diesel generator dies under load.. help 1

[BBGigante]

hello.
i have a 250KVA CAT diesel generator, 3208 engine, as standby generator suplying power for my factory. under a 0.8 pf it should supply about 300A according to the name plate. normally the power factor stays between 0.8-0.86 during production, but when the amps drawn from the generator come up to 150A the engine begins to stall and the frequency output starts to fall quickly, followed by voltage. im wondering if this has to do with problems with the governor, or maybe a bad turbo because i've noticed that the oil consumption is very high. any suggestions??
thanks in advance.

 

[waross]

The root cause is that your engine is not producing enough power.
The causes may be;
>Dirty fuel filter.
>A worn out engine.
>A bad turbo, and other problems. Bad turbo alone won't cause this much power loss.
>A faulty aneroid valve or equivalent. This is the mechanism that limits the amount of fuel delivered until the turbo spools up and builds up intake manifold pressure. The purpose is to eliminate smoke plumes from over fueling when a heavy load hits a lightly loaded engine and the turbo is turning slow.
>Bad fuel stop setting or dead rack adjustment. This is the maximum amount of fuel that the governor will allow to be delivered.
>Worn out governor/fuel pump.
>Badly clogged air filters.
>Check your instrumentation. The ammeter may be registering 50% of the actual current.
>Plugged muffler.

Don't worry about the voltage drop. When the frequency drops more than 3Hz, the AVR ramps the voltage down to maintain the V/Hz ratio. This avoids damage to inductive equipment such as motors and transformers, reduces the load to help the engine recover speed and avoids AVR burnout. The feature is called Under Frequency Roll Off. Before UFRO became a standard feature on AVRs, gen sets were fitted with a switch to turn off the AVR whenever the set was to be run below rated speed. With the pre UFRO AVRs, if you forgot to switch off the AVR when slowing a set for any reason you could expect to lose the AVR in a few minutes.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[nawao]

Any maintenance work was done before this incident happen
like cleaning of air filters?
Check if any rag was sucked by the turbochargers
Check water in the fuel

 

[rbulsara]

Regular maintenance and testing by qualified people (not self-proclaimed ones) would have avoided problem. This is not something started happening all of a sudden, is it?

Rafiq Bulsara

http://www.srengineersct.com

 

[BBGigante]

hello guys.
a little background: we acquired the generator last november, which is a used generator with the engine fully repaired. after it was installed and tested for a few days, the guys who selled it changed the fuel pump and the water pump for new ones because the engine was burning hotter on one side than the other, the problem was solved (it's unlikely that the fuel pump is the problem now) . an incident accurred on december arround 50 working hours after a maintenance. we noticed some black smoke coming out of the muffler so we called a mechanic, he stated that the air filter was clogged, and that this problem was caused by a construction work undergoing next to the generator room, which generated a lot of dust, and warned us that the turbo might have suffered damage.>>>>
the actual problem has been present for quite some time now. we began using the generator around november, but it was never put under full load until january when production started on the factory, hence the problem went unnoticed until then.
the maintenance jobs have been performed under schedule, so i would discard the fuel filters. last week we had the oil, fuel and air filters replaced by new ones. i assume that the turbo hasn't sucked in any piece of cloth or something because there's a protective grid at the air intake just below the filter, but thanks anyways nawao.
i guess wee will need someone to check the governor and the turbo in the mean time.
thank you all for your support.

 

[rbulsara]

This unit needs a serious overhaul from a factory authorized service company or buy a new one or another one in good condition that is full load tested for at least 4 -6 hrs.

I would not be surprised, if this unit has shades of each of the issues that Bill (waross) has listed.


Rafiq Bulsara

http://www.srengineersct.com

 

[waross]

Check the fuel stop setting. I have seen several generators with this problem as a result of an overhaul. I saw a generator overhauled needlessly and still not pull ANY load as a result of fuel stop settings.
Engine was just overhauled? Check the fuel stop setting.
Load tested for a couple of days? That set would burn about 700 gallons of fuel during a 48 hr. full load test. Would your suppler spend that kind of money on a test?
The fuel pump was changed AFTER the testing. That kind of negates the test on the fuel pump.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[ccjersey]

You don't say whether the exhaust smoke from the engine when it lugs down is black or clear/normal. Black would fit a failing turbocharger. Clear/normal would fit some other fuel supply or governor related problem.

The quickest thing you can check on the 3208 CAT engine is to take the boost air hose/pipe loose from the outlet of the turbocharger and look for oil inside. It's very likely the turbocharger bearing and seal has failed and is wasting a lot of oil into the intake manifold whenever the engine is running. This coupled with the drag on the impeller will cut boost pressure and hp output.

It's also possible that the air filter could have let dust through and the engine now needs an overhaul. If the filters were replaced when the unit was serviced and installed initially, I would tend to discount this scenario. This usually happens when filters are old and become brittle so that the paper media actually breaks and lets contaminants through.

 

[catserveng]

I'm a bit concerned about the comment regarding replacing the water pump because one side ran hotter than the other. On a 3208 with a cooling flow related problem, you usually see the rear of the engine hotter than the front, but actually hard to tell without instrumentation. "Hot on one side" also wouldn't call for a fuel injection pump change.

On the clogged air cleaner, the turbo on a 3208 is pretty robust, a clogged and bypassing air filter usually causes a clogged aftercooler and cylinder bore polishing. The only thing the turbo is likely to show is some erosion on the leading edges of the compressor wheel blades. In years past I stuck the same turbo back on a "dusted" engine more than once just to get it back on line with no problems.

Another possiblity, if you ran under very light loads for a few months, it's possible the hot wheel of the turbo is coked up, packed with carbon and debris from unburned fuel and oil. Doesn't let the turbo spool up under load.

Does the engine serial number and its prefix match a generator set engine? A few years ago there were a bunch of gen sets hit the world using reworked truck engines and generators installed, turbo match and fuel pumps were not good for constant speed gen sets and several units had problems similar to yours.

As Bill said, someone who knows the pump should check the part number, timing and fuel stop setting of the fuel pump and governor. If it has a torque spring the governor is not from a gen set engine. Same with a smoke limiter, if it has one (can tell if a boost line is run over to a solenoid looking device on the back of the governor) then you may have an engine from another application, CAT didn't put smoke limiters on gen set engine governors.

Hope that helps.