Generation Question 3

[UKEng]

Could someone please explain the difference between 'Isochronous mode' and 'droop mode' when talking about two diesel generators connected in parallel on it's own common bus and not connected to a utility. Which method would be the best way to run these.

many thanks

 

[pwrengrds]

'Isochronous mode' is when the generator runs at a constant voltage reguardless of load. 'droop mode' is when the load droops as the load increases. This is so the generators can share load. If connected to multiple generators you should be in droop mode.

 

[bigamp]

Isochronous mode means that the generator will operate at constant speed irrespective of load. This control mode is normally used when you have one generator set running by itself isolated from the grid.

Droop mode means that the generator speed decreases a little with load. This allows generator load control when the generator is running in parallel with the grid or in parallel with other generators but isolated from the grid. It allows for stable parallel operation.

When you have two (or more) generators connected in parallel with each other, but isolated from the grid you can have one in isochronous mode and the other(s) in droop mode. The generator(s) that are in droop mode will operate at the same frequency as the generator that is in isochronous mode. The generator(s) in droop mode will be at constant load whilst the generator in isochronous mode will be the "swing" machine and its load will move up and down as required to ensure that the generatod power matches the load demand.

Refer to the Woodward website for lots of good information on governors and control of generating plant.

http://www.woodward.com

Regards

 

[jbartos]

Suggestion: Visit

http://www.tpub.com/celec/66.htm

http://www.tpub.com/celec/64.htm

etc. for more info

 

[UKEng]

Thanks bigamp, a star for you.
Would it be possible for two or more generators to be run in Isochronous mode or would you you only have one of them in this mode.

thanks

 

[bigamp]

PaulUK,

You can have two or more generators running in a sort of isochronous mode, but to do this you need to have an overall controller for each generator "above" the governor. With Woodward equipment, that would mean using an EGCP2 for each generator. One EGCP2 ends up being a master unit and trims all the other generators via their EGCP2 controllers. The trimming is done via serial link between all of the EGCP2's. This system only works when the generators are running in parallel with each other but isolated from the grid. EGCP2's are fairly expensive.

If you did not have such a system, I think it would not really be possible to operate two or more generators in isochronous mode. To do so they would need to be identical machines, have identical responses and all the governors would need to have identical control settings. Not practically achievable I think.