Main Turbine (MT)

Question 1

What are the functions of the MT system?

Answer 1

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

Question 2

Which valves in the MT system are provided with control oil?

Answer 2

Main Turbine Stop Valves (SV)
Control Valves (CV)
Combined Intercept Valves (CIV)

Question 3

What system provides hood spray for LP turbine shell exhaust cooling during turbine startup?

Answer 3

Condensate System

Question 4

Concerning the turbines, what is the purpose of the nozzle boxes?

Answer 4

Act as thin walled pressure vessels, which contain the highest energy steam and also direct the steam properly into the first stage buckets

Question 5

The turbine consists of what three major components?

Answer 5

Rotor Assembly, Nozzles, and Turbine Shell

Question 6

How many stages are in the HP turbine?

Answer 6

7

Question 7

The nozzle assembly is comprised of what major components?

Answer 7

Nozzle boxes
Diaphragms
Shaft packing

Question 8

The turbine shell is designed to withstand what temperature and pressure?

Answer 8

Temperature changes in excess of 200F

Pressure drop of 700 psi

Question 9

LP turbine and HP turbine are similar in design, with what exceptions in regards to the LP turbine?

Answer 9

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

Question 10

What are the three primary functions of the LP turbine exhaust hood?

Answer 10

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

Question 11

Exhaust hoods are designed on the assumption that operating temperatures will not exceed what temperature? Effects if exceeded? How do we alleviate such deviations?

Answer 11

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

Question 12

What are the temperature alarm and turbine trip setpoints for the Exhaust hood?

Answer 12

Alarm at 200F and turbine trip at 225F

Question 13

What is used to prevent the exhaust hood operating with a positive pressure?

Answer 13

Three Atmosphere Relief Diaphragms (Rupture Disks) mounted on top of each LP turbine shell

Question 14

What is the purpose of the Main Turbine Thrust Bearing?

Answer 14

Absorbs axial thrust of the turbine and generator rotors, which are connected by a solid coupling

Question 15

What type of bearing are the journal bearings?

Answer 15

Spherical seat type mounted in the bearing rings, which have an internal spherical surface fitted to the ball seat on the bearing

Question 16

What is the purpose of the Main Turbine Turning Gear?

Answer 16

To rotate the shaft slowly and continuously during shutdown periods when rotor temperature changes occur

Question 17

What would be the adverse effect of leaving the turbine shaft stationary during cooldown periods?

Answer 17

Shaft Distortion

Question 18

When starting the Turning Gear, what interlocks must be met before the piggyback motor will start?

Answer 18

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

Question 19

Once the piggyback motor is started, when will the turning gear engage?

Answer 19

If rotor speed is less than 2 rpm and if a low speed permissive signal is generated by the EHC

Question 20

Control PACs consist of what components?

Answer 20

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

Question 21

What are the two general types of control PACs?

Answer 21

One for controlling steam valve

One for non-controlling steam valve

Question 22

Where are the Main Turbine Stop Valves located?

Answer 22

150’ level of the Turbine Building

Question 23

The bypass valve provided in MSSV-2 is capable of passing approximately twice no load flow to permit what?

Answer 23

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

Question 24

What happens is if a single CV fails open during a Turbine Trip?

Answer 24

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

Question 25

What is the purpose of the Main Turbine Control Valves?

Answer 25

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

Question 26

What two valves make up the CIVs? Purpose of the two valves?

Answer 26

Intercept valve and intermediate stop valve

To protect the turbine against overspeed from stored steam in the cross around system

Question 27

Concerning the CIVs, which valves are the ‘masters’ and which ones are the ‘slaves’?

Answer 27

CIV-4, 5, and 6 are the “slave” valves

CIV-1,2, and 3 are the “master” valves

Question 28

How do the CIVs respond to a rapid load rejection?

Answer 28

Master valves will close to control the overspeed condition

Question 29

What happens when the Master valves close 50%?

Answer 29

A slave closing limit switch is activated, which will trip closed the slave valves

Question 30

When would the slave valves fully reopen?

Answer 30

When the master valves reopen to 90%

Question 31

Where is the Turbine Supervisory System located?

Answer 31

140’ of the Control Building at the west end of the Control Room behind B03

Question 32

What is the Automatic Hi Vibration Trip setpoint?

Answer 32

12 mils unfiltered at all turbine speeds

Question 33

How many speed sensors are on the Turbine?

Answer 33

Six magnet speed sensors – five are dedicated to the EHC speed control system and one to the Turbine Supervisory System

Question 34

When is the generator synchronized to the grid?

Answer 34

Speed at 1800 rpm and all testing is completed

Question 35

Describe the Process an MSR Startup

Answer 35

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%)

Question 36

Describe the Process for MSR Blanketing

Answer 36

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

Question 37

c. MT trips (~23 trips)

Answer 37

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