Main Turbine (MT) Flashcards
What are the functions of the MT system?
Convert thermal energy from the SG system into mechanical energy to drive the Main generator
Provide extraction steam for feedwater heating to increase plant efficiency
Provide hot reheat steam for operation of the Main Feedwater Pump Turbines
Which valves in the MT system are provided with control oil?
Main Turbine Stop Valves (SV)
Control Valves (CV)
Combined Intercept Valves (CIV)
What system provides hood spray for LP turbine shell exhaust cooling during turbine startup?
Condensate System
Concerning the turbines, what is the purpose of the nozzle boxes?
Act as thin walled pressure vessels, which contain the highest energy steam and also direct the steam properly into the first stage buckets
The turbine consists of what three major components?
Rotor Assembly, Nozzles, and Turbine Shell
How many stages are in the HP turbine?
7
The nozzle assembly is comprised of what major components?
Nozzle boxes
Diaphragms
Shaft packing
The turbine shell is designed to withstand what temperature and pressure?
Temperature changes in excess of 200F
Pressure drop of 700 psi
LP turbine and HP turbine are similar in design, with what exceptions in regards to the LP turbine?
Wheels in the latter stages of the low pressure unit are larger than those in the high pressure unit to facilitate maximum energy transfer of low quality steam
Stellite erosion shields are located on the back of the leading edge of the vanes to minimize the affects of water droplet impingement
Grooves are cut in the back of the vanes to aid in the removal of water accumulation
What are the three primary functions of the LP turbine exhaust hood?
Serves as a transition structure between the last stage exhaust and the condenser
Serves as the supporting structure for the rotor bearings
Sustains various external forces imposed upon it
Exhaust hoods are designed on the assumption that operating temperatures will not exceed what temperature? Effects if exceeded? How do we alleviate such deviations?
300F will lead to harmful distortions resulting in clearance deviations
Water spray manifolds are installed downstream of the last stage buckets, out of the normal steam path
This spray may be initiated automatically on high exhaust hood temperature or manually by operating a bypass valve
What are the temperature alarm and turbine trip setpoints for the Exhaust hood?
Alarm at 200F and turbine trip at 225F
What is used to prevent the exhaust hood operating with a positive pressure?
Three Atmosphere Relief Diaphragms (Rupture Disks) mounted on top of each LP turbine shell
What is the purpose of the Main Turbine Thrust Bearing?
Absorbs axial thrust of the turbine and generator rotors, which are connected by a solid coupling
What type of bearing are the journal bearings?
Spherical seat type mounted in the bearing rings, which have an internal spherical surface fitted to the ball seat on the bearing
What is the purpose of the Main Turbine Turning Gear?
To rotate the shaft slowly and continuously during shutdown periods when rotor temperature changes occur
What would be the adverse effect of leaving the turbine shaft stationary during cooldown periods?
Shaft Distortion
When starting the Turning Gear, what interlocks must be met before the piggyback motor will start?
The main generator circuit breakers or motor operated disconnect are/is open
A bearing lift pump is running
Bearing lube oil pressure is adequate
Turning Gear is disengaged
Once the piggyback motor is started, when will the turning gear engage?
If rotor speed is less than 2 rpm and if a low speed permissive signal is generated by the EHC
Control PACs consist of what components?
Hydraulic cylinder, which operates on oil from the 1600 psig control oil system
Disk dump valve assembly that mounts on the bottom of the hydraulic cylinder
Various servo-valves, solenoid valves, and pressure controlled shutoff valves mounted to the lower end cap block “B” of the hydraulic cylinder
What are the two general types of control PACs?
One for controlling steam valve
One for non-controlling steam valve
Where are the Main Turbine Stop Valves located?
150’ level of the Turbine Building
The bypass valve provided in MSSV-2 is capable of passing approximately twice no load flow to permit what?
Slow warming of the stop valve below seat areas and control valve bodies
Pressurizing the stop valve below seat areas necessary for opening the SVs
What happens is if a single CV fails open during a Turbine Trip?
All SVs would need to close to isolate main steam from the turbine because the steam chest located below the SVs cross connects all the CV inlets
What is the purpose of the Main Turbine Control Valves?
To control main steam flow into the high pressure turbine during startup and shutdown, regulate steam flow to suit load requirements during normal operation, and serve as the first line of defense to prevent excessive over speeding during emergency operation
What two valves make up the CIVs? Purpose of the two valves?
Intercept valve and intermediate stop valve
To protect the turbine against overspeed from stored steam in the cross around system
Concerning the CIVs, which valves are the ‘masters’ and which ones are the ‘slaves’?
CIV-4, 5, and 6 are the “slave” valves
CIV-1,2, and 3 are the “master” valves
How do the CIVs respond to a rapid load rejection?
Master valves will close to control the overspeed condition
What happens when the Master valves close 50%?
A slave closing limit switch is activated, which will trip closed the slave valves
When would the slave valves fully reopen?
When the master valves reopen to 90%
Where is the Turbine Supervisory System located?
140’ of the Control Building at the west end of the Control Room behind B03
What is the Automatic Hi Vibration Trip setpoint?
12 mils unfiltered at all turbine speeds
How many speed sensors are on the Turbine?
Six magnet speed sensors – five are dedicated to the EHC speed control system and one to the Turbine Supervisory System
When is the generator synchronized to the grid?
Speed at 1800 rpm and all testing is completed
Describe the Process an MSR Startup
i. Do a line up, remove AS from MSRs by closing the associated valves, and open the steam trap bypass valve
ii. Ensure there is no tube leaks by checking the decay rate
iii. Purge the MSRs, close some RTHG and open some RHTG valves
iv. Open up steam supply stop check valves when turbine is 1800 rpm to initiate steam flow
v. 1st stage is started
vi. 2nd stage steam can’t be initiated before 140 MW but at 400 MW, 2nd stage can be filled (2nd stage is 5% of all steam so it has to be done before 95%)
Describe the Process for MSR Blanketing
i. Ensure all the reheating steam valves are closed and the shell drain valves are open
ii. Purge the 1st and 2nd stage scavenging
iii. Open 2nd and 1st stage RHTG stm line drain valves
iv. Steam blanket mode to purge
v. Put aux steam pressure reducing valve into service (52.3 psig)
vi. Crack open all the blanketing steam feed valves, document time
vii. Throttle valves to maintain heat up rate less than 125 deg F
viii. Before 5 min has elapsed, put all hand switches to stm blktg
ix. Close drain valves
x. Open blanketing steam feed valves and monitor pressure
c. MT trips (~23 trips)
i. CE generator inlet low pressure – 549 gpm 70 sec
ii. CE generator outlet high temp – 85 C 70 sec
iii. CE connection ring header low flow 90 gpm 70 sec
iv. CE low flow 549 gpm 70 sec
v. Generator rectifier low flow 54 gpm 70 sec
vi. Generator bushing low flow 64 gpm 70 sec
vii. Low MSOP pressure 100 psig
viii. TSI high vibes
ix. High exhaust hood temp 225 deg F
x. Low EHC fluid pressure 1100 psig
xi. MSR high level 3” below MSR 10 sec
xii. Low vacuum trip 7.5” Hg A
xiii. Thrust bearing wear detector
xiv. Low bearing oil pressure 12 psig
xv. Master trip push button
xvi. Generator trip
xvii. Reactor trip
xviii. Loss of 24 V power
xix. Loss of 125 v power
xx. Mechanical overspeed 110%
xxi. Backup overspeed trip 110.5%
xxii. Manual trip handle
xxiii. Loss of both speed signals
