Dear All,

we just completed our CI on GT frame 9, and unfortunately the generator been replaced with standby unit from other power plant due to internal shorting. Our existing generator is 120MW and the replacement generator is 108MW and we were using our existing excitation system. Our maximum load before this is 97MW but after the replacement we only got 94MW, with excitation parameter still below alarm and no indication excitation limit has been reached. is there any setting need to be on on the excitation or control system mark V regarding load angle or anything? We checked all the condition on the turbine/mechanical side so far we not fine anything abnormal.

regards
William

 

william.chong,

What fuel is being burned in the turbine?

Does the turbine have DLN or conventional combustors?

What Process Alarms are active when the unit is experiencing this problem (list all of the Process Alarms, please)?

Usually, the generator is not the limiting factor when it comes to power production--it's the prime mover (in your case, the GE-design Frame 9E heavy duty gas turbine). The turbine is limited by exhaust temperature control--which is used to limit firing temperature (the temperature of the hot gases exiting the first-stage turbine nozzles). The generator just converts the torque supplied by the prime mover to amperes (MW) at a very high efficiency, so if the output of the generator is low then it's likely the input to the generator is low.

So, you need to understand what is the source of the "limit?" It's most likely that the Mark V has determined that the axial compressor discharge pressure or -pressure ratio and exhaust temperature are at the limit to protect the turbine from over-firing. This can be checked by looking at the operator interface to see if it's indicating BASE LOAD (exhaust temperature control), and by looking at the exhaust temperature control reference value (TTRX) and the actual exhaust temperature (TTXM). If TTXM is equal to TTRX then the unit is operating on exhaust temperature control, and is said to be at Base Load. (The IGVs should be fully open (84 or 86 DGA, depending on your machine's configuration) when at Base Load as well.)

The next thing to do is to look at the primary exhaust temperature control setpoint value (TTRXP) and the back-up, or secondary, exhaust temperature control value (TTRXS). TTRXP should be greater (more) than TTRXS; if TTRXS is greater than TTRXS then there is some kind of controls issue which needs to be investigated and resolved.

The more information you can provide, the more help we can provide.