we have currently 1- gas turbine running on base-load and other gas turbine we put on cool-down mode last 10 days.
1- just we put in operation continuously cool-down due to availability of gas turbine for fast start-up.
2- As a operation crew, my concern related turning motor or lift-oil and related auxiliaries for continuous cool-down. I need to confirm that all parameters in range, but is this normal? Can we put 1 month a stand-by turbine on turning?
I have certainly never seen any GE recommendation for how long that you can keep a machine on Cooldown. For sure there advisories on when a machine can be removed from cooldown and for how long a machine should be put on cooldown before restart. If anyone else has GE supplied information, please reply.
This has been a long discussed issue but I reckon that within the GE set boundaries there s nothing to stop you keeping a machine on cooldown for as long as you want. Personally if I had an operational situation where a machine needed to be started urgently, I would rather that it was being started from cooldown.
As for the minor maintenance considerations of continuous cooldown, I would be interested to hear other users comments.
Once people get these ideas in their head about absolutely having to have the unit on cooldown for some minimum period of time before starting the unit (with flame and accelerating it to FSNL for synch and loading), it's just about impossible to get them to reconsider. Granted, it's a very good idea. And, ESPECIALLY if the rotor has been sitting for a very long period of time with little or no rotation (such as during shipping and installation and commissioning; or long periods of non-use, even including some long maintenance outages).
BUT, as long as the L.O. temp isn't allowed to get below approximately 80 deg F (that's the temperature of the L.O. flowing to the bearings during starting and acceleration, so the temperature of the L.O. in the tank) a few days or even a couple of weeks isn't going to make a lot of difference in reducing vibration during starting. THE KEY IS THAT THE UNIT WAS PROPERLY OPERATED ON COOLDOWN AFTER THE LAST FIRED OPERATION BEFORE IT WAS TAKEN OFF COOLDOWN SO THAT THE ROTOR DIDN'T HAVE A SET (WARP) BEFORE IT WAS SUFFICIENTLY COOL.
I, personally, have started many turbines with NO cooldown prior to the START, and after several weeks of non-operation (and NO cooldown prior to the START). Yes, the vibrations in a very few instances were high, high enough to cause a trip in two instances. But, when the unit coasted back to zero speed or low enough to permit another start it had almost no vibrations during the subsequent acceleration to FSNL. AS LONG AS THE L.O. TEMP REMAINED ABOVE APPROXIMATELY 80 DEG F. And low L.O. temp just causes increased oil whip in the bearing which isn't related to rotor warping, though it can accentuate vibrations from a warped rotor.
People just want one answer--as you WELL know--and they don't want to take into account all circumstances. They just want ONE answer--like they want any problem to be the result of a single cause, which we both know is often not the case. And once they get something in their mind, it's like a race horse which "takes" the bit and can't be stopped by the jockey.
They want to have a vibration-free start-up every single time, regardless of how long between fired operations, with no damage to turbine bucket/rotor dovetails and minimum electrical load due to auxiliaries (pumps; turning gears; etc.). But, we both know it's very difficult for one to preserve their birthday cake and eat it, also. It either rots after time, or it gets eaten and it can't be visually enjoyed. But, it's extremely difficult to preserve one's birthday cake to visually enjoy it, and enjoy the taste of it at the same time as visually enjoying it, and preserve it for a long period of time before it eventually spoils. It just doesn't work.
But, that doesn't stop some people from trying, does it?
DEAR CSA AND Glenmorengie
I DISCUSS with my operation team. As you know i have also 6 years experinced in frame 9e, but still no clear about cooldown continous operation. After I discussed, now we daily start stand-by gas turbine for 1 hour, but i have still concern about crank. as you all know every motor have startup life time. if we daily start crank for cooldown, so, i think its effect on crank lifetime. kindly share what we have to do contionous operation, weekly or monthly.
we have three stand-by gas turbine. as per new instruction start daily all 3 gas turbine for an hour for cooldown mode.
As I know, it's impossible for us to know what, or how long, your experience is. I'm keenly aware of the language barrier, as well. In my advanced age, I'm also coming to realize that discussing something with one's staff is all well and good, but at some point in the process a decision has to be made. Staff will generally choose a conservative plan in a situation such as this, but a decision has to be made and it's likely that it may not fully follow the recommendations of any individual or group.
Here's my first, and final, suggestion. Make a series of tests. First, HAVE FAITH, and try starting a turbine after 48 hours at zero speed after a proper cooldown. With the L.O. temp no lower than 80 degrees F. Trend speed and vibration all during the start and acceleration. Of the unit is not to be synchronized and loaded run it for a minimum of 30 minutes at FSNL and then select STOP and let go on cooldown for the minimum requisite time. Repeat the test with three days at zero speed, then four, then five. It would be best if the unit could run at load (any load) for several hours, but it's not critical for the purposes of the test.
On another unit, after a proper cooldown and at least 24 hours at zero speed, select Cooldown ON and let it run for one hourb then select Cooldown OFF. Wait 23 hours and repeat the Cooldown cycle of one hour. Wait 23 hours and repeat. Then after a minimum of 23 hours and with the L.O. temp at least 80 deg F initiate a fired START while trending speed and vibration all the way to FSNL.
This is the ONLY way to get staff on board with understanding the effects of various cooldown processes that reduce vibrations and increase confidence. Make up your tests, but you need to decide what works best for you and your site. And by gathering actionable data that everyone can review and analyze you can make the best decision for you and your site.
I, and I believe, glenmorangie, can assure you (and everyone reading this!) that you WILL NOT damage your unit(s) with tests like this. If the vibration during any start is higher than tolerable b STO or trip the turbine. It's as simple as that.
Write back when you've made a decision and can share your data and rationale for your decision!!!
thanks CSA, to describe about cool-down procedure. i shall discuss with my operation engineer.
but really every day startup for cool-down on 0 stand still position, my mind no adsorb as operation crew, this operation.
As you know for every time cool down start after 0 speed, crank brake the torque and currently my concern for every day startup is this directly effected on the life of crank motor.
i think absolutely effected.
i shall convene my immediate operation crew regarding my concern and ask about your test advice also.
Further to my and CSAs comments, I have had a look at GER-3620N(10/17) Heavy Duty Gas Turbine Operational & Maintenance Considerations (you can download this document from the GE site). In Appendix F of this document they give minimum Turning Gear/Ratchet times for turbines in different operational conditions. Case E.2 is for a turbine with a cold rotor, unbowed and of TG >48 hours. The advised TG hours is 6 hours before start. This is I guess advisory rather than mandatory.
It just adds another bit of information to the the On vs. Off TG discussion.
To CSA & others
Our Emails crossed but it just shows how confusing this subject is. I have absolutely no problem with and totally agree with CSAs last comments on cold start on machines and have done the same myself in over 40 years of playing around with GE turbines.
Sorry to the first poster, we are not really giving much definite help to answer your question, but I think that you can see that there is more than one answer to your question.
We for a 9FB, we stop the turning gear when the metal temperature of the steam turbine reaches 200ºC, taking the GEK110999a as reference.
Thank you CSA...elomoon for detailed information, but can send me
the GEK110999a as reference please?
my email: email@example.com
I've tried to find a link to this document on any GE site but nothing. If you have, can you post a link to it?
This is our experience in our Plant. We have several 6FA, generator drive application in an isolated 500 MW peak grid. Some of our gas turbines are only started occasionally but sometimes they need to be started very quickly on the event of the tripping of any other unit in the grid.
After commissioning (around 2004) the philosophy we followed in our plant was 24/7 turning gear operation. After TIL-1049R3 â€œB and E class gas turbine wheel dovetail material lossâ€ was released in 2012 it was decided not to continue with extended turning gear operation.
We carried out different tests. After shutdown of any of the units, once reached TTWS < 150ÂºF, the turning gear would be stopped. Lube oil and cooling water would be kept in operation (we had a nasty incident with our load gear in 2009 and since then it was decided to keep always in operation lube oil/cooling water in the event of a fast start of the units). We would start the turning gear for 1 hour/day and then take the unit to FSNL. Monitored the vibrations during all the startup, stop the unit, waited for TTWS < 150ºF, stop the turning gear and continued with the same test but with the turning gear in operation for 30 minutes per day, then 15 min/day and finished with 5 min/day. Never had a trip on high vibrations. On the safe side, and as recommended in GER 3620, it was decided to have the units after cooldown on turning gear for 1 hour/day (with lube oil/cooling water on 24/7).
For the time being, never had a trip on high vibration after a fast start up from standstill.