Research On Reliability And Risk Evaluation Methods Of Distribution Network

Reliability evaluation and risk assessment of distribution network as the basic means of identifying the weak link of network structure are important guarantee for the reliable operation of the power grid. It is important theoretical and practical significance to conduct in-depth research on these two issues.Reliability evaluation of distribution network is an effective method for the planning and operations of distribution network. After introducing the basic theory of reliability evaluation for distribution network, the current commonly used reliability evaluation methods of distribution network are analyzed and compared. Fault features of distribution network connected with distributed generations(DGs) and energy storage devices, and impacts of DGs on distribution system reliability are discussed.Based on the traditional traditional reliability evaluation methods of distribution network and the characteriscs of DGs, a novel reliability evaluation method suitable for both traditional distribution network and distribution network connected with DGs is proposed. Firstly, according to the islanded operation mode of Microgrid, the fault classification mode for traditional distribution network is modified. Secondly, through the research on the generation characteristics of traditional DGs and renewable DGs,probabilistic models of various kinds of DGs are given. Finally, synthetically considering load shedding and load rejection, a probabilistic model of the abundance of supplying power by DGs during islanded operation of microgrid to consumers is put forward and successfully applied in the reliability evaluation of complex distribution network containing microgrids. The effectiveness of the proposed evaluation method is validated by simulation example.Risk assessment of distribution network which can eliminate the potential safety hazard of distribution network is the basis of achieving self-healing. After introducing the basic theory of risk assessment for power system, the component outage model,state probability model and systems of evaluation index are analyzed. With reference to safety assessment methods for transmission grid and considering the differences between the transmission grid and distribution network, a suitable risk assessment approach of distribution network based on the fault outage economic losses is proposed.This method considers both the failure rates of all kinds of components and losses caused by all kinds of components for failure. Firstly, according to the characteristics of the distribution network, its structure is appropriately simplified, and thedistribution network is partitioned with various types of switches as boundaries.Secondly, adopting the customer survey method, the unit power economic losses of different kinds of power users is attained. Based on the linear correlation analysis of the data, the unit power economic losses function of different kinds of power users is fitted by using least square method. Finally, according to the theory of risk assessment,the risk values of each region, sectionalizing switch and the whole feeder are calculated by regarding each region and all kinds of switches as the evaluation unit and treating the blackout economic losses as the severity. The weak link in the distribution network can be found through the risk values. A simulation example is used to verify the proposed assessment method. The results show that the risk values by the proposed method are clear, which can accurately obtain the weak points in the distribution network, and can provide effective reference for the scheduling department.