Generator Start Up vs. Full Speed Operation
Generator Start Up vs. Full Speed Operation
(OP)
I am sorry to pose the following basic question. I am not an EE.
I have a general question regarding the efficiency in or cost of starting a power generator cold to full speed/full load. I suspect the efficiency/cost of this can be broken down into fuel, and wear.
Are there any rules of thumb for determining the impact of this type of start up vs. regular operation at full speed/full load?
Also, is there a rule of thumb in terms of cost or efficiency for running at full speed/no load to going to full speed/full load?
Finally, I suspect the situation would be similar between hydro power and fossil fuel power except for the cost of the fuel?
Thanks a lot.
I have a general question regarding the efficiency in or cost of starting a power generator cold to full speed/full load. I suspect the efficiency/cost of this can be broken down into fuel, and wear.
Are there any rules of thumb for determining the impact of this type of start up vs. regular operation at full speed/full load?
Also, is there a rule of thumb in terms of cost or efficiency for running at full speed/no load to going to full speed/full load?
Finally, I suspect the situation would be similar between hydro power and fossil fuel power except for the cost of the fuel?
Thanks a lot.






RE: Generator Start Up vs. Full Speed Operation
As for efficiency... If this is an emergency generator efficiency has little to do with anything based on the supposition that life, safety, corporate, or business loss, will be avoided by use of the generator. The numbers of which utterly eclipse the expense of 'a start' efficient or otherwise.
Further a generator that is in standby waiting to start into full load without even a one or two minute warm up will normally be kept hot with electricity. This might be anywhere from 100W to 1000W of electrical heat. These days that represents a sizable piece of change that constantly dribbles off the bottom line. (reducing efficiency)
There will be no comparison between running an unloaded generator constantly as a trade off to a rapid start/full load. Running a generator unloaded constantly will destroy it. Will cost 10% fuel usage constantly, and is flat illegal in some locals due to air quality. It will be less expensive to rapid start.
The difference between hydro and fossil are so vast as to render the question.. um..er... does not compute.
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Generator Start Up vs. Full Speed Operation
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Generator Start Up vs. Full Speed Operation
In all cases, the generator itself will respond much faster than the prime mover, no need to worry about the generator.
RE: Generator Start Up vs. Full Speed Operation
RE: Generator Start Up vs. Full Speed Operation
respectfully
RE: Generator Start Up vs. Full Speed Operation
RE: Generator Start Up vs. Full Speed Operation
Inspection is typically required after a given number of starts or equivalent baseload hours.
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RE: Generator Start Up vs. Full Speed Operation
Your point is well taken. I may have meant "What is the energy source of your prime mover?"
Another assumption I jumped to was that "Hydro" power meant utility power. I am now in an area where the word "Hydro" is used to denote either the utility company or power from the utility company.
Respectfully
RE: Generator Start Up vs. Full Speed Operation
AN1,
If that was your question, then the answer would be technically yes, but practically no. There is a difference in the winding resistance with different temperatures. For the most part, stator coils have a negative coefficient of resistance, meaning as the temperature goes up, the resistance goes down. Less winding resistance equates to better efficiency. You should also know however that winding resistance plays only a small part in overall generator efficiency, and the difference between hot and cold resistance will not be that great. So overall the generator efficiency on a cold start vs a hot start or continuous run is very very slight, probably not worth considering. A cold generator will warm up very quickly as well.
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RE: Generator Start Up vs. Full Speed Operation
Thank you for the responses.
I should have been clearer in my question related to power plant generation.
I am trying to determine the added cost of starting up a natural gas turbine/generator to full speed and full load versus its normal operating cost. I was wondering in general terms what the added cost for fuel consumption was and if there was any factor for added wear. Also, I was wondering if this generator was spinning at 3600 rpm but no load was put on it, and then the load was initiated, what added costs there would be.
Finally, for my general knowledge, I was wondering the same for a hydroelectric turbine (Of course, there would be no fuel cost.).
I am a construction manager with a structural engineering background trying to understand the risks of a project. Once this project moves forward, I will consult an EE for the actual numbers for this job.
Thanks a lot.
RE: Generator Start Up vs. Full Speed Operation
Is this in Nigeria? New York? Singapore?
If the generator is on standby doing no useful work for 2 years before loading it.. I can guarantee it would be cheaper to start it!
If it is needed every 20 minutes then it would be cheaper to leave it run.
All the same goes for hydro. Plus umpteen other details. Spilling water may be needed for run off or may cause a later shortage.
What do you want for an answer?
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Generator Start Up vs. Full Speed Operation
Lots of project, site, and machine specifics that would have to be evaluated. One question that would have to be thoroughly worked out is the amount of advance warning for the need of the generated power; you won't be able to rush the startup process.
For a single unit, hydro probably has the ability to add load faster than any other type of prime mover. It would depend on how fast you can open the wicket gates. The first step would be getting the machine up to rated speed, then run up the load.
I think it is probably time to find a consultant who can address the project specifics rather than depending on generalities that may or may not apply for the specific project.
RE: Generator Start Up vs. Full Speed Operation
The fuel consumption figures shouild be available from any manufacturer of turbine sets. Just a phone call away.
You can get a fuel consumption curve vs loading for the set in question.
I don't yet see a size for the set. I am under the impression that the larger the gas turbine, the more of an issue will be the light loading and frequent startups. The manufacturer should also be able to give a "Run time equivalent" for each start. I suspect that the figure will also be dependant on the size of the set.
Gas turbine generators achieve their best economy when a combined cycle is implemented. The heat of the exhaust gas is used to generate steam which powers a steam turbine. If you are asking about frequent starts and light loading, I doubt that you will be able to utilize a combined cycle.
For a project that will require light loading and frequent starting, I suggest diesel up to about 2 Megawatts. Above that size is out of the range of my experience and I'll leave that call to someone with hands on experience with larger sets.
davidbeach, Hydro with a short penstock may beat the diesel response with a short penstock. With a long penstock, the diesel may be able to pick up a block load faster than the water in the penstock can accelerate. Shedding load with a long penstock is an issue.
That said, I think that both hydro and diesel have excellent response and I'm just splitting hairs a little.
In regards to hydro power, I used to live near a series of hydro electric plants that were quite elderly. The utility found that the most economical way to operate the plants was to keep them online at about 10% or less load at all times. This kept the windings warm and dry and kept the bearings lubricated and avoided babbit rubbing, which may occur during startup and which may be the major cause of wear of the bearings. When the system needed more power at peak consumption hours, the central dispacher would phone the plant operator who would open the gates until the machines were developing about 90% power. They never were stopped.
I realize that this control method is not suitable for an islanded installation.
respectfully