Answer EKM Question 50
Q50. Explain with a sketch “speed droop” in a governor; Answer the following:
A. How is a main engine governor different from an auxiliary engine governor?
B. Explain how load is transferred to an incoming generator explaining your actions with relation to the governor’s droop line.
or $\displaystyle \small \mathrm{\frac{N-n}{n}\times 100}$ percent.
The droop is said to be 'negative' if the speed decreases with an increase of load. A negative droop will cause instability in a governer. Too little droop can cause instability in the form of Hunting, Surging or difficulties in load change. Too much droop can result in slow governor response in picking up or dropping off a load.
A. How is a main engine governor different from an auxiliary engine governor?
B. Explain how load is transferred to an incoming generator explaining your actions with relation to the governor’s droop line.
Answer: Speed Droop: In an Engine fitted with a governor having proportional control, there will be an "offset" i.e gradual fall in speed with increase in load. This is called "droop", usually expressed as the percent speed drop between no load and full load.
In the above graph N is the no load speed and n the speed at full load.
The droop is $\displaystyle \small \mathrm{N-n}$
or $\displaystyle \small \mathrm{\frac{N-n}{n}\times 100}$ percent.
The droop is said to be 'negative' if the speed decreases with an increase of load. A negative droop will cause instability in a governer. Too little droop can cause instability in the form of Hunting, Surging or difficulties in load change. Too much droop can result in slow governor response in picking up or dropping off a load.
Droop is of particular importance in alternators. Without a droop it is not possible to run two or more alternators in parallel. Furthermore the droop characteristics of individual alternator must be similar for proper load sharing. According to class rules, for alternating current installations, the permanent speed variation of the machines intended for parallel operation are able to be equal within a tolerance of (plus or minus) 0.5 percent when load change occur.
A. Difference between Auxiliary engine and Main engine governor:
Auxiliary engines are fitted with isochronous governors with some droop. They are responsible for maintaining the prime mover at a constant speed by adjusting the fuel supply to the engine as per the load change and facilitate paralleling.
Main Engine governors are constant load governors they are responsible to maintain the engine at the load set by operator.
Auxiliary engines are fitted with isochronous governors with some droop. They are responsible for maintaining the prime mover at a constant speed by adjusting the fuel supply to the engine as per the load change and facilitate paralleling.
Main Engine governors are constant load governors they are responsible to maintain the engine at the load set by operator.
B. To Transfer the load from one generator to another they are required to run in parallel. Droop setting is of particular importance in running alternators in parallel. The droop of individual engine governor determines the load sheared by the engine.
Once the alternators are running in parallel load to be reduced on one generator sufficiently so that when put off load the running generator should not experience a load surge.
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