Barring Stalling

Advisory to avoid Barring Stalling & Vacuum Killing

Reasons for Barring Stalling

• Abnormal Gland steam containing condensate
• Abnormal Mechanical clearances, casing/ glands
• Wet steam/ Water entry into casing
• Air chilling of Glands
• Loss of jacking oil Lift Pressure/ Hose Puncture / Groove on Journal.
• Loss of CW and emptying Waterbox in spring deck-some units
• Speed of slow down on CW pump stoppage

To Prevent Barring Stalling

• After tripping, Lube oil Temperature to be maintained around >=45 Deg.
• CW Waterbox remains filled wih Water In case of Barring Stalling
• If JOP Pr OK and individual Lift Pr OK
• HPT/IPT Casing Top/Bottom DT normal
• Hand Barring with one person possible then Seal steam should be kept charged along with evacuation
• Raise Aux PRDS temp to 300 Deg
• This is not to be done for more than 4-5 hours
• If no success then control cooling can be resorted to for faster cooling
• Gland steam Temperature as per rated parameters (i.e. 300 Deg) and ensure no steam is condensed upstream of Seal steam Supply control valve
• Continuously t track Gland steam temperature and maintain close to source temperature
• Keeping continuous Warm-up line open ASV-152 with bypass manual valve open
• Check steam trap provided in APRDS are working
• Check source HT Station Header Temp >300 Deg

After Unit Trips out:

• Do not keep Gland seal steam charged for more than 1 to 2 Hours
• Do not empty Condenser Water BOX till HPT temp <290 Deg is achieved. Keep at least one CW pump running till then (due to effect on disturbance in turbine seal fin clearances
• Air Chilling of Glands:

Post Trip Vacuum Killing Sequence of Operation:

• BSV closed. Isoalte its power supply. Open all drains to UFT.
• Open HP/LP bypass for complete Depressurisation of MS/ HRH line. Close HP/LP bypass. Open drains of MS/ CRH/HRH to UFT
• Isolate HPBP spray manual valve at 8.5 m
• MS line Depressurised.
• TDBFP A &B Aux steam at APRDSfloor isolated.
• Stop Vacuum Pump
• Kill vacuum by opening vacuum Breaker
• Isolate Seal steam at Vacuum of 0.2 or 0.3 ksc or Back Pressure of 0.7 or 0.8 ksc
• Stop GS Exhauster fan immedaiately after isolation of Gland Seal steam
• Switch off SLC Vacuum Pump
• Monitor Barring Speed reduction after vacuum killed it should be around 80 rpm tp 90 rpm.
• Hotwell maintained throughout= -100
• Monitor D/A level. It should not Overflow into Hotwell.
• Both CW pass chrage till HPT >290 Deg
• When Speed Stabilises Note down jacking oil pressures at inlet to all 7 Bearing alongwith TMD
• Keep MAL 81, ASV-152 Open