05-03-2013, 12:48 PM
Battery System.
Battery.doc (Size: 35 KB / Downloads: 22)
INTRODUCTION
The main purpose of DC Power Supply System is to provide DC power during shutdown operation with an autonomy of five hours minimum.
Batteries are used to supply power to control, protection, regulation and signal circuits.
Types of Batteries
(1) Lead Acid Batteries
(2) Nickel Cadmium Batteries
Lead Acid Batteries
Essential components are positive plate, negative plate and electrolyte
Positive plate or Anode Plate is made of PbO2
Negative plate or Cathode Plate is made of Pb
Chemical Reactions
Discharging
At anode PbO2+ H2 + H2SO4 PbSO4 + H2O
At cathode Pb + SO4 PbSO4
On both plates PbSO4 is formed which is whitish in color.
Due to formation of water, specific gravity of acid (electrolyte) decreases, thus voltage of cell decreases.
Cell give out energy.
Charging
At anode PbSO4 + SO4 + H2O PbO2 + H2SO4
At cathode PbSO4 + H2 Pb + H2SO4
Anode is dark chocolate color and Cathode gray metallic.
Due to decomposition of water, specific gravity of H2SO4 increases, thus voltage of cell rises.
Energy is absorbed by the cell.
Capacity
The choice of capacity in AH mainly depends on:
(1) Discharging current (2) Discharge time (3) Voltage Range (V max – V min)
48 V DC = 800 AH
125 V DC = 320 AH
220 V DC = 250 AH
Charging / Discharging = 0.1C10
Charges = Load + 0.2C10
I Discharging = 220 A V min = 195 V max = 243 V
Discharge Time = 45 min permissible charging voltage 2.25V/Cell
Max number of cell = 243/2.25 = 108 cells
Minimum voltage per cell = 195/108 = 1.8 V / cell
From the curve
ie/ C10 = 0.48 so C10 = Ie/0.48 = 220/0.48 = 459 AH (for safer operation taken as 500AH)
Advantage and disadvantage of alkaline batteries
Greater mechanical strength easy to maintain long life space and weight requirement significantly small free from corrosive liquids and fumes
Lower voltage of cell 1.2V / cell more expensive
Sensitive to temperature