GE Frame 5 Maintenance Intervals

[dmcnew]

So I'm baiscally brand new to the world of combustion turbines and I was looking for some input on industy typical maintenance frequency.

I work at a small utility with two GE Frame 5's that are run basically as peaking units. This year we ran about 40 hours, last year not at all, and two years ago about 100 hours. So I'm wondering with as little as we run these two units what the appropriate maintenance frequency for them is?

I want to make sure we are doing periodic maintenance at appropriate intervals, but I don't want to go spending money needlessly.

Any input on maintenance frequency or directions to appropriate source would be great. I'm just looking for some advice on replacement of basic things like air filters, oil filters, and generator brushes.

Thanks.

 

[rmw]

How many total fired hours does each unit have, and how many total starts?

What year were they installed?

rmw

 

[ccfowler]

Also, when they were operated, how fast were they ramped up to what loading? Were they run on load control or exhaust temperature control? In either mode, at what temperatures were they being operated?

If they are operated at sufficiently mild temperatures, they can run continuously for many years without any concern. If they are operated at very high exhaust temperatures to serve in an emergency role, they can be effectively trashed in a few hours.

You really need to know as much as possible about their operating history as possible to be able to make prudent decisions.

As a practical matter, it may be a good idea to verify the calibration of the operating instrumentation. If they are not run very much, how well were the instruments maintained.

Since their duty is apparently very infrequent operation for very unusual peaking needs, I would not be surprised if they were ramped up very fast to very high exhaust temperature loadings under near-panic conditions.

Valuable advice from a professor many years ago: First, design for graceful failure. Everything we build will eventually fail, so we must strive to avoid injuries or secondary damage when that failure occurs. Only then can practicality and economics be properly considered.

 

[dmcnew]

Total recorded running hours for Unit 1 is 90,380 and total running hours for Unit 2 is 87,441 but I believe that is only since their install at at site. The units are 40 years old but have only been here for 20 after we purchased them from another utility.

Unfortunately, we have no record of total starts.

I can't speak too much about past operations but these days they are ramped up fairly slowly. We have an agreement with some other utilities in our area where we are all dispatched to run by a central authority when cheaper power can not be bought off the spot market. So we usually know at least an hour or more in advance of run time and we try to bring them up fairly slowly and we usually run around 10-13 MW per unit. It has not always been this way and as you can tell from our total running hours we have ran them quite a bit in the past, but not much in the past few years since we have 'teamed up' with some other utilities to buy and generate together.

We manage them based on average exhaust temperature and our max we run them at is about 950F. I'd like to think we take it pretty easy on them these days, but I don't think that has always been the case with past operators.

 

[rmw]

Seems like the reason you aren't running them very much is because they are tired old dogs. I think I remember that 50K hours is the point for a (rotor out) major, so if that is right (my Frame 5 stuff is at the office so I can't check) then you are heading for a second major and they probably aren't worth the expense of doing that what with their heat rate. They still have enough hours left in them to be a peaker and especially if you bring them on slowly. When brand new, they should have been worth 15 MW or maybe even more. You typically can't get that out of them with that many hours.

See if you can find out when they had the last hot gas path inspection. If that wasn't done at the last recommended interval, that would be your next major maintenance and maybe that would stove off a major long enough for you to retire at 140 hrs in 3 yrs.

Other than that, check your oil, have it sampled and keep it clean. Keep your generator heaters on when not in on line. (It does still have generator heaters doesn't it?)

If your lube oil tank has a heater, keep it on to keep moisture out.

If it has a ratchet, make sure the shaft turns every once in a while. If it has a turning gear, operate it from time to time.

Are they electric start, engine start, gas start, or other?

rmw

rmw

 

[ccfowler]

Do these old units have 180 or 360 degree coverage for the exhaust thermocouples? If it is only 180, there is no small risk that some of the fuel nozzles could be over-firing and cooking some of the stationary blading a bit.

Valuable advice from a professor many years ago: First, design for graceful failure. Everything we build will eventually fail, so we must strive to avoid injuries or secondary damage when that failure occurs. Only then can practicality and economics be properly considered.

 

[dmcnew]

My mistake, that is total running hours over the life of the units. We completed an overhaul a few years back and haven't ran too much since then, though we do have some problems with the units and controls that need to be addressed soon. We typically get 12-13 MW out of one and 9-10 out of the other. I'm not sure how much they managed to get out of them when they were first installed here but the load gear is rated 19.5 MW and the generator 23.

We are planning for a borescope and possibly a hot gas next year.

We've been keeping up on oil sampling and just had the oil cleaned a few months ago.

We keep the heaters on and the units on ratchet.

One is engine start and the other is electric start.

I'm not sure on the thermocouple question...but we haven't had any problems with that in the past. We have had issues with warpage of the nozzles though

 

[ccfowler]

Output on those units is highly dependent on ambient temperature. In sub-zero (F) conditions, they can put out well above 20MW with normal exhaust temperatures. Long ago, I heard that one unit had stripped the teeth off of its pinion gear during very cold weather while lacking a load limit control function.

I've seen units do 22MW at about -10F, so I know that they can deliver power in that range.

The 12 - 13 MW seems reasonable for gentle loadings, but I would be concerned about the one that can only do 9 - 10 MW. I would suspect some problem with that one in the form of I&C calibration errors or internal problems.

What about compressor fouling particularly on the weak one?

Valuable advice from a professor many years ago: First, design for graceful failure. Everything we build will eventually fail, so we must strive to avoid injuries or secondary damage when that failure occurs. Only then can practicality and economics be properly considered.

 

[dmcnew]

Right, we can watch the MW go up even as we go from a hot summer afternoon to night where the ambient temp can drop 10 or so.

We do have some I&C issues on that one. The primary operator believes it is a problem with the calibration of the fuel regulator.

I don't believe we have had any issues with the compressor...but let me check on that.

 

[ccfowler]

During acceptance testing procedures and preparations on GT's, I have been surprised by the MW difference before and after compressor cleaning. Sometimes, the increased capability was quite significant (10% or more) even when the "almost new" unit was believed to have a clean compressor.

Valuable advice from a professor many years ago: First, design for graceful failure. Everything we build will eventually fail, so we must strive to avoid injuries or secondary damage when that failure occurs. Only then can practicality and economics be properly considered.

 

[dmcnew]

Is that so? Sounds like something that needs added to our project list then. Thanks for all the info guys, I'm really learning a lot here.

Coming back around to my original question, given the current state of the units and our operating conditions, what kind of maintenance intervals should I be looking at for all these things? (i.e. compressor cleaning, hot gas path, etc.)

My problem is our lack of documentation on these units. I understand the purpose and value of all of these things, but I'm not really sure what the recommended intervals for this type of maintenace is.

 

[ccfowler]

I don't have any good specific schedule information for you, but the way you are running them, given their recent major work, I wouldn't worry about much beyond keeping them clean and keeping the all the I&C stuff in good order, including periodic calibration work depending on what you find (good or bad).

Oh yes, there is one old problem for instrumentation that presumably shoud have been fixed by now. GE depended on the voltage of a stack of Ni-Cd cells for its voltage reference. Since the Ni-Cd's were in a state of eternal charging, they ceased to function as batteries and were more like very sorry capacitors. Their voltage drifted and caused lots of seemingly odd instrument problems. Once a better voltage reference was established, the instrument problems disappeared.

You may want to check your circuitry for such a potential issue.

Valuable advice from a professor many years ago: First, design for graceful failure. Everything we build will eventually fail, so we must strive to avoid injuries or secondary damage when that failure occurs. Only then can practicality and economics be properly considered.

 

[rmw]

Ge has a lot of public reference materials on this type of unit called GER's. You will find answers to more than you know to ask among these.

http://www.gepower.com/prod_serv/products/tech_docs/en/all_gers.htm

ccFowler, All the frame 5's that I installed and started up in the vintage of these (yes I was installing frame 5's just about 40 years ago) had 360 degree thermocouples, typically 12 for indication plus 6 more for trip circuitry.

My experience with machines that old is that they are just too loose and the blade profiles just too worn away to get the output they got when they were young stallions.

rmw

 

[dmcnew]

Thanks again for the help you two. It's much appreciated.

I will probably be back with more specific questions in the future.

 

[ccfowler]

dmcnew,

I've been thinking a bit more about your situation, and I would be most concerned about the weak unit. I would want to study its fuel consumption rate vs, generation and ambient temperature. I would run some tests at a stable load while isolating each exhaust thermocouple to verify reasonably uniform temperatures at all points. rmw's information that most have 360 deg coverage is good news, but I know that some early ones had precious few exhaust thermocouples. (I've seen some very impressive stator damage as a result.)

If one or two fuel nozzles are over-firing a bit, the rest would then be under-firing to maintain the desired average exhaust temperature with the result being reduced net output and some increase in localized stator temperature affected by the over-firing nozzle(s). This would not necessarily result in the catastrophic damage that I mentioned above.

I would run the same tests on both units both to verify their individual operating characteristics and to compare the weak one to the strong one at the same site, weather, etc. The strong one seems likely to be OK, given its age, but my main concerns would be about the weak one.

I would run reasonable, practical performance tests on both units as is and again after compressor cleaning. I would want to verify instrument calibration before any of this testing begins. Since these tests would not be for acceptance or any other superbly formal purpose, there is no need for them to be any longer than needed to establish stable, credible operation for your analytical purposes.

You know your system's generation needs, weather stability conditions, cost sensitivities, ... so you will have to make some judgement calls as to what constitutes testing practicality in your situation.

I would want to check whatever performance history records that may be available to determine if there is a pattern of deteriorating performance on the weak one compared to the strong one since their last major repairs or inspections. It is possible that there are some more serious physical problems with that unit, but it is also possible that the weak output is actually the result of I&C problems.

It may be that the weak one is just more tired with a higher heat rate than the strong one. If that is the case, then it would make sense to dispatch it after the strong one when system conditions dictate that its more expensive power must be tolerated.

Valuable advice from a professor many years ago: First, design for graceful failure. Everything we build will eventually fail, so we must strive to avoid injuries or secondary damage when that failure occurs. Only then can practicality and economics be properly considered.