- DC voltage is most stable and reliable in nature for which the control and protection circuits in substations and power stations are designed to work on DC supply.
- The DC voltage is obtained either from Battery Set or from the charger by the use of a rectifier unit (Conversion of AC supply to corresponding DC supply).
- Maximum time DC voltage is obtained from Rectifier Unit Charger. But during emergency conditions like a failure of AC supply, maintenance/modification of charger unit, etc. to obtain the DC voltage, Battery Set is required. Moreover, it is also required for emergency lighting in the system, when there is a total failure of the AC supply.
- This is the front side and inside view of Float, cum boost charger panel used at 132/33KV air insulated substation control room.
- A battery Charger, when used in the stand-by application is not a standalone dedicated Battery Charger. Here battery charger along with a floating battery provides an uninterrupted DC power supply to a critical load.
- This is Float-cum-boost battery charger or FCBC feeds the critical load without any break and also charges the discharged battery.
- Though FCBC denotes “Float-cum-Boost” which clearly means a single rectifier/converter for AC to DC conversion, for higher capacity or higher load “Float-and-Boost” charger is used which has two rectifiers, one for feeding load and another for charging the battery.
- TECHNICAL SPECIFICATION OF AUTOMATIC FLOAT & FLOAT CUM BOOST BATTERY CHARGING EQUIPMENT SUITABLE FOR 220V 645AH PLANTE BATTERY
- FLOAT CHARGER – SCR CONTROL:
- Input Power Supply – 415 Volts ±10%, 3-Phase, 4 Wire,50 Hz. ± 5%.
- Output Voltage :
- Auto – 247.5 Volts (2.25V/cell)
- Manual – 0V – 247.5 Volts.
- Output Current – 64 Amps DC continuous plus trickle charging current.
- Output Ripple – Within 3% RMS at full load of 247.5 V DC
- Output Regulation – Within ±1% for ±10% supply voltage fluctuation and 10-100% load variation.
- Mode of Operation – Automatic / Manual
- Control Configuration – 3-Phase full wave full control thyristors bridge fed through the 3-phase transformer and controlled by constant potential controller unit with load limiting feature (AVR).
What is FCBC battery charger?
FCBC denotes “Float-cum-Boost” which clearly means a single rectifier/converter for AC to DC conversion, but for higher capacity or higher load “Float-and-Boost” charger is used which has two rectifiers, one for feeding load and another for charging the battery.
CHARGING PROCEDURE OF LEAD ACID BATTERY:
To keep a battery in healthy condition and to achieve optimum life of the battery, two modes of charging are required (i) Boost charging and (ii) Trickle/Float charging
(i)Boost Charging:
Boost charging means, the charging of a battery from discharged condition to a fully charged condition. In this mode, a constant current process is followed for efficient charging. During boost charging battery voltage varies from 1.85V/cell to 2.75V/cell. In between these, the point 2.35 V/cell is called the gassing point i.e. gassing starts at this point. Beyond this point, the charging current must be restricted to a certain limit, otherwise, that may damage the plates or may affect the life of the battery. Therefore, to charge a discharged battery efficiently, a two-step constant current process is the best process.
(ii) Trickle / Float Charging:
Trickle charging means, charging a battery at constant voltage to compensate for local discharge. For optimum trickle charging, the voltage should be maintained at 2.25V/cell. But for float operation, this voltage is restricted to 2.23V/cell.
OPERATION OF BATTERY CHARGER
The three-phase AC supply voltage is fed to a suitably rated step-down double-wound transformer through a suitably rated MCB. The secondary voltage of which is fed to a 3-Phase full wave full control thyristors bridge through line surge suppressor and semiconductor protection fuses. Thyristors of the bridge circuit are adequately protected by a snubber network as protection against voltage transients. The bridge circuit consists of 6 nos. of Thyristors.
The triggering of the thyristors is controlled by the electronic voltage and/or current regulator unit, which senses feedback from both output voltage and current. These feedback signals are suitably processed and compared with the reference generated in the control circuit (Controlled by the electronic SCR control module). Then the error is amplified and phase compensated by the high gain operational amplifier. The output of the final amplifier is fed to the triggering circuit, which controls the output voltage and current of the charger by adjusting the firing angle of the thyristor. The incorporation of feedback ensures automatic correction of any deviation of the set voltage/current, which may arise due to line or load fluctuations.
