conventional thermal power plants

Turbine Bypass Operation Unstable

Plant: Plant: 370 MW PF-fired Power Plant with HP&LP Turbine Bypass Systems.
Query: Turbine Bypass Operation Unstable
Explanation of Query: During unit start-up operations, I am experiencing great difficulty with establishing and stabilising the Turbine HP and LP Bypass systems. When I set the initial opening position of the HP Bypass Control Valve, then put it on to Auto, the LP Bypass Control Valves (already on Auto), then ramp open and the HP Bypass Control Valve closes again. Usually, this cycle of opening and closing repeats itself, numerous times, until it eventually settles down and starts to work normally. As a consequence of these cycles, everything else also becomes unstable (especially the Boiler Drum, Feedwater Tank and Condenser Hotwell levels, along with the Boiler Feed Pump operation). Sometimes, it can get so bad that we suffer an MFT, and have to re-start all over again. I have tried initially leaving the Turbine Bypass Control Valves in manual (both HP and LP sets), until everything looks stable. But, as soon as I then place them into Auto, then it all happens again (and sometimes is worse). This is very stressful, and embarrassing, and I don’t understand why it is happening.

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