220V DC FAILURE

220V DC FAILURE

IDENTIFICATION:
  • Boiler and Turbine will trip.
  • 220V DC failure alarm will appear in facia & DCDB voltage will read 0V
  • Generator will start motoring & motoring alarm will appear.
CONSEQUENCES:
  •  Boiler will trip on “220V DC failure” protection by FSSS.
  1. HOTV & LOTV will close.
  2. All running mills CAD’S & HAG’S will close.
  3. All running mills feeders will trip.
  4. SADC will full open.
  5. All HT (11kv & 3.3kv) drives will continue to run.
  6. All mills, PA fans, CC pumps, ID&FD fans will continue to run.
  • Turbine will trip on boiler trip protection through MFT.
  1. all stop valves & control valves will close.
  2. TDBFP A&B will trip.
  3. MDBFP if not in service will not take start.
  4. Extraction FC NRV will close.
  5. Vacuum breaker remains close.
  • Generator will start motoring & will not trip (All electrical protection will not work)
  • Field breaker inoperative.
  • All HT breakers protection is not available.
  • All DC oil pumps & scanner air fan are not available.
  • Generator breaker DC is from SY hence Breaker is operable from UCB but “DO NOT OPEN GEN BREAKER”. This will cause:
  1. BA,BB & CA bus dead as UT to station change over will not takes place.
  2. All critical equipments AOPS, JOP, Seal oil pump, AC scanner air fan Power supply will not be available.
ACTIONS:
  1. Start DG set from UCB.(DG set control supply (DC) is not available)
  2. Rush to local, trip emergency SWGR normal incomer breaker & close tie from DG set
  3. Trip UT incomer breaker from local.
  4. Start TG AOP#2, TDBFP’sAOP#2, and seal oil pump #2 from UCB.
  5. AC scanner air fan will continue to run.
  6. Trip generator breaker.
  7. Switch off De-excitation switch at AVR panel.
  8. Switch off field breaker from AVR panel.
  9. Start jop#1 at TG speed of 510 RPM.
  10. Restore DC as quick as possible.  

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