11KV UNIT BUS ISOLATION/NORMALIZATION:

11KV UNIT BUS  ISOLATION/NORMALIZATION:
ISOLATION PROCEDURE:-

1. Stop IDF-A channel – 1& 2,trip source breakers of both channels & isolate it .
2. Stop PAF-A, CW p/p-1, & isolate their respective breakers.
3. Ensure following procedure to isolate UAT-A,UST-A,ESP LTMSB-A/B/C/D, CT TRF-A, ESP Vac.
TRF-A
              Charge 3CA bus (3.3kv) sec-1 from bus coupler .Trip 3.3kv incomer breaker
                  &Isolate it. Trip 11kv UAT-A breaker at 3BA bus & isolate it.
             Charge 3DA bus (415V – unit service swgr) sec-1 from bus coupler .Trip 415V
                  incomer  &isolate it. Trip 3.3 UST-3A breaker at 3CA-1  & isolate it.
             Charge CT MCC-A from CT transformer-B. Trip LT incomer from CT transformer-3A &
                 isolate it. Trip CT transfer-3A HT (3.3 kv) breaker  & isolate it.
             Charge ESP Vacuum PH MCC sec-A from bus coupler.Trip LT incomer breaker & isolate                   it.
             Charge All ESP LTMSBs (A/B/C/D) from bus coupler ).Trip incomer breakers& isolate.                     Trip 3.3 KV ESP LT MCC breakers & isolate them.
4. After all the feeders from 3BA bus tripped. Once again, ensure that 3BA bus cannot be back
fed from any source.
5. For BUS shutdown following two scenarios –
             CASE-1: If 3BA bus charged from station transformer, tie breaker  is in close
                condition and UT incomer is in open. Isolate incomer breaker . Trip tie breaker &                           isolate it.
             CASE-2: If 3BA bus charged from UT incomer , and tie breaker from  OBA bus (at 3BA                  bus end) is in open condition .Isolate tie breaker. Trip incomer breaker & isolate it.
6. Trip tie breaker  from OBA bus (at OBA end) & isolate it.
7. Ensure voltage/current in all phases showing 0 volt/amp.
8. Switch off both 220V DC control supply sources to 3BA bus from 3FA.


NORMALIZATION PROCEDURE :-

1. Ensure all ptw on the bus cancelled.
2. Before going to charge the bus, physically inspect that there should not be any opening on
backside of the bus & on the top, grounding strip connected properly.
3. Check healthiness of both 220V DC source.
4.Normalize Tiebreaker from OBA bus, (at OBA end) & (At 3BA end). Close
Tiebreaker.
5.Close breaker tiebreaker to charge 3BA from OBA. Check voltage in all phases.[Tie
breaker  may get closed in auto as per logic of turbine trip].
6. Normalize Incomer breaker from UT .Station to UT changeover can be done
whenever required.
7. All feeders from 3BA can be normalized& charged after cancellation of their respective ptws.