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)!!!)
 
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, I really thank you for the information you have shared, my question is, could a bad torque converter leads to an overload of the diesel engine while spinning the turbine? then harm the diesel engine?
we have Hitachi/ Ge gas turbine using a diesel starter, the torque converter has never undergone maintenance before. we overhauled the diesel engine and dyno tested with a full load without issue. after being coupled to the gas turbine, it did so many starts but failed with a bent pushrod only one cylinder from 6 cylinder total) on the overhead of the diesel engine.

we had repaired the failed cylinder but a gain after a while same failure occurred in the other cylinder. we really consumed all solutions but without finding the root cause.
the start sequence is as follows:
diesel starts at low idle to warm up for 5 min.
then rev up to rated 2100 rpm, at the same time engage device initiated and the turbine starts to spin.
turbine reaches 2650 rpm and starts firing.
the centrifugal force pulled the coupling and disengage the diesel engine.
diesel engine returns back to idle speed for cooldown then stopped

gas turbine rpm = 5100 rpm
 
Elbadri,

It's difficult to answer your question easily based on the information provided.

When you say the diesel engine was tested at full load after the first rebuild, how was that done? What was the load and how was the full load reached--slowly or quickly? And how long was the diesel operated at full load?

GE-design heavy duty gas turbine starting means are quite often subjected to very serious overloads--sometimes intentionally, and often out of not understanding the application. Without knowing the control system in use and how it's configured and programmed, and if the torque converter has a "spoiler" solenoid or not, it's very difficult to say if the way the diesel is being operated is correct or not. Extended periods of CRANKing the turbine (usually for fast cooling of the unit) can also cause heavy wear of the diesel, as can multiple, repeated, unsuccessful attempts to START (a LOT of sites just keep trying to START the unit four or seven or ten times in rapid succession if it doesn't start, which is HARD on the starting means (engine/motor AND torque converter).

The diesel should (normally) go through a warm-up period, one or two minutes of "idle" speed operation to ready the engine for a heavy load. Then the diesel should (normally) accelerate in 5-10 seconds or so to near full speed while the hydraulic ratchet mechanism helps to break the turbine-generator shaft away from zero speed. Once the purge time is complete then often (but not always), the diesel engine might accelerate even a little more to something near it's rated speed, sometimes slightly above it's rated speed as the gas turbine firing sequence is initiated and flame is established. The turbine-generator shaft speed should also increase once flame is established and the unit should accelerate to around 60% speed at which time the turbine-generator half of the jaw clutch (or SS clutch if so equipped) will over-run the starting means half of the clutch mechanism and the diesel will decelerate to "idle" speed again for a minute or two for a cooldown after a heavy load of accelerating the turbine-generator shaft. This usually requires about 10 minutes--more or sometimes slightly less--for break-away from zero speed to firing to around 60% of rated speed. MANY sites want to decrease the time during purging, firing and acceleration and do so by increasing the acceleration rate of the diesel starting means.

BUT, if the time from acceleration of the diesel to the disconnection of the clutch mechanism is "normal" (around 10 minutes or so) then it's probably not likely that the diesel is being overloaded. If the torque converter were overloading the diesel engine, it's very likely the torque converter casing would be very, very hot and the times for acceleration would be less than normal.

USUALLY there is a means to test the diesel when the unit is not running. I would suggest that this feature be used to test the diesel when the turbine-generator shaft is at rest (NOT on COOLDOWN (ratchet) and with the Aux. L.O. Pump running) and that a person knowledgeable in the operation of the diesel governor manually increase the diesel speed to what is normally experienced operating the unit during STARTing while monitoring the fuel rack positions. This is an UNLOADED test, and if the fuel rack is at a "low" position then it's not requiring a lot of fuel for this test--as would be expected. IF the fuel rack is at a high position during this unloaded test, then it would seem the diesel is struggling to reach rated speed for some reason. This test shouldn't take long (or be run for a long time (more than a few minutes)); it's a simple test to see if there's a problem with the diesel governor or something else--possibly (but not likely) the torque converter.

If the torque converter casing gets VERY hot during this brief unloaded test of the diesel engine, then it could be a problem with the torque converter. They do require maintenance/refurbishment after a decade or so (we don't know how old the unit is at your site). But, that's about all we can say based on the information provided. Yes; many refurbishers say the diesel is "full load tested"--but how is that done? (Not easily, and how is load measured?)

Best of luck. Personally, I doubt the torque converter is the problem. Usually, failed or failing torque converters do not transmit sufficient torque which means the engine/motor driving the torque converter is NOT loaded normally.
 
Elbadri,

It's difficult to answer your question easily based on the information provided.

When you say the diesel engine was tested at full load after the first rebuild, how was that done? What was the load and how was the full load reached--slowly or quickly? And how long was the diesel operated at full load?

GE-design heavy duty gas turbine starting means are quite often subjected to very serious overloads--sometimes intentionally, and often out of not understanding the application. Without knowing the control system in use and how it's configured and programmed, and if the torque converter has a "spoiler" solenoid or not, it's very difficult to say if the way the diesel is being operated is correct or not. Extended periods of CRANKing the turbine (usually for fast cooling of the unit) can also cause heavy wear of the diesel, as can multiple, repeated, unsuccessful attempts to START (a LOT of sites just keep trying to START the unit four or seven or ten times in rapid succession if it doesn't start, which is HARD on the starting means (engine/motor AND torque converter).

The diesel should (normally) go through a warm-up period, one or two minutes of "idle" speed operation to ready the engine for a heavy load. Then the diesel should (normally) accelerate in 5-10 seconds or so to near full speed while the hydraulic ratchet mechanism helps to break the turbine-generator shaft away from zero speed. Once the purge time is complete then often (but not always), the diesel engine might accelerate even a little more to something near it's rated speed, sometimes slightly above it's rated speed as the gas turbine firing sequence is initiated and flame is established. The turbine-generator shaft speed should also increase once flame is established and the unit should accelerate to around 60% speed at which time the turbine-generator half of the jaw clutch (or SS clutch if so equipped) will over-run the starting means half of the clutch mechanism and the diesel will decelerate to "idle" speed again for a minute or two for a cooldown after a heavy load of accelerating the turbine-generator shaft. This usually requires about 10 minutes--more or sometimes slightly less--for break-away from zero speed to firing to around 60% of rated speed. MANY sites want to decrease the time during purging, firing and acceleration and do so by increasing the acceleration rate of the diesel starting means.

BUT, if the time from acceleration of the diesel to the disconnection of the clutch mechanism is "normal" (around 10 minutes or so) then it's probably not likely that the diesel is being overloaded. If the torque converter were overloading the diesel engine, it's very likely the torque converter casing would be very, very hot and the times for acceleration would be less than normal.

USUALLY there is a means to test the diesel when the unit is not running. I would suggest that this feature be used to test the diesel when the turbine-generator shaft is at rest (NOT on COOLDOWN (ratchet) and with the Aux. L.O. Pump running) and that a person knowledgeable in the operation of the diesel governor manually increase the diesel speed to what is normally experienced operating the unit during STARTing while monitoring the fuel rack positions. This is an UNLOADED test, and if the fuel rack is at a "low" position then it's not requiring a lot of fuel for this test--as would be expected. IF the fuel rack is at a high position during this unloaded test, then it would seem the diesel is struggling to reach rated speed for some reason. This test shouldn't take long (or be run for a long time (more than a few minutes)); it's a simple test to see if there's a problem with the diesel governor or something else--possibly (but not likely) the torque converter.

If the torque converter casing gets VERY hot during this brief unloaded test of the diesel engine, then it could be a problem with the torque converter. They do require maintenance/refurbishment after a decade or so (we don't know how old the unit is at your site). But, that's about all we can say based on the information provided. Yes; many refurbishers say the diesel is "full load tested"--but how is that done? (Not easily, and how is load measured?)

Best of luck. Personally, I doubt the torque converter is the problem. Usually, failed or failing torque converters do not transmit sufficient torque which means the engine/motor driving the torque converter is NOT loaded normally.
Turbine model MS5001 frame5.
Many thanks for your kind support, with reference to the subject, the diesel engine is KT19 Cummins 450HP.
The load applied is using dynamometer test bench. full load (450hp) reached in 30 mins, and last for one hour. we have done that for three times.

GT Operation team saying that before rebuild the diesel engine, the disengage speed was 46% of rated speed. now after rebuild we observed that the percentage was 52% of rated ( is it normal? ).

One thing I observed that the torque convertor casing was very hot while diesel engine is running, I will make sure to get all the informations about control system. and will be back here to update you. You can find the torque convertor details in the attached pictures.

Now we are still investigating the failure in the diesel engine components, and its all around overheating, overspeeding, or overloading that will make this particular failure. we have contacted the TQ factory to check and repair if required or replace theTQ.

WILL COME BACK HERE SOON WITH UPDATE.
 

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