Main Turbine - 1.0 Flashcards
What are the main Turbine trips?
- Hi RPV Level (54”)
- Hi Moisture Separator Level (9 5/16”)
- Hi EXH Hood Temp (225°F)
- Low Vacuum (7.5”HgA)
- Low EHC Fluid Pressure (1100#)
- Low Shaft Oil Pump Disch pressure (105# if >1350 RPM)
- Low Bearing Oil Pressure (8 psid)
- Primary Overspeed (108%)
- Emergency Overspeed (110%)
- Loss of Primary or Emergency Speed Signal (2/3)
- Loss of SWC
- Gen load not <78.84% two mins after loss.
- Gen load not <22.25% 3.5mins after loss.
- Generator Trips
- Power/Load Unbalance
- Axial Position (+/-35mils)
- Deviation of >5% between Pri. and B/U speed signals.
**3 Hi, 4 Low, 2 Loss, 2 Overspeed and … GAPD
What is the response to a turbine trip signal?
- TSV, TCV, IV, ISV all close
- ARDV reposition to vent off air causing the BTVs to be active, open extraction steam drain valves and main turbine drains to open- this prevents a turbine overspeed
- RPS Scram if Prx > 18% (> 98.1# 1st stage pressure)
* TSV <95% open
* TCV pressure <530psig - EOC Recirc pumps trip if Prx >18%
- Main Generator Trips on reverse power
What occurs when there is a power to load unbalance?
- The TCVs and Intercept valves automatically close on a mismatch between stator amps and main turbine 7th stage HP exhaust (cross-around) pressure. When this occurs, ETS drops below 530 psig resulting in a scram signal (if >18% power). (sensed by 1st stage pressure > 98.1#) (armed > 40% power, so… if <40%, turbine will trip on O/S)
What are the Bypass valves rated for?
They are rated for 25% steam flow and the nitrogen Accumulators will keep bypass valves open for 1 minute following loss of EHC pressure turbine trip.
What is the sequence for Control Valve operations?
TCV’s 1, 2, & 3 open first, then 4 opens to 88%. (Partial Arc)
What is the steam quality after moisture separators?
98%
Describe the turning gear operation.
- Operated automatically or manually from control room, or manually from local cabinet.
- Pre-engagement motor (Piggy back motor starts automatically (if in auto))
- Turbine speed <100rpm
- Both gen output breakers open OR Main gen disconnect open
- At least 1 turbine lift pump running
- Normal bearing oil supply pressure (~ 25-30#)
- Low speed switches picked up (rotor “stopped” or “<1.5 rpm”)
- No quill shaft failure
- Once pre-engagement motor is running, an air cylinder engages the turning gear if the following conditions are satisfied:
- Turbine speed <100RPM
- Turbine Stopped
- No quill shaft failure
- Once engaged the pre-engagement motor stops and turning gear drive motor starts. (Turns rotor at ~2 RPM).
What is the purpose of the exhaust hood spray?
Keeps low pressure exhaust hoods cool during low steam flow operations.
What are the requirements to roll the turbine?
- Chest and shell warming have been completed
- Must have 2 & ½ bypass valves open
- Turbine on turning gear for 4 hours.
Describe the operation of the reverse power relays?
Reverse power relays are sensitive to pf changes, therefore op action is required to trip the output breakers manually after a turbine trip. (15 sec if <150 MWe, 90 sec if >150 MWe).
What are the setpoints and IOAs for high vibs?
Bearings 1-10 ≥ 12 mils
Bearings 11-12 ≥ 8 mils
IOA: If > 18%, Lock MSS in S/D and Trip Turbine.
What are the setpoints and Retainment Overrides for high vibs?
Bearings 1-10 ≥ 12 mils
Bearings 11-12 ≥ 8 mils
RO: If > 18%, Run Recirc to Min, Lock MSS in S/D, and Trip.
When should vacuum be broken?
Break vacuum when <1200 RPM except for and extreme emergency,
What is important to monitor at low RPMs?
When turbine speed is maintained at less than 800 RPM for periods exceeding 5 minutes, turbine damage could occur from non-detected rubs.
What is backpressure maintained at during low loads and why?
Backpressure should be maintained ≥1.5” Hg Abs., to mitigate shell and rotor distortion, which could result in a rub induced vibration condition.
