Abstract
PowerSecure (PS), a subsidiary of Southern Company, operates over 1600 microgrids including a large fleet of standby diesel generators. Machines range from 125 to 2800 kW. There are two missions: standby power after utility failure and load management when utility is available. This report updates generator reliability data published over 20 years ago. These results are first derived from uniform records from a distributed data acquisition system. The unique aspects of this effort include automated data collection, analysis, and storage producing a standardized record for all machines and events. This greatly reduces the effort required to prepare reports and analysis. The automated collection largely eliminates human errors in data entry, and prevents post hoc adjustment of mission success or failure. We are not aware of previous published generator data using automated data acquisition. This study counts all failures and excludes none, whereas previous studies exclude more than half. This analysis expresses reliability as experienced by the customers. The number of machines, years in service, and years of operation greatly exceed the sum of previous published studies, enabling calculation of useful confidence limits. The fleet is heterogenous with machines from over a dozen manufacturers and many power ratings. Machine reliability was consistent across brands, and there is no significant difference in reliability for different size machines. This common assumption was not supported by the prior studies. High-quality data enables reliability growth management practices. The fleet reliability for outage demands of all durations increased from 95% in 2011 to 98% in 2014-18. Analysis of failures arrival time shows that the failure rate is strongly dependent on mission duration. The failure rates after 14 h are approximately 1% of the value for the first 30 min of operation. This has important implications for designing systems to meet specified reliability targets, and in interpreting and comparing results from fleets with different mission durations.
Highlights
A S OUR society grows ever more dependent on continuous availability of high-quality electric power, critical facilities are increasingly protected by arrays of standby generators
By 2014, the fleet reliability had increased to 98%
Several previous studies were based on records from the US nuclear power stations, which employ emergency diesel generators (EDGs) to provide power when offsite utility power is not available
Summary
A S OUR society grows ever more dependent on continuous availability of high-quality electric power, critical facilities are increasingly protected by arrays of standby generators. The standby mission requires successful generator start after utility failure and provision of power to the load until utility power returns. The load management missions include generator start, synchronizing and operating in parallel with the local utility, and safe disconnect from the utility to conclude the mission. Both standby and load management missions can be of any duration. This work does not report on fleet availability, the long-term average fraction of time that the diesel engine generators are in service and satisfactorily performing their function. Failures where operators were able to restart machines were counted as mission failures
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