The objective of this thesis is to update the outage management system (OMS) in Taipower by verifying the phasing of distribution transformers and the connectivity of customers served by each distribution transformer. The GPS based phase measurement unit (PMU) is used to measure the voltage phasing of the transformer. The power line carrier (PLC) based identifier has been developed to support the identification of distribution transformer and all the customers served. In the thesis, four practical distribution feeders in Fengshan District of Taipower are selected for the update of distribution transformer phasing of OMS system for the update of distribution transformer phasing of OMS system. After correcting the phasing of distribution transformer in the OMS database, the attributes of distribution components are retrieved for the OMS system. The network configuration of distribution feeders is identified by exacting the topology process and node reduction to prepare the input data for load flow analysis. With the monthly energy consumption of customer from the customer information system (CIS) and the typical load patterns of various customer classes, the hourly loading of each transformer can be derived. By retrieving the actual power data of test feeders from the distribution dispatch control center (DDCC), the three phase load flow analysis is executed to solve the three phase currents of trunk line sections, laterals and distribution transformers. The three phase currents solved can therefore be applied to derive the strategy of three phase balancing of distribution feeders.