Page 158 - Practical Power System and Protective Relays Commissioning

158 Practical Power System and Protective Relays Commissioning

dissipated. The charge slowly dissipates from charged cells over a period of
time. Keeping the cells continuously connected to the charger ensures they
will be fully charged at all times.

15.1.5 Safety Considerations

The charge stored in the cells can cause shocks, even if the battery has been
disconnected. Electrolytes can cause burns. The hydrogen given off by the
cells can cause explosions. Battery rooms should be kept clean, well-
ventilated, and locked. When working on batteries, electricians should wear
protective gloves, aprons, boots, goggles, and face shields.

15.1.6 Additional Checks

Safety equipment, such as eyewash stations or showers, should be located
and checked to ensure proper operation. The temperature of the room should
be verified. The battery racks and the floor under the racks should be
checked for signs of acid spills. Spills should be reported and cleaned, fol-
lowing facility procedures.

15.1.7 Acid Concentration
The initial concentration of acid in a cell is determined by the manufacturer.
When a cell is discharged, acid concentration is low; when a cell is charged,
acid concentration is high. The concentration of acid in the electrolyte is a
good indication of the amount of charge in the cell.

15.1.8 Specific Gravity and Acid Concentration
The specific gravity of a liquid indicates how heavy the liquid is when com-
pared with pure water. The specific gravity of electrolyte depends on the
concentration of acid. Therefore, the specific gravity can be used to deter-
mine the amount of charge in the cell. Specific gravity measurements must
be corrected for temperature and level of the electrolyte.

15.1.9 Determining the Condition of a Battery

The final determination is usually made by facility engineers or supervisors
based on data usually supplied by the electrician. Two measurements are
needed: the corrected specific gravity measurement and the direct voltage
measurement.