GS- Gland Seal Steam Flashcards
[GS] purpose?
Prevents air leakage into, and steam leakage out of, the Main Turbine and Feed Water Pump turbines through the turbine shaft glands and through various Main Turbine valve stems
Valve GSN-PV-28B, 9th stage extraction point steam seal feed valve, moves from full-closed to full-open with what pressure air signal change?
15 to 9 psig
Valve main/aux. steam supply to GS regulator valve, GSN-PV-28A, moves from full-closed to full-open with what pressure air signal change?
9 to 3 psig
How are the steam supply to GS regulator valves, GSN-PV-28A and -28B, affected by a loss of instrument air?
They will fail open to protect the turbine
What pressure is the GS system header maintained at?
4 psig
Concerning the GS system, where in the shaft packing is low pressure steam applied?
The inner cavity formed by the first two sets of packing
Leakage is withdrawn from the outer cavity formed by the second and third sets of packing
What is the purpose of the GS Steam Packing Exhauster?
To maintain a vacuum on the steam exhaust header and annulus between the middle and outer shaft packing rings, which causes the steam/air mixture to flow from the packing ring annulus to the exhauster, and prevents steam from contaminating the oil used in journal bearings adjacent to the packing’s
What is the purpose of GSN-PCV-27, the GS steam condenser unloader valve, and how is it controlled?
Automatic acting, back pressure regulating valve
Operated directly from the GS system pressure and therefore does not require IA to function
What powers the main/aux. steam supply to GS regulator valves??
NH
During low Rx power, where can I get sealing steam from?
normal AS or SG, through GS steam seal regulator PV-28A
LP turbine 9th stage extraction point through GS steam seal regulating valve PV-28B
(both isolate as turbine power increases)
What can the operator in the control room do if GSN-PCV-28A and -28B capacity is insufficient to maintain pressure at 4 psig?
May open regulator bypass valve HV-6
At full power operations, where do we get Gland Seal steam from?
HP turbine
(shaft seal packing leakage)
valve shaft leakage from the HP turbine control valves, stop valves and combined intercept valves
What happens if HP turbine shaft packing leak-off is greater than the sealing steam requirement?
The excess steam unloading valve discharges steam to main condenser
If discharge flow is insufficient, control room operator may open the excessive steam unloading bypass valve to maintain 4 psig
What will happen if GS is lost?
Loss of condenser vacuum
When is GS required to be in service during a startup?
Prior to starting and during the operation of the Air Removal Pumps, when establishing and operating with vacuum
How is the GS system affected by a loss of IA?
Steam seal feed valves fail open, which will cause header pressure to increase
(Steam unloading valve (not air operated) will open to control pressure. If desired, the regulators can be isolated and a bypass MOV can supply gland seal steam.
The GS exhauster drain tank drain valve fails closed which will cause the tank to overflow
What cools the heat exchanger of the GS steam packing exhauster?
Turbine Cooling Water
Concerning the GS steam packing exhauster, where do the Exhaust fans take suction from and where is it discharged to?
Suction on the heat exchanger shell side and discharge to atmosphere via the condenser air removal system exhaust piping
Exhaust can be diverted through an exhaust filter unit if a set amount of radioactivity is sensed by RU-141
What is the GS exhaust header vacuum normally maintained at and how is it controlled?
12-20 in H20, by manually throttling the air flow
What is the main purpose of the GS system?
to prevent air leakage in, and steam leakage out, of the main turbine and feedwater pump turbine
returns air/steam mixture to the steam packing exhauster to be condensed, drained to the main condenser and exhaust non condensable gases to atmosphere
What does the GS steam packing exhauster consist of? Where does the condensate drain to?
HX and two exhaust fans
to a drain tank and then the main condenser
As turbine load increases, the low pressure turbine extractions flow increases and the low power ops steam supplies isolate, where does GS get supplied steam from?
ED (extraction steam and drain system)
Low Pressure turbine 9th stage extraction point
What system provides power to the GS control and instrumentation panel?
NN
In the GS system, what is the purpose of the Steam Seal Regulator?
hydro-pneumatic control unit automatically positions the main/auxiliary steam and extraction steam supply valves to maintain 4 psi in the seal steam supply header
What is the purpose of the main turbine shaft seal packing rings?
to seal the turbine shells from the atmosphere
keep the steam in and the air out
What controls the level in the GS exhauster drain tank?
air-operated level control valve, GSN-LV-8
Concerning the GS steam supply regulating valves, which one opens first and closes last?
9th stage extraction point seal steam supply regulator valve PCV-28B
Regarding the GS system, if LP turbine 9th stage extraction steam is lost, what can supply enough steam until the HP turbine seal leak off is established?
aux steam or main steam
