Hi Group,

I have couple questions related to GE gas turbine and the associated instrumentation

1. I am trying to replace the TCs in next outage, wondering if the bearings come with embedded TCs? or do we need to order them separately
2. I believe the thermocouple to be directly installed on bearings without any thermowells? Is that right? The only thermowell I foresee is on the bearing drain line.
3. Offtopic but can someone confirm if all the instrumentation around gas turbine is rated to IP65 as a minimum? Ae we intend to do water mist testing for fire protection and wondering if there is any risk with instrumentation?

Thanks

 

@WTF? can you kindly review this query

 

@Instenthusiastic,

1) Most of the GE-design heavy duty gas turbines I worked on as a commissioning or maintenance engineer had embedded bearing metal temperature thermocouples. The were not removable/replaceable without removing the bearing and sending to a suitable shop for removal/replacement.

2) No thermowells for bearing metal temperature thermocouples. The caveat here is for machines built at GE in Belfort, France. They have often changed materials/methods/control schemes/parts simply because the BEST ideas for construction, maintenance and operation come from Belfort, France--not anywhere else in the world, even if it is from the same company. They can, and have, and will likely continue, to deviate from decades-long practices, methods and schemes. With a poor record of success on the first, second or even fourth attempt at disrupting the status quo.

3) I am unfamiliar with IP65. I provided a LOT of information in the other post about testing, design criteria and methods. With the exception of the Accessory Compartment, most of the "higher voltage" (120/240 VAC; 125 VDC) devices were water-proof. About the time of the construction of your machine GE was replacing a lot of switches (temperature; pressure; level; limit; etc.) with switches which had very fine threads on caps and bodies and I think that was to meet some explosion-proof/ignition-prevention regulations. AND, many of those switches which were monitoring conditions inside the turbine compartment were purposely mounted OUTSIDE of the turbine compartment. Those inside the turbine compartment were rated for high temperature and hazardous atmospheres. Again, I'm unfamiliar with using water as a test medium for fire suppression systems. It seems, ..., well, ..., odd. And it's not known what the test is supposed to be proving/demonstrating. I provided some recommendations if it is decided that water will be the test medium; that's all I can add to this discussion beyond what I already have in the other thread.

Best of luck!

 

@Instenthusiastic,

We have no way of knowing what machine you are working on. While all GE machines operate using the same physical principles (suck; squeeze; burn; blow) the enclosures and auxiliaries (valves; field devices/instruments; pumps; fans; ventilation dampers; etc.) can be VERY different. PLEASE help us to help you by providing some identifying information when posting in the future.

And, as mentioned, when it comes to machines built by GE in Belfort, France--just about anything is possible because they can make just about any changes they wish to make. And they do (make changes), sometimes with very poor results.

 

Thanks @WTF?

Couple other questions, appreciate your guidance

I understand that the part numbers for different TCs are different from bearing metal temperature TCs to Generator bearings TCs and wheelspace TCs, my question is and sorry if I am repeating myself, does any of it require thermowells in addition to TC? I understand answer should be no but in one of the GE drawings I can see there was a mention if thermowells.

Also during replacement if TCs is it recommended to replace the cable and extension wires as well?

 

and sorry its a MarkVie system with frame 7 GE turbine

 

@Instenthusiastic,

There are Frame 7s, and there are Frame 7s…. GE did a really stoopud thing when they used Frame 7 for the F-class machines (and Frame 9 for the F-class machines) AND the H/HA-class machines. So, it’s also not enough just to say you are working on an F-class machine

GE makes the Frame 7E/EA and Frame 7 F-class machines. In the last 20 years or so they have been buying generators from other manufacturers (Brush; ELIN; etc.) for the E/EA machines as the profit margins are higher on the bigger hydrogen-cooled generators for the F-class machines and the newer steam turbines so their factory concentrates on the higher profit machines and lets other manufacturers supply the generators for the E/EA machines.

BUT, the part of GE that makes generators typically has their own parts built to their own specifications and they weren’t sharing a lot of similar parts between the turbine division and the generator division. (That’s why it’s usually difficult to find parts lists and drawings for many generator parts in the manuals provided with the turbine-generators provided by the turbine division.)

Again, in my experience, the turbine bearing metal T/Cs were physically embedded in the bearings as were the generator bearing metal temperature T/Cs—when both were made by GE factories. Now that there are generators from multiple manufacturers packaged with the turbines I don’t really know (and this isn’t really a controls-related issue in my mind).

When looking at GE parts lists and drawings it’s critical to understand how the parts lists and drawings are produced. GE tries to make their system drawings to be used with many different configurations. The parts list for a system usually has a “group number” (as many of the parts do as well). The system group number is import when looking at the system drawing which may be used for several configurations—and some might have thermowells and some might not—for the same system. There are usually notes on the system drawings with G1 and G2 and G3 in circles and some kind of important note…. Isn’t this fun???

So, you need to get the system group number from the top of the associated Parts List drawing and use that number to determine what aspects of the system drawing are specific to that group number. Again, isn’t this fun stuff?? Sometimes one needs a secret decoder ring to understand the whole thing, and even then, sometimes it’s wrong. Yes; sometimes it’s wrong.

When looking at the group number descriptions you will often find a for-letter mnemonic; OWSA. It translates to: OtherWise Same As. So, a G2 might have thermowells but a G1 won’t, so the note for G2 might say: Thermowell Req’d. For Thrust Bearing, OWSA G1. (I love this stuff. NOT. To my knowledge when they used to train GE field service engineers they never spent even an hour of the hundreds of hours of class time on how to read, understand and apply parts lists and associated system drawings. And I know FOR A FACT they never taught or covered this for controls people—because it’s a parts issue and those are handled by the mechanical people.)

I presume the T/C wire you are referring to is what is known as thermocouple extension wire, and no; it’s generally not necessary to replace it when replacing any T/C, unless it gets damaged by the mechanics during disassembly (which can and does happen too often).

And, unless the thermowell is damaged during disassembly or operation it’s usually not necessary to replace it either.
FINALLY, when the machine is open and bearings are exposed GET OUT THERE AND CRAWL AROUND THE MACHINE AND TAKE PHOTOS AND MAKE NOTES!!! A controls person doesn’t just sit in front of an HMI all the time every day. It’s necessary to know where field devices and instruments are physically located on the machine and how they work. The BEST time to get this exposure is when the machine is not running and it’s opened up.

OVER and OUT!

 

amazing, so much knowledge and I love reading your posts. Thanks a lot