Starting Means for Gas Turbine

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Thread Starter

muddasir

As control.com is very informative to the beginners like me, which are helped by highly experienced professional Engineers. i thought of posting my problem of getting information about starting means of gas turbine.

I am a trainee engineer undergoing O/m of gas turbines. i have really put all my efforts to get information about starting means of gas turbine but my efforts went in vain. I want threads to access the information of the above said topic preferably with pictures, you can also help me with links or websites to access the above information which you prefer.

Replies will help a lot:
email:- [email protected]
 
muddasir,

The thing that most people are somewhat surprised to learn about starting means is that the amount of torque being transmitted from a prime mover of some sort (electric motor; diesel engine; etc.) must be variable. One just can directly couple an induction electric motor--which runs at a constant speed--to the turbine shaft and accelerate the turbine shaft from zero speed to near rated speed without some method of being able to vary the shaft speed. And, some kind of variable torque transmission device (usually a torque converter) is used for varying the torque provided from a prime mover that runs at a relatively constant speed to the turbine shaft which must be accelerated from zero speed to purge speed to rated speed.

Different gas turbine manufacturers use different starting means, and sometimes the application (the place where the gas turbine will be installed and the way in which the gas turbine will be used) will also determine the type of starting means provided with the gas turbine. For example, there are some units which use a steam turbine for a starting means, and once the gas turbine reaches operating and is producing power steam is again admitted to the steam turbine and it's used to increase the power output produced by the generator being driven by the gas turbine. So, the steam turbine is being used as a "motor" to start the gas turbine, and then as a steam turbine to augment the power production of the gas turbine-generator.

Many newer gas turbines use the generator as a motor during starting--negating the need for a separate starting means. This requires some sophisticated electronics to vary the frequency of the applied AC to the generator (to vary the speed of the 'generator' which is really a motor at that point) and switching but it's proven very reliable in recent years.

Still other gas turbines use small "expander" turbines, some of which use high pressure gas (natural gas) to develop the torque required to start the gas turbine. These are usually located on natural gas pipeline compressor stations and comes from the natural gas that's already flowing through the pipeline at high pressure. And, amazingly enough, the natural gas that passes through the expander turbine is usually just exhausted to atmosphere (unburned)!

The most common starting means, though, is an induction electric motor, which is usually coupled to the turbine shaft through a hydraulic torque converter and clutch of some kind (jaw; SSS; etc.). And, diesel engines are also a common starting means, also coupled through a torque converter and clutch mechanism. A couple of the advantages of using a diesel engine for starting is that it doesn't require any electricity (just a battery or compressed air for the diesel engine starter), and some sites just don't have the electrical capacity to power a 1- or 2 MW induction starting motor from the grid, so a diesel engine is useful in these circumstances.

Other gas turbines (usually smaller units, or aircraft engine derivative units) use hydraulic motors as starting means--meaning there must be a hydraulic pump driven by an electric motor to produce the hydraulic pressure and flow required.

As for pictures and drawings, the best place to find such things would be in the maintenance and instruction manuals provided with the turbines and auxiliaries. There are some power generation and gas turbine reference books with limited information and descriptions.

If you have specific questions about aspects of starting means (some manufacturers include the cooldown mechanism (turning gear; hydraulic ratchet; etc. in the definition of starting means) then we can try to help with answers and understanding if you can tell us your questions.

Hope this helps!
 
Heart full thanks for the reply sir;

Your reply really helped me and i got an idea of the starting means of gt. I have an access to frame 9Fa gas turbine manual which i assume it will help me with a thorough knowledge of each and every concept of gas turbine.
 
muddasir,

Um, ..., er, ..., eh, ..., GE manuals--even the ones produced by their Belfort division (which are largely responsible for Frame 9s these days (9Es and 9Fs)) aren't usually very helpful in understanding a lot of things in detail. They are usually pretty good at the basics, as most of them have some one or two-page write-ups on systems--which is how one should think of and consider GE-design heavy duty gas turbines, as comprised of systems that all work together and interact to produce torque which is applied to the generator which converts the torque into amperes. So, the system descriptions--along with the P&IDs should be what you want to learn and study.

I want to caution you, though--many system descriptions <b>are NOT</b> specific to the turbine/site, as one would expect they would be. Many system descriptions were written for older units and aren't updated regularly, or when new systems or components are added. With but a couple of exception, the P&IDs have always been very good at a schematic description of the system and components actually supplied to a site, and the system descriptions--which should be written/edited to match the P&IDs--are not always up-to-date. They are great for describing the <b>intent</b> of the system, but not so good at describing the actual system and components that were provided with the turbine and auxiliaries.

Also, many times the descriptions of operations, such as for vent fan operation, are not very accurate. Only the application code/sequencing actually running in the turbine control system truly "describes" the way things are really operated.

So, while one can trust the manuals to give generic information in any written description, one must verify that written description by using the P&IDs and the sequencing/application code running in the turbine control panel to verify or "correct" the written description.

I would be very interested to read the Belfort description of the "static starter" (variable frequency drive used to allow the generator to spin the turbine during starting and acceleration). That would be very interesting, indeed.

Best of luck! We're always here to help with your questions; doubts are another thing, but we're good at answering questions. Realize, though, that we can't see your P&IDs or the sequencing/application code running in the machine for which you have a manual--but we're pretty good at most systems and operations here at control.com. Or, rather, the contributors are very good at providing information and answering questions.
 
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