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This paper presents an econometric analysis of curtailment costs of renewable energy sources (RES) in Germany. The study aims at explaining and quantifying the regional variability of RES curtailment, which is a measure to relieve grid overstress by temporarily disconnecting RES from the electricity grid. We apply a Heckit sample selection model, which corrects bias from non-randomly selected samples. The selection equation estimates the probability of occurrence of RES curtailment in a region. The outcome equation corrects for cross-sectional dependence and quantifies the effect of RES on curtailment costs. The results show that wind energy systems connected to the distribution grid increase RES curtailment costs by 0.7% per MW (or 0.2% per GWh) in subregions that have experienced RES curtailment over the period 2015-2017. The implication of this finding is that policymakers should set price signals for renewables that consider the regional grid overstress, in order to mitigate the cost burden on consumers due to excess generation from RES. Keywords: RES Curtailment, Spatial econometrics, System integration cost, Grid-related cost, Renewable energy sources, 1. INTRODUCTION In order to mitigate climate change, governments all over the world have been transforming their electricity generation systems from conventional power plants to renewable energy sources (RES). This [...]

A power system is a collection of individual components that compete for system resources. This paper presents a game theoretic approach to the control decision process of individual sources and loads in small-scale and dc power systems. Framing the power system as a game between players facilitates the definition of individual objectives, which adds modularity and adaptability. The proposed methodology enhances the reliability and robustness of the system by avoiding the need for a central or supervisory control. It is also a way to integrate and combine supply and demand side management into a single approach. Examples are presented that use a simple nine bus dc power system to demonstrate the proposed method for various scenarios and player formulations. Index Terms--DC power systems, demand side management, distributed control, distributed energy, game theory, microgrids.

Maintaining the integrity of an electrical distribution network for the supervisory control and data acquisition (SCADA) database is a challenging task due to the increasingly changing network topology. Despite the labor-intensive database maintenance that is prone to human error, the use of inaccurate data can lead to erroneous computational results. This paper proposes an automated framework to extract geospatial datasets for SCADA of distribution systems using two standardized exchange formats: 1) Common information model (CIM/XML) which describes the topology, and 2) CIM graphics in scalable vector graphics (SVG) format from the world wide web consortium (W3C), which illustrates the dynamic and static geographical schematics. A comparator which determines the changes between different datasets is proposed to avoid importing all data. The proposed framework is evaluated using case studies consisting of thousands of CIM-based elements. Index Terms--Common information model (CIM/XML), distribution system applications, electronic data exchange, geographic information systems (GIS), power distribution planning, visualization.

In this paper, an expert system is designed to derive the rephasing strategy of laterals and distribution transformers to enhance three-phase balancing of distribution systems. The heuristic rules adopted by distribution engineers are incorporated in the knowledge base of the expert system in the problem-solving process. The neutral current reduction algorithm is developed to support the inference engine to derive the rephasing strategy to reduce the neutral current of distribution feeder so that the tripping of over-current relay can be prevented and the customer service interruption cost and labor cost to execute the rephasing strategy can be justified by the power loss reduction obtained. To demonstrate the effectiveness of the proposed expert system to enhance three-phase balance, a practical distribution feeder in Taiwan Power Company (Taipower) is selected for computer simulation. By minimizing the objective function subjected to the rephasing rules, the rephasing strategy has been derived to identify the laterals and distribution transformers for phasing adjustment. After executing the proposed rephasing strategy by Taipower engineers, the phase currents and neutral current of test feeder has been collected by the SCADA system to verify the reduction of neutral current. The power loss reduction obtained by three-phase balancing has been solved by three-phase load flow analysis, which is then used to justify the customer service interruption cost and labor cost for rephasing of test feeder. Index Terms--Customer information system, expert system, outage management system.

Lagrangian relaxation with subgradient iterations is applied to the problem of optimal restoration of distribution systems after a blackout. The method breaks the restoration horizon into intervals and develops a restoration plan by finding the status of each of the feeders at each time interval. The Lagrangian relaxation approach allows a computationally efficient calculation of the timing and selection of feeders to be energized. The subgradient iterative approach relates to the selection of a vector of Lagrange multipliers in the optimization process. A restoration index obtained from the dual formulation of the problem is also shown. This index identifies the feeders that are closer to restoration. The proposed algorithm applies to radially configured distribution systems and is an operator-permissive, automated approach. Exampies are shown including a 100-feeder restoration case. Index Terms--Distribution system restoration, distribution systems, Lagrangian relaxation, load restoration, restoration index, subgradient iterations.

This paper presents a hybrid power flow formulation unifying three-phase and single-phase (positive sequence) models. Positive sequence modeling is considered at the transmission level network and three-phase modeling is considered at the distribution level. A passive interface between these networks is proposed. The interface is based on a [pi] element that can represent transmission lines or transformers. The formulation allows both subsystems to be solved simultaneously using the classic Newton-Raphson method. The three-phase subsystem can either be represented in phase or sequence components. Tests in large-scale power systems indicate that the proposed hybrid formulation has the same robust convergence properties of the conventional all-single-phase or all-three-phase Newton-type methods. The use of the proposed formulation is motivated for studies where the focus of the analysis is in the unbalanced three-phase subsystem highly influenced by operating conditions in the single-phase-modeled subsystem. Index Terms--Distribution power flow, network equivalent, unbalanced system.

In this paper, the concepts related to loss partitioning among the phase currents in three-phase distribution systems are revisited in the light of new findings identified by the authors. In particular, the presence of a paradox in the classical loss partitioning approach, based on the use of the phase-by-phase difference between the input and output complex power, is highlighted. The conditions for performing effective loss partitioning without the occurrence of the paradox are thus established. The corresponding results are then used to extend the branch current decomposition loss allocation method for enabling its application to three-phase unbalanced distribution systems with distributed generation. Several numerical examples on a three-phase line with grounded neutral and on the modified IEEE 13-node test system are provided to assist the illustration and discussion of the novel conceptual framework. Index Terms--Distributed generation, distribution systems, loss allocation, loss partitioning, losses, paradox, unbalanced systems.

This paper presents a method for evaluating external equivalent in electric distribution networks (EDN). The proposed method has as its main objectives the reduction of the computational costs in distribution network reconfiguration, investigation of the optimal allocation of banks of capacitors, investigation of the allocation of distributed generation, etc. In these sorts of problems, a large number of alternative projects must be assessed in order to identify the optimal solution. The optimal solution comes up with the voltage level in the load points within specified limits. Consequently, the EDN must retain the external network load points but without major increasing in the dimension of the equivalent circuit. The proposed method has been tested and validated in a substation of the Electricity Utility of Maranhao-CEMAR, in Brazil. Index Terms--Distribution network, external equivalent, network reconfiguration.

On a hilltop in the small city of Vancouver, Washington, just across the Columbia river from Portland, Oregon, sits a concrete building owned by the the Bonneville Power Administration (BPA), [...]

In this paper, a grid-connected distributed generation system, which consists of engine-generator, dc link with multiple energy sources, and inverter, is proposed. All six of the stator leads of the generator, which is the surface-mount permanent-magnet machine, are brought out to the terminal of the generator. Three leads are connected to the inverter, and the others are connected to the utility grid. In this proposed system, the power from the engine-generator and the power from dc link can be controlled simultaneously by only one three-phase power converter. Furthermore, the inductance of the generator functions also as the reactor of ac--dc converter. A control algorithm for the system is developed and verified by experimental results. Index Terms--Distributed generation system, enginegenerator, open-winding machine.

This paper solves the distribution system restoration problem using dynamic programming with state reduction. The algorithm is an operator-permissive, automated approach to the restoration of distribution systems after a blackout. The timing and selection of feeders to be energized are represented as states in a dynamic programming formulation. An enhanced dynamic programming method reduces the number of states by grouping states that are close to each other and selecting the best state. The algorithm was tested on an 8 feeder/32 load distribution system. The method is applicable to radially configured systems. Index Terms--Distribution automation, distribution systems, dynamic programming (DP), service restoration.

The introduction of new energy carriers, such as natural gas and district heating, to energy systems dominated by electrical power will certainly relieve stress on the power system. Some of the end uses initially served by the power system will be gradually decoupled and served by alternative energy carriers. As a result, the specific customer interruption costs and load profiles will change. In this paper, we analyze how the optimal level of switchgear in electric power distribution systems is affected by such changes. The proposed optimization method is based on a genetic algorithm and takes into account the constrained network capacity. Index Terms--Customer interruption cost, genetic algorithms (GAs), network constraints, power distribution protection, power distribution reliability.

In this paper, we study the energy-efficient distributed estimation problem for a wireless sensor network where a physical phenomena that produces correlated data is sensed by a set of spatially distributed sensor nodes and the resulting noisy observations are transmitted to a fusion center via noise-corrupted channels. We assume a Gaussian network model where (i) the data samples being sensed at different sensors have a correlated Gaussian distribution and the correlation matrix is known at the fusion center, (ii) the links between the local sensors and the fusion center are subject to fading and additive white Gaussian noise (AWGN), and the fading gains are known at the fusion center, and (iii) the central node uses the squared error distortion metric. We consider two different distortion criteria: (i) individual distortion constraints at each node, and (ii) average mean square error distortion constraint across the network. We determine the achievable power-distortion regions under each distortion constraint. Taking the delay constraint into account, we investigate the performance of an uncoded transmission strategy where the noisy observations are only scaled and transmitted to the fusion center. At the fusion center, two different estimators are considered: (i) the best linear unbiased estimator (BLUE) that does not require knowledge of the correlation matrix, and (ii) the minimum mean-square error (MMSE) estimator that exploits the correlations. For each estimation method, we determine the optimal power allocation that results in a minimum total transmission power while satisfying some distortion level for the estimate (under both distortion criteria). The numerical comparisons between the two schemes indicate that the MMSE estimator requires less power to attain the same distortion provided by the BLUE and this performance gap becomes more dramatic as correlations between the observations increase. Furthermore, comparisons between power-distortion region achieved by the theoretically optimum system and that achieved by the uncoded system indicate that the performance gap between the two systems becomes small for low levels of correlation between the sensor observations. If observations at all sensor nodes are uncorrelated, the uncoded system with MMSE estimator attains the theoretically optimum system performance. Index Terms--Distributed estimation, wireless sensor network, power-distortion region, MMSE, BLUE.

The Swedish energy agency (STEM) has developed a regulatory model to supervise the revenues of the distribution system operators (DSO). The model is referred to as the network performance assessment model (NPAM). The NPAM calculates customer values for a fictive electrical distribution system, with a total cost referred to as the network performance assessment (NPA). The debiting rate for a DSO is defined by the quotient of the revenue and the NPA. If the debiting rate is higher than a certain value, the DSO is placed under review and could be forced to pay back revenue to customers. A lawsuit is currently in progress on this use of the NPAM. This paper shows results from a comprehensive sensitiveness study of the NPAM investigating the robustness of the model. The investigation shows that the model is not robust, since small stochastic variations in input data could lead to larger differences in the results than those from the model. For example, it is shown that a five-meter difference in the coordinates of the nodes in the reference system could result in a difference of 5 million Euros, i.e., approximately US $6.5 million. The understanding of weaknesses in the NPAM presented in this paper provides an important means for future developments of regulatory models in the world. Index Terms--Customer value, electrical distribution system, network performance assessment model (NPAM), outage cost, performance-based regulation, probability, redundancy, reference networks, regulatory model, robustness and reliability.

A method for optimal planning of radial distribution networks is presented in detail based upon a combination of the steepest descent and the simulated annealing approaches. The object of investigation is the complete network of available routes and the optimization goal is to find the routes that provide the minimal total annual cost. The minimum capital cost oriented solution created by applying the steepest descent approach is used as the initial solution for the optimization procedure that is further improved by simulated annealing to obtain the minimum total cost solution. The method takes into account the capital recovery, energy loss and undelivered energy costs. Index Terms--Annual costs, optimal routing, radial networks, simulated annealing.

Asset management is an important activity in present day distribution system planning and operation. Utilities are constantly striving to optimize the use of resources available for maintenance while ensuring system reliability is within satisfactory limits. This paper proposes a method to allocate maintenance resources to various distribution system assets. To determine the effects of maintenance, a predictive reliability assessment tool is developed. This paper describes the model on which this tool is based. The results obtained from reliability assessment can be used along with an optimizer to allocate resources to various maintenance tasks in a distribution system. Index Terms--Power distribution maintenance, power distribution planning, power distribution reliability, risk analysis.

In distribution systems, network reconfiguration and capacitor control, generally, are used to reduce real power losses and to improve voltage profiles. Since both capacitor control and network reconfiguration belong to the complicated combinatorial optimization problems, it is hard to combine them efficiently for better optimization results. In this paper, a joint optimization algorithm of combining network reconfiguration and capacitor control is proposed for loss reduction in distribution systems. To achieve high performance and high efficiency of the proposed algorithm, an improved adaptive genetic algorithm (IAGA) is developed to optimize capacitor switching, and a simplified branch exchange algorithm is developed to find the optimal network structure for each genetic instance at each iteration of capacitor optimization algorithm. The solution algorithm has been implemented into a software package and tested on a 119-bus distribution system with very promising results. Index Terms--Capacitor control, genetic algorithm, joint optimization, loss minimum, network reconfiguration.

Optimization of network configuration involving the switch statuses is important for the operation in the distribution system. This paper presents a network configuration optimization approach based on the plant growth simulation algorithm (PGSA), which is specially suited to large-scale distribution systems. An elegant design method of the decision variables, which describes the radial feature of the distribution network and considerably reduces the dimension of the variables in the solved model, is developed. Moreover, a detailed description on switch states further improves the efficiency of calculation. The main advantage of the proposed approach in relation to previously published random algorithms is that it does not require any external parameters such as barrier factors, crossover rate, mutation rate, etc. These parameters are hard to be effectively determined in advance and affect the searching performance of the algorithm. The proposed approach is applied to a 33-bus sample system and a large-scale real system. The best solutions of the two systems, which were published in the technical literature, have been found in shorter time than the existing random algorithms. The numerical results demonstrate well the validity and effectiveness of the proposed approach. Index Terms--Distribution system, network configuration optimization, plant growth simulation algorithm (PGSA), power loss reduction.

This paper deals with distribution network (DN) reconfiguration for loss minimization. To solve this combinatorial problem, a genetic algorithm (GA) is considered. In order to enhance its ability to explore the solution space, efficient genetic operators are developed. After a survey of the existing DN topology description methods, a theoretical approach based on the graph and matroid theories (graphic matroid in particular) is considered. These concepts are used in order to propose new intelligent and effective GA operators for efficient mutation and crossover well dedicated to the DN reconfiguration problem. All resulting individuals after GA operators are claimed to be feasible (radial) configurations. Moreover, the presented approach is valid for planar or nonplanar DN graph topologies and avoids tedious mesh checks for the topology constraint validation. The proposed method is finally compared to some previous topology coding techniques used by other authors. The results show smaller or at least equal power losses with considerably less computation effort. Index Terms--Distribution network (DN), genetic algorithm (GA), graph theory, matroid, minimal loss reconfiguration, planar graph, spanning tree.

Distribution restoration process is done by switching actions of sectionalizing and tie switches on the feeders. The state of these switches can be determined by applying logical reasoning. Thus, knowledge-based systems are ideal tools to accomplish the task. In this paper, an expert system is developed by utilizing its fast reasoning mechanism and object-oriented features. The feeder component and configuration data are organized in a hierarchy way using the object-oriented programming paradigm. On the other hand, facts are used for representing the information during inference process. Service restoration procedure proposed in this paper takes load variation into consideration. The simulation results indicate that more solutions can be obtained for service restoration problems when load variation is considered. Another unique property of the proposed system is that it is capable of proposing multiple restoration plans. Multiple plans are important for the system operators since the best solution proposed by the system may not be workable in reality. By proposing multiple plans, the system operator can choose a plan which is more suitable to the real situation for service restoration problems. Index Terms--Expert systems, object-oriented programming, power distribution planning.

This paper describes the principle and implementation of a new MW+MVAr-Miles charging methodology, which was developed to reflect three key cost drivers in distribution network development: the distance used to support nodal real and reactive power injection/withdrawal; the degree of support offered by the network assets; and the operating condition of the supporting assets in terms of their power factors. The inclusion of the latter driver allows the developed charging methodology to reward network users who are contributing to better power factors and better network utilization, while penalizing customers who worsen power factors and network utilization. As a consequence, the charging model is able to provide forward-looking incentives for network customers to behave in a manner to better the network condition, which will in turn help to reduce the cost of future network development. In addition, the separation of real and reactive power pricing would give network users clear indications of the cost of their reactive power draw from the network, which in turn could help them to evaluate the economics in investing in reactive power compensation devices. The proposed charging methodology is demonstrated on a practical eight-busbar distribution system with a mixed demand and embedded generation (EG). This paper results from work undertaken in a project on distribution charging methodologies for Western Power Distribution. The views in this paper expressed are not those of Western Power Distribution. Index Terms--Distribution network charging methodology, embedded generators, network condition, power factor.

This paper presents a monitor positioning algorithm to determine the optimal number of power quality monitors and to decide the locations for a given distribution system. From graph theory, the system topology is formulated into a coverage matrix. The weighting factors of each component are newly defined from the guidelines of monitor positioning suggested. Weighting factors represent the degree of importance in the system topology. Ambiguity indices are suggested to evaluate the monitor locations in terms of topological ambiguity. The optimal number and locations are determined from the optimization routine utilizing the weighting factor and the ambiguity indices. The proposed approach can realize the expert's knowledge on monitor positioning into a sophisticated automatic computing algorithm. Index Terms--Ambiguity, distribution system, event, optimization, power quality, power quality monitor, topology, weighting factor.

During overloads in the mains, the load curtailment applied to interruptible loads is often the only solution to keep the network in operation. Normally, in contingencies, the difference between the power absorbed and the power produced is very low, often less than 1% of the latter. Therefore if all the loads participated in the load shedding program, the discomfort would be minimal, considering its usually short duration. According to this point of view, we present a new approach to the load shedding program to guarantee the correct electrical system operation by increasing the number of participants. This new load control strategy is named Distributed Interruptible Load Shedding (DILS). Indeed, it is possible to split every user's load into interruptible and uninterruptible parts, and to operate on the interruptible part only. The optimal load reduction request is found by minimizing the expected value of an appropriate cost function, thus taking the uncertainty about the power absorbed by each customer into account. Presently, several users such as hospitals, data centres, supermarkets, universities, industries, etc. might be very interested in typical shedding programs as a way to spare money in their electrical account. However, in the future, when the domotic power plants are likely to be used widely, the distributors could interest the end users in participating in DILS programs for either economic or social reasons. By adopting the DILS program, the distributors can resort to the interruptible loads not only in case of emergency conditions but also during normal and alert operations. Index Terms--Black out, demand side management, interruptible load, load shedding, stochastic approximation, uncertain system.

Slow oscillations, with a period of around 15 min, were observed in an 11-kV electrical distribution system. Initial investigations were unable to reproduce the oscillations. Through the use of hybrid system modelling and analysis concepts, however, it was determined that the oscillations resulted from interactions between tap-changing transformers and switched capacitors. The hybrid systems framework was needed to account for the nonsmooth (switched) nature of these interactions. Trajectory sensitivities were used to identify influential parameters. It was found that existence of the oscillations was dependent upon factors that included system fault level, capacitor rating, and regulator deadband limits. In all cases, grazing-type conditions separated oscillatory from steady-state behavior. A system of cascaded tap-changing transformers was also investigated, with the hybrid systems framework revealing coexisting limit cycles. Index Terms--Grazing phenomena, hybrid dynamical systems, limit cycles, postmortem analysis, tap-changing transformers, voltage oscillations.

A major goal for managers of electric power networks is maximum asset performance. Minimal life cycle cost and maintenance optimization becomes crucial in reaching this goal, while meeting demands from customers and regulators. This necessitates the determination of the optimal balance between preventive and corrective maintenance in order to obtain the lowest total cost. The approach of this paper is to study the problem of balance between preventive and corrective maintenance as a multiobjective optimization problem, with customer interruptions on one hand and the maintenance budget of the network operator on the other. The problem is solved with meta-heuristics developed for the specific problem, in conjunction with an evolutionary particle swarm optimization algorithm. The maintenance optimization is applied in a case study to an urban distribution system in Stockholm, Sweden. Despite a general decreased level of maintenance (lower total maintenance cost), better network performance can be offered to the customers. This is achieved by focusing the preventive maintenance on components with a high potential for improvements. Besides this, this paper displays the value of introducing more maintenance alternatives for every component and choosing the right level of maintenance for the components with respect to network performance. Index Terms--Asset management, component reliability importance, maintenance, multiobjective optimization, power distribution systems.

Grid Computing is a promising infrastructure and technology that involves the integrated and collaborative use of Computers, networks, databases and scientific instruments owned and managed by multiple organizations. In this context our research primarily aims at developing an application framework for monitoring the Performance of Power Transmission and Distribution System using Grid Computing. Power Transmission and Distribution System of Electrical Network supplies power to millions of consumers. The demand for electrical energy is ever increasing. Today over 21% of the total electrical energy generated in India is lost in transmission and distribution. It is possible to bring down the distribution losses to the minimum level in India with the help of newer technological options in information technology called Grid Computing in the electrical power distribution sector which will enable better monitoring and control. By monitoring and controlling the parameters such as voltage, load, frequency and power factor in electrical power transmission and distribution systems the line loss will be reduced. When the Power factor is monitored using this Grid computing method, the Substations can maintain their norms by giving proper instructions to the operators dynamically to add the capacitor banks to maintain the power factor so that the line loss will be reduced and the revenue will automatically be increased. Key Words: Grid computing, Transmission and Distribution system, monitoring and control, Line loss, INTRODUCTION The Growth of the Internet, along with the availability of powerful computers and high-speed Networks as low-cost commodity components, is changing the way scientists and engineers do computing, and [...]

The informational problems arising with the privatization process of electric utilities are examined by focusing on energy distribution privatization in Delhi.

This paper describes the development of a solid-state fault current limiting and interrupting device (FCLID) suitable for low-voltage distribution networks. The main components of the FCLID are a bidirectional semiconductor switch that can disrupt the short-circuit current, and a voltage clamping element that helps to control the current and absorb the inductive energy stored in the network during current interruption. Using a hysteresis-type control algorithm, the short-circuit current can be constrained according to a predefined profile. Insulated-gate bipolar transistors and diodes are used to construct the semiconductor switch. Varistors are used as the voltage clamping element. An effective method is adopted to improve the current sharing between parallel varistors in order to provide the required capability of energy absorption. An overall protection scheme for the FCLID is described. A prototype FCLID for 230-V single-phase, or 400-V three-phase, applications is developed and tested. Analyses and experiments are carried out to define the stresses that the main components in the FCLID are subject to. The results show that the developed prototype is capable of limiting a 3-kA prospective short-circuit current to 120 A for a period of 0.8 s, without exceeding the thermal limits of the chosen switches and varistors. Index Terms--Current limiter, electrical power distribution, fault current, semiconductor switch, varistor.

In deregulated power markets, generated power can be time-shifted from a period of low price to that of high price by energy storage with an efficiency penalty. Pumped storage is a common form of energy storage. The total amount of power stored (megawatt-hour) is set by the reservoir capacity. The rate of recovery of stored energy (megawatt) is set by the capacity of the pump/generator and related equipment. A model is developed to maximize the return on investment in pumped storage by varying the generation capacity for a given reservoir to optimize the daily operating hours. Two examples from Alberta, Canada, confirm that the size of pump/generator relative to the reservoir capacity that optimizes daily operating time and return on investment depends on each of the deregulated power market (diurnal price pattern), the site within the power market (site-specific interconnection charges), and the storage technology (energy efficiency). Index Terms--Energy storage, power generation, power industry, power system economics, pumped storage power generation.

This paper proposes an alternative data envelopment analysis method to explore the efficiency, the resource allocation, and the benchmarks of the electricity distribution districts (EDDs) of Taiwan Power Company in 2003. Several empirical results are shown: 1) the EDDs covering the high-tech industry park are more efficient, on average, than ones involved in the nonhigh-tech industry park; 2) the EDDs located in urban areas outperform those located in rural areas; 3) the large-sized EDDs generally are more able to integrate their resources and to operate efficiently; 4) the benchmark-share measure shows that while small-size efficient EDDs can easily become benchmarks, large-size efficient EDDs are deemed as competitive niche players; and finally, 5) the effect on these EDDs merging their activities should be investigated to explore the possibility of increasing competitive advantage in the future. Index Terms--Benchmark-share measure, data envelopment analysis (DEA), performance measurement, technical efficiency.

This paper provides a unified method to model three-phase transformers for distribution system load flow calculations, especially when the matrix singularity caused by the transformer configuration arises. This paper shows that the singularity appears only in certain transformer admittance submatrices and only in certain transformer configurations. The unified method presented in this paper can solve the voltage/current equations in the forward/backward sweep algorithm for various types of transformer configurations, whether or not the corresponding admittance submatrices are singular. Comprehensive comparisons have been made between the proposed approach and other methods. Test results demonstrate the validity and effectiveness of the proposed method. Index Terms--Admittance matrix, load flow analysis, power distribution, power transformers.

The traditional design of distribution networks does not target the satisfaction of individual quality standards such as maximal frequency and duration of customer interruptions. Yet, standards on individual quality are at the basis of most modern quality of service (QoS) regulations. In this paper, we use a matured evolutionary-based application to search for the optimum tradeoff between individual QoS and system reliability. Tradeoff results are presented to compare the traditional with the modern regulation designs and to illustrate that system optimum reliability must be decreased in order to improve individual quality at constant investment. The tradeoff sensitivity to the standards is then illustrated to discuss regulation effectiveness. Index Terms--Optimization methods, power distribution planning, quality of service, regulation, reliability.

The electricity industry is significantly affected by weather conditions both in terms of the operation of the network infrastructure and electricity consumption. Following privatization and deregulation, the electricity industry in the U.K. has become fragmented and central planning has largely disappeared. In order to maximize profits, the margin of supply has decreased and the network is being run closer to capacity in certain areas. Careful planning is required to manage future electricity demand within the framework of this leaner electricity network. There is evidence that the climate ill the U.K. is changing with a possible 3[degrees]C average annual temperature increase by 2080. This paper investigates the impact of weather variables on monthly electricity demand in England and Wales. A multiple regression model is developed to forecast monthly electricity demand based on weather variables, gross domestic product, and population growth. The average mean absolute percentage error (MAPE) for the worst model is approximately 2.60% in fitting the monthly electricity demand from 1989 to 1995 and approximately 2.69% in the forecasting over the period 1996 to 2003. This error may reflect the nonlinear dependence of demand on temperature at the hot and cold temperature extremes: however, the inclusion of degree days, enthalpy latent days, and relative humidity in the model improves the demand forecast during the summer months. Index Terms--Climatic variables, forecasting, load pattern, monthly demand, multiple regression.

This paper describes all innovative scheme based on a pluralistic load frequency control (LFC) and aimed at performing cross-border power control, secondary frequency regulation, and internal congestion resolution. Such an LFC scheme applies to a pluralistic block of control areas, whose regulators can adjust the production of their generators with respect to the request of the coordinating area when the power flows through grid sections exceed their maximum admissible values. This paper introduces the theoretical aspects and functional design of such an advanced LFC scheme, capable of controlling at the same time the cross border exchanges of the pluralistic block and the power flows between network subareas defined as market zones. Simulations on the Italian power system show the performance, main advantages, and limits of the proposed control method. Index Terms--Load frequency control (LFC), power flow congestion, secondary frequency regulation.

It is widely known that corrective switching, including transmission line switching, bus-bar switching, and shunt element switching, may change the states of the power systems, and consequently, affect the distribution of power flows, transmission losses, short circuit currents, voltage profiles as well as transient stability of power systems. In this paper, a new algorithm is developed to find the best line and bus-bar switching action for relieving overloads and voltage violations caused by system contingencies based on a sparse inverse technique and fast decoupled power flow with limited iteration count. A general model of bus-bar switching action is also presented such that the new algorithm can simulate any kind of complicated bus-bar switching action. Furthermore, on the basis of a newly proposed voltage distribution factor by multiple iterations in power flow calculation, a novel algorithm for corrective voltage control by shunt switching is developed. These two algorithms are then integrated into a corrective switching algorithm. Simulation results on the WECC 179-bus system indicate that the new corrective switching algorithm proposed in this paper can effectively solve certain problems of line overloads and voltage violations. The computation time required is also satisfactory. Index Terms--Bus-bar switching, corrective switching, fast decoupled power flow, line switching, overload, shunt switching, voltage distribution factor, voltage violation.

Deregulation of electricity markets is occurring all over the world. This trend introduces new risks and uncertainties into the electricity industry, the most significant being price risk. The spot price of electricity is highly volatile, and the ability to price risk management contracts on this commodity is contingent on a robust and realistic model of the underlying price process. One key driver of electricity spot price is the forced outages of generating plants in the system. The current paper describes a system aggregate model of short-term generating capacity that can be adapted to any generating system of interest. After describing the model, we test it using the IEEE Reliability Test System (RTS). Index Terms--Electricity spot price, risk management, system reliability, Weibull distribution.

The large size of power systems makes behavioral analysis of electricity markets computationally taxing. Reducing the system into a smaller equivalent, based on congestion zones, can substantially reduce the computational requirements. In this paper, we propose a scheme to determine the equivalent reactance of interfaces of a reduced system based upon the zonal power transfer distribution factors of the original system. The dc power flow model is used to formulate the problem. Test examples are provided using both an illustrative six-bus system and a more realistically sized 12 925-bus system. Index Terms--Congestion modeling, congestion zone, dc power flow, distribution factors, electricity deregulation, equivalents.