Hi all, I have recently joined a power plant of 35 MW (steam turbine). though I have already read almost all the threads related to droop and isochronous, still some confusion.

We give the power to cement plant also unit imports and exports from the grid. want to ask on which mode my unit is working droop or isochronus. also is the droop setting is done to minimize the fluctuation of load when grid frequency changes. Plz help

 

Hi DD

If your unit is importing from or exporting to a Grid then your unit will not be running in Isochronous mode but Droop mode.

The Droop settings does not minimise fluctuations in load due to changing frequency rather the opposite occurs ! the droop controller regulates the load on your machine as a repsonse to fluctuating system frequency.

If there is an increase in System Frequency the droop controller will start to reduce the load on your machine by reducing fuel to the Govenor/prime mover(in your case steam flow would be reduced through a control valve).

There is a lot of information out there about Isoch/droop some of it utterly baffling !

I put together a PDF file that i think explains Isoch/droop clearly.

copy and paste the website address into your browser to view the file.

https://docs.google.com/viewer?a=v&...zgtN2VjMS00ZTExLWFkNjMtNzRlYmZkNzNkN2Nh&hl=en

regards
Liam.

 

DD and Liam... if you search the Control.com archives, you will find some 160 threads, related to Droop & Isoch-Mode operation, were posted... with little agreement as to what represented Fact of Fiction!

Perhaps, you can present a fresh approach!

Good Luck, Phil Corso

 

Hi Liam,

Want to ask when the unit comes in the island (separated from grid) does it comes to the isochronus mode. As at that time it only feeds power to the cement plant. also there is a set point given of 49.5 in the frequency controller. does this set point comes in picture when isolated from the grid. what is the significance of this set point.

Plz help
DD

 

Hey DD

I couldn't honestly say that your machine switches to Isochronous mode when it is islanded (separated from the grid) your DCS or local HMI should indicate which mode the turbine is operating in at any given time.

However in your post you mentioned a frequency controller set point of 49.5 Hz which suggests that the machine could indeed switch to Isoch.

Assuming the turbine IS in Isochronous mode then the turbine speed will be regulated (via steam flow) to maintain a frequency of 49.5 Hz regardless of any change in load.

When you are operating independently from the grid and supplying the cement plant does the speed (frequency) of the turbine remain stable as the load changes (when the cement plant is stopping/starting large pumps for example) ?

If yes then you are in Isoch.

If you have to adjust the speed of the turbine when there is a load change then you are in Droop mode.

Both Isoch and Droop are feasible ways to run an Islanded machine. It all depends on requirements.

what I find strange is your Frequency set point 49.5 Hz ? normally 50 Hz or 60 Hz.

regards
Liam.

 

Hi Phil

I have just waded through the archives and see your point !

Perhaps one of the problems with this topic is there are so many ways to explain and interpret peoples explanations that its difficult for people to be on the same page ?

as for presenting a fresh approach i'm sure better men than me have tried .

it could be a long time before we have a definitive universally accepted explanation of Isoch/droop.

that being the case i think the best we can do is Agree to disagree

regards
Liam.