08-14-2012 08:37 AM
I have a relatively simple problem but I need a quick answer, please
We are running two 320 ekW 400 kVA 60 Hz 1800 rpm 480 Volt sets for 12 hours a day, each set runs on alternate days. The generators are running at 50% load (200kVA). We have been told by a generator expert that serious engine damage can occur running the generators at this load. I'm not an expert but I find this claim strange. One because If I use the same analogy for a diesel vehicle that means if I drive at 50 kms/hr rather than 100 kms/hr the engine will wear out faster and two why would CAT give no warnings of this in their specification sheets and declare the fuel consumption at 50% capacity on the spec sheets?.
08-14-2012 10:41 AM
Extended run times at lower loads can cause a number of issues, such as poor combustion, "slobber" and deposits forming on cylinders and turbo hot sections. Newer engines depend on cylinder pressures generated by higher loads to properly seal the combustion chamber for best combustion. Also newer engines are more highly turbocharged and operate at settings designed not for optimum combustion but to have best balance between performance and emissions. This narrows the operating range and long term operation at lower loads, typically below 45%, can reduce engine service life.
While I don't find your stated loads levels particularly alarming, you will likely find that there could be increased combustion chamber deposits, coking on the turbo hot wheel, and possbily deposits forming in your exhaust system. Ideally if you could operate the engine at a higher load for a few hours each week, you could probably mitigate most of those problems.
In practise, you just meed to be aware of the symptoms and take appropriate action before small problems turn into bigger ones.
Has the visible exhaust smoke for your "normal" load levels increased?
How is you lube oil life? Do you use sampling?
Do you note any signs of slobber, black streaks coming out of exhaust joints at the head and turbos?
Do the engines maintain stable frequency? Do they start OK?
You also did not state you real power load, in kW. This equates to the flywheel horsepower and is what the engine sees. You may have a low power factor load that would give you a lower kW (real power) load while your kVA (apparent power) is higher. If that is the case then you may be operating the engine at a point where it could have problems.
This is a concern among all engine manufacturers, especially of engines in the size ranges to meet strict US and European emissions standards. Newer design engines are less fuel and load factor tolerant than older designs, the trade off for better fuel consumption and lower emissions, and usually better power density.
Hope that answers you question.
08-14-2012 11:26 AM - last edited on 08-17-2012 02:15 PM by woody
Pretty comprehensive and informative reply. We will check the signs that you have elaborated upon and act if they manifest.
Thanks and regards
09-05-2012 02:32 AM
Reference to 50% Load
Minimum recommended load is about 33% for short periods anything under even then a load bank is recommended. Prolonged underloading without a loadbank will cause Generator to start glazing.
Diesel engines can suffer damage as a result of misapplication or misuse - namely internal glazing and carbon buildup. This is a common problem in generator sets caused by failure to follow application and operating guidelines. Ideally, diesel engines should be run at least 60-75% of their maximum rated load. Short periods of low load running are permissible providing the set is brought up to full load, or close to full load on a regular basis.
Internal glazing and carbon buildup is due to prolonged periods of running at low speeds and/or low loads. Such conditions may occur when an engine is left idling as a 'standby' generating unit, ready to run up when needed, (misuse); if the engine powering the set is over-powered (misapplication) for the load applied to it, causing the diesel unit to be under-loaded, or as is very often the case, when sets are started and run off load as a test (misuse).
Your sescription indicates a prime power rating and if so it appears you have oversized the Generator for the load required
Lawrence De Silveira
Perth UON PTY Ltd
09-05-2012 02:53 AM
I would advise you to look up the Caterpillar OEM recommendations, The best possible load factors to run a generator is between 75% to 90%.
Mike has given you some sound advice here.
I have opened up engines that have been operating on low load conditions only to find a lot of carbon build up on valves,stems, causing valves to stick and making contact with the piston, I always recommend the load factors as recommended by Caterpillar.
09-05-2012 05:39 AM
09-05-2012 09:02 AM
Running the generators at 50% load is not dangerous or harmful, but you must not go below 50% load to avoid certain engine fault that could develope.
However, I think it is better to run the Cat generators continuously until it is due for routine maintenance as long as you have all the elements(water, engine oil & fuel ) okay. Cat generators that are managed that way serves better and lasts longer than the alternate option you are currently adopting.
03-10-2017 09:20 AM
Howdy folks! I have a sort of odd problem. WE have a small gold mill that uses a handful of 600v motors. The load is approx 30kw. The only genset we can get is Cat 3306 w/175kw generator. I have read all the comments regarding under load issues.
My question is, Can you mitigate the issues by simply running engine at full throttle for an hour or two each day?We need to run the plant for about 1400 hours this summer.
This unit was a back up power gen for a hospital. It has 532 total hours on it. Showroom condition, averaging 15 hours runtime per year to comply with government spec.