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To deal with the deregulated challenges in future power system operations, Taiwan Power Company (Taipower) has taken a strategic approach to implement an extensive Distribution Automation (DA) project including feeder automation (FA), trouble call management, load management, and remote metering functions in its Tai-Chung District. The project was completed in December 2002. For future extension purposes, Taipower tries to develop a comprehensive generalized step-by-step methodology for the economic evaluation of the DA project. This paper presents the methodology and results for the economic evaluation of the Tai-Chung DA project. The potential benefits of the implemented DA functions are quantified using standard mathematic formulas. An economic evaluation method using value-based analysis and present-worth analysis is performed to identify the most beneficial functions in the Taipower's implemented DA functions. Those DA functions that have great benefits should have high priority to be implemented in other distribution districts. Moreover, to find the candidate feeders for further FA extension, the sensitivity analysis of the benefit/cost ratio with respect to different customer types, feeder loads, feeder lengths, numbers of switch, and failure rates is also conducted. Accordingly, the optimum number of switch can be determined under the expected service reliability. The results and formulas obtained in this paper can also be used for return-of-investment or possible performance measure of the DA systems. Index Terms--Customer interruption cost (CIC), Distribution Automation (DA), economic analysis, feeder automation (FA).

A fast harmonic analysis method designed for three-phase radial distribution systems is proposed in this paper. The proposed method is developed based on the exact three-phase component models, frequency-scan formulation, and a commonly used forward/backward sweep technique. The backward sweep is used to build the relationship between branch currents and bus current injections of a distribution system, and then the forward sweep can use the aforementioned relationship to calculate bus voltages. The forward/backward sweep technique is a powerful method and has been widely used in distribution system analysis; however, it cannot be used for harmonic analysis directly. Therefore, the proposed method designs some specific data formats, integrates them into the commonly used forward/backward sweep technique, and derives useful formulas to calculate the effects of system status induced by harmonic pollution. The proposed method is more efficient than the conventional harmonic analysis algorithms since the time-consuming procedure of the admittance matrix inverse is not necessary in the solution procedure. Test results demonstrate the accuracy and efficiency of the proposed method. Index Terms--Distribution automation (DA), forward/ backward sweep, harmonic analysis method, total harmonic distortion (THD), unbalanced three-phase system.

Commercial lithium-ion batteries are playing important roles as supplies for mobile phones, laptop computers, and other electronics. In order to maximize the performance of lithium-ion batteries, an advanced rapid charging pattern is required. In this paper, an Ant-Colony-System (ACS)-based algorithm is presented. The proposed ACS-based algorithm can be integrated into a commercially available battery tester to search for the optimal rapid charging pattern. Experimental results show that the obtained rapid charging pattern is capable of charging the lithium-ion batteries to 70% capacity in 30 min. The obtained pattern also provides 25% more cycle life than the conventional constant current-constant voltage method. Index Terms--Ant Colony System (ACS), lithium-ion battery, rapid charging pattern.

A direct approach for unbalanced three-phase distribution load flow solutions is proposed in this paper. The special topological characteristics of distribution networks have been fully utilized to make the direct solution possible. Two developed matrices--the bus-injection to branch-current matrix and the branch-current to bus-voltage matrix--and a simple matrix multiplication are used to obtain load flow solutions. Due to the distinctive solution techniques of the proposed method, the time-consuming LU decomposition and forward/backward substitution of the Jacobian matrix or Y admittance matrix required in the traditional load flow methods are no longer necessary. Therefore, the proposed method is robust and time-efficient. Test results demonstrate the validity of the proposed method. The proposed method shows great potential to be used in distribution automation applications. Index Terms--Distribution load flow, distribution automation system, radial network, weakly meshed network.

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.

Most electricity service interruptions are due to failures in the distribution network. In a competitive market, service quality and reliability have become an essential part of the business. In order to enhance the reliability in the distribution system, a value-based method is proposed in this paper to take load distribution changes into account and search for new locations of feeder sectionalizers such that the customer interruption costs (CIC) can be reduced. Two stages are involved in the search. Using local information, the first stage determines the search direction and, in the second stage, it decides whether a crossover of the load point is beneficial. To avoid being trapped in a local minimum, a mutation technique is also applied to look for the global optimum. Actual feeders were used in the tests and test results have shown that with a proper adjustment of the feeder sectionalizers, service reliability can be improved and the customer outage costs are reduced. Index Terms--Customer interruption cost, distribution reliability, SAIDI, sectionalizer relocation, value-based planning.

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.

A highly-linear branch-current-based state estimation model for distribution system is proposed in this paper. This algorithm is based on the concepts presented in Baran and Kelley (1995). Baran and Kelley (1995) proposed a novel branch-current-based approach to solve distribution state estimation. However, the treatment of current magnitude measurements and the complicated gain matrix in Baran and Kelley (1995) greatly degrade its value in real-world applications. The approach presented in this paper substantially revised the original method. A new algorithm with constant gain matrix and a decoupled form was developed. Tests have shown that the proposed method is robust, efficient and needs minimal storage requirement. The new algorithm provides a very good theoretical foundation for developing more applications and researches in this area. Index Terms--Branch-current-based, distribution automation system, fast-decoupled, state estimation.