Ariovaldo V. Garcia

Fast decoupled load flow: hypothesis, derivations, and testing

A framework is presented that allows systematic studies on the hypothesis underlying a variety of versions of the fast decoupled load flow method, and their derivation. Decoupling is not seen as merely zeroing coupling submatrices of a full Newton Jacobian matrix. Instead, it is treated as an intelligent two-step procedure that solves the full Newton iteration equations without extra approximations. A new derivation of the standard fast decoupled method is presented, and the mechanisms governing the good performance of the general-purpose version of the method are clarified. Test results and illustrative examples supporting the basic theory are reported. Testing includes studies on very difficult real-life systems, e.g. a 1138 bus transmission system and a 308 bus low-voltage underground distribution system. >

A Constructive Heuristic Algorithm for Distribution System Planning

A constructive heuristic algorithm (CHA) to solve distribution system planning (DSP) problem is presented. The DSP is a very complex mixed binary nonlinear programming problem. A CHA is aimed at obtaining an excellent quality solution for the DSP problem. However, a local improvement phase and a branching technique were implemented in the CHA to improve its solution. In each step of the CHA, a sensitivity index is used to add a circuit or a substation to the distribution system. This sensitivity index is obtained by solving the DSP problem considering the numbers of circuits and substations to be added as continuous variables (relaxed problem). The relaxed problem is a large and complex nonlinear programming and was solved through an efficient nonlinear optimization solver. Results of two tests systems and one real distribution system are presented in this paper in order to show the ability of the proposed algorithm.

A heuristic method for reactive power planning

An approach for solving power system reactive power planning problems is presented, which is based on binary search techniques and the use of a special heuristic to obtain a discrete solution. Two versions were developed, one to run on conventional (sequential) computers and the other to run on a distributed memory (hypercube) machine. This latter parallel processing version employs an asynchronous programming model. Once the set of candidate buses has been defined, the program gives the location and size of the reactive sources needed (if any) in keeping with operating and security constraints.

Identifying multiple interacting bad data in power system state estimation

This paper presents an intelligent search strategy for the conforming bad data errors identification in the generalized power system state estimation, by using the tabu search meta heuristic. The main objective is to detect critical errors involving both analog and topology errors. These errors are represented by conforming errors, whose nature affects measurements that actually do not present bad data and also the conventional bad data identification strategies based on the normalized residual methods.

Power System Observability Analysis Based on Gram Matrix and Minimum Norm Solution

This paper presents a numerical method for observability analysis and restoration in power system state estimation based on Gram matrix factorization. A method to identify observable islands based on minimum norm solutions is also presented. The method has the advantage of being easy to implement because all information used for the new formulation can be extracted or adapted from operations that are present in conventional state estimation. The observability analysis and restoration are performed in a single step in which measurements and pseudo-measurements are processed. If the system is nonobservable, minimum norm solutions obtained with nonredundant measurements are used to identify observable islands and, in the sequel, with the results of Gram matrix factorization, a set of nonredundant injection measurements that restore the global observability of the system is obtained. This approach is an alternative to the classical observability analysis and results in methods that are robust and suitable to be used in real-time applications. Numerical examples to show the performance of the methods are presented.

On the Use of Gram Matrix in Observability Analysis

This letter presents some notes on the use of the gram matrix in observability analysis. This matrix is constructed considering the rows of the measurement Jacobian matrix as vectors, and it can be employed in observability analysis and restoration methods. The determination of nonredundant pseudo-measurements (normally injections pseudo-measurements) for merging observable islands into an observable (single) system is carried out analyzing the pivots of the gram matrix. The gram matrix can also be used to verify local redundancy, which is important in measurement system planning. Some numerical examples are used to illustrate these features. Others features of the gram matrix are under study.

Heuristic Algorithm to Solve the Short Term Transmission Network Expansion Planning

In this paper, a method for solving the short term transmission network expansion planning problem is presented. This is a very complex mixed integer nonlinear programming problem that presents a combinatorial explosion in the search space. In order to find a solution of excellent quality for this problem, a constructive heuristic algorithm is presented in this paper. In each step of the algorithm, a sensitivity index is used to add a circuit (transmission line or transformer) or a capacitor bank (fixed or variable) to the system. This sensitivity index is obtained solving the problem considering the numbers of circuits and capacitors banks to be added (relaxed problem), as continuous variables. The relaxed problem is a large and complex nonlinear programming and was solved through a higher order interior point method. The paper shows results of several tests that were performed using three well-known electric energy systems in order to show the possibility and the advantages of using the AC model.

A specialized genetic algorithm to solve the short term transmission network expansion planning

In this paper, the short term transmission network expansion planning (STTNEP) is solved through a specialized genetic algorithm (SGA). A complete AC model of the transmission network is used, which permits the formulation of an integrated power system transmission network expansion planning problem (real and reactive power planning). The characteristics of the proposed SGA to solve the STTNEP problem are detailed and an interior point method is employed to solve nonlinear programming problems during the solution steps of the SGA. Results of tests carried out with two electrical energy systems show the capabilities of the SGA and also the viability of using the AC model to solve the STTNEP problem.

Regularized Least Squares Power System State Estimation

Summary form only given. In this paper, a new formulation for power system state estimation is proposed. The formulation is based on the regularized least squares method, which can deal with ill-posed problems. In this approach, the mathematical unfeasibility which results from the lack of measurements is eliminated. A test procedure based on the variance of estimated linearized active power flow is proposed to identify the observable islands. Some systems of the technical literature are used to show the effectiveness of the proposed method.

Dendritic Microstructure Affecting Mechanical Properties and Corrosion Resistance of an Al-9 wt% Si Alloy

It has been reported that the mechanical properties and corrosion resistance of metallic alloys depend strongly on the solidification microstructural arrangement. The correlation of corrosion behavior and mechanical properties with microstructure parameters can be very useful for planning solidification conditions in order to achieve desired final properties. The aim of the present work is to investigate the influence of dendritic microstructural parameters of an Al-9 wt.% Si alloy on mechanical properties and corrosion resistance. The experimental results establish correlations between secondary dendrite arm spacings (λ2) and ultimate tensile strength (σ u ), yield strength (σ y ), corrosion potential (E Corr ), and corrosion rate (i Corr ).