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Wednesday, 7 September 2016

220 VOLT DC SYSTEM-BATTERY CHARGER PRE-COMMISSIONING PART -I -ABC OF THERMAL POWER PLANT.

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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