Exercise Interval for Emergency Generators

[Jay]

At work, we're debating how often we should exercise the two emergency power diesel generators that we have at our telecom station. The two diesels are inside and electrically heated. We currently run them 1/2 hour each, at 50% maximum power, every other week. We're thinking of reducing that interval to once a month to save money on fuel and to reduce emissions.

Any thoughts on how often we should run these engines up?

 

[salesrep]

My first thought is an hour a month.

 

[michael harris]

I have been in charge at several diff. companies that relied on some very very big emer. gen. and among strict maintenance and impeccable records it was almost always once a month, and no less than 60 minutes. mainly for a full heat cycle and load variation and then we also tested the main UPS system and also the battery backups while it was running. did a fuel sample every 6 months, and oil analysis based on run times.
44H

 

[nobadges]

Surely the manufacturer provides some recomendations?

6:00 am every Friday ours boot up for 1 hour.

 

[MolaKule]

quote:

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The two diesels are inside and electrically heated. We currently run them 1/2 hour each, at 50% maximum power, every other week. We're thinking of reducing that interval to once a month to save money on fuel and to reduce emissions.

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Since they are inside and electrically heated, 0.5 hour each once a month at 50% load should be sufficient, assuming the starting batteries are kept fully charged.

 

[MN Driver]

Are backup batteries usually kept incase there is a failure amongst batteries. I know someone with a household standby generator that he started once a month but then when a snowstorm hit and the power went out, the battery wasnt able to start it. It had a pull start, but there is no way a large industrial backup would have a pull start. Once a month sounds like a good plan, it's what the company that I work for does for their three generators, except they actually do a full load transfer onto the buildings battery UPS and generators when testing them. I've been in the building when the power went out in an ice storm we had and there was only a slight dim of the lights for a fraction of a second but every computer and all of the equipment was uninterrupted.

 

[Jay]

Thanks for the suggestions so far. Please keep them coming. More info on the gensets and conditions:

The generators are quad turbo-charged Caterpillar 3512Bs that make 1600kW (2145 hp). The oil, water, and turbo-charger temperatures all seem to stabilize within 1/2 hour at 50% max power.

I think the Caterpillar dealer originally set them up to automatically exercise weekly at 1/2 max power for 1/2 hour. Since then, we do the runups manually every other week. I don't recall any recommendations in the manuals for exercising, but I'll look again.

Our batteries are inside and kept fully charged between starts. We do a loaded test on the batteries periodically to make sure they'll perform.

Diesel fuel, as you know, is to too tight to mention, and we're getting some pressure from the county AQM folks to reduce emissions. I think our present schedule has served us pretty well, judging from the UOAs, so I'm reluctant to change it.

 

[Shannow]

Jay,
at work, ours are run at the max that the station load will allow (about 800kW) for an hour or two a month.

Remember that back-up diesels are there to be run in anger, at the time that they are most likely to be required.

Looking after the fuel (bugs, water corrosion) is an often overlooked issue with diesel gen sets.

 

[LarryL]

I've built a lot of gen sets and it's been my experience that once you get the fluids up to some reasonable temp that the load for your exercise should be more like 80%+. Diesels like heat and run cleaner and don't wet stack when you run them a bit harder. They should be tested to 100% at least 4 times a year, if you have the load. Sometimes the idle speed is set for conserving fuel, and that should not be done with standby gen sets. They should idle a bit faster and exercises should be done with much more load than 50%. Most of our gen sets are unattended all year round, and if not used are run up every month, and once warm are loaded to 100% rated output, until everthing is completely up to temp, then tapered down and shut off. For some engines that's a half hour, and for most other it's about an hour, sometimes longer because the ambient temp's are below zero.

 

[1040 WreckerMan]

One of my jobs is working for a County run outfit and each location has emergency gen sets as we are supposed to be "Crisis Centers" in the event of a major disaster. We run each generator once a week at 85-100% load for half an hour, which is long enough to get the fuel/coolant up to temp. We actually switch the building onto gen power and load the gen in the same way it would be in a power failure. LarryL pretty much nailed it I think.

 

[kenneth neeley]

I agree with Larry also. I was a gen. tech for a Cat dealer for several years before moving over to a prime power plant.

If you do not have enough base load to fully load the engines or at least 75%/750*F exhaust temp. at the turbo, the units will at least need to be load banked once a year to ensure no wetstack is built up and to keep the rings fully seated.

 

[Jay]

What is wetstack?

 

[1040 WreckerMan]

Wetstack generally refers to the fuel slobber out of the exhaust pipe. This happens when the engine is over-fueling due to low combustion temps. It the cylinder temp isn't hot enough, it can't burn all of the fuel being injected and most of the fuel is sent out the exhaust. Ever seen black streaks down the stack on a big truck or tractor that looks like someone spilled tar?
Wetstacking can also be the result of mods to the fuel system. If the pump has been turned up or bigger injectors, etc. added you can get too much fuel for a given RPM.

 

[NYEngineer]

I'd like to add to the wetstack explaination. You also end up with a glaze on the cylinder walls and the rings don't seal very well. You get fuel in the lube oil and a smoking engine. I have four 2000 kW 3516's in my building. They all parallel to a bus. I only have enough load bank to load them approx. 50%, so I sometimes open the breakers on two units so two will carry 100%. I still have to run the two unloaded engines to cool the load banks. Then, next time, I run the opposite two under full load. Weekly, though, I run all four for 45 minutes or so on the load banks at 50%. You could run weekly for ten minutes unloaded in order to cycle the batteries and just lube them up, whatever you do, do not accunulate more no load time than load time. You'll end up with wetstacking for sure.Once it starts, the only way to stop it is to load the engine up to rated load and "burn" it out with nice high exhaust temps.

 

[NYEngineer]

If your engines are the electronically injected units (mechanically injected, electronically metered) 50% load testing should keep you out of trouble.

 

[lewdwig]

We run each of our's (Worthingtons) up to full load for 2.2 to 2.3 hours once a month. The back ups to the emergency diesels (yes!) are run for one hour a month (Caterpillars).

 

[doubleclutch]

We have 38 Life Safety and Data Center generators located thoughout our sites. They are exercised weekly.

 

[cosynthetics]

Most of the hospitals I work at exercise theirs once a month for 60 minutes. If they are mission critical I think it'd be better to do it once a week to catch problems than to extend them out. Just my opinion....

 

[Panther]

Originally Posted By: NYEngineer
I'd like to add to the wetstack explaination. You also end up with a glaze on the cylinder walls and the rings don't seal very well. You get fuel in the lube oil and a smoking engine. I have four 2000 kW 3516's in my building. They all parallel to a bus. I only have enough load bank to load them approx. 50%, so I sometimes open the breakers on two units so two will carry 100%. I still have to run the two unloaded engines to cool the load banks. Then, next time, I run the opposite two under full load. Weekly, though, I run all four for 45 minutes or so on the load banks at 50%. You could run weekly for ten minutes unloaded in order to cycle the batteries and just lube them up, whatever you do, do not accunulate more no load time than load time. You'll end up with wetstacking for sure.Once it starts, the only way to stop it is to load the engine up to rated load and "burn" it out with nice high exhaust temps.


Wow! Mind if I ask what kind of organization needs 8 MW of emergency generator capacity? Just curious -- that's a lotta power!

 

[NYEngineer]

Panther, I work at the Time Warner Center in NYC. We house Time Warner corporate and CNN. CNN is my Critical load. I also care for a 1500 kW UPS system that carries two Datacenters and all the CNN studios. Our part of the building is about 1.3 million square feet.