| The electrical distribution network (EDN) has a significant impact of the reliability performance on load points due to directly connecting with customers. Interruptions of load points are mainly caused by the outage of EDN components. It needs the power system operators and designers to collect, assess and analyze the power system reliability based on the adequate statistic data, and recognize the weak parts of the EDN, and make measures to improve the reliability performance of the EDN. Therefore, the electric power with good quality, high reliability and economy can be transfered to customers of EDN. This paper discusses the reliability indices, evaluation models and algorithms for medium voltage (MV) EDN and high voltage (HV) EDN, and their applications to the Yinchuan EDN in Ningxia province. The main contents are as follows:①The basic concepts, reliability indices, models and algorithms of reliability assessment for EDN were discussed. The algorithms of reliability assessment for EDN were partly described simply. The reliability evaluation algorithm based on fault-spreading method for MV EDN was discussed in detail. The algorithm of reliability evaluation based on A.C. power flow method for HV EDN was also discussed in detail.②The algorithm based on the fault-spreading method for evaluating the reliability of complex MV EDN was applied to the Yinchuan EDN. An A.C. power flow method was used to calculate the power flow. A wide range of indices including the indices of load points, feeders and the system were evaluated using the proposed method. Reliability performance comparisons of different substations, different feeders in a substation and different load points in a feeder were conducted.③The impacts of different reliability parameters on the Yinchuan EDN were analyzed. The factors were mainly focused on the failure rates of transmission line and transformers, and scheduled maintenance rate. Impacts of these factors on the feeders and system reliability were compared using a practical EDN in Yinchuan. Several measures, such as installation of switch devices, shortening the supply radius of feeders, installation of tie lines were investigated in this EDN for improving the system reliability performance.④The power flow and the reliability indices of the Yinchuan HV EDN were evaluated. The reliability of this EDN was evaluated based on the following four modes: summer-heavy operation mode, summer-light operation mode, winter-heavy operation mode and winter-light operation mode. The results of power flow and reliability of the EDN were also compared and analyzed.⑤Measures for improving the reliability of the Yinchuan HV EDN were analyzed. As an example, analysis of the impacts of several factors on the system reliability, which are the scheduled outage rate of components, single citcut for transferring power and the "T-connection", were investigated. Based on the winter-heavy operation mode, some measures were suggested to improve the reliability performance of the Yinchuan HV EDN.
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