HI.

We have in our site two turbines MS6000 both running on gas fuel (not DNL), control system MKV TMR <I>. We have noted that with a target of 19 MW (demanding of the grid) both turbines run with 19 MW each of them. CPD:9,21 bar (both), fsr:36,73% / 36,41%, TTXM:375 / 373 ºc, igv:85,8 (both), tnr: 101,96% (Both), respectively.

Now when the target of the grid is for example "Base Load," we note a significant difference in load of both as following:

CPD:9.51 / 9.67 bar, fsr:59.65% / 60.09%, igv:85,3 (both), tnr: 103,82% / 104,03%, respectively. dwatt: 31.9 MW / 33.5MW.

We suspect that difference of load of both turbines is due to the difference in cpd. But why we don't have that difference in cpd when both turbines run in a load below 20 MW. The stroke of the GCV and SRV and IGV are within the values of control spec.

Is it a problem with the compressor discharge?, Do we need a wash compressor?, since we have checked the cpd transmissor and 20 CB and both are ok.

Thank you very much.

 

CTLP,

Yes. Compressor cleanliness, or, rather, the lack of compressor cleanliness, is one of the biggest contributors to loss of efficiency at Base Load.

The next biggest contributor to loss of CPD is inaccurately calibrated IGV LVDTs. I continually find IGV LVDT calibration to be very inaccurate, and on many GE-design Frame 5 and Frame 6B heavy duty gas turbines the IGV actuator is in a VERY bad place, adding to the lack of attention they deserve--not only because of their location, but because they seem to experience a faster wear rate than the actuators used on GE-design Frame 7E/EA and -9E and F-class heavy duty gas turbines. I have seen the bolts which hold the actuator stationary to the base that have become loose and even sheared off, and the heim joint also be very worn and loose--all contributing to extremely inaccurate LVDT calibration and drift.

Dirty inlet air filters can be a problem, also. Restrictions in the gas turbine exhaust (especially if the GTs exhaust into an HRSG (Heat Recovery Steam Generator ("boiler")) can cause back-pressure to increase as air flow increases, which also contributes to the loss of efficiency.

Finally, believe it or not, improperly terminated exhaust thermocouple wiring can cause problems, as can high exhaust temperature spreads--and when these are both found the loss of efficiency can be very high.

Other intangibles include increased clearances between stationary and rotating parts in the axial compressor and turbine sections, and leaky compressor bleed valves (VA13-1 & -2--which are opened when 20CB-1 is energized).

Please write back to let us know what you find.

 

HI.

What is exhaust temp./IGV opening of GTs in all cases? in base load your machine will be governed in exhaust temp. control mode.

Are these values just after water-wash of machines? Is one machine running for a longer period than the other?

If all values area found same try IGV cleaning. same was recommended by our OEM, and has slightly improved the base load (if not greatly).

reagards
Manoj