24 V DC Fail

24 V DC Fail

Identification of the Emergency:-

(1) Boiler trips on loss of 24V DC. Turbine trips on boiler trip protection followed by generator

(2)All controls operating on DDC becomes inoperative

Actions:

1. Confirm tripping of turbine. In local governing rack the trip oil pressure should be ‘0’ otherwise trip turbine from emergencytrip lever in governing rack. Trip TD BFPs from local governing rack

2.Confirm tripping of generator i.e. opening of GCB. If GCB has not opened, open  from switchyard

3.Confirm starting of AOP (local) on turbine trip, otherwise start EOP from local for both main and TDBFP turbines.

4.Confirm running of ACSOP(local) if no seal oil pump is running immediately start DCSOP from local

5.Confirm AC scanner fan is in service(local),else start DCscanner fan from starter panel in LT switch gear room in TG Floor

As controls are in operative do the following operations

6.Stop FD fan, ID fan and BCW pumps (from local push buttons or switch gear). Close boiler stop valves

7.Stop MD BFP (from local push buttons or switch gear), if it was in service as D/A and drum levels cannot be monitored.

8.Depressurise MS, CRH and HRH lines, Kill vacuum. Open atmospheric drains of MS,CRH and HRH lines

9.Stop CEPs and isolate make up to hot well since hot well level indication is not there

10.At 540 rpm turbine speed start DC JOP from local, and at 210 rpm open turning gear valve manually

11.Continue to run ECW pumps. Monitor and maintain ECW tank level from local