Generator Low Load

[enghmn]

Dear forum members;
Our electrical generator starts consume oil rapidly (Oil level decrease therefore daily oil top-up is needed!).
The generator supplier claims that the power consumption (measured 110 amp) is less than the generator rating (250 KVA)!
My question is:
Is this the possible reason for the unusual oil consumption? Is there something like MINIMUM power consumption requirements for a given electrical genrator?
Your feedback and help are highly appriciated.
Thank you

 

[Skogsgurra]

I have never heard anything like that. Never. And I have heard a lot.

Waross and Catserveng, among others, are the experts on such matters. They'll be in soon.

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[davidbeach]

If you aren't running it hard enough to keep all the hot parts thoroughly hot all sorts of bad things can happen, including pumping the lube oil up into the cylinders.

 

[Skogsgurra]

As I said, never heard of such a thing. It seems to be a possibility and it could probably happen with older designs. But it would be a poor design that can't tolerate part load. 110 A seems to be high enough a load. Or is the load mostly reactive or capacitive? Then the prime mover doesn't have to work so hard. What is the power factor?

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[wayne440]

First, more information would help. Start with telling us the voltage in use or the actual load in kW. I'm guessing your 250kVA set is rated for around 200Kw, but depending on the voltage in use, a 110A load could be about 13% (240V single phase), 30% (480V 3 phase)or any number. Tell us how many hours the set has - if a very high hour set could be it needs overhaul. If low hours, and assuming the light load your 110A number indicates at lower service voltages, maybe putting it on a load bank for a while will reduce the oil consumption. Research "wet stacking" for relevant information.

 

[wayne440]

Here

http://www.generator.com/experts.php

is a brief article with examples of why light loading may cause issues. DISCLAIMER- not affiliated, blah, blah etc.

 

[electricpete]

I hadn't heard of it either. Here's another reference:

http://www.powerlite.com.au/default.asp?id=30

What happens if I underload a generator?

Engines are designed to operate under varying load, which ranges from maximum to minimum. In relation to diesel generators it is recommended they run at a minimum of 60% load, this insures the engine runs at maximum efficiency. A diesel engine that operates on a light load for long durations runs the risk of glazing the cylinder bore. Should this occur the engine will not hold high loads, it will use excess oil, and blue smoke will be visible from the exhaust. The engine then may require costly major repairs.
Petrol engines are normally not effected by light load running.

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(2B)+(2B)' ?

 

[Skogsgurra]

OK, that's the engine. I read GENERATOR first, but started to think engine later. And there, I have no clue. Pete's quote makes a lot of sense then.

For a car engine - does the same apply? I will tell the sheriff next time I'm caught for speeding "I have to load the engine to avoid glazing". Wonder if that helps?

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[enghmn]

Dear All;

* Thank you for your feedback and please accept my apology for my poor knowledge in this feild.

* Below are some information which may be helpful to understand the existing situation:
- This is a Desiel Engine Electrical generator, 3 phase, 415 volt, 50 Hz and is connected to a transformer that reduce the voltage to 350 volt and 60 Hz to power a soil washing plant.
- The maximum output is 250 Amps.
- The average operation hours of the generator is 16 hours/ day. Total operation hours of the engine is 1,808 hours (268 Starts)
- The generator is working in hard climatic conditions, very dusty & hot (>45 oC)
- The total kW of the plant is 195 kW

* I am not comfortable at all with the supplier feedback about low load. We are topping up 5 liters/ day oil (BP C3 50 Vanellus)

 

[FreddyNurk]

Regardless of any loading of the set, 5L (in what is assumed a 24 hour period) of oil consumption per day is not good, particularly on a set that hasn't had that many hours run.

The numbers don't seem to add up though, 195kW is probably about flat out for a 250kVA set in those sorts of conditions, which doesn't really match up to a maximum of 250A. Nor does a transformer have the ability to change frequency, and the change in voltage would give a different perspective on what the actual maximum current is.

Whilst we're discussing low loading, its also possible to overload a set, and somewhat surprisingly, running it at 100% for long periods of time can also be detrimental.

Either way, with 5L a day of oil consumption, your generator is sounding a bit sad. If its really low loading, waross and catserveng (and others) may be able to comment on loading up the set to alleviate the issue, but I suspect we'll need more numbers to go on first. I've had no experience with engine recovery, though I've seen a few smaller sets run at (around) 20% nameplate rating without too many issues (subject to certain conditions of course).

 

[electricpete]

Maybe the supplier is saying that there was damage caused by sustained operation at low load (in which case we don't expect the condition and oil usage to go away with load increase). That would seem more consistent with the link.

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(2B)+(2B)' ?

 

[TheBlacksmith]

If the engine is a 2 stroke cycle, it is more senstive to light loading. A 2 stroke has air ports cut into the cylinder at bottom dead center, obviously the piston rings are unsupported at the port openings. Low cylinder pressure from light loading will exercarbate this issue. I have seen this design engine stack unburned fuel/oil in the exhaust passages (slobber) during prolonged light loading and then have a stack fire when loading and exhaust temperatures increase.

 

[waross]

Wet stacking, slobbering, this is a condition that does occur occasionally.
The compression ring or fire ring of a diesel engine is designed so that the pressure of combustion acts on the ring to increase the force on the cylinder wall. It is rare but it happens from time to time that the rings of a new engine do not seat or seal properly. Running with a substantial load forces the rings to seat and they will eventually seal under light loads also.
I have cured one set by load banking for several days. Another set cured itself by pumping out all its oil in a few hours and shutting down on low oil pressure. Suppliers have expressed concern a few times when standby sets were over-sized for the normal load.
Another set about the same size as your was load banked for about a week at the insistence of the supplier. The full capacity was needed for motor starting, but normal running load varied from 10% to 25% of the set rating.
At 1800 hours the cylinders may be glazed and it may be too late to correct the condition by load banking.
Has the set been run at less than 110 Amps for a significant time?
Another possibility is a faulty air cleaning system. If your air intake system has a leak that has allowed dirty air to enter the engine the accelerated wear would give the symptoms that you describe.
With your loading and the hours on the set, wear due to dirt ingestion may be more probable than glazing.
Compare the cost of repairs to the cost of a new or rebuilt replacement engine. When you have the numbers in hand, you may consider an old school remedy. I have never done this but I have heard of it from several sources. With the engine running at speed, slowly add about one teaspoon of Bon_Ami (pumice powder) to the air intake. You may try this on two or three consecutive days. This will often break the cylinder glaze but will not help if the problem is excessive wear.
How long have you had this problem?


Bill
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"Why not the best?"
Jimmy Carter

 

[catserveng]

Bill pretty much covered in general what I would have. I'm a bit surprised you're running a 50wt mono grade oil, at least that is what you have referenced in the post above.

Maybe some more details from your end could help you get more specific answers.

How long has the oil consumption been excessive?

What is the rated BSOC (Brake Specific Oil Consumption) of your engine? Usually is given in grams per brake horsepower or kw hours.

Is this a natural aspirated or turbocharged engine?

You state you're running in a "dusty" environment, do you have heavy duty air filters with a precleaner?

Can you provide make, model and year of the engine?

Have you performed any lube oil analysis? I would be interested to see if there are elevated levels of iron, chrome and silicon.

Extended periods of light load operation can be a contributor, but for the size unit you're talking about the amount of consumption in about 16 run hours seems really high. I would suspect based on what's been provided so far that you may have ingested dirt into the engine and "dusted it".

Older engines with rectangular ring packs and low average cylinder pressures were more tolerant of low load operation for long periods of time, newer engines optimized for low fuel consumption and to meet current exhaust emissions regulations are much less tolerant, and are more prone to problems with slobber, wet stacking and excessive oil consumption.

Hope that helps, Mike L.