We carried out MI (2nd) on our frame6 GE gas Turbine. Also our control system is upgraded from Mark-IV to Mark VIe. We face problem of high wheelspace temperature (3rd stage forward-both FO1 & FO2). Also remaining temperatures had increased by @ 30 deg. Cent. what may be the reason for this.

 

Hi,

Did you check with Engg/Maintenance to know whether the compressor bore plugs are removed to allow enough air to flow (like before MI).If they are plugged after MI,then the WS temp.is going to be high.As the machine just finished the MI,the chances of cooling holes chokage is less but did you experience any problem with your inlet filters after MI.

Are the temperatures changing with the ambient temperatures.Are these TC's new or the same before MI.

Best Regards,
Ravi

 

DRP, the reasons that come to mind for me in seeing a rise in wheelspace temperatures after a major inspection are either incorrect tolerances of componenets, or a restriction in cooling air supply. In your case you could have wiring issues due to the controls upgrade that could be the cause.

I do not have documentation to review that would show the source of cooling air for the 3rd stage wheelspace area, you would need to refer to your documents to understand the source of cooling air for this region.

I would be very concerned about this rise in temperature, is it above the alarm setpoint for the machine? If so you may be causing damage to the rotor by running with this increased temperature.

I would ask who provided your hardware for the major. Were there any changes to 2nd or 3rd stage nozzles for unit uprating that might have changed avialable cooling air for turbine components?

As suggeted the first course of action would be to determine if the temperature rise is real. Could wires have been landed incorrectly during the controls upgrade? If the temperature rise is real then determine if any hardware changes were performed that would impact this area. Boroscope the area to identify any clearance or hardware issues that might be causing this change from what was seen before the major.

 

Thanks a lot Mr Ravi.

As I was busy in M.I. and subsequent startup I couldn't reply you in time.

 

Thank You Sir for your reply.

Sorry for delayed reply as I was busy with S/D activities and then subsequent startup.

We have just replaced first stage nozzle. Nothing done to 2nd & 3rd stage.

At present our GT is running with High W/S temps. alarm Third stage temps are 600 (Forward) and 580 (After). TA advised us to run the machine. they have further talks with our higher ups and don't know about the conditions to run.

Thanks for your valuable reply. I had also gone through past posts regarding W/S temps. and it help me to clear about some doubts regarding W/S.

 

Dear Sirs,

We was faced same problem.

I think you need to crosscheck the clearance (Distance) of temperature scanner.

Regards
Amar

 

A few Questions:

1) Did you replace the 3RD. Stg. thermocouples during the MI (or remove and re-install)?

2) You said in your first Email that remaining W/space temps had increased by 30 Deg. What did you exactly mean by this?

3) Can you post a bit more data. What was the load when you took these readings. What are all the other W/space temps. What is the CPD & CTD.

It would seem strange that it is only 3rd. stage temps that are affected and would point more to instruments than cooling air flows

 

I would suggest that you verify correct thermocouple insertion depths per the associated GE drawing (turbine device diagram). Our 7EAs have wheelspace penetration depths that vary from 27 to 66 inches, depending on the stage. We have experienced similar temperature indication shifts after unit overhaul, and determined the cause to be incorrect insertion depth.