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LOIT 2020 exam prep > Exam 5 prep > Flashcards

Exam 5 prep Flashcards

MG and Excitation, Cond and Cond Transfer, GS, AR and Isophase and Stator cooling

1
Q

Which of the following supplies cooling to the generator collector housing?

A: WC

B. TC

C: It is air cooled via its own AHU

D: PW

A

A: WC

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2
Q

State the Main Generator ratings and where the armature windings and field windings are located.

What is the purpose of the collector rings?

A
  • Main Generator outputs 24kV
    • 22.8kV-25.2kV terminal voltage band
    • 560 MVAR (boost) to 310 MVAR (buck)
    • Stepped down through the Aux Transformer to 13.8kV
    • Stepped up through the Main Transformers to 525kV
    • Armature windings on the stator, Field windings on the rotor
    • Collector Rings take the DC from excitation and transfers it to the rotor via brushes
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3
Q

Why is the generator pressurized with H2 gas to 75 psig?

What is the normal purity and H2 temperatures within the generator?

A

Removes heat from windings, stator and generator dome. Cooled by TC via 4 H2 coolers. Normal purity is >90%. H2 gas temperatures are kept between 48C and 30C.

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4
Q

What is the purpose of the Generator core monitor?

A

monitors H2 gas for insulation breakdown (pyrolysates)

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5
Q

How is the GCM aligned?

A

The pyrolysate filter is normally bypassed.

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6
Q

What is the GCM monitoring and what is a normal reading?

State when the pyrolysate collector filter is placed in service and what it is detecting.

A
  • Normally 90% current flow, when it goes down to 75% or less it actuates an alarm, @ 60% a 2nd alarm comes in.
  • After 5 continuous seconds overheating validation cycle automatically initiates
  • Filter is then placed in service, if Ion Chamber current goes >/= 75% the event has been validated. If not then a malfunction alarm is now in.
  • Once validated the pyrolysate colector collects sample of the particulate
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7
Q

What are the Main Xfmr amp limits with respect to isophase cooling?

A
  • With cooling:
    • Main Transformer bus rating: 40,000amp
  • No cooling ratings
    • For 30 min you can maintain rated amperage
    • Aux Transformer: 4000 amp limit
    • Main Transformer: 23,000 amp limit
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8
Q

How is cooling supplied to the MAIN XFMR?

What happens on a MXFMR trip?

A
  • Upon Excitation 1st bank starts, @ 70C winding temp 2nd bank starts, @ 75C winding temp 3rd bank starts
    • This is both the oil pump and the cooling fans for the associated bank
  • If cooling is lost to the main transformer then 30 minutes to restore if it cannot be restored then Generator must be tripped
  • All pumps/fans trip on MT trip due to electric stratification (caused by excessive circ of cold oil)
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9
Q

How is cooling supplied to the UAT?

If Winding/Oil Temp > 80C, what actions should be taken?

A
  • Natural Circ Oil and Forced Air
  • If temperature exceeds 80C then the transformer must be de-energized immediately (generator trip)
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10
Q

What is the purpose of the generator bkr sync check?

A
  • Prevents closing in the Generator output breaker unless within 10 degrees from top center.
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11
Q

How is the second generator beraker closed when paralleling the generator on to the grid?

A

MUST USE THE SYNCH BYPASS TO CLOSE IN THE SECOND GENERATOR OUTPUT BREAKER

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12
Q

Will the Rx trip on a UAT fault at 100% power?

A

No. The turbine will trip and NAN-S01 and 2 will FBT to NAN-S03 and 4, but the Rx will not trip.

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13
Q

Describe a simultaneous trip and what will happen to the unit.

A

Simultaneous Trip = direct trip of MG(also UAT lockout) (it trips first) = highest MG protection

  • Excitation TRIP
  • Turbine TRIP
  • Unit Auxiliary Transformer supply breakers to NANS01 and NANS02 TRIP
  • Fast Bus Transfer of NANS01 and NANS02
  • TRIP and block re-closure of 525KV Generator Breakers
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14
Q

Describe a sequential trip and what happens to the unit.

A

Sequential Trip = auto actions in order to prevent MG from motoring when the turbine trips first. Gen trips on reverse power

  • Trip and block re-closure of 525KV Generator Breakers
  • Unit Auxiliary Transformer supply breakers to NAN-S01 and S02 TRIP
  • Fast Bus Transfer of NANS01 and NANS02
  • Excitation TRIP
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15
Q

Describe a coastdown trip and what happens to the unit.

A
  • Coastdown trip (used to maintain voltage from the output of the generator to the RCP motors)
    • MUST meet the following conditions
      • Turbine Trip
      • Reverse Power condition
      • Loss of power on NANS03 and/or NANS04
      • Reactor Trip
    • When these conditions are met then:
      • Load shed all breakers on NANS01 and NANS02 except those that supply the RCPs
      • Trip and block re-closure of 525KV Generator Breakers
      • Initiate the MN GEN COAST DOWN TRIP annunciator
      • 20 second timer times out or NANS01 or NANS02 voltage reaches 80% then the following:
        • Trip Unit Auxiliary Transformer supply breakers to NANS01 and NANS02
        • Trip RCP breakers
        • Trip the Main Generator Exciter
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16
Q

State the Main generator and transformer trips.

A
  • Backup distance relay
  • Reverse Power (inoperable if not connected to the grid) (backup 30 sec later)
  • Loss of Field
  • Negative Sequence

Startup/Shutdown

  • S/U OC
  • Stator grounds
  • UF
  • Differential
  • Volts/Hz
  • Potential unbalance

UAT:

  • OC
  • Ground
  • Differntial

MT

  • Ground
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17
Q

What will cause the hotwell drawoff valve to fail closed?

A
  • Loss of IA
  • Feed Pump low suction pressure
  • High cation conductivity in hotwells
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18
Q

What is used to rapidly slow the trubine?

How are they operated?

In what position will it fail?

A
  • Vacuum breakers on each shell allow rapid lowering of turbine speed
    • Spring shut & air opened. This means they fail closed on loss of air
    • Controlled from single handswitch on B07.
      • Indication will be dual unless all 3 are in the same position
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19
Q

What will happen if a LPFW heater experiences a HI HI condition?

A
  • HI-HI Level in any heater will cause its associated string to automatically close its associated inlet and outlet valves
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20
Q

Why is MFWPT lube oil system started before starting the first Cond pump?

A

Start MFP lube oil system before starting cond pp because MFP may rotate/damage brgs (alarm if you do)

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21
Q

How are the B Cond pump mini flow and lo lo level trips aligned when the B cond pump is aligned to one hotwell or the other?

A

The suction MOV switch aligns B Cond pump miniflow valves based on which one or both suctions are opened. It also aligns the LO LO lvl trip to the appropriate hotwell section.

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22
Q

State the Cond pump trips.

A

Trips:

  • Low Flow (< 3600 gpm for 45 sec)
  • B pump must have one suction valve full open
  • 30” in hotwell half (lo-lo level); (B - 30” on either hotwell aligned to)
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23
Q

In what position does the cond pump miniflow fail?

A
  • FAIL OPEN on loss of air or power
    • “A” and “C” powered from NNN –D12
    • “B” NNN-D11 (both)
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24
Q

Regarding the Condensate polishing demins:

How does CDV-195 operate to bypass around the demins?

What will cause the bypass to open?

A
  • CDV-195 provides a bypass around the demins in case flow gets blocked or demins are not in service
    • Reverse acting controller
    • Controller normally in Manual
    • Interlocks (regardless if in Manual or Auto)
      • Condensate demin High D/P (>55 psid)
      • IA header pressure low
      • Condensate polishing skid inlet or outlet valve not fully open
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25
Q

Why is hotwell level maintained at 41”?

A

to accomodate a HDP trip at normal power. If this occurs hotwell level would drop approx 9”. Keeping HW level at 41” means that even during a HDP trip there is no danger of dropping below the 30” LO LO Cond pump trip.

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26
Q

How is excitation added to the generator?

A

On VR signal, excitation is added by the SCRs. They are forward biased SCR’s that when fired ON, raise field excitation. Full on firing = Full field strength.

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27
Q

State the MVAR limits associated with the main generator, to include H2 pressures and purity.

A
  • MVAR limits – 560 boost, 310 buck
  • H2 pressure limits = 30 to 75 psig (30 psig is for adequate density for cooling)
  • Min H2 purity = 90% (explosion)
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28
Q

What is double sequencing with regards to ESFAS and what auto action prevents it from occurring?

A

Double Sequence – SIAS with degraded grid causes LOP and another load shed – time for HPSI pp to inject

Trips WRF bkrs

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29
Q

What is the PCR and how is it cooled?

A

Power conversion room.

  • PCR HVAC
    • 3 Units in a Lead/Lag formation
      • If 1st unit can’t maintain temp then the system will alarm and auto start a 2nd unit
    • PCR HVAC Units shutting down
      • Will lead to Exciter shutdown on high temperature within several minutes.
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30
Q

What method of fire protection exists in the PCR?

A
  • MUST BE MANUALLY ACTUATED by pulling BOTH manually operated pull handswitches
    • One each next to the access stairs outside both of the normal entry/exit doors on the East side of the PCR.
  • On actuation it auto shutdowns the HVAC units which will lead to room high temp shutdown
  • Fire detection is stand alone and will alarm on B06 EXCTN PCR/PPT TRBL
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31
Q

What are the PPT’s?

A
  • PPT’s (Power Potential Transformers)
    • 3 separate step down transformers with power taken directly from the generator terminals (via a tap in to the isophase bus upstream of the Unit Aux Transformer)
    • Steps 24kV down to 1.2 kV this then goes to the exciter bridges
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32
Q

What are the SCRs power bridges and how many are needed for operation?

A
  • 4 power bridges
    • Only 3 needed for operation though normally 4 are in service
  • Bridges basically take the 1.2kV and convert it to the appropriate amount of DC Voltage for maintaining Generator Output
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33
Q

How are the SCR bridges cooled?

A
  • Each bridge has 2 cooling fans totally automated such that no matter malfunction it attempts to at least have one fan running
    • Norm (L25)
    • Alt (L08)
  • Utilizes a power seeking ABT
  • If both fans are not running then it removes the associated bridge from service (Only need 3 of 4 so this doesn’t trip excitation)
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34
Q

How many AC line filter cabinet fans are required and how many are normally running?

What happens if both are lost?

A
  • Large amount of heat load from the AC Line Filters and has two of its own cooling fans. Both are always running when the generator is excited only one needed
  • If you lose both: Initiates an exciter trip
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35
Q

What will operate the Generator Field Breaker?

A
  • Trips open
    • Any turbine Trip
    • Any generator Trip
    • Any Exciter Trip
  • Closes
    • When called by field flashing
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36
Q

How does the AC regulator control MG Vterm?

A

control MG terminal voltage by sending signal to DC regulator

Sends 2 signals to DC regulator to control SCRs; auto shift to DC regulator if one signal is lost.

37
Q

What is the purpose of Impedance Compensation and how does it interface with the AC regulator?

A

Impedance Compensator has an input (adjusts AC VR reference signal as a function of MG current)

Compensates for line loses away from MG; allows control based on remote point away from MG

38
Q

What is the PSS, how does it work and what must occur if it is disabled?

A
  • PSS (power system stabilizer)
    • Supplementary control that acts through the Automatic Voltage Regulator
    • Provides positive damping to generator rotor angle swings (Looks at MW and frequency)
    • In the Disabled mode the PSS is unavailable procedurally requiring that the Energy Control Center (ECC) be notified within 30 minutes of being disabled
39
Q

How does the DC regulator control field excitation and thus Vterm?

A
  • Instead of the software generating a deviation from setpoint and adjusting field voltage to maintain an operator directly controls field excitation
  • All auto adjustments and signals are removed.
40
Q

What is the V/Hz limiter and what does it protect?

A
  • Limits the automatic setpoint that is input into the automatic regulator (AVR)
  • Don’t want too HIGH of a voltage for a given frequency which could damage the generator itself or its associated step up transformers
  • THIS IS FOR PROTECTING THE MAIN TRANSFORMERS!!!!!!
  • Takes over at >25.99KV and if Volts still increasing:
    • ​>26.3KV = trip in 40 sec.
    • >28.3KV = trip in 2 sec.
  • Protects against excessive current from excessive excitation which could damage insulating materials.
41
Q

What is the purpose of the OEL?

A
  • Generator Field Current On-Line Excitation Limiter (OEL)
    • Limiter prevents the unit from exceeding thermal limits of the generator field.
    • 140% for 1 sec, 125% for 30 secs, 100% for unlimited
    • Stays active until an operator reduces voltage to less than 100%
42
Q

What is the purpose of the UEL?

A
  • Under Excitation Limiter (UEL)
    • Prevents the automatic regulator from reducing excitation to a level bad for stator and/or unstable regulator transfer to manual mode
    • Stays in until an operator manually raises voltage to clear it.
43
Q

Describe how adjusting voltage will affect VARS.

A
  • VARS out.
    • Positive VARS (+VARS).
    • Lagging VARS.
    • Boost(wtf terminology is this…)
  • VARS in.
    • Negative VARS (-VARS).
    • Leading VARS.
    • Buck(wtf terminology is this also…)
  • Raise Voltage for more VARS out or Less VARs in. Lower Voltage for more VARs in or less VARs out.
44
Q

Explain the sequence of events on an Exciter trip.

A
  • Trips lockout relays
  • Trips the Main Turbine
  • Trips the 525kV breakers and prevents reclosure (think gen output breakers)
  • Trips the exciter field breaker (DC breaker)
  • Trips NAN-S01A and NAN-S02A from Aux Transformer
  • NAN-S01 and NAN-S02 WILL FAST BUS XFER
  • Excitation Trip Alarm in B06
45
Q

I apologize if the quality of the MB(EX2100e) cards are somewhat lacking.

I was frustrated af during the ex2100e lesson and neither reading the LP nor my notes left me with much relief.

A

Sorry but this subject fucking sucks.

46
Q

Where on the main generator does stator cooling water enter?

Why?

A

Enters at top of MG with anti-siphon valve.

So that on a loss of stator cooling, the stator bars remain filled with water.

47
Q

What is the stator cooling heat exchanger configuration?

A

Two coolers in series.

48
Q

How is stator cooling water temperature controlled and at what temperature?

A

2 HXs (series) with TC (tube side) with a TCV that controls SCW temp (42C) – fails to full flow thru HXs

49
Q

Why is the coolant tank vented to atmosphere? What is the source of makeup water?

A

To remove any H2 absorbed. DW

50
Q

What is the MG output limited to when performing maintenance on a stator cooling heat exchanger while online?

A

80% or 1120MW

51
Q

What are the locations in the stator cooling system that will give a LOW FLOW alarm and turbine trip?

A

Stator: 549GPM

Bushing: 64 GPM

Connection ring: 85 GPM

52
Q

State the auto starts and trips associated with the Stator Cooling pumps.

A

Auto start

LO andLO LO disch pressure-uses flow: (549/581 gpm)

Trip on Gen Differential & Stator Ground or on Unit Diff Lockout

53
Q

Which of the following will give an amber light on the Stator Cooling water pump switches?

A. nothing

B. Standby pump auto start only

C. Standby pump failed to start

D. whenever the pump is running and green flagged

A

D whenever the pump is running and green flagged. if the pump is running and was last taken to stop, the amber light will be on. This light is showing breaker position based on the handswitch. It is just like PW, TC, NC breaker logic in that an auto start from the green flagged pump or local breaker operation will give the amber light.

54
Q

What will be lost in terms of the stator cooling system on a loss of NKN-D41?

A

125 VDC from NKN-D41. tripping is disabled on loss of NKN-D41.

55
Q

State the Turbine trips associated with the Stator cooling system.

A
  • Low Inlet Water Pressure 549 gpm 2/3 PS
  • alarms at and below setpt
  • Stator Inlet Low Flow 549 gpm orifice
  • High Outlet Temp 85C 2/3 TS
  • alarm at setpt
  • Connection Ring Low Flow 85 gpm
  • Bushing Low Flow 64 gpm FS

Alarms immediately, starts a 70 sec timer that if exceeded with the setpoint still met, generates a turbine trip.

*

56
Q

What is the purpose of the SLMS?

A

Stator Leak Monitoring System – monitors for excessive H2 in tank vent (stator bar leak)

provides a means of adding O2 (O2 forms corrosion layer to prevent H2 leaking in stator)

57
Q

State the flowpath of the isophase bus cooling system.

A

Cooled air sent down “B” phase and returns in “A” and “C” phase

58
Q

What are the limits on MG output if isophase cooling is lost?

A

If lost – MG output limited to 23,000 amps ~ 65% (required to get there in 30 min)

59
Q

What is the isophase bus temperature limits?

A

Bus temp limit = 105C; enclosure temp limit = 80C

60
Q

What cools the air flowing thru the isophase cooling system? What limits are associated with air inlet timperatures?

A

2 air to TC HXs (manually throttle TC to limit air in temp to < 130F)

61
Q

How is a H2 leak detected in the isophase bus cooling system?

A

H2 Gas Detector (0-100% of LEL) – indicates a failed bushing = lower H2 pressure to slow leak

Hi-Hi alarm = remove MG from service to repair

62
Q

State the design criteria for the CT system

A
  • Design:
    • CST maintains sufficient reserve of water to maintain the unit in hot standby for 8 hours followed by a cooldown to 350F @ a C/D rate of 75 F/hr
63
Q

What systems does CT provide make up for?

A
  • EW, EC, DG (during a LOP)
  • Alt source of water to SFP
64
Q

What will happen to AFN if CTA-1 or 4 are <80% open?

A
  • Must be > 80% open or the “N” AFP will trip or not start
65
Q

What is the minimum volume of the CST required for safe shutdown?

What is the TS minimum limit?

What suctions are below the 25 ft level?

A
  • 330,000 gallons reserved for safe shutdown of the plant.
    • Corresponds to 25 ft. 29.5 ft. is min Tech Spec Limit
    • Only suctions for CT and AF pumps are below the 25ft level
      • Mini-flows go into the tank above that level.
66
Q

What auto starts the CT transfer pumps?

A
  • CT Pump Auto Starts:
    • LOP, SIAS, CREFAS, or CRVIAS
      • Override is available
67
Q

What is the purpose of LV-75?

A
  • LV-75 opens for hotwell reject if keyswitch in NORMAL unless high hotwell conductivity or low FWP suction pressure.
  • In BYPASS – high conductivity function overridden
68
Q

What will occur to LV-81 and 82 on LO LO CST(30.7ft) level?

A
  • Makeup to Hotwell will close and will not modulate.
    • This prevents nitrogen intrusion into the hotwells.
69
Q

What actions are provided to continue AF flow on a CST EMPTY level at 8’?

A

AFA and AFB can be aligned to the RMWT on CST low level. However, AFN can not take a suction on the RMWT and AF mini flow can not be aligned to the RMWT. Miniflow still exists but that inventory is lost.

70
Q

How does the GS system maintain pressure during operation?

A
  • How the system operates:
    • 28A pressure regulating valve maintains Gland seal supply pressure during low load times
      • Aux steam is the normal pressure source due to being unaffected by an MSIS due to the Unit Cross-tie
      • Main steam can be used during low load with aux steam not available
    • As secondary steam plant loads go up then the 28A valve goes closed
    • 28B pressure regulating vale is already open at low loads and will start regulating as extraction steam starts to supply more pressure
      • BOTH 28A & 28B FAIL OPEN on loss of IA
    • Eventually steam loads get high enough that the leakage from the HP turbine shaft leak-off steam is enough to supply alone and cause 28B to close
    • PCV-27 will direct gland steam pressure to the condenser to keep pressure in band (from getting too high)
      • Accomplishes this by sensing upstream STEAM pressure and USING that pressure to position the valve

This means this valve is unaffected by a Loss of IA since it is operated by header steam pressure

71
Q

What position do the following valves fail:

PCV-28A

PCV-28B

PCV-27

A

PCV-28A and 28B fail OPEN on loss of IA.

PCV-27: is unaffected by loss of IA due to using steam pressure to reposition itself.

72
Q

State the GS supplies and when they are used.

A
  • Main Steam (backup at low pwr)
  • Aux Steam (normal at low pwr) preferred due to MSIS & x-tie hdr
  • LP turbine 9th stage extraction (low pwr)
  • MSV/CV leak off (normal at high pwr)
  • HP turbine seal packing leak off (once pressure gets high enough)
73
Q

Why is Aux Steam the preferred source of GS supply at low powers?

A

Aux steam is preferred source at low power because on MSIS it comes from AS cross-tie header

74
Q

What removes air and noncondensible gases from the GS condenser? Where are they discharged to?

A

2 GS exhausters suck on GS condenser and exhaust to AR exhaust piping and RM

75
Q

How is level maintained in the GS drain tank?

A

LV-8 controls drain tank level and discharges to the condenser. LV-8 will fail closed on loss of air.

76
Q

What will be the effect on the plant if a loss of GS occurs while at power?

A
  • Loss of GS – trip Rx and turbine (Rx because vacuum will be lost = no SBCS)
  • Break vacuum to prevent air drawn into seals/rotor (labyrinth seals damage and thermal shock to rotor
77
Q

State the operating characteristics of the Air Removal pumps.

A
  • 2 stage water-ring vacuum pumps, Powered from NG
  • 1st stage partially compresses the gas and then discharges the air and water into the 2nd stage which then compresses further and discharges to a moisture separator
78
Q

What is the interlock associated with the AR pump suction valve and the AR pumps?

A
  • Pump suction valve interlock
    • Receives permissive on pump start to open then once D/P across the valve is < 1.5” D/P the valve will open to preserve vacuum.
    • Valve fails closed on loss of IA
79
Q

What cools the AR seal water?

What supplies the AR seal water?

A

PW

Cond Service header

80
Q

What auto starts the D AR Pump?

A
  • Auto starts for “D” AR Pump:
    • 4.2” in “A” Shell
    • 4.8” in “B” Shell
    • 5.3” in “C” Shell
      • Auto aligns the suction valve as well. Can operate on all 3 shells at once
81
Q

How is the AR pump operated on initial startup when drawing vacuum?

A
  • Check valve in the first stage discharge line allows the vacuum pump to automatically shift to the “hogging” mode when the first stage discharge volume exceeds the capacity of the second stage
  • To expedite establishing a vacuum during plant start-up, ARN-HCV-10 (post-filter startup bypass valve) can be opened manually
82
Q

When drawing initial vacuum and bypassing the post-filter, what must be kept in mind with regard to the AR system?

A
  • This is an unmonitored release path now since this also bypasses RU-141A and is only allowed when there is no expectation of radioactivity on shutdown
83
Q

Describe the operation of the Post Filter Unit.

A
  • Auto aligns the Post Filter Unit based on a high level on RU-141A
  • Normally bypassed and discharges goes to plant vent
84
Q

How is the post filter manually aligned?

A
  • manually aligned by taking the switch to THRU FILTER MODE
    • When the handswitch is taken to this position the following happens:
      • Inlet & Outlet Valves Open
      • Bypass Valve Closes
      • Then the Post Filter Blower Starts
    • UNTIL THE PREVIOUS SEQUENCE IS COMPLETED IN ITS ENTIRETY THEN THE HANDSWITCH WILL REMAIN DARK!!!!!!!
      • Green light will go out, switch stays dark, once all valves are realigned and post filter blower is running then the handswitch turns red.
85
Q

State the difference between HOLDING and HOGGING(seriously, who talks like this).

A

Holding = both stages of AR pump operation.

Hogging(wtf) = only first stage and discharges to moisture separator.

86
Q

What is done at <25” of backpressure with regard to the AR pumps?

A

seal water is sent to inlet of vacuum pump to condense steam that is formed.

87
Q

What causes the amber light to illuminate on the D AR pump?

A

Auto start when green flagged or the AR pump breaker operated locally.

88
Q

What will cause the AIR REM SYS TRBL alarm to come in?

A
  • “D” suction valves auto open or not in auto, hogging valve open, “D” AR pump not in auto
  • Don’t break vacuum until < 1200 rpm unless an emergency
89
Q

State the possible consequence of the post filter unit valves failing to reposition during a mode switch.

A

Based on valve position, this could cause lowering vacuum as there is no path for the air removal pumps to discharge to.

LOIT 2020 exam prep (12 decks)

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