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Main Steam System > Main Turbine System > Flashcards

Main Turbine System Flashcards

0
Q

What rate of change is the nuclear steam support system capable of?

A

The NSSS is capable of accepting a step change of 10% and a ramp load change of 5% per minute over the load range of 15-100%.

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1
Q

What are the three purposes of the main turbine system?

A
  1. Convert thermal energy into mechanical energy
  2. Provides extraction steam for FW heating to increase plant efficiency.
  3. Provides hot reheat steam for operation of the main FW pump turbines
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2
Q

What rate of change is the nuclear steam support system capable of with the SBCS operating?

A

The reactor is capable of accepting step load rejections of up to 55% without causing a reactor trip.

Capability provided by ability to bypass steam to condenser or atmos if required.

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3
Q

What rate of change is the nuclear steam support system capable of supporting with the SBCS and reactor power cutback system in operation?

A

With all systems in operation the turbine generator is capable of 100% step load rejection without causing a reactor trip.

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4
Q

How many main turbine stop valves are there in the main turbine system?

A

There are four and all four are open at full power.

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5
Q

What is the purpose of the main turbine control valves?

A

Located downstream of the stops valves, they control the amount of steam sent to the HP turbine.

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6
Q

How are the main turbine control valves operated?

A

They CVs are hydraulically operated and respond to signals from electro-hydraulic control (EHC).

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7
Q

What is the term for steam exiting the HP turbine?

A

Cold reheat…

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8
Q

After steam leaves the HP turbine where does it go?

A

It is directed through the four MSRs.

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9
Q

What is the steam leaving the MSRs called?

A

Hot reheat…

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10
Q

How is steam fed to the three LP turbines?

A

Hot reheat flows through normally open combined intercept valves (CIVs)

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11
Q

Where does the steam leaving the three LP turbines go?

A

Directly to the main condenser shells.

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12
Q

How does the lube oil system interact with the main turbine system?

A

Provides lube oil to the main turbine and generator bearings

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13
Q

How does the gland steam system interact with the main turbine system?

A

Supplies sealing steam to main turbine shaft packing glands and receives shaft packing gland and turbine valve steam leak off.

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14
Q

How does the control oil system interact with the main turbine?

A

Provides control oil for operation of main turbine SVs, CVs, and CIVs via the main turbine trip and overspeed protection devices.

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15
Q

How does aux steam interact with the main turbine system?

A

Aux steam provides steam to GS to allow for main turbine startup.

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16
Q

How does the electro-hydraulic control system relate to the main turbine system?

A

Governs speed, acceleration, load, loading rateand steam flow to the main turbine.

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17
Q

How does the extraction steam and drain system interact with the main turbine system?

A

Receives extraction steam and MSR reheating steam to preheat the condensate and FW before it enters the SGs.

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18
Q

How does the condensate system relate to the main turbine system?

A

Receive LP turbine exhaust

Supplies hood spray for LP turbine shell exhaust cooling during turbine start up.

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19
Q

How is steam directed into the HP turbine?

A

After the four CVs steam passes through four integral 90* nozzle box segments and then flows in both directions across the seven stages.

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20
Q

What do the nozzle boxes in the HP turbine do?

A

They act as thin walled pressure vessels and direct steam properly into the first stage buckets.

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21
Q

What is the purpose of the rotor assembly in the HP turbine?

A

Absorbs thermodynamic and kinetic energy from the steam and transforms it to usable rotating mechanical energy.

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22
Q

Where are the journal bearing located?

A

At either end of the HP turbine casing.

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23
Q

Where are field balance adjustments made?

A

First and last stage wheels.

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24
Q

What type of rotors are found in the LP and HP turbine?

A

MON BLOCK rotors aka integral wheels.

Mean they were cut into the rotor after the initial forging

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25
Q

What are the main components of the nozzle assembly?

A

Nozzle boxes
Diaphragms
Shaft packing

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26
Q

What is the purpose of shaft packing?

A

Prevents steam from bypassing the nozzle boxes or diaphragms (which would result in reduced efficiency and output)

Also prevents steam from escaping the turbine at low loads, air in leakage.

27
Q

What is the purpose of the HP turbine shell?

A

Acts as a pressure vessel with a horizontal flanged joint.

Main external structure that transmits expansion forces.

Contains stationary nozzle diaphragms.

28
Q

Describe the structure of the HP turbine shell.

A

Two halves bolted together with a metal to metal horizontal joint.

29
Q

Describe the construction of the LP turbine

A

MONO Block design.

Each turbine has two flow paths of exhaust to the condensers.

30
Q

What component in the LP turbine acts as the support structure for the rotor bearings?

A

The exhaust hood or outer casing.

31
Q

What is the purpose of the LP turbine inner casing?

A

Supports and positions the stationary nozzle, diaphragms, incorporates the inlet steam crossover bowl, and extraction pockets which divert steam from the turbine steam path for use in heating the feed water heaters.

32
Q

What is the purpose of the LP turbine’s atmospheric relief valves?

A

They prevent a positive pressure from developing in the exhaust hood in the loss of CW; such pressure could lead to catastrophic failure. (Open when pressure reaches 5psig)

33
Q

How many atmospheric relieve valves are on each LP turbine shell?

A

Three valves per shell mounted on top of the shell.

34
Q

What is the purpose of the the MT thrust bearing?

A

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

35
Q

Where are the main turbine thrust bearings located?

A

Located on the main turbine shaft between the HP turbine and the first LP turbine.

36
Q

Describe the main turbine journal bearing…

A

Similar to a car engine bearings.

37
Q

Where are the main turbine journal bearings located?

A

One at either end of the HP turbine, LP turbine and main generator for a total of ten.

38
Q

Describe how the journal bearings operate…

A

Oil is fed into the bearing at the horizontal joint and flows through an orifice located external to the bearing. As the oil passes through is removes heat from the journal.

39
Q

Describe the purpose of the main turbine turning gear.

A

Rotates the shaft slowly and continuously during shutdown periods when rotor temperature changes occur.

Driven by an electric motor through the reduction gear train.

40
Q

What interlocks must be met to start the piggy back motor and eventually the turning gear?

A

The main. Generator circuit breakers or motor operated disconnect are/is open

A bearing lift pump is running

Bearing lube oil pressure is adequate

The TG is disengaged.

41
Q

When will the turning gear engage?

A

Once the piggyback motor is energized…

Also the rotor speed must be less than 2 rpm.

42
Q

What is the purpose of the piggy back motor?

A

Built to handle locked motor amps,

Too small to turn the rotor but will take up the gear backlash on engagement of the two gears.

43
Q

What must be done to allow maintenance personnel to locally operate the turning gear?

A

CR switch must be in the “stop” o r “pull to lock” position to use the jog push button.

44
Q

Where are the main steam stop valves located?

A

Located the main steam piping upstream of the control valves.

Each SV has one inlet and outlet.

Each SV outlet is welded directly to the inlet of a separate CV casing.

SVs are all welded together through below seat equalizers

45
Q

Why is there a bypass valve on the main steam stop valve MSSV-2?

A

Permits slow warming of the stop valve below seat areas and control bodies.

Also pressurizes the stop valve below seat areas necessary for opening the SVs.

46
Q

What other function do the MSSVs perform?

A

Act as a back up to the CVs to quickly shutoff steam flow to the turbine under emergency conditions.

If a CV fails open during turbine trip all SVs need to lose to isolate main steam.

47
Q

What is the purpose of the MT control valves?

A

Controls main steam flow into the HP turbines

Also acts as the first line of defense to prevent excessive overspending during emergency operation.

48
Q

Where are the MT CVs located?

A

Installed downstream of the turbine stop valves in the main steam piping.

49
Q

Describe the operation of the MT CVs.

A

Throttle open in response to load commands from EHC.

Throttle closed at a turbine overspeed.

50
Q

Describe the location of the combined intermediate valves in relation to the LP turbines.

A

All six(1 per supply line to the LP turbine) are installed as close as practically possible to the turbine inlet to minimize the possibility of an overspeed.

51
Q

Describe the construction of the combined intermediate valves.

A

Two valves in one casing. Intercept valve and intermediate stop valve.

52
Q

What is the purpose of the CIVs?

A

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

Both valves share a common seat.

53
Q

What is the difference between the IVs and ISVs?

A

IVs shut off steam flow to the LP turbine from the cross around section. Preventing an overspeed.

ISVs serve as a second line of defense.

54
Q

Describe the master/slave relationship of the CIVs.

A

IV 1,2,3(master) are controlled by servo valves while IV 4,5,6(slaves) are not.

55
Q

What happens when a large load reject occurs and CIVs 1,2,3 close to control speed (close to 50%)

A

The slave closing limit switch is activated and CIVs 4,5,6 will be tripped closed.

56
Q

What happens when the master CIVs are reopened to 90%?

A

The slave valves fully reopen.

57
Q

What is the purpose of the turbine supervisory system?

A

Indicates and records shaft straightness of the turbine while on the turning gear.

Measured using an air gap type pickup detector.

Data displayed on B06 in the CR.

Units in thousandths of an inch.

58
Q

Where is the turbine supervisory system located?

A

140’ level of the control building at the west end of the control or on behind control panel B03.

59
Q

Describe the purpose of the vibration pickups on the main turbine.

A

Monitors the magnitude of motion of the turbine shaft in a plane perpendicular to its axis.

Monitored at all turbine bearings.

Displayed on B07 or computer displays on PMS, or ERFDADS.

60
Q

What is the purpose of the shell and rotor and differential expansion detectors?

A

Shell Expansion detector measures HP turbine shell movement wrt a stationary point on the turbine foundation. (Measured at the thrust bearing between the HP and LPA)

Differential expansion detector indicates the clearance between stationary and rotating parts of the HP turbine

Rotor expansion is measured at the east end of the LP C rotor and is a measure of the overall expansion of all the LP rotors.

61
Q

How does the main turbine overspeed trip device function?

A

Consists of an unbalanced ring which is actuated by centrifugal force.

When overspeed occurs ring is put in an eccentric position striking the trip finger.

Trip finger closes turbine steam admission valves.

62
Q

How do the thrust bearing wear detectors detect wear?

A

A hydraulic device continuously detects axial position of the turbine shaft wrt thrust bearing casing.

If reading to the pilot valve is out of spec emergency trip system activates.

63
Q

Where is tram extracted from the main turbine and where is it directed to?

A

3rd stage extraction goes to 7th point FW heaters and MSRs 1st stage reheater bundles.

5th stage extraction goes to 6th point FW heater lines.

64
Q

Where is first stage MSR steam supplied from?

A

3rd stage hp turbine extraction.

65
Q

Where is second stage MSR steam supplied from?

A

Main steam system…

Main Steam System (4 decks)

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