Hi,

Can any one explain me the mode selector switch fitted on 12MW GE steam turbine generator. To me Isochronous mode is for running in island mode maintaining fix frequency (Not synchronized condition). Droop mode is for synchronized operation. The third selection of base load is not clear whether in this mode the TG set will maintain fix power in synchronized condition or maintain 100% of rated power in synchronized condition or use for any other function?

Regards,
Shaheed

 

Shaheed,

You're correct about the function of Isoch and Droop modes.

Base Load cannot be selected when Isoch mode is selected, as the turbine needs to respond (very quickly) to changes in load/frequency and can't do that if it's producing maximum power.

Base Load for a steam turbine is most likely a maximum allowable load and selecting Base Load in Droop mode tells the governor to put as much steam in the turbine as possible to maintain the maximum allowable load setpoint.

Note that steam temperature and pressure and condenser "back-pressure" (vacuum) affect power output, as well as ambient pressure. So, "maximum allowable load" may not be the same every day unless all the relevant parameters are as close as possible to nameplate conditions.

 

Thank you for reply.

Do you mean that before selecting the base load with droop mod I have to define (put value in controller) the amount of base load? The generator will maintain that set point of power am I right?

 

Shaheed,

No; I don't mean that at all.

I mean that most every turbine governor has some kind of "sense" of rated power output, either a hard-programmed limit in watts, kW, or MW, or in steam flow, or in some cases control valve position in conjunction with steam temperature and/or pressure. (The efficiency of the steam turbine is known to the programmer of the control system, and so the power output as a function of steam conditions at the inlet can be known. Things get more complicated if there are controlled extractions, or just extractions, in general.)

Personally, I've never seen a "Base Load" selection switch on a steam turbine; I have only heard of it in the last couple of weeks on another posting in a different World Wide Web forum--and the respondent to that thread (a man with decades of experience in the world of steam turbines) said he had never heard of such a switch, either.

So, my presumption is that when Base Load is selected for the steam turbine at your site the turbine governor is monitoring one or more parameters that it uses to determine power output (which can also be determined by power input--steam flow, temperature and pressure; or, control valve position and steam temperature and pressure; for example). And, so when Base Load is enabled and active it will move the control valve(s) to such a position as to cause the steam flow, and/or the control valve position along with steam temperature/pressure such that it believes it is putting out rated power. And, then, as long as Base Load is active it will continue to adjust operating conditions to maintain rated power output. Again, that might even be by use of monitoring generator output (watts, kW, MW).

Many GE-designed Speedtronic Mark x control systems used on steam turbines use a signal "TPWR" to represent percentage of rated power output. And may times that's just a function of steam and/or control valve position. You chose not to tell us what kind of control system the turbine is equipped with, so we're at something of a disadvantage. And, without being able to see exactly how your steam turbine control system is configured we can't answer as specifically as we--or you--would like to.

Have you consulted the manuals provided by the turbine packager with the turbine to see if they have any information about "Base Load" operation?

How do you currently load the machine to or near it's rated output? Do you have some kind of setpoint (flow; watts; etc.)? What happens if you enter a value greater than you think the turbine should be capable of producing? (A properly configured control system will "ignore" the erroneous value; some will just load to rated maximum; some just won't accept the command at all--again, it depends on who the control system was configured.)

Base Load for a GE-design heavy duty gas turbine is defined to be the maximum power output for the current machine and ambient conditions. This is determined by monitoring the axial compressor discharge pressure and the turbine exhaust temperature. There is a known relationship between the two which defines the maximum power output of the unit for the machine and ambient conditions. (Gas turbine power output, since it uses a LOT of air, is greatly affected by ambient temperature and axial compressor cleanliness, and can vary by as much as 10% or more over the course of a year as ambient conditions change.) So, when an operator selects Base Load the control system increases fuel flow until the relationship between axial compressor discharge pressure and exhaust temperature reaches a limit--and then adjusts fuel flow to maintain that limit as long a Base Load is active. This ensures the turbine is operating at it most efficient point for the machine- and ambient conditions and producing as much power as is possible for the current conditions. I offer this just a little background on what 'Base Load' means for another type of GE turbine, and because without being able to examine how the turbine control system at your site is configured I can't be sure exactly what it means at your site--but I have a pretty good idea, I think, without knowing all of the particulars.

If you want more help, you'll need to provide more information.

Here's wishing everyone at and reading control.com a Healthy, Happy and Prosperous New Year!

 

Sorry for the delay in responding, like my reluctance with controls upgrades, my older computer did not like the new layout here.

CSA, for that other forum, would that be LinkedIn? (did you reply)

after reading this query and a similar on on LinkedIn, I have spent a little time on line, mainly with "sales" type publications and observed "base load" could be an adjustable value, along with adjustable loading rate. I have not been able to determine/verify that there was an imposed deadband utilized to prevent the speed governor from responding to normal grid swings.

I was hoping someone could provide a control system algorithm to assist with responding to these questions.

 

CSA-Thanks for wishing happy New Year same wishing to you.

1. The control system on turbine is a combination of woodward governor 505 woodward controller DSLC (Digital synchronizer & load controller), MSLC(Master synchronizer and load controller) and the Basler AVR DECS200 (Digital excitation control system and hydraulic/electronic actuator. The steam turbine is 12MW back pressure turbine inlet is 65Bar with 500C steam. The Generator is GE 12MW 11KV. Using to export power to utility grid station.

2. I could not consult the manual but now I will.

3. At presently we load (synchronize) the machine almost manually in selection with droop mode, up to its maximum power.

4. Whenever the load turn off the turbine get trip by over speed.
Whenever we select the base load switch the maximum power of generator not increase.

I think the parameters in governor 505, DSLC and MSLC not fine tuned because the machine was not properly commissioned due to unavailability of service engineer for the Brazilian NG company the supplier.

Regards,
Shaheed

 

Shaheed;

If you want more detailed help with the 505 / DSLC, please contact Woodward help desk at [email protected].