Effects Of Overloading On Generators

It would appear that the <...effects of overloading on life of generators...> can be determined from reports on the <...problems...><...we are facing...> without recourse to international documentation, for this information is available within on the basis that the <...units were overloaded over the past 30 to 35 years...>. That's a contemptible admission.

The concept of an allowable overload is nonsense; if the units were <...allowed...> to be operated at 115%, then 115% is the new 100%.

<unsubscribes>

The problems in winding are as in the pictures(whitish spots on the stator bars outside slots).

The winding of one unit got punctured in MAY this year.new bars were installed in 1/3rd winding(new bars were in storage for 30 years).

So it's fu knackered. What are you going to do now? Look for other people's reports, or replace it?

Any 3 phase generator rated X at 100% can be operated at 115% for a short time.

Apparently, that is not the case at your installation, and you gents have made a case study of your generators. I expect you will have to re-megger the generators, who knows if the winding insulation is still in spec, and if the windings are tight enough to keep using them. If the rotor has held together, it still may need to be gone over with a fine tooth comb by factory reps. GE or Siemens probably would appreciate your business.

Usually, the policy is to add capacity (other fuel source if not hydro) to the system after the first season where you are bumping load limits.

Is "overloaded over the past 30 to 35 years" considered a short time?

Depends if it were periodic practice or sustained overloading greatly reducing equipment life.

H E double hockey sticks NO! We used to do this on what seemed like a daily basis here when the load was high, and the company we were purchasing power from would curtail us for a couple of hours, meaning - we had to scramble and come up with another 20-30 MW somewhere in our system, and it usually meant going over 100% for a couple of hours during the hottest days of summer at the hottest hours.

Tell me you don't think this created some havoc with our equipment?

Based on the tiny sliver of information provided by the OP, I'd say we don't know the extent of the overloads.

My guess is they were under spec'd in the fir$t place and grossly overloaded for 30 years.

NOTE TO OP: You asked for, "Recommendations of international repute like IEC will be preferred."

My recommendation is rewind them and DON'T overload your generators.

As with a lot of places if they figure their budgets and profit margins on near 100% output duty cycles then running at 115% of rated output is 15% more profit out of the same 100% based budget.

it's about one step up there from 'zero maintenance equals zero operating cost' mentality where nothing gets fixed until the machine is totally beyond the ability to function at all regardless of how many bandages are put on it.

BTW before I came along my family were masters at that concept. Barely functional was still functional enough if it didn't cost them any money was their mindset

That is just dumb (if they were to actually believe that). That is not how incremental power works. At the top end of the load curve for a unit, the incremental heat rate is not as low as it is in the middle range of output, simply because elements (mechanical and otherwise) of the cycle are no longer in the optimum range. The generator coils are heating up more, results in more output resistance, etc. Magnetic saturation may set in. There are limits to the physical characteristics of the materials, and the mechanical strength of the system. 15% increase in output probably comes at the cost of a lot more than 15% increase in fuel burn, when going over the 100% mark.

In the lower end of the range past minimum load, 15% increase in load may incur quite a bit less than a 15% increase in fuel burn.

Well you know that the only people who believe that only the smartest and most capable make it management are management themselves.

The rest of of us know better from first hand example.

What an engineer knows and can prove is not the same as what management thinks and feels should be true.

True that.

At least your family was not back in the horse and buggy days, expecting a dead horse to get up and pull the buggy! I diverge into politics by comparing that image to the present course the country is on, and likely to continue.

I'd also remind him that, according to some of his tall tales, the apple hasn't fallen far from the tree.

Pretty much, the only way the apple gets away from the tree is if the tree is on a steep hillside.

No but some days our equipment was dang close to being that old outdated and functional.

It's only been about 5 - 6 years now since the concept of buying good used oversized machines cheap Vs buying smaller undersized machines for similar cost sank in.

Around here a fair condition 50 - 100 HP tractor is very popular for utility use and thus brings a good price. $3000 - $4000 is pretty common.

However larger 120 - 180 HP tractors fit into a category of being physically too big for the little guy who only needs a 50 - 100 HP tractor and being too small for the big farmers who needs 250 - 300+HP field machines so they are dirt cheap. Often times cheaper than the 50 - 100 HP machines sitting next to them at the auction.

As of the last two years I am running a 14' Haybine with a MF 2745 (140+ HP, got it for $3000) which is more than double what the Haybine needs (60 - 80 HP but the tractor handles it effortlessly.

Same with the baler which only needs 40 - 50 HP but we have it on a AC 7050 which is a 175+ HP tractor (got that one too for $3000) to which the baler is an almost unnoticeable load on it.

Similar thing with the bigger loader tractor Vs the old one. The old one is a 1950's Farmall M that's been heavily modified to handle 1200# round bales to which it barely does whereas the newer loader is a AC 8030 (`130 HP we got for $3500) which can pick up two 1200# bales on the front and a third one on the the three point and drive around like that without effort.

Oh come on - EVERYONE runs stuff over loaded at some time. Where I work we have a long standing habit of ordering just a bit less capacity than needed and immediately trying to use what we really require. Our metal shear is a prime example. Specs said it would do 3/8" maximum of 304 ss, but 1/2" of standard carbon steel. The very first cut we did was 1/2" of 304 ss, and it did it. I could list a dozen more similar over loads. Unfortunately, that is the way businesses operate these days.

There is a difference between the old "slip-stick" engineers who designed larger safety margins, than the new generation of computer dynamic simulation designed machines where they shave off these margins to the narrowest levels.

A new machine such as your metal shear, of identical rating....would it hold up to that same test? How many times before the shear breaks, and sends small bits of metal flying through the shop at high speed and kills someone? You tell me....

Don't ask me - I have no say in this. At the time we bought it, I was still serving 2 functions, one of which was maintenance, and I certainly didn't like the idea. The post was to be sarcastic in nature.

I did get your drift, and it is done many times. I also was being somewhat facetious or we would be hearing about many industrial accidents where the shear "exploded" metal shards all over the personnel working nearby.

Have a great day, I am!

Back when I was a service tech for a welding supply business I dealt with those type of customers all the time.

They would come in and tell me what they were working with and ask about what me as a service tech thought was the best machine for the job then when they saw the price tag asked about the next machine down and if it could possibly do the same work to which I usually told them, yes but not well and they would buy that one instead.

The thing was I always told them that if they buy that machine and overwork it they wont be happy with the results and will be back her trying to trade it in towards a correct size machine I recommended they buy in the first place and they are going to lose money on the whole endeavor.

Yep most everyone brought the under sized machines back and lost more money on the trade than had they bought the right machine for the job to begin with. Usually 10% - 20% more than had they did it right the first time which when you're dealing with a multi thousand dollar purchase is a fair hit to the pocketbook and ego of any cheap ass.

Look very closely at the damage you see in your equipment. Document it with a report and pictures. Post it in the internet and come back to read what the effects of continuous overloading looks like.
I can safely say you will get problems with the exciters and windings.

The life of equipment might be limited to 30-35 years by which it will show effects of overloading and needs replacement.

So to guide you where to find the effects of overloading you need to look at your own system.

Sorry I am not certified by any means to tell you anything. It just seemed obvious.

At least he isn't like those guys from India who come here and ask why their windings are turning black when they are running their generators at 200+ % of their ratings and want to push them up to 300% output.

Well yes and no! The history of questions tells me that this might have well been the case....

What you need to do is perform an analysis into the current state of the generators and come up with a plan for repairing or replacing the generator parts or possibly whole generators.

The damage is done (as they say 'the horse has left the barn').

Contact the generator manufacturer for more information on expected life, etc as life is extremely dependent on operational conditions and machine quality and routine maintenance practices and you likely wont find useful life cycle information in standards because of these reasons.

Does this: Core for Stator Winding have any bearing here?

What is your position at the power plant?

Obviously there are no research papers, or reports issued re this subject! I can't believe you have the gall to try to find out more about this issue, even though it is likely that you were not born when it was commissioned and designed.

I am pretty sure you were being tongue in cheek with that last post, so I let it slide.

I am certain both Edison's group, and Westinghouse's group researched the hell out of the "new" Tesla machines (3 phase AC), to see what it took to "break" them. How the hell else would they know what "100%" is, if they didn't take them to the limits of reality, past the limits, and past the limits of the limits? Ever heard of pulling out all the stops? Where did that come from?

Organ players.

I assume pulling out all the stops will result in less harmony, more cacophony?

If the information is not readily available after an internet search, then it could easily be that this particular thread is the <...international...> starting point for the <...preferred...><...Recommendations of international repute...>.

During WWII there was a need to get as much power as possible from existing distribution infrastructure. Studies executed during this time became an ANSI standard, C57.92-1981, the significant portions of the text you can see here:

http://www.usbr.gov/power/data/fist/fist1_5/vol1-5.pdf

The key factor, as mentioned many times above, is the temperature of the insulation system, and the mechanical factors that change as the metallic components expand.

While not aimed at air or gas cooled machines, the considerations are valid, if you consider the thermal capacity of the coolant.

Thank you! I immediately gobbled up that one and socked it away for future reference.

So, it appears that after 35 responses, no one can answer your question. No one has performed a real analytical study that quantifies the impact, which will be derived from a complex set of real operating data on many equipment types and operating conditions, on lifespan of generating equipment. I can't, and I looked. We all know it will be some sort of negative impact, evidence notwithstanding. I think you are wise to ask.

It is good to note that the current state of engineering has gone to hell, compared to the good old days. If we could just get a blow hard billionaire with multiple bankruptcies, trophy wives, and no military or political experience to run the country, it might reverse the trend. Or not.

I did post in #11 above that was what was necessary. Anything else is pure (but reasonable) guess work and assumption given the limited information provided.

Basic effect of prolong overloading of any electrical equipment is temperature rise in conductor and degradation of electrical insulation ,if the temperature rise is above the designated class of electrical insulation. It is estimated that per 8 to 10 degree Celsius rise of insulation temperature over designated temperature class of insulation, the life of insulation is becoming half. Therefore, never overload electrical machinery for a prolong period. Occasionally, short time overload may allowed. For this particular case, detail insulation diagnostic test is required for further use of machine.

Manindra

That answer is anecdotal and informative. It is not, however, conclusive, it is theoretical. Surely some plants runs gensets at rated power, some below rated power, some sporadically 5% above rated power, some consistently 10% above rated power, etc. All eventually will fail or be taken out of service or repaired. The OP wants to know if a study has been done, and now, so do I, since I advise people on load versus supply capacity on very small systems. It is essential non theoretical information created by analysis, not a bunch of retired guys guessing. I love you retired guys, don't get me wrong.

I respectfully disagree that previous poster's comments were anecdotal. Many organic chemistry reaction rates double with 8-10 °C rise in temperature, so I see no particular facts disputing that the oxidation of insulating varnishes should not be doubled in that instance, and the life cut in half (or even less). Of course, this is if and only if the machine temperature is kept that hot constantly. Intermittent temperature spikes might not result in that much damage, but the damage profile increases if a cracking mechanism (where physical cracks form) is involved.

Do you understand the difference between theoretical research, the goal of which is to combine as much empirical data as possible to predict future behavior, and testing analysis, which is a statistical analysis of collected data from actual machinery. Are you trying to say that in this case, you know the answer to the op"s question because you know that high heat causes insulation breakdown?. So what is the answer, If you run a genset for 1% over it's rated output for 50% of the time? At 2% over for 10%? There is an answer, but it has a bunch of 'it depends'. But to say that it is obviously toasted, or not toasted at all are both just guesses. If you could access a broad study, a more informed decision could be made. I can't find a broad study, and apparently, neither can the OP. James I believe you, excessive heat shortens effective life in insulation, which is very likely to negatively impact genset lifespan. That is not the question.