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The recently published idea of treating voltage angles at generator-buses as control variables enables to obtain voltages at load-buses with less computation. However, application of this approach in solving the optimal power flow problem by genetic algorithms may be ineffective if starting values of voltage angles are selected quite randomly. To overcome these difficulties, a new procedure for selection of an initial set of complex voltages at generator-buses is proposed in this paper. With this procedure, one can start the optimization process (i.e., genetic algorithm) with a set of control variables, causing few or no violations of constraints. The application of voltage angles at generator-buses as control variables and the proposed initialization procedure is illustrated on the IEEE test systems. The obtained results are analyzed and compared with the results from the literature. They are competitive, with computational time drastically reduced. Index Terms--Bus admittance matrix, generator-bus modeling, genetic algorithms (GAs), load flow analysis, optimal power flow (OPF).

The admittance summation method is efficient in short circuit analysis of radial and weakly meshed networks. It is especially powerful if all node loads can be represented as any combination of constant impedance and constant current load component. However, in the existing literature one cannot find any explanation how to handle power transformer in that approach. For that reason, the corresponding equations have been developed in this paper along with a procedure for development of a three-winding transformer admittance matrix. In addition, a procedure for handling an arbitrary load was proposed. A large number of tests were performed and results were compared with that obtained by the previously published method. As an illustration, some of the results for single fault currents are presented. It can be concluded that the proposed approach makes the admittance summation method capable to take into account all network elements in a proper way. Index Terms--Admittance summation method, hybrid compensation method, three-winding transformer, short circuit analysis, three-phase network, two-winding transformer.

This paper introduces a novel solution method for solving symmetric tridiagonal systems. The main idea behind it is to construct a specific electric circuit with the same node-voltage equations as the original system. This circuit has a specific "ladder" structure that is efficiently solved using a methodology known as admittance summation method. The proposed method avoids possible zero divisions by exploiting a specific circuit structure. This specific property is an equivalent to a pivoting strategy used in other methods. Performance tests show that the proposed method is comparable to Thomas algorithm, Gaussian elimination adapted for tridiagonal systems and Matlab backslash operator. The procedure executes O(N) times meaning that computation time is linearly proportional to system size. The whole method is coded very concisely. [ABSTRACT FROM AUTHOR]

Many studies and scientific papers have been published that consider the integration of renewable sources in energy systems, using the least-cost optimization models as a long-term generation expansion planning tool. Supplementary to these analyses, this paper focuses on the transmission network capacity for acceptance of variable renewable energy. The hypothesis is that the simplified electric power transmissions system in the long-term planning modelling tools does not reflect properly the capacity for integration of the variable renewable energy. An integrated approach is applied with aim to incorporate the grid expansion needs and costs (using direct current load flow analysis), necessary for increased renewable electricity penetration. The already developed MARKAL-Macedonia model will be used as a case study. After several iterations and feedback loops between the MARKAL-Macedonia and the network model, the expected outcome is to achieve a new cost-effective solution for deployment of variable energy on a larger scale. [ABSTRACT FROM AUTHOR]

The paper presents an approach where traditional Power Transfer Distribution Factors (PTDF) matrix is reduced in size so that it reflects sensitivities of branch flows to changes in nodal power injections at generator buses only. The advantage of the reduced PTDF matrix is in both reductions of decision variables in the optimization procedure and number of columns in branch flow constraints matrix. Furthermore, the number of rows is also reduced on the basis of a simple check, which effectively detects non-binding branch flow limits allowing corresponding rows of the matrix to be omitted. The reduced PTDF matrix was successfully applied in solving two direct current optimal power flow problems: cost minimization and total transfer capacity calculation. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]