MT- Main Turbine/Moisture Separator Reheaters 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 is the purpose of the Electro-Hydraulic Control (MT-EHC)?
Governs speed, acceleration, load, loading rate and steam flow to the main turbine during all aspects of turbine operation
What system provides hood spray for LP turbine shell exhaust cooling during turbine startup?
The 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 (wheel blades)
The turbine consists of what three major components?
Rotor Assembly
Nozzles
Turbine Shell
How many stages are in the HP turbine? Where is steam injected into the turbine?
Seven
at the center and then steam expands axially in both directions
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
Main Turbine 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
Harmful distortions could occur 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 is used to prevent the main turbine exhaust hood operating with a positive pressure when a loss of CW occurs?
Three Atmosphere Relief Diaphragms (Rupture Disks) mounted on top of each LP turbine shell
What is the purpose of the Main Turbine Thrust Bearing? Where is the thrust bearing located?
Absorbs axial thrust of the turbine and generator rotors, which are connected by a solid coupling
between the HP turbine and first LP turbine
How many journal bearings are on the main turbine rotor and where are they located? How are they cooled?
two, one at each end of the turbine section (one at each end of the main generator)
oil
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
jack rotor small amounts for inspections
What would be the adverse effect of leaving the main 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
Main Turbine steam admission valve 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 main turbine Safety Valve #2 is capable of passing steam 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 main turbine Control Valve 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
serve as the first line of defense to prevent excessive over speeding during emergency operation
What two valves make up the Combined Intermediate Valves? 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 Combined Intermediate Valves, 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 Combined Intermediate Valves respond to a rapid load rejection?
Master valves will close to control the overspeed condition
What happens when the Combined Intermediate Valve Master valves close 50%?
A slave closing limit switch is activated, which will trip closed the slave valves
When would the Combined Intermediate Valve slave valves fully reopen?
When the master valves reopen to 90%
Where is the Main Turbine Supervisory System located? What is its purpose?
Main Control Room
monitor main turbine shaft eccentricity, vibration, expansion, speed and valve position
What is the Eccentricity Unit used for in the MT system?
To indicate and record shaft straightness while the turbine is on the turning gear, using an air-gap-type pickup detector
How many speed sensors are on the Main Turbine?
Six magnet speed sensors – five are dedicated to the EHC speed control system and one to the Turbine Supervisory System
Where is shell warming performed from in the MT system?
EHC control panel
Warming starts prior to starting the turbine. When is Chest warming complete on the Main turbine stop valves?
At 515F
When is the main turbine synchronized to the grid?
reactor power at 11.5-12.5% power
What is the flowpath from the steam generators, through the main turbine, to the condenser?
four steam lines from the steam generators lead to the main turbine stop valves, then to the main turbine control valves, high pressure turbine, 4 moisture separator re-heaters, 6 combined intercept valves, 3 low pressure turbines, condenser
What does the main steam system do for MT?
provides motive force for operation of the main turbine
provides 2nd stage reheating steam for Moisture separator reheaters
How does the LO (lube oil) system support MT?
supplies and receives lubricating oil to the main turbine and generator bearings
How does the GS (gland steam) system support MT?
Supplies sealing steam to main turbine shaft packing glands and receives shaft packing gland and turbine valve steam seal leak off.
What is the main purpose of the Moisture Separator Reheaters?
improve the quality of the high pressure turbine exhaust steam before it enters the low pressure turbine
mechanically removes moisture and then reheats the dried steam
Where are the MSRs in the MT system located? Which two MSRs are on the north wall?
176’ turbine building
A and C
Regarding the MT MSRs, what is cold reheat?
the exhaust of the High Pressure Turbine going to the inlet of the MSRs
What does Auxiliary steam do for the MT system?
supplies steam to the GS system to allow for main turbine startup.
sends steam to the reheater tube bundles during steam blanketing operation
What does NN do for the MT MSRs?
instrumentation
There is a line that branches off the C LP turbine supply from the MT MSR. Where does that send steam to?
Main Feed Water Pump turbines
From the main turbine, where do the extraction points go?
3rd stage extraction goes to the 1st stage reheaters in the MSR and 7th feedwater heater
5th stage goes to the 6th feedwater heater
How does IA interface with the MT MSRs?
operates low load valves and drain tank level control valves
What are the two sections inside the MT MSRs?
reheater section and moisture separator section
Where does the cold reheat steam enter the MSRs after leaving the high pressure turbine?
two inlet nozzles on the bottom of the MSR
Which MSR tube bundle is supplied by HP turbine 3rd stage extraction? Which stage is supplied by main steam?
1st stage
2nd stage
Where does the condensate from the 1st and 2nd stages of the MSRs drain to? Where do the high level dump valves route the condensate to?
1st stage heater drains to 1st stage drain tank, then to 6th feedwater heater
2nd stage heater drains to 2nd stage drain tank, then to the 7th feedwater heater
main condenser
What is the purpose of the MT MSR drain tanks? Where are they located?
where the moisture that’s removed from the cold reheat steam goes
under each MSR, overhead of the 140’ turbine building
What is the purpose of the two air operated level controllers associated with the MT MSR drain tanks? When will the high level dump valve fail open?
normal level control valve directs effluents to the heater drain tank
high level control valve directs effluents, when level gets too high, to the main condenser
when the turbine power is less than 10% and turbine shell warming is not in progress
Say the MSR drain tanks are filling faster than the high level dump valve will drain to the condenser. At what level in the MSR will the main turbine trip?
3 inches
How is the 2nd stage of the MT MSR steam supply controlled?
reheat steam high load valve and low load valve
What is the purpose of the MSR 1st and 2nd stage reheater drain tanks? Where do the contents go after these tanks when flow is through the normal level control valve? High level control valve?
receives the condensate of their respective tube bundles in the MSR
1st stage goes to the 6th stage feedwater heaters
2nd stage goes to the 7th stage feedwater heaters
both go to the main condenser on high level
What type of logic is used for the Main Turbine load pressure switch to prevent single point failures? Where is load sensed?
2 of 3 logic
inlet of LP turbine A
What is the sequence for putting the 1st and 2nd stages in the MSRs in service as turbine load increases?
turbine at rated speed, minimum load, 1st in service with high level control valves open below 10% turbine load. Above 10% turbine load, normal level control valve in service
2nd stage in service after 1st stage with high level control valve open below 20%. Above 20% normal level control valve in service
Concerning the MSRs, what is steam scavenging?
To prevent condensate collection in the tubes, an orificed line is connected from the top of the 1st and 2nd stage reheater drain tanks to the respective feedwater heater that the drain tank discharges to.
With the feedwater heater at lower pressure than the reheater stage, an excess of steam flow will now occur and sweep all condensate from the MSR reheater section tubes to drain to the drain tank.
Concerning the MSRs, what is Air purging? What is done as an additional means of assisting this process?
to evacuate air from reheater tube bundles, prior to the admission of any steam to a bundle to ensure uniform heating as the bundles pressurize.
If steam were to be admitted to an unpurged bundle, the top half of bundle would heat first until steam reached bundle bottom half, causing severe differential expansion and possible resultant tube failure. Air purging is performed prior to admitting reheat steam or steam blanketing steam
reheater stage drain tank drain valve is opened to the condenser to empty the tank and expose it to condenser pressure
Concerning the MSRs, what is steam blanketing? What type of valves are used to supply AS steam? What temperature is blanket steam?
pressurizing the reheater tube bundles to prevent condensation on the tubes, causing corrosion.
motor-operated stop check valves
300*F
Concerning the MSRs, what is leak detection?
leaks in the 1st and 2nd stage tube bundles are found while online by measuring flow rate through orifice flow meters. deviations of more than 10% indicate a leak
while securing the steam blanket, the steam pressure decay rate is monitored
50% over one hour is normal
50% drop in a minute is a potential tube leak
What are the effects of losing a MSR? Can the 2nd stage tube bundles be in service when 1st stage is not?
pressure boundary failure would shut the plant down
tube leaks or reheating steam issues would call for taking the 2nd stage tube bundles out of service or both stages out of service
no. 1st stage can operate without 2nd stage, but not vice versa
What is the purpose of the MSR relief valves? Where are they located?
In the case that a Combine Intermediate Valve closes, the relief valve will pop open and relive full steam flow to the exterior of the turbine building
(MSR relief valve relieving pressures are staggered between the MSRs)
on the top of each MSR
How does the main turbine system interface with the ED (extraction steam and drain) system?
Receives extraction steam and MSR reheating steam to preheat the condensate and feedwater before it enters the steam generators.
What is the purpose of the inter-stage diaphragms and shafting packing in the main turbine?
diaphragms help direct steam at the turbine blades
shaft packing helps prevent leakage along the shaft, directs steam to the turbine blades and prevents steam from leaking out/air leaking in to the turbine
Concerning the LP turbine rupture disks, they are normally dished inward. What happens when 5 psig is reached in the turbine exhaust hood?
rupture disk dishes outward against a cutting knife and relieve exhaust pressure to the atmosphere
When does the overspeed trip device trip the main turbine?
110% or 1980 rpm
What is the purpose of the main turbine drain valves?
depressurize the steam piping upstream and down stream of the HP and LP turbine, hot and cold reheat lines, MSR shell and ED steam lines and directs the steam to the main condenser
