Page 159 - Practical Power System and Protective Relays Commissioning

Batteries Chapter | 15 159

15.1.10 Taking Measurements
A voltmeter may be used to check cell voltage. A hydrometer may be used to
measure specific gravity. In general the batteries are used in power stations
and substations to supply a DC current for tripping circuits and protection
relays and can be found in 110 or 220 V and for communication equipment
of 24 or 48 V. An alkaline battery consists of cell container, positive plates,
negative plates, and ebonite separators. Lead-acid batteries also exist.

15.2 CHARGING AND DISCHARGING OF A NEW BATTERY

To start a new battery, the following steps are required:
Clean the surface of the batteries; check all positive and negative connec-
tions polarities.
Check all tightness of all joints between the battery cells.
Open the battery filling caps then fill the battery with the electrolyte with
specific gravity between 1.150 and 1.200.
Leave the battery about 10 hours for plates to be saturated with
electrolyte.
Measure the electrolyte level which should be above the plates by
12 15 cm.
Connect the battery to battery charger.
Start the charging with the charger in fast-charging mode with a current
equal to battery Amp hour (Ah), for example, for 400 Ah the charging
current will be 40 A for 10 hours.
On the beginning of the charge start the charge with 10 A for 30 minutes,
and then increase the current to 40 A in steps.
When battery reaches 2.35 V/cell, decrease the charging current to 30 A.
After 60 hours decrease the charging current to 20 A.
When battery reaches 2.6 V/cell stop charging, then restart charging at
10 A until the voltage of cells are stabilized and no changes occur for
2 hours.
Put the battery charger in floating mode of charge.
Charging or discharging should not be undertaken if the temperature gets

to greater than 45 C 55 C. For example, for a 400 Ah 220 V lead bat-

tery the following measurements were taken:
Lowest cell 5 1.73 V/cell
Number of cells in the battery 5 164 cells of lead-acid
Highest cell 5 2.6 V/cell

Highest temperature: 55 C—hence stop charge or discharge immediately;
let the battery temperature decrease over time.
Complete the charging cycle of the battery: first charge, discharge, sec-
ond charge.
Start the discharging process