Spare Assessment of Distribution Power Transformers Considering the Issues of Redundancy and MUS Capability

Abstract

Probabilistic methods based on Markov models were developed in the last few years to determine the optimal number of spare transformers (regular spare units and mobile substation units) for a group of similar distribution power transformers. These methods accounted for a number of factors that affected the number of spare transformers. The two issues that would have an impact on the number of spare units are transformer redundancy and whether or not the station has a mobile unit substation capability. These two issues were not fully investigated in the earlier spare assessment work and need to be studied in more detail. This paper describes the recent reliability study performed at Hydro One to address the two issues. The study includes a review of three spare assessment methods, two existing and one new, and a detailed analysis of how each method handles the two issues. Examples are provided to illustrate and compare the various assessment methods and to draw some recommendations with regard to the use of these methods.