Study Of Reliability Assessment For Distribution Systems

This paper studies the method of reliability assessment for an electrical distribution system which is composed by mid-voltage and low-voltage power system, and presents the scheme of statistics and analysis for the reliability of low-voltage power system.The assessment method integrates the series equivalent approach and minimal cut-set to evaluate the reliability of electrical distribution net which consists of mid-voltage and low-voitage net on the assumption that there are sufficient and accurate datum. Firstly, reliability models of different element are built in the paper. Secondly, the reliability parameters of virtual series element on the main feeders are computed by series equivalent method. Lastly, indices of different load points are calculated by the method of minimal cut-set. Thus the reliability indices of distribution system are gained. Many practical factors, such as effects of line fuses protection, disconnected switches, scheduled maintenance, spare electrical source, spare transformers in distribution system, are considered in the assessment arithmetic. In the assessment, it is more practical that low-voltage power system is equivalent to an element on the lateral section of mid-voltage system. Especially, the minimal cut-sets are divided into direct cuts and indirect cuts, which makes the effects of elements in cuts on system more legible and exact. The relevant software is programmed by C++ language in the paper. At last, through the reliability calculation of IEEE RBTS 2 bus reliability test system, the method is proved effective.As a separate system, the system of statistics and analysis for the reliability of low-voltage user records reliability datum of every low-voltage user by gathering terminals,collects and deals with these datum with the technique of low-voltage power line carrier by lumped instrument. Last, the datum in the lumped instrument are read in the database of the master station computer by telephone network. The software analyses and computes the datum in database, and gains every reliability index of low-voltage system and creates report forms. The trial operation of this system in Xi'an Power Supply Bureau is satisfactory and demonstrates its feasibility and validity.