J.M. Yusta

Ant colony system algorithm for the planning of primary distribution circuits

The planning problem of electrical power distribution networks, stated as a mixed nonlinear integer optimization problem, is solved using the ant colony system algorithm (ACS). The behavior of real ants has inspired the development of the ACS algorithm, an improved version of the ant system (AS) algorithm, which reproduces the technique used by ants to construct their food recollection routes from their nest, and where a set of artificial ants cooperate to find the best solution through the interchange of the information contained in the pheromone deposits of the different trajectories. This metaheuristic approach has proven to be very robust when applied to global optimization problems of a combinatorial nature, such as the traveling salesman and the quadratic assignment problem, and is favorably compared to other solution approaches such as genetic algorithms (GAs) and simulated annealing techniques. In this work, the ACS methodology is coupled with a conventional distribution system load-flow algorithm and adapted to solve the primary distribution system planning problem. The application of the proposed methodology to two real cases is presented: a 34.5-kV system with 23 nodes from the oil industry and a more complex 10-kV electrical distribution system with 201 nodes that feeds an urban area. The performance of the proposed approach outstands positively when compared to GAs, obtaining improved results with significant reductions in the solution time. The technique is shown as a flexible and powerful tool for the distribution system planning engineers.

Integral planning of primary-secondary distribution systems using mixed integer linear programming

Important research effort has been devoted to the topic of optimal planning of distribution systems. However, in general it has been mostly referred to the design of the primary network, with very modest considerations to the effect of the secondary network in the planning and future operation of the complete grid. Relatively little attention has been paid to the optimization of the secondary grid and to its effect on the optimality of the design of the complete electrical system, although the investment and operation costs of the secondary grid represent an important portion of the total costs. Appropriate design procedures have been proposed separately for both the primary and the secondary grid; however, in general, both planning problems have been presented and treated as different-almost isolated-problems, setting aside with this approximation some important factors that couple both problems, such as the fact that they may share the right of way, use the same poles, etc., among other factors that strongly affect the calculation of the investment costs. The main purpose of this work is the development and initial testing of a model for the optimal planning of a distribution system that includes both the primary and the secondary grids, so that a single optimization problem is stated for the design of the integral primary-secondary distribution system that overcomes these simplifications. The mathematical model incorporates the variables that define both the primary as well as the secondary planning problems and consists of a mixed integer-linear programming problem that may be solved by means of any suitable algorithm. Results are presented of the application of the proposed integral design procedure using conventional mixed integer-linear programming techniques to a real case of a residential primary-secondary distribution system consisting of 75 electrical nodes.

Uniform marginal pricing for the remuneration of distribution networks

A new method for distribution access via uniform pricing for the remuneration of distribution networks is presented. The proposed approach merges in a unified framework the investments, the optimal network operation requirements, the effect of the price elasticity of demand, and the application of hourly pricing for demand side management purposes. Hourly uniform marginal prices-understood as tariffs of use of the network-are obtained from maximum social welfare condition sending efficient signals to the utility and consumers, related to the optimal operation of the grid and use of the energy at peak and valley hours. This method is used in the context of a Performance Based Ratemaking regulation to get model companies from operational optimized real networks. Capital fees are integrated in the marginal tariff of use, by means of the New Replacement Value concept, broadly used in yardstick competition. The model is stated as a mixed-integer linear optimization problem suitable to be solved through well-known linear programming tools. The methodology has been successfully tested in a 42-bus test distribution network.

A probabilistic methodology for distribution substation location

A probabilistic methodology is presented, conceived to assist the electric system planning engineers in the selection of the distribution substation locations, taking into account the hourly load changes or the daily load cycle. The hourly load centers, for each of the different hourly load scenarios, are calculated deterministically. These location points, properly weighted according to their correspondent load magnitude, are used to calculate the best fit probability distribution. This distribution is used to determine the maximum likelihood perimeter of the area where the substation should preferably be located by the planning engineers, taking into account, for example, the availability and the cost of the land lots, which are factors of special relevance in urban areas, as well as other obstacles that may be present in the final selection of the substation site. Results are presented and discussed for the application of the methodology to a real case, assuming three different bivariate probability distributions: the Gaussian distribution, a bivariate version of Freunds exponential distribution, and the Weibull probability distribution.

Using interconnected risk maps to assess the threats faced by electricity infrastructures

Abstract This paper describes a methodology for risk identification and risk assessment in electricity infrastructures. The approach leverages risk maps and can be applied to general infrastructure networks. A semi-quantitative assessment strategy that incorporates the creation of risk charts within a risk management framework is also presented. This strategy engages an intuitive graphical representation to identify the most significant threats affecting infrastructure networks. As a result, it is possible to conduct risk analyses of energy supply (and other) infrastructures within a region or country by engaging interconnected risk maps. The application of the methodology is demonstrated using a case study of a Colombian electricity infrastructure, which includes an estimation of the risk components.

Standard levels of energy losses in primary distribution circuits for SCADA application

The reduction of energy losses in distribution systems is an important issue during planning and operation with important technical and economical implications. The standard or normal level of energy losses in primary distribution circuits represents an important indicator for the planning and operation of electrical distribution circuits. It depends upon a number of parameters and variables such as the nominal circuit voltage, the installed transformer capacity, the number of transformation points, the load level, etc. In this article the application of a statistical procedure for the determination of the standard levels of energy losses in primary distribution circuits is proposed. The methodology is applied to a subset of 312 primary distribution circuits out of the total of 819 circuits of the electrical distribution network that serves the city of Caracas and its surroundings. The resultant standard upper and lower levels of energy losses are presented for the 15 different groups of circuits that were formed by the statistical procedure. These limits are used online for the identifleation of those distribution feeders with an operating level of energy losses out of the standard levels of its correspondent statistical group, as candidates for the application of energy losses reduction measures. The developed application software is presently running on-line at the distribution energy management system of the of C.A. La Electricidad de Caracas-AES Venezuela.

Optimal dispatch with reactive power compensation by Genetic Algorithm

this paper presents a Unit Commitment model with reactive power compensation that has been solved by Genetic Algorithm (GA) optimization techniques. The GA has been developed a computational tools programmed/coded in MATLAB. The main objective is to find the best generations scheduling whose active power losses are minimal and the reactive power to be compensated, subjected to the power system technical constraints. Those are: full AC power flow equations, active and reactive power generation constraints. All constraints that have been represented in the objective function are weighted with a penalty factors. The IEEE 14-bus system has been used as test case to demonstrate the effectiveness of the proposed algorithm. Results and conclusions are dully drawn.

New Load Flow Method S-E Oriented For Large Radial Distribution Networks

There is a growing interest in the electric utilities to raise their efficiency in the operation and design of transmission and distribution of systems. This work proposes a new, fast, robust and efficient method for the load flow solution, in balanced and unbalanced radial distribution systems. It is about a sequential method, based on the S-E load flow algorithm devised for transmission networks by Zaborszky in 1981, which has been adapted to distribution systems, orienting the powervoltage (S-E) iterations, to take advantage ot the radial condition of the latter and extending it to handle unbalanced three-phase systems. The iterative process consists of progressively concentrating the load plus network losses at each node, starting from the farend ends nodes and moving toward the substation. Secondly, the nodal complex voltages are calculated from the substation toward the demand nodes, carrying on with this relatively simple procedure, till reaching convergence. The effectiveness of the algorithm is shown when comparing it against other methods widely used in the specialized literature. In particular it is tested against methods proposed by Ardvinson, Shirmohammadi, Ghosh and Das, Jovanovic and Cespedes. The here-in proposed methodology represents a valuable tool that substantially improves the state-of-the-art of the load flow

An efficient method for optimal location and sizing of fixed and switched shunt capacitors in large distribution systems

This paper proposes a computationally efficient methodology for the optimal location and sizing of static and switched shunt capacitors in large distribution systems. The problem is formulated as the maximization of the savings produced by the reduction in energy losses and the avoided costs due to investment deferral in the expansion of the network. The proposed method selects the nodes to be compensated, as well as the optimal capacitor ratings and their operational characteristics, i.e. fixed or switched. After an appropriate linearization, the optimization problem was formulated as a large-scale mixed-integer linear problem, suitable for being solved by means of a widespread commercial package. Results of the proposed optimizing method are compared with another recent methodology reported in the literature using two test cases: a 15-bus and a 33-bus distribution network. For the both cases tested, the proposed methodology delivers better solutions indicated by higher loss savings, which are achieved with lower amounts of capacitive compensation. The proposed method has also been applied for compensating to an actual large distribution network served by AES-Venezuela in the metropolitan area of Caracas. A convergence time of about 4 seconds after 22298 iterations demonstrates the ability of the proposed methodology for efficiently handling large-scale compensation problems.

A General Framework for the Remuneration of Costs and Benefits of Distributed Generation

This paper presents a general framework to remunerate the benefits and costs introduced by distributed generation (DG) by means of generation use of the system (GUoS) tariffs in order to send locational-based and time-based price signals to the market agents. The proposal has two scopes: in the short term, the economical impact of DG on the power loss cost is assessed using an AC fuzzy power flow tool; and in the long term, the economic impact of DG on the investment costs of the network is evaluated in the scope of the optimal distribution network planning including fuzzy risk indexes associated to the intermittency of DG resources by means of a multiple objective linear programming model (MOLP). The models developed were applied and results discussed from a large-scale distribution network