GE Mark VI turbine control system

Does anyone know what intercept valve reference means in a General Electric Mark VI turbine control system.
The valves will try and control speed in a pre-emergency overspeed situation. This system is for a G.E. reverse flow turbine we roll up and load the unit to approx 30% megawatt load on the intercept valves then place the turbine in forward flow: i.e. Steam flow through the main steam stop valves and control valves. This is where the “IV” reference comes in it determines through some cal if the turbine will stay in forward flow this is what I don’t understand


IV valve “reference” is the “desired” valve signal that is summed with regulated speed error to derive the EsubL-IV signal to the IV flow control loops (there is a loop for each servo controlled IV). the reference is ganged with the CV reference so that a CV reference for 0% CV will provide 100% IV reference. the gain of SE is such that a 2 to 3 % over speed will close the IVs. the IV reference can be reduced to perform reheater safety valve testing.

Some times some people interchange the phrase “reference” for “EsubL-IV”. Also “CV reference” can be confused with “load set” and when there is no loading rate control the two are the same.

If you don’t mind, I will guess at how the normal system could be used to roll on the IVs….

The CV reference and IV reference are ganged together, in fact they are same value. The CV reference is summed with a set 100% bias to derive the IV reference. A 0% CV reference will have the IV’s 100% open, and a -30% CV reference will have the IV’s at 0% open.

Thus set the CV reference to -30% and speed error will control the IVs near 0% open to roll the unit. once “at set speed” rated, the CV reference will be increased, increasing the IV reference to synch and load the unit. As the IVs open and increase load, the CV reference will be approaching 0%, once IVs are at 100%, the CVs will be opening and continue to increase load.

Above is a snippet.