Sir,

from above explanation I have understood that steam or fuel inlet will be constant to turbine whatever may be the load is if it is in droop mode and steam/fuel inlet will change only if operator or any other system increase/decrease the speed reference.

I have one question if one turbine is running in island mode but in droop mode at 80% load and suddenly its load shed and remaining load is 10% and operator do not take any action than will this turbine trip on over frequency? because fuel/steam inlet will remain same and in this case prior to load shedding fuel inlet was for 80% load and because load is shed away than excess steam/fuel should increase the speed and so the frequency of generator and trip on over frequency because steam/fuel inlet will not change in droop mode without operator action. is it like this?

 

Sir,

The answer to the question: Would the generator set (prime mover and generator) trip on over frequency would depend on the setting of the over frequency relay. I have been to some sites where the over frequency relay is set extremely high, because of frequency fluctuations in the grid, or the inability of the governor to maintain speed when isolated from the grid; the plant supervisors have determined it's more "desirable" to live with frequency excursions than blackouts.

So, it really depends on the setting of the over frequency relay. But, you are correct--the speed and frequency of the generator set would increase, significantly, but whether the unit would trip on over frequency depends solely on the setting of the relay.

 

Manoj Dubey,

Hmmm..... Seems someone didn't like my response. Let's assume the turbine was operating by itself with no other generator-sets synchronized with it, the load on the generator is nearly purely resistive (it has very little, if any, resistive component) and that the prime mover's governor has 5% droop. If it was operating at 80% of the prime mover's rated load that means the prime mover speed reference would be (100 + (0.8 * 5)) 104%. If the load reduced by 70% of the prime mover's rated power output that would translate to a frequency change of (0.7 * 5%) 3.5%; for a machine which operates (nominally) at 50 Hz, that translates to a frequency of (1.035 * 50) 51.75 Hz.

So, if the over-frequency relay was set for something less than 51.75 Hz, then the answer is: Yes; it would trip.

If the over-frequency relay was set for something more than 51.75 Hz, then the answer is: No; it would not trip.

This presume the prime mover and its auxiliaries are in a new and clean condition and that the ambient conditions of operation at at or very near rated, and the energy supply conditions are at or near rated (BTU content; pressure; temperature; etc.). Again, the answer above presumes there is only one generator-set supplying the load in this discussion and that its governor is operating in Droop Speed Control mode when the loss of load occurs. As stated above, it is presumed the prime mover's governor has a 5% Droop Setpoint, and that the nominal frequency of the generator is 50.0 Hz. These are all ideal conditions and do not take into account any reactive "load"--that is, it also presumes a nearly purely resistive load.

The operator would have to reduce the turbine speed reference to somewhere around 100.5% in order to return the frequency to near rated if the load remained stable at approximately 10%.

Better?

 

gshan,

In my experience, most all of the governors I have worked with or been exposed to were all capable of Droop Speed Control, and most of those were also capable of Isochronous Speed Control. I can only recall one instance of a governor that was only capable of Isochronous Speed Control and not Droop speed control, and that was on a shipboard application on an emergency generator that could only be operated if none of the other ship's generators were on-line producing power.

How do I know that if the Diesel engine governor is equipped with only Isochronous capability, droop capability or is it capable of fixed kW? or both?
Say, I would like to operate all three generators (two large units and one smaller unit in parallel) while running in island mode. The small generator is intended to run in base load mode (fixed kW output) with power factor control and the large units to be run in droop.
Is it possible to manage this setup only through the Power Management System (PMS)? I’ve come across information online suggesting that a dedicated controller may be necessary to parallel a small generator with larger units to achieve the set up of running the smaller one in fixed kW mode.

 

@Selk,

See the answer to your nebulous question in another thread. You would need to know how the three generators are capable of being operated and how they are normally configured to operate. Reading the manual provided with DG3 is a good start, but it's possible that it's not configured to be capable of any other operation than the one the original system designers were told to make the system operate.

 

@Selk,

See the answer to your nebulous question in another thread. You would need to know how the three generators are capable of being operated and how they are normally configured to operate. Reading the manual provided with DG3 is a good start, but it's possible that it's not configured to be capable of any other operation than the one the original system designers were told to make the system operate.

As I read the datasheet, the engine has a electronic governor so it should have capability to operate both in Isochronous/droop; so the target is if the Emergency tie breaker is closed, the emergency generator should operate in fixed kW mode and if the tie breaker is open, the emergency generator should be operate in Isochronous mode. Now the question is to achieve this, do I really need the dedicated controller for this or should only PMS sufficient