple three-phase no-mutual equivalent circuit is derived for the AC part connected to the three-phase converter bridge. By using the circuit, the analyses relevant to AC/DC power systems under both steady state and dynamic unbalanced conditions could be performed more precisely and more concisely.As an application, three-phase AC/DC power flow is also discussed. A set of complete but minimized converter equations is developed, with which the computational requirements of the power flow could be reduced.
A new mathematical model is presented for analysis of self-excited oscillations in a synchronous machine connected to a long EHV transmission line with different configurations of series and shunt compensation. The model has been developed in terms of line constants of long lines which includes the effect of line shunt susceptance and reactance of line end transformers. The model has been used to directly analyse self-excited oscillations in a transmission system for five types of compensation scheme. The stability limit curves in the R-Xc parametric plane for the five compensation schemes have been compared with that for a series compensated transmission line.
Saddle-node bifurcations are dynamic instabilities of differential equation models that have been associated with voltage collapse problems in power systems. This paper presents the conditions needed for detecting these types of bifurcations using power flow equations for a dynamic model of ACIDC systems, represented by differential equations and algebraic constraints. Two methods typically used to detect saddle-node bifurcations, namely, direct and parameterized continuation methods, are briefly analysed from the point of view of numerical robustness.
It is accepted that the dynamic stability of an integrated AC/DC power system can be enhanced by adopting an appropriate strategy for controlling the power flow in the embedded DC portions. This paper envisages a decentralized optimal control strategy under a hierarchical structure to achieve this objective. Faced with the intrinsic needs of heavy computing resources when the DC systems has grown into a multiterminal connection, strong motivation for using a distributed computing environment is envisaged. The scope for the application of this new technological potential is demonstrated with the aid of a dynamic simulation example.
A simple and general method of determining the maximum efficiency of a transmission line is described. The method can be applied to both compensated and uncompensated lines. The maximum efficiency for a given load power factor and the power factor angle at which the highest value of the maximum efficiency occurs are determined from very simple analytical expressions. The method was tested on a 500 kV transmission line with several series and shunt compensation schemes. The influence of various factors such as the load power factor, line length and the degree of series and shunt compensations on the maximum efficiency was also investigated.
A simple improvement to the sequential AC/DC power flow algorithm is described. The improvement involves modifying a Jacobian matrix of the fast decoupled power flow algorithm to account for the voltage-dependent reactive power consumption of AC/DC converters. The improved sequential algorithm is capable of finding a power flow solution for weak AC systems where the standard sequential algorithm fails.
The transmission of electricity differs from transportation of any typical commodity by some inherent aspects such as: the production needs to match the consumption at the same time; system control is not an easy task; the electricity flows do not usually follow the economic law. The last aspect is normally observed when transmission systems are included in, for instance, an economic dispatch problem. One way to minimize the operational costs caused by an overloaded transmission system is through the installation of Flexible AC Transmission System (FACTS) devices in the system. They are able to change power flows by modifying the network parameters. This paper focuses on the ability of FACTS devices to change the overall costs of the system and their impact on transmission pricing. The allocation and the determination of the FACTS required are also discussed. Some examples using the IEEE-14 system and the Brazilian electrical system of the Southern region are given to illustrate the concepts introduced in this paper.
Economic dispatch (ED) is one of the key functions of the modern energy management system. Conventional gradient based methods can solve the ED problem effectively only if the fuel cost curves of generating units are assumed to be piecewise linear, monotonically increasing in nature, otherwise these methods are likely to converge to suboptimal or infeasible solutions. Classical particle swarm optimization (PSO) algorithm is capable of achieving near global solutions for such problems but it tends to converge prematurely. The practical NCED problem is solved here using PSO with a novel parameter automation strategy in which time varying acceleration coefficients (TVAC) are employed to efficiently control the local and global search, such that premature convergence is avoided and global solutions are achieved. The performance of this method has been compared and found to be superior compared to the results of a few PSO variants and some recently published results.
The Latin American deregulated markets have based their open access schemes on a concept that considers a multilateral use of the transmission system, with all agents contributing to the financing of a common network based on physical and economic usage, irrespective of commercial arrangements. The paper describes the concept and the existing schemes and contributes with the formulation of alternative numerical approaches for open access pricing, taking into account energy and capacity use of the system by the participant agents. Distribution factors based on DC power flows are the basic elements of the formulation, which is built based on different physical and economic considerations. The approaches are numerically evaluated in the Chilean main interconnected electrical system, with a comparison of the resultant impacts on generators and consumers.
Under a deregulated environment, electricity consumers and suppliers generally establish various bilateral power transactions/contracts. The transmission company normally honors and executes these bilateral contracts within the limits permitted by the system design and operating conditions. This article describes determination of optimal bilateral contracts by using line flow factors (LFFs). An innovative approach for obtaining the set of line flow factors is presented. The line flow factors are evaluated from existing load flow information. A generalized linear programming formulation is proposed to determine the optimal bilateral real power contracts under a deregulated environment subjected to the steady-state security constraints (e.g. generation and line flow limits). It is demonstrated that the proposed methodology would be an effective tool to study the intricate relationships between the bilateral contracts and system security. Examples are presented to illustrate the use of this formulation to minimize the cost of any bilateral contract to comply with the security requirements. The results obtained show great prospects for practical application of the proposed algorithm for optimal bilateral contracts on a real-time basis.
This paper demonstrates the development of a Java-based application that can be used for information exchange by a variety of market participants, such as generators, brokers, market operators, and network owners. For an illustration, a SCADA Laboratory Applications Program (SLAP) has been implemented. Java Graphical User Interface (GUI), Object Management Group's Common Object Request Broker Architecture (OMG's CORBA) and multi-tiered Client/Server Architecture are some of the software technologies used. A three-phase design approach, which ensures a high probability of success for developing the Java-based application for data access via Intranet, Extranet and Internet, is also presented. Based on this Java-based application, an open geographical distributed environment where power system data can be shared, reused and accessed from anywhere can be created at a much reduced cost.
This paper presents an interactive line switching algorithm for overload alleviation under line outage condition. Line outage distribution factors are used to determine line flows. It has the advantage that a contingency from a base case can be computed for an actual flow on a line in a real time situation. A relation has been derived for calculating load bus voltages under post-contingency condition and after line switching. In the event of bus voltage limit violation the algorithm explores the possibility of the other line to be switched. The algorithm also investigates the possibility of overload rotation amongst two disjoint sets of overloaded lines obtained after line switching, if overload elimination is not possible. The algorithm has been tested on the IEEE 25 bus system.
A simple deterministic frequency stability model is developed in this work together with its stochastic counterpart. While the deterministic model captures the fundamental characteristics of short-term frequency dynamics such as abnormal frequency tripping of generators, the stochastic model further maintains the probabilistic characteristics of frequency dynamics, such as stochastic characteristics of frequency relays. The models are particularly suitable for studying system cascading failures introduced by frequency distortions. Our simulation results reveal that the relationship between blackout power loss and frequency has the characteristics of power law.
A general procedure is presented for the construction of a Lyapunov function with regard to a multimachine power system that includes both transfer conductances and equivalent damping constants. This function extends the known Lyapunov-energy function relating to the case in which the transfer conductances are disregarded and allows the determination of a partial estimate of the stability domain. A numerical example shows the application.
This paper presents a new neural network based transmission line distance protection module. The proposed module uses samples of voltage and current signals to learn the hidden relationship existing in the input patterns. Simulation studies are preformed and influence of changing system parameters such as fault resistance and source impedance is studied. Details of the design procedure and the results of performance studies with the proposed relay are given in the paper. In addition, an extended ANN-based technique which, uses the proposed neural network distance relay as its basis is described. The extended technique uses neutral current as its new input. Since, this technique adds a new dimension to the input decision space, the accuracy of the algorithm is increased. Various simulation studies are performed and capabilities of the extended algorithm are investigated. Performance studies results show that the proposed algorithm is fast and accurate. Some of the simulation studies are presented in the paper.
This paper describes the development of an adaptive window length algorithm for high speed digital distance protection. The sampling window length will be increased automatically from fault inception until the computed fault impedance stabilises. The final window length is adaptable to the severeness of the disturbance. The use of a moving average technique further improves performance. Extensive simulation results show that this algorithm possesses excellent performance for both strong and weak system configurations.
This paper presents a new and accurate fault location algorithm based on distributed time domain line model for a transmission line compensated with series connected FACTS device. In the proposed algorithm, in order to compute the voltage drop across the series device during the fault period, the series device model and knowledge about the operating mode of the compensating device are not utilized. For this reason, the proposed technique can be easily applied to any series FACTS compensated line. Samples of voltage and current at both ends of the line are taken synchronously and used to calculate the location and resistance of the fault. The proposed algorithm is not sensitive to fault resistance and fault inception angle and does not require any knowledge of equivalent source impedances. This method has been tested using EMTP/ATP model of a 400 kV, 300 km transmission line compensated with a series FACTS device. The results of computer simulations for different operating conditions demonstrate the very high accuracy and robustness of the algorithm.
In the competitive environment in which US utilities operate, auctions are becoming an accepted means for procuring resources to meet utilities' projected needs. The rationale for instituting auctions is to effectively harness the competitive forces in electricity resource markets in order to implement least-cost planning objectices. PG&E, in cooperation with the other California investor-owned utilities. Southern California Edison and San Diego Gas and Electric, has developed a multi-attribute auction framework for the procurement of future resources. The framework uses the attributes of capacity and energy price, dispatchability, location, start date flexibility, price diversity, project viability and environmental impacts to evaluate customer benefits. This allows comparability between and tradeoffs among attributes. Other key features include the use of multiple scenarios to explicitly account for fuel price and load growth uncertainty, the explicit evaluation of long-term impacts and dynamic operating benefits of dispatchability, and the use of portfolio theory for the evaluation of price diversity. The bidding evaluation also uses optimal power flow derived loss adjustment factors and incremental network reinforcement costs and takes into account uncertainty in determining start-date flexibility. The framework is sufficiently general to be usable not only for auctions, but also for utility evaluation of maintenance, power contracts and other investment decisions. This paper describes the framework and its implementation into a PC spreadsheet software package.
Many systems require the periodic undertaking of major (preventive) maintenance actions (MMAs) such as overhauls in mechanical equipment, reconditioning of train lines, resurfacing of roads, etc. In the long term, these actions contribute to achieving a lower rate of occurrence of failures, though in many cases they increase the intensity of the failure process shortly after performed, resulting in a non-monotonic trend for failure intensity. Also, in the special case of distributed assets such as communications and energy networks, pipelines, etc., it is likely that the maintenance action takes place sequentially over an extended period of time, implying that different sections of the network underwent the MMAs at different periods. This forces the development of a model based on a relative time scale (i.e. time since last major maintenance event) and the combination of data from different sections of a grid, under a normalization scheme. Additionally, extended maintenance times and sequential execution of the MMAs make it difficult to identify failures occurring before and after the preventive maintenance action. This results in the loss of important information for the characterization of the failure process. A simple model is introduced to determine the optimal MMA interval considering such restrictions. Furthermore, a case study illustrates the optimal tree trimming interval around an electricity distribution network.
Optimal reconfiguration of Radial Distribution System (RDS) is done under the umbrella of Supervisory Control and Data Acquisition (SCADA) systems to achieve the best voltage profile and minimal kW losses amongst several objectives. This problem requires the determination of the best combination of feeders from each loop in the RDS to be switched out such that the resulting RDS gives the optimal performance in the chosen circumstance. The problem has a discontinuous solution space and certain problem variables assume discrete values of zero or one. This paper proposes a method that uses fuzzy adaptation of Evolutionary Programming (FEP) as a solution technique. FEP technique has been chosen as it is particularly suited while solving optimization problems with discontinuous solution space and when the global optimum is desired. Fuzzy adaptation of EP is necessitated while considering optimization of multiple objectives. The proposed method is tested on established RDS and results are presented.
This work presents a model to evaluate the Distribution System Dynamic De-adaptation respecting its planning for a given period of Tariff Control. The starting point for modeling is brought about by the results from a multi-criteria method based on Fuzzy Dynamic Programming and on Analytic Hierarchy Processes applied in a mid/short-term horizon (stage 1). Then, the decision-making activities using the Hierarchy Analytical Processes will allow defining, for a Control of System De-adaptation (stage 2), a Vector to evaluate the System Dynamic Adaptation. It is directly associated to an eventual series of inbalances that take place during its evolution.
When an isolated power system encounters a serious disturbance or a large generator unit trip, the system frequency may drop if total generating power is not able to supply the load demand sufficiently. Since an isolated power system possesses a lower inertia with limited reserves, load shedding becomes a critical solution to restore system frequency. In this paper, the initial rate of change of frequency is first detected. A designated time interval and a modification algorithm that considers the maximum frequency change at the last step are integrated to complete a load shedding task. Features of the method include the easy determination of shedding loads and fast trip of the load in anticipation of avoiding the occurrence of over-shedding or under-shedding. Numerical simulations have solidified the effectiveness of the proposed method for the application.