In UPSEB almost on all the 132 kV & 220 kV Sub-stations two sets of 110 V (for protection) and one set of 48 V (for carrier communication) lead Acid station batteries along with battery chargers are installed. The battery charging equipments comprises of a float charger and a boost charger. Stabilization  output voltage is provided in the float charger to float the battery at the correct level. The battery can be boost charging after a prolonged mains failure by the boost charger. These chargers have been provided protection for under voltage DC & earth fault. DC Board is installed to feed various essential DC load from a separate feeder.

Recommended specific gravity of cells at 270C (electrolyte temp) should be 1.210 ± 0.005. Actual temp should be measured in the electrolyte of the cell. If the temp is different than 270C the correction ± 0.0007/0C change in temp. should be made in sp. gr. (Subtract for temp. below 270 C  and add for temp. above 270 C).

Voltage of each cell (float charger in 'ON' position) should be.2.16-2.2 volts.

Volt across 55 cell (110 V) should be maintained between 118.8-121 volts.

Volt across 24 cells (48 V) should be maintained between 51.8-52.8 volts.

Top up cells to the correct level (red mark of float indicator of cell) with pure distilled water only.

Check for corrosion of connectors and if present remove with fresh water pure distilled water only.

Check for any lose connection, wipe out old petroleum jelly and apply new jelly.

Carry out boost charging of battery when the sp gr. falls below 1.200, charging current 10% of the AH capacity and on free gassing reduce current to 50% of the charging current till :-

The voltage has reached maximum and steady for 3 hours and sp.gr. of electrolyte in the pilot cells has also reached maximum and is steady for 3 hours. All the cell should gas freely. Any cell failing to gas freely or having sp.gr. lower than 1.140 or having gravity more than 1..230 should be attended immediately. Remove defective cells and charge on a separate charger (Milky booster). Put it in the circuit if sp.gr. is maintained Temp. during boost charging should not exceed 450c, if rises, reduce the charging current.

When different sp.gr. is noticed in different cells equalising charge should be given to the entire battery i.e. boost charge battery for 2-3 hours. If sp.gr. is not maintained repeat process after fifteen days.

Even if the sp.gr. is normal, equilising charge should be given to the battery once in a month i.e. Boost charge battery for 2-3 hours at current 10% of AH capacity.

After service of 5 years the entire cells of the battery should be discharged completely and recharged to ascertain battery life.

On fully Charged battery sp.gr. adjustment can be done in consultation with firm if found less, by putting higher specific gravity acid (1400 so,gr,).

Without consulting firm acid should never be added.