14-1. Battery usage.
there is a large volume of free electrolyte. The elec-
trolyte maintains uniform contact with the plates.
Storage batteries are used in exterior facility elec-
Vented units are characterized by a removable vent
trical distribution systems to provide a power sup-
cap which allows the electrolyte to be checked and
ply to devices whose control response will be dam-
adjusted as needed. Overcharge will produce gases
aged by an electrical system power outage. This
which vent through the cell, requiring regular wa-
chapter describes station batteries as they are gen-
ter replacement. Vent caps must be accessible, so
erally called, as opposed to uninterruptible power
batteries are larger than valve-regulated types and
system batteries or automotive type batteries. A
are provided with flame arresters. Gassing requires
storage battery is composed of one or more re-
chargeable electrochemical type cells. Systems are
ventilation to avoid explosive possibilities and pos-
designed for full-float operation, with a battery
sible corrosive damage to battery terminals.
charger to maintain the battery in a charged condi-
d. Valve-regulated batteries. Valve-regulated cells
tion. Batteries used for control of substation and
are sealed, with the exception of a valve that opens
power equipment are required to provide low cur-
periodically to relieve excessive internal pressure.
rents for long periods and high currents for short
To limit water consumption, cells are designed to
periods. A battery's reserve capacity requirements
provide recombination of charge gases by passing
are based on a duty cycle (usually an 8-hour operat-
oxygen evolved from the positive plate over the
ing time period) when all continuous and momen-
negative plate, where the recombination reaction
tary loads must be supplied by the battery with no
occurs. The valve regulates the internal pressure to
recharging available from the battery charger.
optimize recombination efficiency (hence the term
valve-regulated). The valve opens when the cell's
14-2. Battery types.
internal pressure exceeds a set limit and once the
The two electrochemical types in general use for
pressure is relieved the valve closes and reseals. No
station batteries are lead-acid and nickel-cadmium.
cell check of an electrolyte level nor the specific
Construction types include vented (flooded) and
gravity of each cell is required. These batteries are
valve-regulated (sealed) units. For specific informa-
not maintenance-free as some 10 or more mainte-
tion on a particular type, refer to the manufactur-
nance checks are still necessary. Outgassing of
er's instructions. There are five basic components to
these batteries is low at normal charge rates, but it
a battery cell: the container, the positive plate
can occur when there is a battery or battery charger
(electrode), the separator or retainer, the negative
failure. Cells can pose a hazard if enclosed so as to
plate (electrode), and the electrolyte.
inhibit cooling air, or installed so as to place them in
a. Lead-acid units. Lead acid batteries have an
the heat flow of electronics which may occupy the
acidic electrolyte solution of sulfuric acid
The active materials used are lead dioxide (PbO2)
14-3. Battery safety.
for the positive plate, and sponge lead (Pb) for the
negative plate. The active materials for both the
Safety precautions cannot be ignored, since every
positive and negative plates are incorporated in a
station battery installation presents hazards. The
plate structure composed of lead or a lead alloy. The
importance of using safety equipment, such as rub-
NEC defines their nominal battery voltage at 2.0
ber gloves, goggles, aprons, and of having an eye-
volts per cell.
wash water bottle present, cannot be overempha-
b. Nickel-cadmium units. Nickel cadmium batter-
sized. The three major hazards are from the
ies use an alkaline electrolyte (potassium hydrox-
electrolyte in the battery, the gases emitted by the
ide). The active materials used are nickel hydroxide
battery, and the potential electrical short circuit
for the positive plate and cadmium hydroxide for
capability available from the battery's stored en-
the negative plate. The NEC defines their nominal
ergy. Most persons trained to work in an electrical
battery voltage at 1.2 volts per cell.
environment are aware that batteries are danger-
c. Vented batteries. Vented (flooded) cells are con-
ous, but need to be warned and advised again as to
the extent of the hazards posed by all station bat-
structed with the liquid electrolyte completely cov-
tery systems, regardless of size or type.
ering (flooding) the closely spaced plates, so that