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MarkVI-e, PFR ON an PFR OFF
GE MarkVIe operating option PFR ON/OFF

Hello,

Could you please explain the details about the function of PFR ON & PFR OFF in MarVIe?

Another question, How to calculate TIT (Turbine inlet Temperature)?

Regards,
Rokan

2 out of 2 members thought this post was helpful...

Rokan_123,

PFR usually stands for Primary Frequency Response.

GE designed PFR to use to control generator load using an operator-adjustable load setpoint while still allowing the turbine control system to properly respond to grid frequency excursions.

Some grid regulators are not allowing the use of the former means of generator load control, known as Pre-Selected Load Control, because it does not properly respond to grid frequency excursions.

PFR is a means of controlling generator load while still allowing the unit to properly respond to grid frequency excursions to support grid stability--something Pre-Selected Load Control does not do. (Pre-Selected Load Control actually makes grid frequency excursions worse, rather than helping to stabilize the grid during frequency excursions.)

Grid operators/regulators rely on generator prime movers to properly respond to grid frequency disturbances (excursions) to help support grid stability, and PFR is one method of doing so while still allowing for stable generator load control during normal grid operation (stable grid frequency), as well as during unstable grid frequency.

It's a VERY common misbelief that generator load should be stable at all times--even during grid frequency excursions. Generator load must be "free" to vary with grid frequency excursions or the grid can become even more unstable. Droop Speed Control is the method of allowing proper generator response to grid frequency disturbances, but when some methods of load control are used that essentially over-ride Droop Speed Control then he grid can become more unstable. PFR allows Droop Speed Control to properly respond to grid frequency disturbances to help support grid stability.

The thing to know about PFR, when enabled and active during grid frequency excursions, is that generator load will not be stable when grid frequency is unstable, and that if grid frequency is high or low for extended periods generator load will be low or high, respectively, for those periods. This is expected, and necessary, for grid support, even if it seems the unit is operating erratically and in an unstable manner. Because the unit is synchronized to the grid with other units they all respond in the same way to grid frequency disturbances--they must. If the prime mover governor (the turbine control system) does not permit proper response during grid frequency disturbances the grid can become even more unstable.

If the operations department insists on using load control to operate the unit while at Part Load, then it's strongly recommended to enable and use PFR for that purpose. There's usually a method for the operator to enter/change the desired load setpoint and
once enabled the turbine control system will maintain that setpoint as long as grid frequency is stable--but when grid frequency is not at nominal then PFR will adjust load as necessary to support grid stability (even if that seems unstable at that time!).

As for the question about Turbine Inlet Temperature, what kind of gas turbine are you referring to? And what kind of combustion system does it have (conventional (diffusion flame), or DLN (Dry Low NOx (low emissions))?

Thank you very Much CSA for your generous reply.

About second question..(1) For standard burner like 9E dual fuel machine & (2)For DLN burner[2.0/2.6+] machine like GE 9FA.

Regards,
Rokan

1 out of 1 members thought this post was helpful...

Rokan_123,

GE doesn't typically use TIT terminology for any of its turbines.

For DLN combustors-equipped GE-desig heavy duty gas turbines there is a calculation which approximates 'firin temperature' which GE defines tone first-stage exit temperature (for units with air-cooled nozzles) and its signal name is TTRF or often times TTRF1. But there is no equivalent calculation performed by the turbine control system for conventional combustors-equipped units, only for DLN combustors-equipped units.

All GE-design heavy duty gas turbines are designed for a particular firing temperature (GE's version of TIT), but the actual firing temperature is never measured by the turbine control system. It's calculated for DLN combustors-equipped units by the turbine control system, and that temperature calculation is used to decide when to change DLN combustion modes, but nothing more as it's only an approximation (calculation) of firing temperature--not a measurement of actual firing temperature (which would require special technology equipment and sensors and software which are all very expensive and extremely prone to early failure and could also cause physical damage to rotating turbine components when it fails , so it's generally only used for short-term testing and not for long-term continuous operation.

Hope this helps!

Dear CSA

Thank you very much again.

Regards,
Rokan

Rokan,

A couple of people have contacted me to say I didn't say what the difference between PFR ON and PFR OFF was. Not specifically, anyway.

When PFR OFF is active and there is no other control scheme active (Pre-Selected Load Control; Remote Load Control; Base Load Control; etc.) the unit will be operating at Part Load on Droop Speed Control (when synchronized to a grid with other prime movers and generators). Droop Speed Control functions to control the proportion of fuel in response to the error between actual turbine speed and turbine speed reference. If the error between the the actual speed change and the speed reference changes for any reason--whether the actual speed changes (because the grid frequency is changing), or the turbine speed reference changes (because the operator clicks on RAISE- or LOWER SPEED/LOAD) the amount of fuel fuel flowing to the unit will change, which will change the load being produced by the generator.

If, with no other control scheme active, the operator uses the RAISE- and LOWER SPEED/LOAD buttons to adjust the load to a desired value and then does nothing else the unit load will remain stable as long as the grid frequency remains constant/stable. It's not required to use Pre-Selected Load Control, or even PFR ON, to set a load setpoint for the unit to produce a stable load. That's what Droop Speed Control does--and if the grid frequency changes then the unit load will change as it should to support grid stability.

PFR ON does exactly the same thing--just that the operator sets a load setpoint. And, as long as the grid frequency is stable the load will be stable at the setpoint. But, if grid frequency changes then PFR will allow the turbine control system to change load to support grid frequency.

Pre-Selected Load Control, on the other hand, will try to maintain a load at the Pre-Selected Load Control setpoint if grid frequency changes--which is exactly what should not happen. Hence, why PFR was developed.

The thing to note here is that load control (Pre-Selected Load Control, or PFR) is NOT necessary to adjust the turbine/generator output to a desired load value and maintain that desired load value. Pre-Selected Load Control, and PFR, are just lazy-man's ways of operating the unit. For DECADES before Pre-Selected Load Control was available hundreds of GE-design heavy duty gas turbines operated just fine, with stable load outputs at Part Load, operating solely using Droop Speed Control. It's actually the way MOST prime movers and generators operate when synchronized to a grid with other prime movers and generators.

And, in reality, improper tuning of the parameters for Pre-Selected Load Control and PFR can cause hunting of the load around the setpoint, which will NOT occur when operating at Part Load on Droop Speed Control. I have seen as much as a 2-4 MW oscillation while operating on Pre-Selected Load Control, and PFR, which stops immediately when either is selected OFF. And yet operators and their supervisors WILL NOT operate a unit without Pre-Seleceted Load Control, or PFR, active while at Part Load.

Anyway, PFR ON allows a user-adjustable load setpoint to be entered and the unit to (attempt to) maintain that setpoint, AND to properly respond to grid frequency changes. Pre-Selected Load control allows a user-adjustable load setpoint to (attempt to) maintain the setpoint, BUT NOT properly respond to grid frequency changes. Droop Speed Control "forces" the operator to use the RAISE- and LOWER SPEED/LOAD buttons to adjust the unit output to a desired value and if left unattended will maintain that load, until a grid frequency excursion occurs--and then the turbine control system will appropriately respond to the disturbance. (Again, the response will NOT be what is typically expected, but it will be appropriate if not stable--until the grid frequency stabilizes.)

That's about it. Hope this helps (clarify the difference between PFR ON and PFR OFF).