operating generators in parallel in island mode 1

[tchagui]

Hi,
we are running a power plant composed by 4 identical gas-engine generators (3MW rated power) to power an oil&gas field. The load is equally shared between the sets in line.
We are planning to add 2 gas-turbine generators (4.7MW rated power). First, to cope with the power increase of the field and second having in mind to limit the load variation on the gas-engine generators.
Therefore, we foresee an operation philosophy where turbo gensets would work in load sharing mode (droop mode or isochronous) and gas-engine gensets with a fixed power output set-point.

Will it work? I am wondering if we can set generators' output power setpoints when not connected to an infinite bus (grid)?

Thanks in advance,
Sebastien

 

[rovineye]

Yes. You can use a power management system that allows your gas-engine generators to have a fixed load target, with the tgs sharing the rest of the load.

 

[waross]

Do you want basic and dependable or do you want complex and sophisticated.
With a modern load control panel you can set almost anything you want. If the panel you are considering will not fullfill your wishes just look for one that will. But, if the load control panel ever goes down, your plant may go down until you can locate an expert and transport him to the site.
If you have the expertise on-site to deal with possible failures you don't have a problem.

If you want basic, and basic has worked well for power generation for generations then run all your sets in droop mode.
If your commissioning team has accurately set the dead-rack or maximum fuel adjustment on the sets you have a few options for non-linear load sharing.

When all sets are running in droop,advance the frequency of the base load sets slightly and reduce the frequency of the variable load sets slightly. When the base load sets are at full power output, the maximum fuel setting will limit the load and the other sets will handle load variations.

You may have better results by loading up the gas turbines and letting the internal combustion engines support the load variations.

You will have slight frequency variations, but droop control depends on these variations to provide stable control.

For an installation close to support staff, go with a load control panel.
For a remote area where parts and technical assistance are not readily available, use droop.

I was familiar with one small multi-generator plant that ran in droop mode. The operators checked and recorded all readings every 15 minutes, and tweaked the frequency as required. As a result the frequency variation was much less than the maximum 3% that is common with droop control.

It is also possible to set up a load control panel in such a way that in the event of a malfunction in the load control panel the plant can fall back to droop operation until the load control panel can be repaired. The fall back to droop may require operator intervention, the choice depends on the control philosophy of the plant engineers.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[tchagui]

Thanks Bill,
this gives me the a wide range of actions.

 

[glendale]

You may find it useful to install a load management device such as the BRUSH PRISMIC system. This will automatically ensure that all machines share load proportionally regardless of size, and overcome droop by providing governor/AVR raise and lower commands. If the load management system fails the machines remain stable as they are still operating in droop mode.
PRISMIC can also ensure spinning reserve is maintained by starting and stopping machines as required by the load. It will also act as an under frequency load shedding device on failure of one or more machines.

 

[ScottyUK]

If you enjoy being virtually held to ransom when you need spare parts then that's probably a great idea. Oh, and you'll need to be able to live with 12 - 16 weeks delivery. We have been virtually crucified by Brush over spare parts availability and delivery too many times in the past.


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If we learn from our mistakes I'm getting a great education!

 

[slavag]

Isn't my area.
I heard from guys lot of good words about Woodward systems.

http://www.woodward.com/pubs/pubpage.cfm?

Best Regards.

 

[catserveng]

I have done a number of systems with a mix of recip (gas or diesel and sometimes both) and gas turbines, Usually the systems are in isoch loadshare, and sometimes a mix with some units in baseload and some in loadshare. Most success has been with Woodward DSLC based systems, but have also used PLC based systems from CAT/ISO and Enercon, and a few Encorp "gold box" systems (not my favorite). Lots of offshore and land based drill rigs, some utilites and a few cogeneration systems.

Woodward also has recetnly released the EasyGen control system, but I am new to it and my first few projects have had some minor bugs, but can likely be worked out as the product matures. A number of switchgear manufacturers have their own load share systems, like ASCO, Thomson Technlogy and Enercon.

How you do it depends on how much control you want your operators to have, droop systems have been around for a long time and work quite well, but require a fairly skilled and diligent operations staff to make sure the system operates as expected. A fully automated system with load demand start/stop control and ability to interact with site load shed/load add systems are farily common now in the size system you are looking at, takes the load off the operators but requires good servcie support.

Go to the link that Slava posted above and look for the publication on load management, you can also find some very good information on the Basler Electric website at

http://www.basler.com

Hope that helps

 

[rmw]

Scotty, are you still a Brush user in your new position? It would seem to me that the Prismic system is a little bit of overkill for this application. I once heard of one of their systems controlling all the generators on 4 or more platforms in the North Sea.

rmw

 

[ScottyUK]

Hi rmw,

No, I'n an ex-user now so I can speak freely! I'll see their machines reasonably often in the new position, just I won't have to live with them 24/7/365. Hopefully the operators of the equipment I'm specifying for future plants will benefit from some of my experience. I didn't want to be overly critical of Brush, just they have made hard work of some simple problems in the past.

I agree that Prismic is probably an expensive solution but is certainly a capable system.


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If we learn from our mistakes I'm getting a great education!

 

[NCTHAI]

While running mupliple units, in iland ode, only one generator / unit can be on isochronus mode of control (Frequency control). All other can be on droop control.

Any variation in load will be taken by machine on isochronus control and it will maintain the frequency.

NC

 

[waross]

Hello NCTHAI;
That is the short answer and is correct, BUT, The following machines are actually operated in a pseudo fixed throttle mode. That is, they may be run with the throttles at 80%, 90% or whatever load setting is required. Droop is not required, but is an easy way to both set the throttle to a fixed position when in parallel with a frequency controlling source and to provide speed control in the event that the load is lost on the droop set.
However, in the instance of a dropping load, once the load drops below the capacity of the droop sets, they will increase the frequency as per the droop characteristics and will motor the isochronous set. Operator intervention is needed, possibly at 15 minute intervals. If you automate the control, then your load control panel will replace the operator intervention.



Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[NCTHAI]

Bill,

Yes, I agree with your views.

thanks for your inputs!!

regards,

NC