Reliability Modelling of Uninterruptible Power Supply Using Probability Tree Method

The unreliability of public power lines have led to the need of uninterruptible power supply (UPS). Utility power failures will cause unacceptably high risk to the profitability, existence and growth of the vital aspect of business that depends heavily on uninterrupted power supply. For this reason it is important to develop a method to estimate the reliability of such system, to ensure that it will perform satisfactorily when needed. This paper describes and discusses an approach to predict the reliability parameters of the UPS system using the probability tree method. Important UPS reliability parameters such as failure rates (lambda), mean time between failures (MTBF), and reliability (R), can be obtained from this method. These quantitative reliability parameters can play an essential role in selection and application of the UPS. The method was applied to different topologies of UPS systems and comparisons were made between the results obtained form probability tree method and the reliability block diagram (RBD) method