Frequency Deviation 2

[edetaen]

I have a 33mW Load and intend to drive it with 3 GTGs running and 1 on standby each rated 12.9 mW,i also have the option of running 2GTS with one on stanby each rated 19mW.
can any one explain to me what frequency deviation issues could arise with either of these options

 

[Desrod2]

I suspect that you are talking MW not mW!
Steady state frequency should be your nominal frequency (50 or 60hz). You will have frequency variations on transient like large motor start/stop. Actual variation value will be related to your load variation and generators parameters. Frequency will change as you switch on/off load and the end of the day, you should have an average frequency value close to nominal.If you have small load variations (<3%) both system should work fine.

 

[edetaen]

My qusetion now is how does this frequency deviations affect the no of GTGs my client is telling me to use 3 + 1 philosophy as against the 2 + 1 philosophy due to frequecy deviations.

 

[crshears]

It doesn't.

The amount of frequency deviation is a direct function of loads being started versus total generating capacity on line; provided the speed droop settings of all units are the same and all units are loaded to approximately the same percentage of their full load capacity, whether you have two GTG's @ 19 MW or three @ 13 MW a piece on line at the time is immaterial.

Generation source reliability and redundancy are anothe matter entirely - but you haven't asked about those!

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[Desrod2]

Usually the number of units is based on load usage, contingency plan, maintenance schedule and expected reliability. How do you plan performing heavy maintenance? Are you ok having one generator out of service for a couple of days while performing maintenance? Is you design for 100% load supply + one unit standby + 1 unit in maintenance? DO you have a different seasonal loading? Never heard of a frequency constraint being considered in such a decision. If you expect large frequency variations on a given event (large load startup for example) you can always have a special operating procedure putting on line the standby generator to help mitigate the impact. If you have indeed a concern with frequency variations, I would suggest performing a transient analysis.