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In this paper, a cooperative agent algorithm, the ant colony system (ACS), for optimum switch relocation is proposed. Switch relocation is a useful tool for distribution automation, since it can reduce the interruption costs without additional capital investments. The formulation of switch relocation is a combinatorial optimization problem with nonlinear and nondifferential objective functions. In this paper, the authors choose the ACS to solve the problem since the ACS has the characteristics of positive feedback, distributed computation, and the use of a constructive greedy heuristic. One of the main goals of this paper is to investigate the applicability of the ACS-based algorithm in the power system optimization problems. Test results show that the proposed ACS-based algorithm can offer a near-optimum solution for switch relocation. The comparisons of the proposed method with a genetic-algorithm (GA)-based method are also shown in the test results to demonstrate the values of the proposed method. Index Terms--Ant colony system, customer interruption cost, distribution automation, genetic algorithm, reliability improvement, switch relocation.

A novel and fast three-phase load flow algorithm for unbalanced radial distribution systems is proposed in this paper. The proposed method uses branch voltages as state variables and employs the Newton-Raphson (NR) algorithm to solve the load flow problem. By utilizing branch voltages as state variables, a constant Jacobian matrix can be obtained, and a building algorithm for Jacobian matrix is then developed from the observation of the constant Jacobian matrix. A solution technique, which takes the network structure into account to avoid the time-consuming lower and upper triangular (LU) factorization, is also developed. Since the factorization procedure can be avoided, the proposed method can save computation time. For any power system equipment, if its equivalent current injection or admittance matrix can be obtained, it can be integrated into the proposed method. Test results demonstrate that by integrating the Jacobian building algorithm and efficient solution technique, the proposed method is an effective three-phase load flow method and has great potential for real-time use. Index Terms--Branch voltage, current injection mismatches, Newton-Raphson method, three-phase load flow, unbalanced distribution system.

An exact three-phase fast decoupled power flow solution is introduced in this paper. This method uses traditional Newton-Raphson algorithm in a rectangular coordinate system. The Jacobian matrix of the proposed method can be decoupled both on phases as well as on real and imaginary parts. In addition, the memory requirement of the traditional fast decoupled load flow can be reduced to only one-sixth. The need of the complicated mutual coupling terms can be avoided. It is even possible to solve the distribution system with line conductances only. That is, an exact three-phase distribution load-flow program can be executed with minimum data preparation to substantially off-load the burden of distribution engineers. Tests have shown 10 to 100 times performance than other methods for test systems with 45 to 270 buses. Keyword: Power Flow, Fast Decoupled, Newton Raphson.

In this paper, a new fast decoupled state estimator with equality constraints is proposed for the three-phase distribution systems. The Lagrange multipliers were utilized to deal with the zero injections. The proposed method is based on the equivalent-current-measurement and rectangular coordinates. The method uses a compact constant-symmetric Gain matrix which can be decoupled into two 'identical' sub-Gain matrices. The update and factorization of the gain matrix needs to be done only once. Tests have shown that the proposed low-storage method is efficient, accurate and robust in solving the unbalanced three-phase distribution systems. Keywords - State Estimation, Distribution Automation System, Zero Injection, Equality Constraint, Observability Analysis.