Isochronous Control

Hi,

We have a GTG GE Frame 6 controlled by Mark V TMR. We intend to run the machine on isochronous mode, but need to clear all doubts on that first before trying. Please help.

I went through the CSP and noticed that TNRI is calculated based on an input from TNRI_CMD but in the main display there is no such field to input the desired value to the MarkV. Is that supposed to be the speed command? Is is manipulated by the Raise/Lower Speed/Mw command button?

Thanks for your help.

It doesn't sound like the control system is fully configured to operate in Isoch mode if there is nothing writing to TNRI_CMD. And, though you didn't say, the discussion below presumes the unit will be operated independently of any other generator(s) and prime mover(s).

But I have a question. In Isochronous mode the Mark V is generally configured to control turbine speed (and therefore generator frequency) ro between 99.83% and 100.17%. When operating in Isoch mode, the Mark V will automatically control the fuel in order to keep the turbine speed (and therefore generator frequency) between 99.83% and 100.17% *as long as the load doesn't exceed the maximum power output of the turbine*. The only changes an operator can make to a unit running in Isoch mode is to change the turbine speed setpoint (and therefore the generator frequency setpoint), and that would only be necessary when attempting to manually re-synchronize the unit to a grid or with other generators.

So, are you asking because you need to know how to be able to manually control the unit speed (generator frequency) when manually re-synch-ing the unit? Because an operator cannot control the "load" of an Isoch unit; the load is the amount of lights and motors (and the loads they are driving) which the turbine (and generator) is supplying, and in Isoch mode the most important thing the turbine control system does is control the fuel to maintain a relatively constant turbine speed (and therefore generator frequency). Is there some need to have the turbine (and therefore the generator frequency) operate at something higher than 100.17% or less than 99.83%? Because one can't change the load of an Isoch unit from the turbine control, only the frequency.

But, from what you've described it doesn't sound like the control system is properly configured to operate in Isoch mode. While most turbine control panels were shipped with the basic components of Isoch control, unless the control system was specifically configured for Isoch operation it can't be easily modified to make it work in Isoch mode. Usually, *but not always*, there was a block that wrote to TNRI_CMD (usually a Logic Setpoint Command block) that had some logic inputs (from some switches or remote contacts or some targets on the operator interface) to move TNRI_CMD up or down. But this is really only necessary when attempting to re-synchronize the unit to a grid or to other units.

For MKV - On main display there is no provision to change TNRI_CMD. You have to go to "EXIT" >> "USER DIFINED DISPLAY" in this page select "ISOCHRONOUS MODE". Now here you can change TNRI_CMD, i.e. "ISOCHRONOUS SET POINT" between 98% to 102%, but you can change it when you are in "ISOCHRONOUS MODE". Before selecting isochronous mode, check TNRI_CMD and match TNR value by RAISE/LOWER with TNRI_CMD. and then select ISOCHRONOUS on main page.