Graphical and analytical methods for stalling of engine generator set

Natural gas based distributed energy resources (DERs) are likely to be favored by electric utilities in the near future because of the newly found shale deposit resources. Reciprocating engine based generator sets are a leading class of energy conversion equipment from the low kW upto 100s of kW ratings. Standalone engine generator sets with isochronous governors are susceptible to stalling when they are loaded beyond 80% of the rated engine capacity. This paper presents graphical and analytical methods to determine the stalling conditions of an engine generator set. Analytical methods are developed from the first principles of electromagnetic energy conversion to establish the conditions for the synchronous generator to reach equilibrium in steady state. Active power-speed characteristics including the engine fuel map is employed together with the electrical load torque characteristics. Stalling prevention by applying an underfrequency load relief (V/Hz) scheme is also discussed.