GE Gas Turbine Corrected Speed

J

Thread Starter

Johnplayers

Hello Experts!

Could you please tell me that "what is the primary purpose & importance of calculating "<b>corrected speed</b>"?
And why it is calculated?
(Machine details- GE Frame6, Mark V)

Thanks & Regards,
John players.
 
JohnPlayers,

You should be able to see how TNHCOR is calculated and find every occurrence/usage by looking in Toolbox.

Its primary purpose is to bias shaft speed based on axial compressor inlet temperature for the purposes of calculating fuel control flows for firing and warm-up (if I recall correctly, I don't have access to a Mark VI. m6b file at the present time).

When the ambient temperature is low the air density is high so a little extra fuel is added to ensure a successful light-off. When the ambient temperature is high the air density is low so less fuel is required for a successful light-off and so the fuel is reduced to help reduce the exhaust temperature spike on light-off.

It's effect is usually small if the bias is as per Control Specification, and over the course of many starts it helps to improve reliability and reduce thermal stresses. It should not be used to compensate for any other issues or problems.

If you find other uses and have specific questions please let us know. If this is causing a specific problem (never encountered this before) please let us know.

Hope this helps.
 
J
Dear CSA,

you are meaning that corrected speed is calculated for calculating the fuel flow for starting & warm up based on CTIM and TNH; As you said that the same is measured for successful light off and to reduce the exhaust temperature spike on start-up.

Okay, I'll note down those points additionally.

But I'm referred in GE O&M manual that,
<b>PULSATION PROTECTION CONTROL </b>
The inlet guide vanes are automatically positioned during a start-up and a shutdown sequence to avoid gas turbine compressor pulsation. The pulsation limit is expressed as a function of IGV angle & corrected speed. Corrected speed is a compressor design parameter that is a function of the actual running speed of the compressor and the inlet air temperature.

The control system utilizes the measured variables of turbine speed and ambient temperature to determine the IGV angle and automatically modulate them to that position.

So that only I've doubt in, what is the relation between Corrected Speed & Compressor surge?

And according to corrected speed percentage how the IGV angle will behave and why it is behaving like that?

Thanks & regards,
Johnplayers
 
I just follow the method advised by CSA:

The THNCOR take into account of compressor inlet temperature (CTIM).
If we don't take the CTIM in account, then the cprlim = f(TNH,IGV), but the CTIM do affect.

the cprlim (maximum compressor ratio before surge) according to the characteristic performance of compressor.

that is cprlim = f(TNH*sqrt(CTIM),IGV),
and that is cprlim = f(TNHCOR, IGV).

I hope it helps.
Best regards.
Neo
 
Johnplayers,

Without being able to see what's running in your Speedtronic panel I can't comment specifically. In the past, corrected speed was only used for fuel control. If you have a turbine with DLN combustors it's entirely possible the IGVs are being used for compressor protection--and that corrected speed is being used as a bias.

I ways caution people to be very skeptical of what they read in the manual. The ONLY written "documentation" that counts is what's running in the Speedtronic. GE and its packagers have a HORRIBLE habit of putting incorrect descriptions in the manual.

That's why I recommended actually looking at the logic/sequencing/application code running in your Speedtronic panel.
 
Johnplayers,

If the IGVs are acting up why not just tell us what's happening--or not happening--and tell what troubleshooting you've done and what the results of that troubleshooting were???
 
Hi Johnplayers and CSA,

Just stumbled upon this old thread and wish to humbly express opinions of mine.

I think the usage of TNHCOR is quite broad, in the context of GE designed heavy duty gas turbines (may to aero type too). From my preliminary study I found that TNHCOR is primarily used to correct or bias the actual measured HP shaft speed to the ISO condition (60 degF/15degC) , where the GT limits and performance was designed and tested in. There are few other control functions that require air mass flow as input parameter for calculation, that will use TNHCOR and IGV angles to closely approximate the air mass flow.

Cheers,
Kevin
 
G

gustavo_marcelo

HI CSA,

Read your explanation. I also wonder in general the use of corrected speed in any turbine.

1. Is it necessary to do the correction? What if we do not use the corrected value but use the actual instead?

2. What does "bias" means as above statement? People always said applying bias to get this and that, what is it actually?

3.The above statement refers to the 'after correction' condition?
 
gustavo_marcelo,

>1. Is it necessary to do the correction? What if we do not
>use the corrected value but use the actual instead?

GE believes it is necessary. See Kevingst's reply below; it is very good.

>2. What does "bias" means as above statement? People always
>said applying bias to get this and that, what is it
>actually?

A bias in GE-speak is a value which is added to or subtracted from some parameter to achieve a desired value. For example, one can determine exactly how much water injection flow-rate is required to exactly achieve emissions compliance, but if there is some temporary disturbance in operations the amount of water might be too low causing an out-of-compliance condition (which can means fines or even jail in some parts of the world). So, a small extra amount of water injection flow-rate, called a Compliance Bias, usually, is added to the amount of water required just to make compliance so that actual emissions are slightly below guarantee and a slight disturbance won't cause an out-of-compliance issue.

>3.The above statement refers to the 'after correction'
>condition?

I don't understand the question.
 
G

gustavo.marcelo

>>3.The above statement refers to the 'after correction' condition?
>
>I don't understand the question.

Sorry. The first replies you submitted to the questioner, is it considering the condition after considering the bias?

Conceptually I think all machines are having the same control with slight modification here and there.
 
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