Spare Assessment of Distribution Power Transformers using Three Markov Models

This paper presents a simple probabilistic method for determining the numbers of spare units (regular spare transformers and mobile unit substations) required for a system of similar distribution power transformers in order to meet a pre-determined level of the system availability. The proposed method is based on 3 Markov models representing transformer minor failures (Class II failures), transformer major failures (Class I failures) and the use of a mobile unit substation (MUS). The MUS model is convolved with each transformer failure model to determine the system availability as a function of the number of spare units. The new method of assessment produces the same results as those obtained using the previously used methods and the Markov models used are much simpler. An example is used to demonstrate the proposed method and to compare its results with the previously used methods.