Advanced Materials Research Vols. 805-806

Abstract: Numerical optimization algorithms and heuristic optimization algorithms in reactive power optimization have been introduced. Analysis of the reactive power balance and the compensation, reactive power optimization mathematical model has been studied. Finally, it takes the least net loss as the object functions to optimize the regional power grid reactive power by genetic algorithm. Optimization results show that this method can effectively reduce network loss, and energy-saving effect is remarkable.

Abstract: With the growing scale of power systems in China, short-circuit current levels of power systems have been significantly increasing. Appropriate grid topology adjustment is an effective method for short-circuit current limitation. The specific measures include transmission line outage, transformer outage, etc. In this paper, a practical optimization algorithm of grid topology adjustment is put forward. A weighted comprehensive sensitivity index is adopted to speed up the procedure of adjustment strategy searching. The detailed calculation method of this index for different measure types is presented. And a security & economy assessment is implemented to ensure the feasibility of potential adjustment strategies. Moreover, the framework of an online topology adjustment decision support software based on this optimization algorithm is proposed. The effectiveness of the presented method is demonstrated by the test on a large-scale power system.

Abstract: This paper introduces a novel comprehensive-sequence components based directional relay to improve the protection performance of the power supply system of important power consumers. Based on the analysis of the characteristic of the phase relationship between the positive-sequence voltage and current in the fault conditions, Active Power Factor is defined to track the loading conditions real-time in the power system. In the proposed technique, the sensitivity of this novel relay is self-compensative by the Comprehensive-sequence components Criteria. Actually, by means of the studies on the characteristic of this novel relay, the proposed technique can be self-adaptive to the loading conditions, suitable for any type of fault and hold their fault direction decision stably.

Abstract: Selecting the power supply mode for important power consumers involves two aspects of reliability and economy. Combining with the power system reliability analysis method and taking full account of each component failure mode and their combination patterns, this paper embarks from the reality, accurately calculated the reliability indices of these power supply modes by minimal-cut sets, and then used the reliability indices to estimate the power losses of the users, finally used the theory of reliability cost-benefit and took the minimizing social costs that consist of reliability costs and outage losses as the goal to compare and analyze the reliability cost and the users outage losses under different power supply modes, obtained the suitable power supply mode for different important level of users.

Abstract: This paper proposes a method to evaluate power supply capability of distribution system considering the connection mode of high voltage network. Firstly, based on the operation mode and load transfer of distribution network, the grid structure is simplified by forming incidence matrices between main transformers and high voltage distribution lines. Then a nonlinear programming model of power supply capability is developed through N-1 contingency analysis of high voltage distribution lines and main transformers, and the power supply capability of a distribution system can be obtained by solving the relevant model. The correctness and effectiveness of the proposed method are verified by a case study.

Abstract: The development of wind power and PV has provided an important force for the development of Micro-Network under the islanding state. This paper first gives component model of different part of micro-network. Then show the method of sampling. Moreover, display the assessment of reliability under islanding state. Finally, give the conclusion on the evaluation of the isolated island.

Abstract: In allusion to the problems of corridor scarcity and substation layout during the rapid development of urban economy, a model and method of distribution contact structure optimization was proposed based on power supply capacity. Aimed at satisfying the area load demand, simplifying contact channel, reducing construction cost, firstly, on the base of clearing the concepts of power supply capacity and distribution contact, the calculation method of power supply capacity is established. Furthermore, a model with a target function of unit power supply capacity cost minimum considering some specific bounds of contact branch length, area load demand, the number of main transformer contact channel is built. Finally, the modified genetic algorithm is used to solve the model. The validity and effectiveness of the proposed model and method is verified through the analysis of practical example.

Abstract: Transformers state comprehensive assessment to provide the basis for the repair and maintenance of power transformers .Based on the fault tree analysis (FTA) to find out the impact of the failure of the power transformer factors, and the establishment of the index system to assess the state of the power transformer, application 3 scale analytic hierarchy process assessment model for the establishment of the state of the transformer , and thus the transformer state is divided into five levels. Through the classification of the more conducive to the staff to understand the transformer condition, reasonable arrangements for the maintenance plan .Case analysis to prove, based on the comprehensive assessment of the fault tree and power transformer condition of the Analytic Hierarchy Process method is reasonable and effective.

Abstract: In the distribution system including distributed generators, it is difficult to meet the requirements of selectivity and sensitivity for traditional current protection. Currently, inverter-based distributed generators (IBDG) are widely used in distribution systems. The transient process of IBDG is rapid, and its transient characteristics are influenced by the control strategy. The controlled current source equivalent model of IBDG with positive-sequence P-Q control is put forward. After analyzing the fault characteristics, the protection scheme using negative sequence current is proposed, which can be used in the distribution systems including IBDG under positive-sequence P-Q control. The simulation results on a 10kV distribution system have verified the correctness of faults characteristics and the effectiveness of protection scheme.

Abstract: For the parameter coordination and optimization of PSS in a multi-machine power system, this paper proposes a new method based on the Phillips-Heffron model to search the optimal install locations of PSS, which employs the sensitivity of the system eigenvalue to the PSS gain as the indicator of its install location, i.e. the larger this sensitivity is, the more the system damping can be improved effectively when the PSS is installed at the corresponding generator. Moreover, based on the block matrix theory and the Newton-Raphson iterative algorithm, the proposed method optimizes the parameters of multiple PSS, where the unknown parameters of each PSS is incorporated into the system state equations and solved by the Newton-Raphson iterative algorithm. Such a method takes the interaction among multiple PSS into account, so that the parameters of multiple PSS can be optimally coordinated. The proposed method is applied to the Sichuan Power Grid under different operating modes, and engineering practices shows that the proposed method is effective and robust.