D.C. auxiliary Power supply:Being most reliable, the D.C. auxiliary power supply is provided for supplying power to protection relays, circuit breakers, indicating circuits, communication system, etc.
D.C. Auxiliary power supply is provided from storage batteries maintained continuously
charged by some source of D.C. supply set or a charger.
The voltage of the D.C. auxiliary supply is maintained at 110/220 volt for all the time for
effective protection & control of sub station equipment.
DC float voltage is to be maintained between 118 to 121 volts for 110 volt system while it is
to be 236 to 242 volt for 220 volt system.
For Maintenance Free VRLA Battery sets:
The Shift In-charge shall, on assuming the charge, measure the voltage of three cells at
random. The voltage should be in the range of 2.16 to 2.20 volts corrected to 27º C. If not,
matter is to be reported to In-charge of Sub-station for remedial action.
be ‘ON’ so that full battery voltage is available to the loads; otherwise the load will
get voltage as appearing at the tapping point which is lower than the full voltage.
d. Healthy trip circuit is to be checked for all panels after assuming the charge of the
shift and after every closing of the breaker by pressing the designated push button. If
the trip circuit is not healthy, the concerned breaker is to be disconnected from the
system and intimation be given to the Incharge of Sub-station for attending defect
immediately.
e. In case of 400 kV/220 kV/132 kV/33 kV panels having trip circuit supervision relays,
if the annunciation shows TC-1 and/or TC-II faulty or the flag of relays 195 CA, 195
CB, 195 CC, 295 CA, 295 CB, 295 CC are operated, the breaker is to be disconnected
from the system as these indicate that the trip circuit is faulty and intimation be given
to Incharge (GSS) for attending the defect immediately.
f. The Shift-in-charge, on assuming the charge of the shift shall check the annunciation
panel/facia by pressing the lamp test push button. If any of the windows do not light
up, the matter is to be reported to the Incharge (GSS) immediately for rectification.
g. If for any reason, there is total failure or non-availability of D.C. supply to the GSS,
the breakers of all the transformers should be immediately tripped manually and
intimation given to Load Dispatch Center as well as Controlling officers. The
reasons of failure are to be investigated and D.C. supply restored. The transformer
should be switched only after D.C. supply is restored and established.