M
In-Active thrust loading, GE Frame 5
I am trying to gain a better understanding of the thrust bearings used by GE on early 1970’s frame 5 turbines.
Earlier this year I was called to one of the company’s gas turbine sites to try and determine why the turbine compartment temperature was so excessively hot. I was able to determine that a cross-fire tube housing flange gasket between combustion cans 4 & 5 had either failed or was not properly installed, also with flexible seal between the turbine shell and the exhaust plenum is needing refurbishment, resulting in the ducting a large amounts of 500 to 600 degree exhaust gas and compressor discharge air into the compartment.
While I was there I received a little history on the unit.
The unit had been recently rebuilt after a major turbine failure. I was told that the unit had tripped and the motor driven lube oil pump had failed to operate there-by allowing the turbine to coast down with no oil on the bearings.
The unit was rebuilt and during the testing phase the thrust bearing failed causing another major turbine failure. During the second turbine rebuild the thrust bear was looked at very closely.
I was told that at some point over the unit’s operating life time the active thrust runner hand been changed to a tapered thrust runner. No one knows why or when it was changed out. During the second rebuild the active thrust runner was changed back to the original style runner. The unit was tested again and passed the testing.
I studied the GE turbine manual and from what I could deduce there were/are two styles of active thrust runners used on the frame 5 turbine. One with straight sided rabbets cut in a radial pattern on the face of the runner and the other with slope sided (Tapered) rabbets cut in a radial pattern on the face of the runner.
The unit is now operational and has seen about one and one half months continuous run time this summer. The unit was loaded to a low load (2 mw and 1 mvar) during the run. I was told the thrust bearing oil temp, while a bit high, stayed with-in acceptable limits. As far as I know the unit has not been operated at higher loads since the return to service except for a short duration during the testing phase after the second rebuild.
I was told that during the second re-build the second stage turbine blades had metal added to them to increase the blade length by about .250 inch as some sort of up-grade. GE was contracted to do the second rebuild so I am assuming the up-grade had their blessings.
During the last 15 minutes of my stay at the plant site the engineer made mention of the up-grade to the turbine blades. He said the turbine seemed to function well with the up-grade but now the in-active side of the thrust was showing to be loaded.
The in-active thrust loading has been nagging at my brain ever since.
I know that a combustion turbine has two opposing forces in play. The forward thrust of the compressor and the aft thrust of the turbine. I understand that on a frame 5 unit the forward thrust is the greater force and that is why the forward thrust runner (active/loaded side) is the larger of the two runners.
I can understand that the loading on the active side of the thrust is going to lessen as the turbine is fired hotter.
I am assuming that in good turbine design the opposing forces should be very close to balanced at the upper operating range of the turbine.
I am wondering if the increase in the turbine blade length up-set the balance between the compressor’s forward thrust and the turbine’s aft thrust resulting in the loading of the in-active thrust.
I have not been able to find out if the abnormal thrust loading occur all the time or just at higher loads.
I sent the engineer an email some time back stating that I had some concerns that the in-active thrust may experience high loading at higher turbine loading due to the blade lengthening but I have never heard anything back from him.
I don’t know if my understanding of thrust bearing design and function is just too far off base or what. I would appreciate any in-sights into understanding the thrust bearing design and how turbine blade lengthening might affect it.
Thanks
Mark Allen
I am trying to gain a better understanding of the thrust bearings used by GE on early 1970’s frame 5 turbines.
Earlier this year I was called to one of the company’s gas turbine sites to try and determine why the turbine compartment temperature was so excessively hot. I was able to determine that a cross-fire tube housing flange gasket between combustion cans 4 & 5 had either failed or was not properly installed, also with flexible seal between the turbine shell and the exhaust plenum is needing refurbishment, resulting in the ducting a large amounts of 500 to 600 degree exhaust gas and compressor discharge air into the compartment.
While I was there I received a little history on the unit.
The unit had been recently rebuilt after a major turbine failure. I was told that the unit had tripped and the motor driven lube oil pump had failed to operate there-by allowing the turbine to coast down with no oil on the bearings.
The unit was rebuilt and during the testing phase the thrust bearing failed causing another major turbine failure. During the second turbine rebuild the thrust bear was looked at very closely.
I was told that at some point over the unit’s operating life time the active thrust runner hand been changed to a tapered thrust runner. No one knows why or when it was changed out. During the second rebuild the active thrust runner was changed back to the original style runner. The unit was tested again and passed the testing.
I studied the GE turbine manual and from what I could deduce there were/are two styles of active thrust runners used on the frame 5 turbine. One with straight sided rabbets cut in a radial pattern on the face of the runner and the other with slope sided (Tapered) rabbets cut in a radial pattern on the face of the runner.
The unit is now operational and has seen about one and one half months continuous run time this summer. The unit was loaded to a low load (2 mw and 1 mvar) during the run. I was told the thrust bearing oil temp, while a bit high, stayed with-in acceptable limits. As far as I know the unit has not been operated at higher loads since the return to service except for a short duration during the testing phase after the second rebuild.
I was told that during the second re-build the second stage turbine blades had metal added to them to increase the blade length by about .250 inch as some sort of up-grade. GE was contracted to do the second rebuild so I am assuming the up-grade had their blessings.
During the last 15 minutes of my stay at the plant site the engineer made mention of the up-grade to the turbine blades. He said the turbine seemed to function well with the up-grade but now the in-active side of the thrust was showing to be loaded.
The in-active thrust loading has been nagging at my brain ever since.
I know that a combustion turbine has two opposing forces in play. The forward thrust of the compressor and the aft thrust of the turbine. I understand that on a frame 5 unit the forward thrust is the greater force and that is why the forward thrust runner (active/loaded side) is the larger of the two runners.
I can understand that the loading on the active side of the thrust is going to lessen as the turbine is fired hotter.
I am assuming that in good turbine design the opposing forces should be very close to balanced at the upper operating range of the turbine.
I am wondering if the increase in the turbine blade length up-set the balance between the compressor’s forward thrust and the turbine’s aft thrust resulting in the loading of the in-active thrust.
I have not been able to find out if the abnormal thrust loading occur all the time or just at higher loads.
I sent the engineer an email some time back stating that I had some concerns that the in-active thrust may experience high loading at higher turbine loading due to the blade lengthening but I have never heard anything back from him.
I don’t know if my understanding of thrust bearing design and function is just too far off base or what. I would appreciate any in-sights into understanding the thrust bearing design and how turbine blade lengthening might affect it.
Thanks
Mark Allen
