IA- Instrument Air/ Service Air Flashcards
What is the purpose of the Instrument Air system?
Provides a continuous supply of filtered, dry, oil-free air at a pressure up to 125 psig for pneumatic instrument operation and control of pneumatic actuators
What is the purpose of the Service Air system?
Supplies oil-free air at a pressure of 125 psig to service air stations located throughout the generating unit.
These stations operate pneumatic tools, resin transfer, refueling machine manual operation, and other service requirements
How can I identify that a pneumatically operated valve has a safety function that may be required to operate to ensure a safe shutdown of the plant following an accident?
It will have a safety related backup air receiver
The Instrument Air system has how many air compressors and what type of compressors are they?
Three 100% capacity rotary screw air compressors
Where do the Instrument Air compressors draw air from and what pressure do they compress to?
Drawn from Turbine building air and compress it to 105-123 psig
What is significant about IAA-UV-2? When will it close?
It’s a DC powered solenoid valve that controls Instrument Air to Containment
Closes on a CSAS (8.5 psig in Containment)
What is the backup to Instrument Air and when will it align?
Low Pressure Nitrogen system will automatically align to supply the Instrument Air Header if pressure decreases to 85 psig or on a LOP
What powers the Instrument Air and Service air compressor motors?
Non-class 480 VAC Power Load Center system (NG)
What powers the Instrument Air and service air compressor motor space heaters?
Non-class 480 VAC Power MCC System (NH)
What does PK system do for the Instrument Air system?
Provides power to the IA Containment Isolation Valve (IAA-UV-2)
What system provides cooling to the Instrument Air Compressor Coolant Cooler and Air Aftercooler?
Turbine Cooling Water
What valve opens to admit low pressure nitrogen into the Instrument Air header?
PV-52
Instrument Air sends compressed gas to the Fuel Pool Cooling system for what purpose?
For the Spend Fuel Pool Gate Seals
How does Instrument Air system interact with the Extraction Steam and Drain System?
Supplies air to the Turbine Air Relay Dump Valves (ARDVs) for Bleeder Air Valve operation.
On a turbine trip, the ARDVs close to depressurize the line and allow the BTV air cylinders to fully stroke close within two seconds
Regarding the IA compressors, why is the Air Inlet Control Valve minimally opened during unloaded operation?
To maintain Separator Sump pressure
Why is coolant (oil) sprayed into the Airend(compressor) in the IA compressors?
Act as an air seal
Lubricate the bearings
Remove heat from the air compression
In the IA air compressors, when does the coolant stop solenoid open and close?
Opens when the compressor is started and closes when the compressor stops
What is the motive force for the coolant in the IA air compressors?
Separator Tank Pressure, normally at 60 psig
Concerning the IA air compressors, the Temperature Control Valve regulates the TC water flow through the Coolant Cooler to maintain the coolant at what outlet temperature? What temp is maintained downstream of the thermostatic control valve after mixing with the bypass flow?
120F
160F
What is the purpose of the IA Compressor Inlet Air Filters?
Installed on each Air Compressor to remove particulate materials and minimize compressor water
What size particles can the IA Compressor Inlet Air filters remove and how effective are they?
Three microns or larger
99.9% effective
When the IA compressor is loaded, what should the Inlet Filter DP reading be(sensed by PT-4)?
Less than 0.7 psi
The local controller on the IA Air Compressor uses PT-4 Inlet Vacuum information for what purpose(s)?
Confirm the drive motor is rotating in the correct direction upon startup
Indicate the condition of the inlet air filter
Provide logic for positioning the inlet valve during unloaded operation based on coolant (oil) injection temperature and separator pressure
During compressor start up, why is the Instrument Air Compressor Air Inlet Control Valve in the closed position? What happens if this valve fails to operate during the start up sequence?
It allows the compressor to startup with minimum current
It allows the compressor to check for proper rotation by checking that inlet vacuum is at least 1 psi within two seconds
causes an alarm
How is the Instrument Air Compressor Air Inlet Control Valve controlled?
Controlled by the Intellysis controller with a stepper motor
During unloaded operation, if plant IA air pressure drops below the pressure setpoint of 109 psig, what would I expect to occur as a result of this?
Intellisys/stepper motor opens the Inlet valve and closes the Blowdown Valve.
Compressor will then operate to deliver full capacity air to the plant system
During loaded operation, how will the IA system respond if plant air pressure rises to the setpoint of 119 psig?
The Inlet valve will nearly close, the blowdown valve will open (Separator Tank vented), and the compressor is operating at minimum power.
Inlet valve is slightly open to maintain the proper sump pressure to ensure positive coolant (oil) flow and smooth, quiet operation.
When the injected coolant temperature is less than 120F, what would I expect the Separator (Sump) pressure to be maintained at in the IA system?
45-50 psig
system pressure plus 10-15 psi
When the injected coolant temperature is above 120F, what would I expect the IA receiver pressure to be maintained at?
24-34 psig
What is the purpose of the Instrument Air Compressor rotary screw Airend?
Single stage rotary Airend compresses air to 105-123 psig for use by the Instrument Air system
What are the IA Single Stage Rotary Compressors rated for?
571 CFM and 125 psig
Briefly describe the oil cooling utilized in the IA Rotary compressor
Oil bath compressor that has oil supplied to the inlet of the compressor for lubrication, cooling, and compressor sealing
How is compression accomplished in the IA Rotary Compressor?
By the meshing of two helical rotors (male and female) on parallel shafts, enclosed in a heavy-duty cast iron housing.
The grooves of the female rotor mesh with, and are driven by, the male rotor
In the IA system, what happens if the Airend discharge temperature exceeds 223F?
It will cause a Warning “AIREND DISCHARGE TEMP” along with a “?” and the actual discharge temperature to be displayed on the display panel.
The compressor will continue to run during a temperature warning
At what discharge temperature will the IA compressor trip? What is the reset temperature? What are the normal values?
228F, Alarm and trip along with “High Airend Disc Temp” along with “!”
217F, Reset temperature
185-210F, Normal values
Regarding the IA system, what is the back-up to the High Temperature Alarm (Trip)?
Temperature Switch High set at 245F with a 30 degree differential to reclose (215F)
In the IA system, if the compressor High Temperature Switch opens on high temperature, what would I expect to see on the display?
“Control Power Loss”
temperature switch is tied into the control power circuit and will open the circuit on high temp
What is the purpose of the IA compressor Separator Tank?
Removes the coolant (oil) from the air to provide clean air to the system while maintaining the coolant for the compressor package
Regarding the IA compressors, what is the coolant/air separating system composed of?
A separator with a two-stage coalescing separator element and provision for return of the separated fluid back to the compressor
How does oil/air separation occur in the IA compressor Separator Tanks?
Coolant and air discharging from the compressor flow into the separator and rotates around the circumference of the Separator Tank, which acts to remove some of the heavier oil from the air before it enters the coalescing separator element radially.
The mist coalesces to form droplets, which collect on the outer first stage and fall to the separator sump.
Those collected on the inner second stage collect near the outlet of the element, and are drawn back to the compressor inlet through a filter-screen and orifice fitting installed in the separator scavenge line
What is the purpose of the Thermostatic Control Valve In the IA compressors?
Controls how much of the coolant flows through or bypasses the Coolant Cooler.
Used as a mixing valve to provide 160F injection of oil into the Airend from the 120F outlet of the coolant cooler and the bypassed flow
In the IA compressors, why do we want the compressor coolant (oil) at a sufficiently high temperature?
Temperature of the discharge air and lubricant mixture will be kept above the dew point to preclude the possibility of water vapor condensing in the Air Receiver
Turbine cooling is normally used to remove the heat from the Instrument air compressor Coolant cooler. During a shutdown, when TC is secured, what system can be used as the heat sink? Any limitations?
Domestic Service Water (DS)
Aligned to only one instrument air compressor and one service air compressor
What is the purpose of the Air Aftercooler in the IA compressors?
Cools the discharge air so that much of the water vapor naturally contained in the air is condensed and eliminated from the downstream plant-piping and equipment
What makes up the Air Aftercooling system in the IA compressors?
Heat exchanger, a condensate separator, and an automatic drain trap
To what temperature does the Air Aftercooler cool the compressed instrument air to? Where is the condensate routed to?
Within 15F of Turbine cooling water inlet temperature
automatic drain traps