Development of a Clutch-Engagement Controller for Single Shaft CCPPs

What is it about?

In single shaft CCPPs a gas turbine and a steam turbine drive the same generator. Gas turbine and generator are located on one shaft, the steam turbine is on another shaft that can be engaged to the gas turbine / generator shaft by a shift clutch. Thus the gas turbine can run up and start to generate power independent from availability of the steam turbine. Some single shaft CCPPs are known to display increased vibrations if engaged at certain angles and a very smooth operational behavior if engaged at other angles. Roughly, the engagement angles can be clustered into four 90° sectors, one of them is deemed ‘bad’ and another one is classified as ‘good’ with respect to vibrations of the overall power train shaft. Although the first priority is to have an assembly that runs smoothly at arbitrary engagement angles, an option to engage at a predefined ‘good’ angle provides a nice back-up solution to avoid undue vibrations. To meet this requirement a control method was developed to run up the steam turbine thus that it will engage at a pre specified angel. Basically, the underlying idea is to increase the acceleration of the steam turbine during run up if a prediction reveals an engagement angle that would be too small to be within the desired area and, conversely, decrease the acceleration if the anticipated angle would be too large.

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Why is it important?

Successful development of this controller emphasizes that intelligent I&C solutions not only significantly support plant operation but can also help to overcome mechanical shortcomings. Off-line investigating and tuning the developed controller - firstly with a simulation model and secondly in the controller test field - allowed for a successful plug-and-play installation on site, without the necessity to consume time (and energy) during commissioning.