Power generation, circulating current problem
Power generation, circulating current problem
(OP)
Could anyone tell me the best method for making two entirely different generator sets load share. The main generator is driven by an old Ruston TA gas turbine with a mechanical governor set at 5% speed droop, the standby generator is a Caterpillar diesel set bought as a prime stand alone generator. When the two are paralleled the circulating currents are 2000A plus! Obviously a new governor will have to be purchased for the Caterpillar so it will be able to load share. Is it possible to accomplish this by connecting the two AVR'S together using VAR load sharing relays and motorised potentiometers? Any suggestion would be gatefully accepted.






RE: Power generation, circulating current problem
Possibly you will need to replace AVR's. If you do then Basler make an excellent range of products and are worth looking at. I have used their digital microprocessor based DECS in the past and found it to be excellent (and reasonably priced). Having AVR's with under and overexcitation limiting would also help.
IMO, you are correct to be looking at the governors. Does the cat governor have droop? It will need to have if it is to share kW load. Check out the Woodward website for more information.
Regards
RE: Power generation, circulating current problem
RE: Power generation, circulating current problem
RE: Power generation, circulating current problem
skeandhu
The problem of circulating current is reffered to the incorrect reactive power sharing as bigamp mentioned; this means there are incorrect/inaccurate settings of voltage magnetude and/or voltage droop.
You have to note that whatever the method of reactive load sharing, the need for parallel droop kit connected to AVR is indespensible to get a stable reactive power sharing.
wbd
Could you please explain the link between the winding pitch and circulating current: are there certain constrains in paralleling full pitch to 5/6 or 2/3 pitch alternators.
Thanks in advance
Regards
RE: Power generation, circulating current problem
RE: Power generation, circulating current problem
Are you able to manually adjust the AVRs to reduce circulating curent? If not, it is possible automatic controls may not be able to do any better.
RE: Power generation, circulating current problem
In order to share correctly you should have the controls set for droop (as Bigamp states) and the AVR's and Governors set regardless of rating of the sets to the same settings, typically 4%. Having one set in Isoch will cause problems as its flat response will fight for the load or reactive load as there will be no stability with the Ruston sets.
The QCC circuit should be connected between the Rutsons and the Cat in order that sharing of the Mvars takes place automatically.
Hope this helps, Coingy
RE: Power generation, circulating current problem
RE: Power generation, circulating current problem
RE: Power generation, circulating current problem
RE: Power generation, circulating current problem
In practical applications we have had to adjust the AVR controls to see if the problem can be balanced by adjusting excitation level. If not, then the problem is reactive and you will need to add reactance to one of the machines on the grounding leg. The reactor impedence can be calculated using Bergen as a reference.
Hope this helps.
Jim
RE: Power generation, circulating current problem