Instrument Air

Question 1

What is the purpose of the Instrument Air System?

Answer 1

To supply clean, filtered, MOISTURE FREE compressed air for air operated control devices and instruments

Question 2

What powers the IACs?

Answer 2

2(3)A - Bus 26 (36)
2(3)B - Bus 27 (37)
3C - Bus 37

Question 3

What is the preferred configuration for IA lineup?

Answer 3

Preferred that set up with parallel output of the IA compressors, Units not cross tied together, with 2 IACs running on each unit.

Question 4

If NECESSARY, what is the preferred IA cross tie line-up?

Answer 4

Set up lined through 2 check valves. This prevents a dual unit failure of the one unit’s IA header. Shift Manager Permission REQUIRED

Question 5

What Unit IA system supplies the common site buildings?

Answer 5

Site Buildings supplied by U2 IAC

Question 6

What is the purpose of the Service AIr Crosstie to the IA system?

Answer 6

Provides backup air supply from service air header

Question 7

What is the automatic actions for the IA/SA Crosstie?

Answer 7

Crosstie auto opens within 30 seconds when 85psig sensed on Units main instrument air receiver
Once crosstie valve opens, solenoid must be manually reset with local pushbutton located on side of main receiver when pressure rises above 87 psig

Question 8

What are the setpoints for SA-IA crosstie?

Answer 8

85psig auto opens

87psig may be manually reset

Question 9

What cools the IACs?

Answer 9

TBCCW via temp regulating valve

Question 10

What happens to the TBCCW Temp Regulating Valve on an IAC TRIP? Why?

Answer 10

The solenoid closes on an IAC Trip to prevent admitting “cold” water into a hot compressor potentially causing brittle fracture of the components

Question 11

How many cooling circuits are there fore each IAC?

Answer 11

2 cooling circuits
2B,3B &3C: 1st- cools oil cooler, intercooler, bleed off cooler, 1st stage water jackets, 2nd stage water jackets
2nd: After cooler
2A: 1) oil cooler, low pressure elements cooling jacket and intercooler
2) high pressure element cooling jacket and aftercooler
3A: 1) Oil cooler and cooling jacket of low and high pressure compresser elements
2) Intercooler and aftercooler

Question 12

What are the power supplies for the IAC Dryers?

Answer 12

2A: MCC 25-2
2B MCC 25-1
3A: MCC 35-2
3B: MCC 36-4
3C: MCC 38-2

Question 13

What happens if the IA dryer discharge pressure drops below 60psig?

Answer 13

dryer bypass valve auto opens and Dryer Trouble Alarm annunciates

• ALL IA DRYERS HAVE THIS
• 2A/B&3A/C have reset pushbutton on dryer
• 3B has auto/close/open c/s needed to reset

Question 14

What is the setpoint for IA Dryer bypass?

Answer 14

60psig

Question 15

How does the U1 - U2 IA crosstie function? How is it normally aligned?

Answer 15

Normally PCV OOS and requires Shift Manager permission to be put in service
When in service, valve opens on downstream pressure of 95psig sense on U2 side of PCV (near U2 main receiver)

Question 16

What kind of indication is given in the MCR if the power breaker for the IACs trips?

Answer 16

The breakers have a 120vAC control Xfmr that feeds the logic to give MCR indications for a compressor trip.

If the breaker trips, there will be no alarm and no compressor trip lights until the MCR receives teh INst Air Low Press Alarm and SA/IA XTie Opens

Question 17

What causes an IAC trip?

Answer 17

Lo Oil Pressure @17psig
Hi Oil Temp 175F (except 2A)
Hi Air Temp at Intercooler Inlet (425F)
Hi Air Temp at Hi Press Inlet (155F)
Hi Air Temp at Hi Press Outlet (425F)
Overload

Question 18

Why does the TBCCW solenoid close on IAC trip?

Answer 18

Prevents admitting TBCCW to hot compressor leading to brittle fracture

Question 19

What is required if IA Header drops to 55psig? WHy?

Answer 19

Manual Scram - Because will lose MSIV air pressure and get an RPS Scram otherwise