What is Speed Droop in Governor ?
In Governor,Speed Droop is the change in speed between No load and Full load as Expressed as a percentage of maximum rated speed.
What is Droop ?
This is Governor function which reduces the governor references speed as fuel position increases.
● It allows engine to run at the lower speed when load increases , and at rated speed at No Load.
●Droop,is expressed as percentage of the original speed setting from No Load to Full Load .It may also be Expressed as
Droop = ( No load frequency -Full load frequency) /No load Frequency
Why Required Speed Droop ?
Let us consider a system without Droop;As the load increases,the speed decreases,the governor will respond by increasing the fuel until engine has returned to the original speed.
Due to combined properties of INERTIA and POWEE LAG the engine speed will continue to increase beyond the original speed setting causing OVERSHOOT in speed.The governor will again respond to decrease feed to correct the overshoot.It will now Overcorrect the speed in the other direction causing UNDERSHOOT.
This over correction of speed in both directions (Instability ) will amplify until the engine trios on OVERSPEED .This problem can be corrected by introduction of DROOP.
WHY SPEED DROOP FOR AUXILIARY GENERATOR NOT FOR MAIN ENGINES ?
For generators,governors are Droop governors with constant speed in order to maintain voltage and frequency while main engine governor need to be able to run at varying speed.
Generator governor use “DROOP” for load sharing where aa for main engine is directly driving the propeller and load sharing is not required.