220 volt dc system with battery
charger commissioning
Till last
dispatch I have discussed about the basic requirement of electrical system in
apower plant . In continuation with that commissioning of DC 220v system will
be described briefly.
The system
consist of :-
i. Battery Bank
ii. Battery Charger - Main and Standby
iii. DC Distribution board.
The battery is installed in the battery room in the HT
switchgear room. This provides a 220 V
DC supply to the relay and control circuits in the Generator. Generator
transformer and Unit transformer protection and control panels, 11KV and 3.3 KV HT switchgear and 4.5 V LT
switchgears Unit and station service boards and aux. Control panels. As told
you earlier 220 volt DC system is backbone of the electrical system .To
energise AC system you need DC system.
Battery
Cells - Data Sheet ( Typical 500 MW power plant
Guaranteed AH Capacity at 10
Hrs.discharge
Rate 1 Volt / Cell at 27 C - 990 AH
Designation - KPH 990 P
Recommended range of floating/trickle
Charging voltage - 1.4 -- 1.42 V/Cell
Recommended range of boost charging
Voltage - 1.53 -- 1.67 V/Cell
Trickle charging current - 1 to 2 MA /AH
Boost charging current - 198 A
Open circuit voltage of cell when
completely
Discharged at 27 C at 5 hrs
discharge rage - 1.0 V
Dimension (mm) - 522 L x 192 W x 405 H
Amount of
specific gravity or electrolyte
Per cell required for first filling at 27 C - 18 Lit / cell, 1.19 +- 0.01
Specific gravity of cell when fully
charged 1.19+- 0.01
Max. electrolyte temp. that cell can
withstand
Continuously - 50 C
Net dry cell weight - 45 Kg
With electrolyte - 68 Kg
Cell container material - Polypropylene
No of cells / Bank - 169
Charger - I & II
Input Voltage - 415 V+- 10%
Output Voltage - 220 V DC
Float Voltage - 236 V DC
Boost Voltage - 287.3 V DC
Rectifier current limit - 400 A
Battery current limit - 198 A
Auto charge over current - 40 A
Steady state output voltage
Regulation (For +- 10% I/P
Voltage variation - +-1%
0 - 100 % load variation
at a time).
The above
data was given from a data sheet of particular power station but this may vary
marginally power station to power
station depending on system design and integration for which I am not expert.
Pre -commissioning
- Battery, battery charger and distribution boards are
installed as per drawing.
- Cabling between
the battery / battery charger and the distribution boards completed .
-
Basic
testing .quality checks of components like insulation testing ,continuity
testing , dimension checking etc are over. Charge the distribution board live
at 220 V DC in a safe and orderly manner
without load and keep it charged for 24 hours.
- To carry
tests and checks to ensure that all the components on the boards are operating
satisfactorily including cables to all the remote points in the 400 KV
substation and control room.
- AC distribution board for input supply to be
charged and commissioned.
- Each module will be checked individually
- Each outgoing supply will be tested up to the
fuses at the remote end.
- Battery E/F will be simulated for both the
poles and E/F relay sensitivity will be
checked.
- Following
services will be required during
,testing and pre –commissioning
- 415 V,
3 Phases, 50 Hz supply ,Adequate running water, Suitable voltmeter,
ammeter,
thermometer and hydrometer,Variable
resistance or water load for discharging the battery.
Electrolyte for cells as per IS-266, Pure
battery grade distilled water, Variable resistance box
of 15 to 150 K Ohms, 1 No. 500 VDC megger, Multimeter , hand tools etc.
-Standard
safety equipment for handling acid and battery . Also fire prevention equipment like
extinguishsers
, Exhaust fans to take out fumes if any , etc should be made available.
Different
precautionary
sign board in and around the panel battery room etc.
continued part -II battery charger commissioning.
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