Gas turbine starting system

M

Thread Starter

mectarek

Hi,

we have a gas turbine that is started by a diesel engine and we want to study the possibility of changing the system to air/gas starter.

what I don't understand is why does the diesel engine has a torque converter even though its torque is usually higher than an air starter.

And I don't understand the starting sequence. does the diesel engine starts to rotate alone to a certain speed then it's coupled to the turbine or that happens from the beginning?
 
Hi,

A torque converter is usually required because the starting means has to spin at a higher speed to develop the torque required to break the turbine-generator shaft away from zero speed and to accelerate the shaft during starting.

The choice of starting means should be strictly made on the basis of reliability and the reliability requirements of starting the turbine to supply power and/or exhaust heat.

In other words, will there ALWAYS be sufficient air available for starting the turbine, perhaps two or three start attempts if necessary? Is it critical to get the turbine running to support the load and/or steam requirements of a plant and if there was insufficient air available for starting could the load/plant "survive"?

This question is asked a lot by people who are experiencing starting problems, usually after many years of relatively trouble-free starting during which time little--if <b>ANY</b>--maintenance was done on the starting means and/or torque converter. Some new manager comes along and says, "Why are you using a diesel starter?" without understanding the history of the plant and the lack of maintenance and is going to save the plant by replacing that "old technology" diesel starter and torque converter with cleaner air starters and then gets promoted to another part of the plant when the change is being implemented.

Diesel starters and torque converters are extremely reliable when properly maintained and serviced by knowledgeable personnel. There are a lot of unscrupulous firms that claim to be able to refurbish torque converters or maintain diesel engines but don't have the right knowledge or take the time to understand how a diesel is controlled when used as a turbine starting means. Which leads to lots of problems, and savior managers.
 
Hi Mectarek,

If you have a diesel engine starter, your gas turbine most probably has black start capabilities, which means that if you encounter a black out due to a disturbance on the transmission system, you can start your gas turbine without support from the grid. So, if you want or plan any change in gas turbine starting device, you have to consider this feature of your plant.

In terms of torque converter, it is a fluid coupling that comprises of three major elements. These are an impeller driven by the input shaft, a turbine wheel that drives the output shaft and an oil pump that fills and pressurrize the torque converter stator.

Torque converter is used because its function is not only to transmit the torque. It also multiplies the torque with a multiplicaton factor. For example, in our plant here, torque produced by the starting motor is multiplied by a factor of 3.5. This is required particularly during rotor breakaway. If a torque converter does not exist, solely torque generated by the starter would not be able to move the rotors.

When the diesel engine starts, the impeller and the internal oil pump also start to rotate and pressure build up quickly inside the converter. When you see pressure, this means that torque is being transmitted. Internal oil pump has a direct suction line from the lube oil tank, which is always kept filled and pressurized by lube oil pump.

Regards
 
farhan317,

Thank you for reading previous threads.

You are replying to a post that is almost six (6) years old.

If your question is related to this thread ('Gas turbine starting system') please--just ask your question. If it's not related to this thread, you should open a new thread (post). (Though I admit--I couldn't find how to do that easily on this new site...)
 
Sounds like a school science project.

Because you haven't stated what the power of the gas turbine asynchronous starting motor (also normally called an induction motor by people in the industry, and an asynchronous motor by people in school) requires.

You need to know that, and you need to know the power factor of the asynchronous (induction) motor.

Not all gas turbines use asynchronous (induction) starting motors. And gas turbines come in ALL sizes and configurations and shapes. Some use diesel engines; some use steam turbines; some use expander turbines which use pressurized natural gas as the energy source (and the natural gas is simply exhausted to atmosphere when it leaves the expander turbine); and some use the synchronous generator as a synchronous motor to start the gas turbine (using a special variable frequency drive).

Lots of questions--and no answers.
 
farhan317,

Usually, there is one (1) starting means for a gas turbine. (A starting means can be an asychronous (induction) motor, an expander turbine, a diesel engine, a hydraulic starter, a pneumatic starter, even a synchronous motor (one temporarily converted from a synchronous generator for the purposes of starting the gas turbine driving the generator). Some asynchronous (induction) motors used as starting means are 440 VAC motors, or 6 KV motors. They can be anywhere from 400 HP to more than 1000 HP. There is one manufacturer's gas turbine line that uses asynchronous (induction) motors that run--during starting and acceleration--at 150-160% of rated output. That can be 1350 to 1600 HP. That's possible because the motors have a very good insulation and construction, AND they don't run full time for extended periods of time at these high outputs. The starting sequence of a gas turbine is usually on the order of 15-40 minutes, and those high power outputs really only occur at 50-60% of that time period, and most are run unloaded for some time after the starting sequence is complete to use the fans on the ends of the motor's rotor to help cool the motor a little faster after the high power output (which requires 150-150% of rated nameplate current! which your battery energy storage system is going to have to provide--so current in excess of the motor nameplate, as high 165% of motor nameplate rated current (since power output is proportional to incoming current)).

So, you see--you really need to know what turbine your battery energy storage system is going to be starting, and the rating of the starting means (if it's using an asynchronous (induction) motor)--and then you also need to understand the starting and acceleration sequence of that gas turbine. And, all gas turbines are not started in the same manner using the same sequence.

Finally, many gas turbines use diesel engines for starting means--because, when properly configured, the gas turbine can be started with very little electricity (from a large 125 VDC battery usually, or possibly an uninterruptible power supply (using a battery and converting the DC to AC, or a large inverter--again, converting battery voltage to AC, for the operator interfaces (HMIs) used to initiate the START and to monitor the start sequence, and sometimes for a short run of a DC motor-powered L.O. pump. Once the turbine-generator shaft starts turning (because of the diesel engine) there are often shaft-driven pumps which provide lubricating oil and high-pressure hydraulic oil for the operation and control of the gas turbine and auxiliaries.

But, that's just one manufacturer--and there are tens of different gas turbine manufacturers, and there are more companies that buy and package some of those turbines using starting means and auxiliaries of their choosing in their design and sequence.

I hope this helps understand the whole process a little better. Get your professor to give you more details. It's a great exercise, this battery energy storage system problem for black-starting a gas turbine. But, it requires a LOT more details.

We're not going to be able to help you too much going forward--unless your questions are about a particular GE-design heavy duty gas turbine (which seems to be most of the experience available here on control.com, though that seems to be changing recently, albeit slowly). And most of the help we could provide would be about sequence(s), and possibly some motor sizing. But not much more than that. You really should have P&IDs (Piping & Instrumentation Diagrams) to understand what systems require what for starting, as well as have some kind of outline or flow-chart or description of the unit starting sequence.

Best of luck!
 
you should open a new thread (post). (Though I admit--I couldn't find how to do that easily on this new site...)
I agree. I, too, found it difficult to locate how to ask a question (start a thread)

- In the red menu bar at the top of the screen, click on 'Forums'
- Select 'General Discussion'
- At the top of the General Discussion page there is a red, 'Post New Thread' button

link to that page:
https://control.com/forums/#general-discussion.23
 
farhan317,

The ability to "private message" people on this forum is a mixed blessing. The really GREAT thing about these kinds of forums is that MANY people can benefit from the questions and answers of one person over many years. It's a very unselfish thing to participate in these open, visible exchanges where many people can benefit and learn and grow--and even contribute their experience and knowledge. As opposed to having one person's question(s) answered by one person that no one else can ever see.

The really BAD thing about being able to private message people on this forum is that people (recipients of private messages) can be inundated with private messages with requests for help and information. AND, when help is given via private message then no one else can benefit from the exchange--ever. It's a very selfish thing.

Forums such as control.com are about multiple people, not individual conversations.

'Nuff said, eh?

I do not respond to private requests for help or information. I want to help as many people as possible now and in the future. Do not be afraid to ask your questions here; there have been very few negative or judgemental responses to request for help and information in my experience on control.com (it's one of the things I like most about the forum). Though there can be testy exchanges at times they are usually limited to personal differences that arise over methodology or procedures and not put-downs of the person asking question for help or information. The journey of growth begins with a single step, and it takes many steps before one can begin to jog and then run to lead a group of walkers and joggers aspiring to be runners (leaders). I know in some cultures it's not considered good to ask for help or information (or to even ask--there's not even a word for "please" in some cultures). Usually, we are pretty good here at control.com about warmly welcoming people to the forum and without any kind of judgement. All we ask is for politeness and good information when it's necessary to get more details about a situation. If we are left to guess about details and situations, ..., well, it usually doesn't end all that well.

Also, note that one of the new features of this new forum website format is the 'Similar threads' listing of posts that might have relevant information to the post being reviewed. It's really quite nice. (I do miss the 'Fortune' feature, though--always food for thought there, and a good chuckle once in a while, too. BIG HINT for the Moderator(s)!!!)
 
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