The plant was built in 1988 with three PG6541B (2020F firing temp) model GE turbines in a 3x1 configuration which then received the PG6571B uprate (2070F firing temp) in 1998. As with most multiple turbine facilities the three never run at exactly the same output. The problem we have here is that the difference can be as large as 4 MW's with one of the units always having the lowest output. Long story short we went into the MARK IV for each machine and pulled up a few of the usual suspects and actually found that CSKGVMAX for each machine was different (Unit 1-87.5, Unit 2-87 and Unit 3 86.5). If you take run data from each machine Unit 1 runs the closest to the 1998 GE supplied design curves while on some days Unit 3 can be down as much at 5.5 MW's. Does anyone else have a Frame 6B running the PG6571B uprate and if so what is your max IGV angle? Looks to me like GE may have tried to cheat to get us the guaranteed power back in 1998.

 

You have basically answered your own question.

An uprate of this kind involves making adjustments to exhaust temperature control constants, and sometimes to the maximum IGV angle, in order to achieve the guaranteed firing temperature. In addition to putting new hot gas path components in the unit, it's necessary to tune the control system to achieve and maintain the uprate's firing temperature. Usually this is done by running a performance test after the new hardware is installed and making adjustments to the control system parameters after reviewing the data.

As you have noted, units installed side-by-side and commissioned at the same time rarely have identical performance and output. This can be attributed to many factors, including internal clearances which can vary between machines, especially over decades of operation.

I presume based on the age of these machines probably have water- or steam injection for NOx emissions reduction. The accuracy of the fuel flow-rate measurement and/or the water- or steam flow-rate measurement is rarely identical for similar machines. And this can have an impact on output, also.

I have recently seen the insides of some of the HRSGs installed at the same time as these units, and there was insulation which had blown out from behind duct panels and was found blocking the superheater creating high exhaust duct back pressure in addition to reducing steam production. So, the condition of the exhaust duct/path is also a factor in output.

The accuracy of IGV LVDT calibration, both at the time of the uprate, and now can also have an affect on performance.

But, in the end, you're probably right. GE has managed to say in business year after year, decade after decade, by cheating their Customers.

Seriously, how is that statement relevant to the problem and getting the information you seek?

 

Thanks for response. We are going to go unit by unit and test the meters (fuel,h2o inj etc) then stroke the IGV's and physically measure their angles. It just seems too coincidental that as you go down the line the max angles are 87.5,87 and 86.5 so I am leaning towards this was done as a test at some point to compare the effects of the IGV angle and somebody never set them back. We really have no way of knowing since it was done prior to our ownership. I've heard that as you go past 86 degrees your risk of IGV "unloading/flutter" increase exponentially. Any experience with this? What is the max safe angle before you risk cracking and eventual failure?