produces or transient currents, to ground without injury
to line insulators, transformers, or other connected
equipment. Use of lightning arresters is essential in all
areas of power line construction. These include
distribution, secondary, intermediate, and station
distribution. The four different specifications of
arresters, mentioned above, have different sparkover
voltages, current discharge capabilities, and maximum
surge discharge capabilities.
Figure 4-34.Distribution cutouts (fused).
Secondary arresters are used on service and other
low-voltage alternating-current circuits. Distribution
arresters are used on primary distribution systems to
protect insulators, distribution transformers, and other
equipment. Intermediate type of lightning arresters are
often used on substation exit cables and other locations
on the distribution system, needing a high level of
lightning and surge protection. Substation types of
arresters are used in substations and generating stations
to provide a high level of surge protection for the major
pieces of equipment. Surge voltages can be generated
by operating switches in the electric transmission
system as well as by lightning.
Various types of lightning arresters are in use today.
The valve, pellet, and air gap (fig. 4-35) are the most
common and likely-to-be-seen types in the field.
A switch is used to disconnect or close circuits that
may be energized. High-voltage switches are operated
remotely using a variety of mechanisms or manually.
Depending on their purpose in the system and their
physical makeup, switches are divided into three
general classes: air, oil, and vacuum switches. These
three classes can be further subdivided (depending on
their function) into what is referred to as disconnects,
circuit breakers, or reclosers.
As their name implies, air switches are switches
whose contacts are opened and use air to insulate their
contacts when current flow is interrupted.
Figure 4-35.Types of lightning arresters.