Hi everyone,

I'm working with gas turbine which is made by GE company, Frame 7 EA with Speedtronic Mark VI, which is designed to work in temps between 50c in summer to 0c in winter.

In winter I face (sometimes) when the GT at BASE LOAD selector the turbine indicates PART LOAD. What does part load mean at that time?

 

Dear ME,
I suspect that from your post that you run your gas turbines at base load (temperature) all the time, and expect to see that displayed on the HMI. How long is turbine at "part load"? If it is for very short periods of time during high ambient temperatures then it may be occurring when a power augmentation system starts, like fogging or inlet cooling. If you are seeing the "part load" displayed during very cold ambient temperatures it may be some compressor protection algorithm sequence running due to the cold temperatures and increased compressor efficiency. If you can provide more information, myself or another contributer may be able to provide a better response.

 

First of all, Part Load means the unit is operating at something less than Exhaust Temperature Control (Base Load). If you manually load the unit after synchronization, you will see that everywhere from 0 MW to the point at which the unit reaches Exhaust Temperature Control (Base Load) the display will indicate Part Load. (If the unit is being operated with Pre-selected Load Control, it will not indicate Part Load between 0 MW and Base Load. It will usually say something like Load Control or Preselect Load, but not Part Load, even though, technically it is at Part Load.)

Usually when something like this happens, particularly on very cold days, the problem is that the power output of the unit is being limited to protect either the load coupling or the generator. This is because the ambient temperature is such that the air flow through the unit is very high (due to increased air density) and the power output is also higher than on a hot summer day for the same value of TNR (Turbine Speed Reference).

On extremely cold days, the power output of some turbines can exceed the ability of the load coupling to transmit torque to the generator or the ability of the generator to cool the stator and rotor windings. So, in some cases, the power output has to be limited to protect the coupling or the generator. The turbine is still making gobs of power, probably in excess of nameplate (which is to be expected with a turbine in good condition operating at very low ambient temperatures), but the power must be limited to protect the load coupling and/or the generator. This is sometimes referred to as "load limiting", and the load limit should *NOT* be changed without understanding why it is set to the value it is set at or serious damage could occur.

You should be able to use Toolbox and find the signal that is preventing TNR from being raised and allowing the unit to reach Exhaust Temperature Control. Look for something that is "blocking" L70R from being a logic "1" and you should find the culprit.

There is sometimes a value called LK90MAX which is the maximum load the unit can produce without damaging the load coupling or the generator. When DWATT exceeds LK90MAX, usually L70R is "blocked" from increasing TNR and allowing the load to increase, or the unit from reaching exhaust temperature control.

All of the above is speculation. There may be some other limit which is active; the only way to be sure is to review the Toolbox application code for the unit. So, while the above may or may not exist in your application code, there may or may not be some other limit which is becoming active earlier for some reason we can't know without being able to examine the application in your Speedtronic control panel. I've even seen limits programmed into the Speedtronic to protect the main step-up transformer or transmission lines from excessive current.

Please write back and let us know what you find.

 

MIKEVI brings up a good point. Many Frame 7EAs have some compressor protection limit functions which can limit power output, such as 17th Stage Stator Vane Protection, and these only generally become active on very cold days when air flow is very high resulting in high power output.

Thanks, MIKEVI.

 

Thank you all.

Now I know what (part load) means. It is some kind of protection, from increasing the load (due to increased air density). Because the FSR controls the unit by the speed.

Which is better - leave the unit at (part load) or decrease the load to pre-selected point (like five mw down)?

 

Part Load is *not* any kind of protection. It is simply an indication that the unit is being operated at something less than exhaust temperature control. That operation might be occurring because the operator is manually controlling load (not using Pre-selected Load Control), or because some protective function is preventing operation at exhaust temperature control when being commanded to or from loading to exhaust temperature control. To be *certain* you need to examine your Toolbox application code.

Unless the unit is being operated on a "soft" grid, when you are synchronized to the grid and producing real power changes in FSR *do NOT* result in changes in speed, only load. The unit is in Droop Speed Control below exhaust temperature control, but changes in FSR do not result in speed changes. Use the Search feature of control.com to search for droop speed control and you will all kinds of descriptions and discussions about how this works on GE heavy duty gas turbines.

There's no need to change the way the unit is being operated (though I would suggest you learn why the unit is being prevented from reaching exhaust temperature control). I would like to know what the TNR (Turbine Speed Reference) is when the unit is being commanded to be at Base Load and is operating at Part Load. Also, is the RAISE SPEED/LOAD target on the HMI "illuminated" when this occurs, meaning that automatic load control is trying to increase the turbine speed reference and the load?

Also, as MIKEVI has asked, what kind of combustors does the unit have: conventional or DLN?