Advanced Materials Research Vols. 1070-1072

Abstract: Reactive power optimization for distribution network with distributed generators is a complicated nonconvex nonlinear mixed integer programming problem. This paper built a mathematical model of reactive power optimization for distribution network and a new method to solve this problem was proposed based on semi-definite programming. The original mathematical model was transformed and relaxed into a convex SDP model, to guarantee the global optimal solution within the polynomial times. Then the model was extended to a mixed integer semi-definite programming model with discrete variables when considering discrete compensation equipment such as capacitor banks. Global optimal solution of this model can be obtained by cutting plane method and branch and bound method. Numerical tests on the modified IEEE 33-bus system show this method is exact and can be solved efficiently.

Abstract: The emergence of electricity transmission with farther transporting distance, extra-higher voltage and greater transporting power and the formation of the regional interconnected power grid have greatly increased the probability of blackout, this phenomenon has fully exposed the vulnerability of large-scale interconnected power systems. In this paper, Electrical betweenness based on load transfer coefficient is proposed to construct structural vulnerability assessment index. Meanwhile, it is verified that the method is rational and available by analysising the difference of the IEEE-39 system between three attack modes.

Abstract: In the process of the optimal allocation of microgrid system, two layers of coordinated dispatch strategies has been used in this paper. In the first layer, diesel generators and batteries are coordinated dispatched each other. The diesel generators begin to work before state of charge (SOC) of batteries reaches the lower limit. In the second layer, the power of batteries and super capacitors are distributed based on the dynamic characteristics of the hybrid energy storage system. Based on the coordinated dispatch strategies, the optimization models of DGs in microgrid system are constructed which considers the comprehensive cost of system as the optimization objective function and adopts the reliability indexes as the constraints. Genetic algorithm is used to solve the objective function. With the example system, it verifies the correctness and effectiveness of the models, the algorithm and the coordinated dispatch strategies.

Abstract: This paper analyzes the difference between conventional power supply and inverter power supply short circuit characteristics, pointing out that the short circuit current does not contain transient DC component. The inverter power supply can be regarded as AC current source with sudden change of current at moment of short-circuit to calculate the current periodic component. The method to calculate the short circuit current of power grid with both conventional rotating generator and inverter power supply is proposed and evaluated.

Abstract: In order to make the relay protection setting value online checking work more scientific and perfect, this paper studies the integration of county of relay protection setting value online verification scheme based on. Firstly, the county to achieve the integration constant value on-line check the general introduction, focuses on the display data acquisition and the checking calculation; then the county integration interface setting strategy of online check, describes the intelligent interface of intelligent don't know County, interface verification principle and interface design check the principle of selection; finally summing junction surface setting technique of on-line verification.

Abstract: A new development technique or method of graphical distribution network theoretical loss calculation software which based on Visio is presented in this paper. The software not only uses the graphical functions of Visio, but also fundamentally overcome the serious shortage of the Microsoft Visio VBA, it makes the drawing program in power system application software from the traditional VBA model to the embedded mode, and it can achieve the real time control of graphical distribution network theoretical loss calculation software. The study and applications show that this technical innovation gives a new effective approach for the development of graphical power system application software.

Abstract: Proposed general distribution power flow algorithm based on the current network equation. The power flow equations of the algorithm based on the node current balance, and the Jacobian matrix is a constant coefficient matrix compared to the conventional Newton method. It has the characteristics of easy programming, and the method has universality at the same time. It can be used for radial distribution network and systems with loops. The example shows that the method is superior to conventional Newton method on speed and convergence.

Abstract: The prominent role of cascading outages in recent blackouts has created a need in security applications for evaluating line outage distribution factors (LODFs) under the multiple-line outages. Two fast algorithms of LODFs with multiple-line outages are proposed in this paper. In the first method, the double-line outage LODFs are expressed in terms of single-line outage LODFs, and it can be extended to N-k (k≥2) contingencies without any complex matrix operation through the recursive theory. In the second method, a computationally efficient expression of LODFs based on power transfer distribution factors (PTDFs) in pre-contingency network is presented. Numerical simulations are carried out on IEEE 14 and 118-bus test systems. The results show that both methods can effectively improve the computation speed of multiple-line outage LODFs.

Abstract: A method for fast search of dangerous lines in power flow transferring was put forward. Search the equal-phase parallel lines of the overload line by graph theory and voltage phasor angle. Search the shortest path between the end nodes of the overload line which went through the equal-phase parallel lines. The lines on the paths belonged to the power flow transferring line set, where the lines with high active power flow distribution coefficient were dangerous lines in power flow transferring. The method is more targeted in the search for power flow transferring path. It will not leave out dangerous lines for only looking for the shortest line between the two nodes of the overload line, and it wil not select the redundant lines for searching the K shortest paths between the two nodes of the overload line. This method is simple and accurate with little calculation. The method is verified by simulation analysis based on IEEE 39 and IEEE 118 bus system.

Abstract: The faulted feeder selection and fault identification under the condition of single-phase earth fault in the neutral un-effectual grounded system (NUGS) has long been a problem. As a matter of fact, existing methods that have been proposed may face some difficulty in the case of some scenarios, as the impact of the Petersen coil must be taken into consideration, or when the accurate location of the faulted point is required and the zero-sequence current cannot be measured. To against this, a novel faulted section identification method based on the transient current distribution is put forward by means of theoretical analysis and simulation study. It is shown by the results that this methods can give accurate location of the fault by comparing the transient RMS value of the upstream and the downstream of the fault point, even though the Petersen coil is switched in.