IT IS DEFINED AS DIFFERENCE IN ROTATIONAL SPEED OF THE GOVERNED ENGINE BETWEEN NO LOAD SPEED AND FULL LOAD SPEED. A SMALL DROOP MEANS A SENSITIVE GOVERNOR WHICH IS ACTIVATED TO SWING INTO ACTION WITH SMALL CHANGES OF LOAD AND SPEED. IT MAY CAUSE HUNTING AND FLUCTUATION OF LOAD IN PARALLEL OPERATION.
DROOP % = (NO LOAD SPEED-FULL LOAD SPEED)/NO LOAD SPEED
NOW THE QUESTION IS WHY DROOP IS NECESSARY?
IF AN ENGINE IS RUNNING WITHOUT DROOP, A LOAD INCREASE WILL CAUSE THE ENGINE TO SLOW DOWN. THEN GOVERNOR WILL RESPOND BY INCREASING THE FUEL UNTIL THE ENGINE SPEED HAS RETURNED TO ORIGINAL SPEED. BUT DUE TO INERTIA AND POWER LAG, THE ENGINE SPEED WILL CONTINUE TO INCREASE BEYOND ORIGINAL SPEED SETTING, CAUSING AN OVER-SPEED OF THE ENGINE. THE GOVERNOR WILL AGAIN RESPOND TO DECREASE THE SPEED TO CORRECT FOR THE OVERSHOOT OF THE SPEED. IT WILL OVER-CORRECT THE SPEED IN OTHER DIRECTION CAUSING UNDERSHOOT OF THE ENGINE SPEED. THIS OVER-CORRECTION OF THE SPEED IN BOTH DIRECTIONS WILL AMPLIFY UNTIL THE ENGINE TRIPS ON OVER-SPEED.
THIS INSTABILITY OF THE SYSTEM CAN BE ELIMINATED WITH THE DROOP. AS THE LOAD INCREASES, THE SPEED SETTING OF THE ENGINE IS DECREASED. WHEN THE GOVERNOR MOVES TO CORRECT THE DROOP CAUSED BY THE INCREASE OF THE LOAD. IT WILL BE CORRECTING TO A LOWER SPEED SETTING. THIS LOWER SPEED SETTING PREVENTS ENGINE FROM OVERSHOOTING.
NORMAL DROOP SETTING IS 3% TO 5%.
2 responses to ““SPEED DROOP” IN GOVERNOR”
Dears
Thank you very much
Very important information