Reliability and Availability Comparison of Common Low-Voltage Industrial Power Distribution Systems

A quantitative reliability and availability comparison has been made of three common circuit arrangements used in industrial power distribution systems. This includes a simple radial system, a primary-selective system, and a secondary-selective system. Published failure rates and outage duration times were used for the reliability data of the electrical equipment. Probability of failure and statistical analysis were used in making the quantitative calculations of the reliability and availability of the three power distribution systems. The simple radial system analyzed had an average forced hours downtime per year that was between 5.9 to 9.0 times larger than a secondary-selective system. The importance of two separate power supply sources from the electric utility has been identified and analyzed. This paper contains an approach that could be used to assist in cost-reliability tradeoff decisions in the design of the power distribution system.