Awaneesh,

If Machine 2's Isochronous Speed Reference is 100.1354 the frequency when running is 50.0677 Hz, +/-0.17 Hz, which is most likely the reason Machine 1 is unloading. The signal names for frequency are SFL1 and SFL2. Even small differences like this can cause the problem being troubleshot here.

I've never seen a Load Gear with an exact rating of 5100/3000. The typical design speed of most GE-design heavy duty gas turbine axial compressors is 5100 RPM, but there is an acceptable operating range of as much as approximately 30 RPM so Load Gear ratios don't have to be exactly 5100 RPM and quite often aren't. Typical ratios I have seen are 5094, 5104, 5120, and 5134.

The problem arises when the Speedtronic turbine shaft speed feedback scaling is set to 5100 RPM from the factory and the commissioning person doesn't check the Load Gear nameplate and change the Speedtronic scaling there can be problems with synchronizing and Isochronous speed control.

I'm only mentioning this because it could also be contributing to the problem being troubleshot here.

This especially happens when two turbines are installed and commissioned at different times.

No; I don't think the problem could be caused by powering-down the Speedtronic panel. <b>Based on the information provided to date</b>, it seems the problem is related to the different TNRI values in the two machines. I don't believe the problem is caused by Machine 1, but rather by the incorrect TNRI of Machine 2.

TNRI can be changed when the unit is operating in Isoch mode, and by the operator observing TNRI while clicking on LOWER SPD/LOAD until the value returns to 100.00, or as close as possible.

I would suggest checking the Load Gear nameplates of both machines for their respective ratios and also checking the speed feedback scaling of the turbine shaft speed sensors of the TTUR card configuration to be certain the scaling matches the nameplate value.

Please write back with more information as you work to resolve this problem.

 

CSA
I have checked the load gear ratings again and found out to be 5120/3000 rpm for both machines.

But I could not trace the speed sensor values in ttur card.
Also, we tried to change the value of tnri of machine-1 to 100.1354, same as machine-2, but the same unloading condition of machine-1 continued.

Awaneesh

 

Awaneesh,

I don't have access to Toolbox to tell you exactly where to look, but you should be able to find TNH or TNH1 and then find the configuration values for this assignment (77NH-1, -2 and -3 are almost always assigned to either TNH or TNH1, which are usually expressed in percent of the configuration value).

For the life of me I can't understand why you would want to increase TNRI to be something greater than the value equal to 50.00 Hz.

Based on the information provided, we can't be of much more help. It's not clear from the information provided what changed after the outage. The only thing I could think of would be that some Control Constant was temporarily changed in the Mark VI of Unit 1 before the panel was powered down (which should NOT be necessary if the panel is properly grounded, by the way) because of the welding works. And, when the panel was powered back up, it used the original value. But I can't think of what Control Constant that might be.

Please write back to let us know what configuration you find in the TTUR, and how you progress in resolving this problem.