Page 376 - Battery Reference Book

Stationary type or standby power batteries 32l3
32.1 Stationary type or standby power safe shutdown of the process. Classic cases of the
batteries use of standby power are in an operating theatre
and an airport where, in the event of mains failure,
Large battery installations which are called upon only power is required for lighting, communications and
occasionally to supply power, usually in emergency the operation of vital equipment. Power stations, tele-
or auxiliary power supply circumstances, are referred phone exchanges, lighthouses and computer installa-
to as stationary or standby batteries. Such installations tions are other examples of the application of stationary
having total capacities in hundreds of ampere hours or standby batteries.
are commonly in use. Figure 32.1 illustrates a large
secondary lead-acid battery installation. 32.1.1 Types of stationary or standby battery
Standby power can be defined as a source of
electricity that becomes available when the mains Several types of standby lead-acid batteries are
source of electricity ceases to be available. The choice manufactured to meet the needs of different types
of application.
of a standby system lies between batteries, usually
lead-acid or nickel-cadmium, and generators, or a
combination of the two. For many applications, the Plante' cells
battery's ability to provide the power required instantly For the long life with very high reliability needed in
makes it more suitable. Indeed, even in large installa- places like power stations and telephone exchanges,
tions for which a generator is essential, batteries are batteries are made up of cells of a kind named after
often used both to start the generator and to provide Plant& They are kept on continuous trickle charge
power for the initial period until the generator is run- and are ready to spring into life immediately there is
ning to speed. a mains failure. The capacity of a cell (the amount
Standby power is required in many situations. For of electricity it can store) and its life depend largely
department stores, offices, factories, cinemas and other on the design of its positive plate. In the Plant6
public places, emergency power to light people to cell, this is cast from pure lead in a form that gives
safety without panic may be enough. In industry, the it a surface 12 times its apparent area. Figure 32.2
need varies from keeping fire and burglar alarms and shows representations of a modem type of PlantC grid.
other communications working to supplying emer- The negative plate is of the pasted grid type made
gency power to vital production processes or even by forcing lead oxide paste into a cast lead alloy
to supply the power necessary to effect a controlled grid. Positive and negative plates are interleaved and
insulated from each other to prevent short-circuits.
The all-important surface of the positive plate is
continuously regenerated during the life of the bat-
tery. Trickle charging compensates for natural open-
circuit losses. The average life of a typical Plant6 bat-
tery is 20 years and some designs extend to 35 years
and sometimes even longer with no fall in capacity.
Although the initial cost is high, the average annual
cost over the life of the battery can be lower than that
of other kinds used for standby power purposes.
Cell capacities are rated by relating current flow to
time in ampere hours. High-performance Plant6 cells
up to 2000 Ah have transparent plastic containers to
allow visual checking of the acid level and general
condition. Large PlantC cells up to 15000Ah, often
found in large telephone exchanges, are most com-
monly housed in lead-lined wooden boxes.

Flat plate cells
Because of the high initial cost of Plant6 cells, spe-
cially designed flat plate cells have been developed to
provide a cheaper but shorter-lived alternative source
of standby power. The layout of a typical modem flat
plate cell is shown in Figure 32.2.
The flat (or pasted) plate cell, pioneered in the
Figure 32.1 Large stationary lead-acid battery installation (Cour- 1880s, has a positive plate made from a lead alloy
tesy of Chloride Batteries) lattice grid into which a paste of lead oxide and