Main Turbine and Auxiliaries Flashcards
Why is Low Speed Bypass Switch used for emergency use only?
Allows for engaging piggyback motor for turning gear regardless of turbine speed
Explain basis for each step used to perform shell warming
Load limit at 100 and Load Set at 0% to allow CVs to fully open
CIVs must be closed to block steam to LP turbine and prevent turbine roll
MSV #2 poppet value recommended at 1-2%
First Stage pressure limit of 100psi to prevent removal of Scram Bypass
Need Turbine on turning Gear to ensure even rotor heating
Max heatup rate 150F/hr due to chest heatup limit
Shell warm until First Stage Upper-Inner surface above 250F and diff expansion readings not in “Red Band” (0.115 and 0.460)
Explain basis of each step for Chest Warming
Less steam needed for chest warming due to smaller area and higher steam pressure
Steam chest heatup rate limited to 150F/hr
Chest Warming considered complete when steam chest pressure is w/in 50psi of Turbine Throttle Pressure
May have to transfer from chest warming back to shell warming to maintain temps and maitain diff expansion
May have to throttle “Control Valves Above Seat Drain” closed to achieve desired Temps
Why should turbine Operation be minimized below 40MWe Power?
Increased erosion on latter stage buckets
Why should turbine not be operated more than 5 minutes below 800rpm?
Low RPM can cause rubbing which would cause rotor bow that would not be detected by vibration instruments at low speeds
Why should Turb not be operated with exhaust pressure <24.5inHg?
Can impose excessive duties on turbine parts based on hi backpressure while a generator trip causes the rotor to reach overspeed condition
Turbine Operation <240MWe should be performed with lowest possible exhaust pressure (avoid exhaust pressure >4inHg)
Why should turbine not be operated less than 240MWe with exhaust pressure greater than 4inHg?
At this load and backpressure, the turbine blading is subjected to increased risks of damage due to aerodynamic buffeting or flutter. In essence, stresses on blades are cyclic which cause metal failure
Why is first stage bowl temp Heatup rate limited to 150F/hr?
Minimizes possibility of surface crack initiation.
Why is Turbine Lube Oil System requiredwith Generator Filled with Hydrogen?
To prevent hydrogen leakage; however, should be able to operate for several days without without turbine lube oil system
What must be done for Turbine Lube Oil Vapor Extractor securing with Lube Oil System running?
can be out of service for ~6 hr with no actions
For greater time, then oil sample is required daily
Why is Turbine Cooler Outlet Temp Controller set to 115F prior to turbine roling?
TO provide proper lubrication throughout bearings
Why should turbine lube oil system be operating when there is hydrogen in Generator?
To provide backup to H2 seal oil system
