good question

[facetoface]

We have GT10C double shaft , HP turbine shaft and LP turbine shaft , HP turbine is variable speed and LP is fixed speed the enrgy from HP is transfered to LP turbine , Now when the load go up the speed at HP turbine is go up but LP is fixed , How this LP turbine keep the speed constant in despite of load go up , and how the torq at LP is calculated and what is the diference between LP and HP turbine

 

[ScottyUK]

What is the LP turbine connected to? A generator? There are two possibilities:

1) The fuel inlet to the HP turbine is regulated by the governor to control the speed of the LP turbine. This controls the generator output frequency, which is a parameter which must be kept constant. Similar controls would be used for a compressor load, or whatever else is connected to the turbine.

2) The load is connected to a network - the grid - which is a constant frequency system. The turbine is far too small to influence the frequency a large interconnected grid, and the generator is locked to it. The grid absorbs power, but remains constant in frequency thus forcing the generator and LP turbine which are locked to it to also be constant speed.


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One day my ship will come in.
But with my luck, I'll be at the airport!

 

[facetoface]

Thanks.LP is connected with reduction speed then to generator , and there is separte between two shaft HP ,LP turbine

 

[rmw]

Actually Scotty, not to get too purist about it, if the electrical grid is large enough that the turbine is not going to have any significant effect on its frequency, then the fuel to the CT controls the torque output of the LP shaft, which controls how much power is put on the grid.

The HP shaft spins independent of the LP shaft at what ever speed it needs to in order to compress enough air for the fuel necessary to provide the driving force for the LP shaft turbine stage(s).

I am not being picky, but sakram seems to be struggling with some of these concepts, and I thought that might clarify it somewhat for him/her.

Of course, if the turbine is on frequency control, then the LP turbine speed is controlled to maintain the generator speed at system frequency.

rmw

PS: sakram has identified in other threads that this is a generator application.

 

[facetoface]

Thnks , but your answer is not talk about the question or not persuded, beacuse I think it related the torque from generator side when it supply excitaion to make balnce of GT torque , but I need to hear from specialist engineer in this field

 

[rmw]

Well, if that wasn't the answer to your question, then so do I.

rmw

 

[abeltio]

the HP turbine is called the gas generator the LP turbine is called the power turbine.

there are adjustable nozzles before the LP these nozzles work in a very counterintuitive fashion...

as the angle of the nozzles INCREASES the load carried by the LP section DECREASES... why? we need to think in terms of [Δ]p across the HP and LP section.
when the nozzles are fully open all the pressure is "used" in the HP section.
conversely, when the nozzles are completely closed they create a back pressure to the HP section... therefore there is a portion of [Δ]p available to the LP section and that is what is used to develop torque and carry the load.

see:

http://www.gepower.com/prod_serv/products/tech_docs/en/all_gers.htm

GER-3701b page 10.

HTH



saludos.
a.

 

[gtsim]

I believe that the GT10 has a fixed geometry power turbine. In this case the gas generator turbine (GG) pressure ratio remains essentially constant for much of the useful power range. This is due to the choked conditions that prevail in the power turbine for the normal operating power range mentioned above, thus forcing the GG turbine pressure fixed point its characteristic. Incidentally, this is why the running line on the compressor characteristic is approximately unique for such an engine configuration.

Regards,
gtsim

 

[facetoface]

Thanks, gtism : but there is no any mechanical contact only there is air , and do you mean by pressure ratio the pressure between the exit GG and inlet PT.
and be inform that the direction of PT is reverse generatot

 

[gtsim]

That is correct and there is only a fluid or aerodynamic coupling between the GG turbine and the power turbine (PT). The GG turbine pressure ratio I am referring to is the ratio of pressures from the inlet to the exit of the GG turbine rather than the GG exit to PT inlet. This pressure ratio remains approximately constant for a fixed geometry power turbine when operating in the normal power range of the gas turbine.

The direction of rotation of the turbines should not influence the performance of the turbines or engine much.

 

[facetoface]

Thanks ,gtism , but how the turbine keep this constant and if the load is increase the GG speed go up and the fuel go up and the torque at PT is go up but the speed is constant so I think the torque from generator oppose this increment to keep the PT is constant , is this correct Please

 

[gtsim]

I presume you are asking how the GG turbine pressure ratio is constant.

With respect to the performance of the gas turbine it is the non-dimensional flows W(T^0.5)/P and speeds N/(T^0.5) that are important. Not the actual flows and speeds. The turbine pressure ratios are primarily determined by the swallowing capacities (i.e. non-dimensional flows) of the turbines (GG and PT turbines in series). Since the PT is choked it restricts the GG turbine pressure ratio. Consider the flow compatibility between the GG and turbine:

W4(T4^0.5)/P4=W3(T3^0.5)/P3 x P3/P4 x ((T4/T3)^0.5)

T4/T3=f(P4/P3,T.Eff and gamma)

Where 3 to GG turbine inlet and 4 refers to PT inlet. T and P are temperatures and pressures respectively. T.Eff and gamma is turbine efficiency (isentropic) and cp/cv respectively. W4(T4^0.5)/P4 and W3(T3^0.5)/P3 are GG and PT turbine non-dimensional flows respectively. (Please note the turbine characteristics are largely independent of their non-dimensional speed).

If the turbines are choked then W4(T4^0.5)/P4 and W3(T3^0.5)/P3 are constant. T.Eff and gamma do not change very much. Thus P3/P4 is constant. Please refer to “Gas Turbine Theory” pages 388, which illustrate this elegantly and discuss engine performance in detail.

As the fuel flow increases, the compressor pressure ratio, GG speed, airflow, TET and thus EGT increases. Since the GG turbine pressure ratio is constant the PT pressure ratio also increases. The increase in these parameters increases the GT power output while decreasing the heat rate. The distribution of the torque and speed of the PT depends on the drive load. In power generation the PT speed remains constant but torque increases as the power output increases as explained above by “ScottyUK”. In mechanical drive applications (gas compression and pumps) the PT speed varies with load and this is determined by the system resistance of the process.

We have developed simulators that illustrate all this including the effects of variable geometry turbines as discussed by “abeltio” above. You can download them for evaluation for our website (

http://www.gpal.co.uk).

I trust the above helps.

Best wishes,
gtsim

 

[ScottyUK]

Somewhat belated reply to rmw:

The first case was intended to apply to an islanded or isochronous mode set, or a turbine driving something mechanical. Not attached to a grid anyway, so the HP turbine indirectly controlled the speed of the LP turbine and load.

The second case was supposed to contrast with the first by showing how the machine behaves locked to an infinite bus.

Obviously I did a poor job of explaining it - sorry! As my teachers used to say "Must try harder. D+".
Apologies if I have muddied the water even further. God knows, it is muddy enough.


----------------------------------

One day my ship will come in.
But with my luck, I'll be at the airport!

 

[turboco1]

sakram:

yes. your PT is driving a generator and is connected to a grid and the electric grid "system" controls the frequency(speed) of your generator and thus your PT via the gearbox. If you put more fuel into the GG then the generator will either raise in load or raise in frequency or both, depending on the unit size and regulation adjustment and system size. The GG must deliver the required heat energy in the form of exhaust gases to the PT for torque as required by the generator load setpoint called for.

 

[facetoface]

thanks gtsim and all , and I think you put good answer for all . for Gtsim your detail open alot of qestion for me how can I see page 388 for your ref:gas turbine theory and good to see this ref and also
what is the difference between LP and HP turbine with more science and technical detail please

 

[turboco1]

sakram:
try this link:

http://www.free-ed.net/free-ed/Aviation/avengines01.asp