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1.4.3 Types of Systems. There are two fundamental types of primary distribution systems;
radial and network. Simply defined, a radial system has a single simultaneous path of power
flow to the load. A network has more than one simultaneous path. Each of the two types of
systems has a number of variations. Figure 1-4 illustrates four primary feeder arrangements
showing tie, loop, radial and parallel feeders. There are other more complex systems, such as the
primary network (interconnected substations with feeders forming a grid) and dual-service
network (alternate feeder to each load). These systems, however, are simply variations of the
two basic feeder arrangements.
The following paragraphs discuss the functions and characteristics of the simpler feeder
arrangements. Tie Feeder. The main function of a tie feeder is to connect two sources. It may
connect two substation buses in parallel to provide service continuity for the load supplied from
each bus. Loop Feeder. A loop feeder has its ends connected to a source (usually a single
source), but its main function is to supply two or more load points in between. Each load point
can be supplied from either direction; so it is possible to remove any section of the loop from
service without causing an outage at other load points. The loop can be operated normally closed
or normally open. Most loop systems are, however, operated normally open at some point by
means of a switch. The operation is very similar to that of two radial feeders. Radial Feeder. A radial feeder connects between a source and a load point, and it
may supply one or more additional load points between the two. Each load point can be supplied
from one direction only. Radial feeders are most widely used by the Navy because the circuits
are simple, easy to protect, and low in cost. Parallel Feeder. Parallel feeders connect the source and a load or load center and
provide the capability of supplying power to the load through one or any number of the parallel
feeders. Parallel feeders provide for maintenance of feeders (without interrupting service to
loads) and quick restoration of service when one of the feeders fails.


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