Reliability Assessment of a Large Diesel Generator Fleet

PowerSecure (PS), a subsidiary of Southern Company, operates over 1600 microgrids and as a result manages a large fleet of standby diesel generators. The machines range in power from 125 to 2800 kW. Most machines in the fleet are used in two different missions. In addition to providing standby power after utility failure, most machines serve one or more utility-driven load management applications, including demand response, coincident peak capacity markets, automatic frequency response, and generation during peak spot market prices. MTechnology, Inc., was retained to study the fleet reliability. We began by assessing the reliability of the fleet in 2011. At that time the reliability was 95%, consistent with previously published studies [1] [2] This study counts all failures and excludes none, unlike some previous studies which exclude more than half of observed failures. The intention of this study is to show reliability as experienced by customers. The fleet reliability for outage demands of all durations increased from 95% in 2011 to 98% in 2014–18. We did not find a significant difference in reliability as a function of machine size. We did confirm previous observations that failure rate is strongly dependent on mission duration, with failures after 14 hours occurring at approximately 1% of the rate observed in the first 30 minutes of operation. A benefit of the dual missions is that the average machine runs 40 hours per year. This is a more thorough test than typical 1-hour per month standby machine test protocols. It also ensures frequent turnover of stored fuel and greatly reduces the contribution of aged and contaminated fuel to failures to start and run. The reliability growth management program includes upgrades to the automated data collection and management systems. This paper reports on data from the most recent version of that system. It incorporates data from 2016 through February 28, 2019.