Page 157 - Practical Power System and Protective Relays Commissioning

Chapter 15

Batteries

15.1 INTRODUCTION
15.1.1 Power Sources

AC power is often preferred because it is easy to generate, to transmit, and
to use. However, in some situations, DC power is preferred because it can be
stored in batteries and used if the generating equipment fails.

15.1.2 DC Power Circuits

A DC power circuit consists of a battery charger with an AC supply, a bat-
tery, and loads. The battery charger converts AC to DC. The resulting DC is
used to supply the load and to supply a charge to the battery (float charge).
The battery stores DC power and is used to supply power to the load if the
AC supply and charger fail; if the demand is high, the battery may also sup-
plement the power supplied by the charger.

15.1.3 Cells and Batteries
Cells are devices that store and deliver DC power. A battery is made up of
one or more cells connected in series. Each cell of an industrial storage bat-
tery provides a specific voltage; the battery voltage depends on the number
of cells. The cells are filled with an electrolyte (a solution of acid and water)
that activates a chemical reaction and provides a path for current flow. The
plates are connected to the appropriate terminal posts (positive or negative,
depending on the plate material). Many plates may be connected together to
increase the storage capacity of the cell. An outer jar contains the plates and
the electrolyte.

15.1.4 Cell Operation

Connecting a battery charger to the terminals of a battery starts a chemical
reaction, causing electrons to leave one plate and build up on the other. One
plate becomes positively charged, and the other is negatively charged. If a
load is connected across the terminals, current flows and the stored charge is

Practical Power System and Protective Relays Commissioning.
DOI: https://doi.org/10.1016/B978-0-12-816858-5.00015-0 157
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