I read here in this web site that "there are Isochronous Load Sharing Schemes whereby multiple units can "share" the task of maintaing grid frequency--but these are not very common and require tuning and testing, both of which make many people very nervous. And, as the size and nature of loads tend to change, the schemes need to be re-evaluated and re-tuned and re-tested to ensure they are working as required--another expense and effort many companies aren't willing to expend once a plant has been commissioned and put in service...."

Can someone explain the concept of "Isochronous Load Sharing Schemes"

Thanks

 

You would be best getting on to the Woodward site, joining up and downloading information rather than have someone here go into a long winded reply here about isochronous load sharing.
http://www.woodward.com

By the way, the AVR has to be set for droop also - usually about 5%.

These systems do not normally require re-tuning if set up properly. The biggest problem that may sometimes cause re-tuning to be required is the engine dynamics can change quite dramatically as the engine wears out. This is usually caused by someone trying to "save a bob" by not doing top end maintenance etc when it falls due.

By the way, generation systems are my main business. I have impelemented hundreds of systems over the years including standby power, power stations, co-generation, SCTT (synchronous closed transfer) etc, nearly all with diesel generators.

 

Many control system manufacturers offer versions of Isochronous Load Sharing--which is allowing two or more (depending on configuration and control system capability) control systems to be operated in Isochronous mode and control/maintain grid frequency.

Without Isochronous Load Sharing, if two or more generators were connected to the same electrical grid while being operated in Isochronous mode they will usually "fight" each other to control grid frequency. The control systems will each be trying to assume as much of the load as possible and what happens is that wild load swings usually occur and grid frequency starts fluctuating; quite often the generators and/or the prime movers are tripped off line which usually leads to even more grid frequency fluctuations.

Isochronous Load Sharing is usually not supplied with most equipment unless purchased as an option. You should contact the manufacturer of the control systems on your units for details of how Isochronous Load Sharing is implemented. Also, it is believed that companies like Woodward Governor have modules which can be applied to many prime mover control systems to implement Isochronous Load Sharing.

As you quoted, implementing Isoch. Load Sharing requires testing and tuning. And, as electrical grids grow and change (as they naturally do) the implementations should be continually tested and tuned. The problem with this is that testing and tuning can result in frequency excursions and even black-outs--which many system operators can't tolerate and so won't complete. As a result, when grid disturbances occur the control systems don't always react as intended--or proven if properly tested--and then lots of people usually get very upset and the phone lines start burning with expletives and threats and all manner of harsh words and recriminations.

And usually some poor soul gets sent to site in a hurry to "fix the problem" only to arrive and be told that under no circumstances will a unit trip or grid blackout be tolerated and if there's any chance that testing/tuning might result in either that it won't be allowed. (Get the idea this author has been in this situation once or twice?)

markvguy