Generator Problem in Afghanistan

[tom baker]

A question came to me regarding a generator problem in Afghanistan, I'm posting it here:

Greeting from Afghanistan. We are having a problem with our two 88KW generators. We run one generator at a time. About 6:00 pm each day it cuts out on us. The same thing happens with the other one. The voltage hold up pretty good. The current pull is about 100 amp on a 389 volt, 3 phase system. It should be able to handle around 133 amp. At one time we thought we had a balancing problem, now its balanced within 10 amps and we are still having the same problem. The altitude is about 6000 feet above sea level. We thought That maybe causing the problem, but it only happens for a few minutes then it recovers. If you have any thoughts on it I would appreciate your help.

Thanks
John

 

[bennie]

Re: Generator Problem in Afghanistan

Tom: Ask for more information. The term cut out, does that mean the unit shuts down? Is this generator separate from all other system? Does a heavy load hit at the same time as the unit cuts out? Is the prime mover a diesel engine? or gas turbine?

 

[dereckbc]

Re: Generator Problem in Afghanistan

Tom the first thing I would like to know is the ambient temperature and air circulation.

[ November 26, 2003, 11:12 AM: Message edited by: dereckbc ]

 

[brian john]

Re: Generator Problem in Afghanistan

Depending by what is met by cut out


Is this a commercial generator or a Mil Spec Unit
Temperature
Ambient
Inrush currents especially with the timing issue
FUEL>>>>>>>>>>>>>>
Do they get an alarm (typically most shutdowns outside those monitored will say low oil pressure).

There are a 1000 and one possibilities, have had lose wire problems in the safety's. Bad governor, fuel ect......

 

[hurk27]

Re: Generator Problem in Afghanistan

Sounds like a temp senser shutting the excite field down then auto resets. look for air flow problems around the field windings and is the generator inside a building or box trailer? it may need more air to remove more heat.
Also thin air removes less heat.

[ November 26, 2003, 06:45 PM: Message edited by: hurk27 ]

 

[c-h]

Re: Generator Problem in Afghanistan

A coworker had this radical suggestion if all else fails: Change the clock one hour so that people do everything an hour earlier (like daylight savings time) for a few days. If the generators still cut out at the same time (original time, not your new adjusted time) it's some ambient factor (temperature, humidity). If it fails one hour earlier, it's something in the way it's used.

 

[bennie]

Re: Generator Problem in Afghanistan

The only known facts appear to be that this problem occurs regardless of which generator is on line. The odds are in favor of the problem being in the system, not the generators.

The generators are of the wye configuration. A wye generator with a floating neutral will cause the current in one phase to elevate, when the load is not symmetrical. The loss of the neutral will cause a shut down due to the phase imbalance or overcurrent.

I would inspect all the terminal connections, of the neutral, for corrosion, or loose connections.

 

[templdl]

Re: Generator Problem in Afghanistan

If the shut down occurs at approximately the same time I would look for something that is happening in the system at that time.
I had a 400a main breaker breaker?at a sewerage lift station with the old style peak sensing SS trip unit that tripped most mornings at 5. Peak sensing trips look at peaks and are not RMS and I suspected it was tripping because of a voltage spike because of a power factor correction capacitor bank switching in. I simply had the breaker replaced with an old style thermal mag. trip unit of the same frame size and the problem went away. That was over five years ago.
You may want to put a brush recorder or similar recording device that would have the capability of recording the event. I chose not to with mine and made a calculated guess as to what the problem probably was cause by.
Bottom line? It may not be that complicated if you think outside the box. See if you can get some recording devices that can show you what's going on, voltage and current wise, at the time of the even otherwise you may end up shooting at shadows.

 

[poushey]

Re: Generator Problem in Afghanistan

Your message does not indicate what type of load you have on the generator. The amp meters on most generators are usually standard rms meters. If your generator is supplying power to army comm shelters and/or other IT equipment you may have a considerable amount of harmonic distortion that will not be detected by the local meter. It is not uncommon to have 30% or more harmonic distortion current when you are using one generator to feed multiple comm shelters. To get an accurate current reading you need to use a true RMS current meter. I suspect the troops are getting off duty around 6:00 PM and turning on their computers so they can write some email letters for back home.

 

[jwh123]

Re: Generator Problem in Afghanistan

Reminds me of the story of the computer department who always had the UPS's power failure alarm go off at about the same time every night, even though the rest of the building didn't have any power problems.

One night, someone was there when the alarm went off, and went downstairs to check it out. The cleaning person was there, unplugged the UPS to plug in his vacuum.

Probably not a true story, but something to think about. Is someone vacuuming??

 

[brian john]

Re: Generator Problem in Afghanistan

JWH:

We did have a job where the customer spent a fair amount of money to find why a main CB was tripping every night. I suggested it might be someone EPOing the system . But they wanted to err on the side of caution. CB primary injection testing, power monitoring.

Result the cleaning woman thought she was turning out the lights (red push button under a plastic cover).

 

[tom baker]

Re: Generator Problem in Afghanistan

Folks:
Thanks for the answers. I posted this third hand, so I hope the orginal person gets the word to help us out here with our questions.

[ December 02, 2003, 06:39 PM: Message edited by: tom baker ]

 

[dcsva@aol.com]

Re: Generator Problem in Afghanistan

Both 88kw.
Both cut out at the same time everyday.
Both have the same ambient conditions.
I would say that BOTH are trying to start SOME LOAD that has too much starting KVA requirements.
Look for what is common to both.
I would say that it is not the generators if both do the same thing.

 

[lu302dan]

Re: Generator Problem in Afghanistan

what time is dinner over there and is it all electric...??? Overload sounds like the issue to me...Maybe we are cooking the same time the exterior lighting is comming on.....I havent done the math but it sounds like you are near maximum output for these generators and they may not be able to handle an additional load spike...Check time clocks for lighting or other loads...Hell, Spend some time looking....you will figure it out...

 

[tom baker]

Re: Generator Problem in Afghanistan

Agina thanks for your help, here is what the problem turned out to be:
"Some valuable information came out of John's generator problem in Afghanistan and I wanted to share it with you who participated with help.

Generator basics: Fuel, oxygen, compression and an electrical spark should guarantee ignition and combustion. At 6,000 feet (over a mile) above sea level, the air mass is very thin which means there is very little oxygen. Air mass constantly changes as the earth rotates. Thus, at 6:00PM each day (as the earth rotates) the air mass is so thin that there is not enough oxygen in the air to sustain combustion
.
Solution: Using liquid oxygen (in tanks) provide oxygen to the air intake manifold of the generator between 5:45PM - 6:00PM for continuous operation."

 

[bennie]

Re: Generator Problem in Afghanistan

Tom, I think John is pulling your leg.

 

[tom baker]

Re: Generator Problem in Afghanistan

Bennie would know!
But maybe it does work, and it is correcting the problem. I'd like to get the person who had the orginal question to get on line instead of third hand.

 

[hurk27]

Re: Generator Problem in Afghanistan

Tom I was thinking about the thin air being a problem removing the heat in the windings. Never thought about the fuel/air mixture. There is another way of doing this that I have heared about. and that would be adding a blower on the intake to the carb. this would concentrate the available oxygen, and provide for a better mixture ratio to be achived. as most low alt. gensets dont have the carb. to lean out for high alt.

[ December 03, 2003, 12:59 AM: Message edited by: hurk27 ]

 

[big jim]

Re: Generator Problem in Afghanistan

Tom, to me, that is one incredable piece of science-fiction. First, for reference, I live in Denver, the mile high city. The physics of combustion engines are well known and any large genset would have altitude-output correlation tables as part of its documentation. It would be obvious to anyone around the operating unit if something remotely resembling that was occuring. Lox fueling an engine? Only in rockets in this world.
If it was really a load issue, I think paralleling the 2 units would be a more practical solution.
I checked my calender and it's not April first. Am I missing something here?

 

[bennie]

Re: Generator Problem in Afghanistan

I installed four 950 KW diesel driven generators at the South Pole research station in Antarctica. the South Pole is 10,000 feet in altitude. The engines were turbo-charged, the air pressure was no problem. Most diesel engines are turbo-charged for running at low RPM.

Of course heating was not a factor either.

LOX and exhaust manifold temperature will launch the generator into orbit. The operator must be practicing to be a suicide bomber.