Figure 2-6.—Typical pole-mounted feeders, primary mains, transformers, and secondaries.
system. It provides the best service reliability to the
through fused or automatic cutouts. Figure 2-6 shows
distribution transformers or load centers, particularly
when the system is supplied from two or more
distribution substations. Power can flow from any
substation to any distribution transformer or load center
in the network system. The network system is more
flexible about load growth than the radial or loop
system. Service can readily be extended to additional
points of usage with relatively small amounts of new
construction. The network system, however, requires
large quantities of equipment and is, therefore, more
expensive than the radial system.
Primary Mains
Primary mains are connected to the primary feeders.
In overhead installations, these mains are always
installed below the feeders on a pole. The distribution
transformers are connected to the primary mains
the primary main to which the transformer is tapped.
The cutouts, one on each primary line, contain the fuses
that protect the transformer against overload and short
circuits.
Distribution Transformers
Most electrical equipment in the Navy uses 120/208
volts. The primary voltage on Navy shore installations,
however, is usually 2,400/4, 160 volts. For this reason, a
distribution transformer is required to reduce (step
down) the high primary voltage to the utilization voltage
of 120/208 volts. Figure 2-6 shows one of various
different types of transformer arrangements and
installations. Regardless of the type of installation or
arrangement, transformers must be protected by fuses
or circuit breakers and lightning protection.
2-4
