Fist of all, Happy Independence day to all Indians.
We have a steam turbine (Multi pressure i.e. HP, IP & LP, Rating 125 MW) having nozzle governing control valve system.
As per the governing valve scheme, there are 03 nos. of HP inlet steam control valve for regulation, which are opening or closing as per load/pressure/manual regulation. During start up, CV1 controls the inlet flow very minutely & then take machine up to around 70MW, then CV2 & after CV3 comes in control at higher load & pressure.
My question is: if turbine is synchronized with grid & at 100 MW, load control is in manual i.e. position of control valve is adjusted manually (NO load control or Pressure control is active) & as per the load requirement CV1 & CV2 are open 100 % & 70 % respectively. if suppose my control valve CV2 closes due to system fault& load reduces to 70MW.
We have following option as per the control system logic in which
1. Using manual mode, we can open CV3 (even though CV2 is closed) and raise the load further up to 120 MW or maximum available. Whether it will do any throttling of steam at nozzle area.
Does it affect the axial shift or diff expansion? what will happen to steam turbine parameter. Does it affect the entry area of CV2(i.e outlet of CV2).
2. We can run the machine at 70MW till the next opportunity.
I hope many of you have experienced the similar type of situation for steam turbine having nozzle governing system.
All are most welcome to share your valuable suggestion& experience.