Analysis of a diesel-engine driven generating unit and the possibility for voltage flicker

Flicker complaints have been received from customers connected to a diesel engine generator distribution feeder and the voltage causing the flicker has been measured in field tests. These tests confirmed that the voltages vary by up to three percent from normal and this variation begins when the engine-driven generator breaker is closed. The reason for the variation is believed due to the poor quality of fuel used in a diesel engine driven generator connected to the distribution feeder, where the low calorie fuel causes occasional misfiring of the engine. Misfiring of the engine can cause large changes in mechanical torque of the prime mover. This paper shows that such torque changes can cause voltage variations with frequency components that may cause lamp flicker. It should not be implied that engine-driven generators will cause voltage variations of the type noted here, since the variation of voltage also depends on other factors, such as the strength of the interconnection to the electric utility system