Take a BWR nuclear plant for example. Steam from reactor core goes into turbine. How though, does the turbine sync to the grid and maintain a constant RPM, even when reactor power is increased and there is more steam, all while maintaining a constant pressure?
In: Engineering
There are multiple control circuits all working together to make sure all physical variables stay where they are supposed to be.
The details differ slightly by powerplant, every of them is a unique solution.
But in general it goes roughly like this:
When the turbine is too fast/slow a valve that supplies the turbine with steam will be closed/opened.
As you correctly figured this would affect the steam pressure before the valve. This is solved in the short term with a bypass valve that lets excess steam out right to the condensator. In the long term it’s solved by controlling the reactor power (with control rods) or by reducing the coal supply in coal powerplants.
Now this would affect the temperature of the steam, wich is fixed by injecting cold water into the steam just before the turbine (spray attemperator), and by controlling the feedwater pump to adjust the amount of water that is turned to steam.
The syncing with the grid is done by controlling the turbine speed with disconnected generator until they match up exactly. The type of generator used then forces synchronicity (it cannot slow down, if it would then the generator goes into motor operation and starts spinning the turbine instead, all generators in the electrical grid are coupled to move in synch through phyiscs)
Yes all these things are highly coupled with each other through different dynamics, so finetuning all these control loops to be stable is quite a task and still a recent research topic on how to do it more efficiently.
Source: I am doing that kind of research
Latest Answers