Custom Search
|
|
 
|
||
|
Primary Feeders Primary feeders are those conductors in a distribution system that are connected from the distribution sub-stations and that transfer power to the distribution centers (fig. 2-2). They may be arranged as radial, loop, or network systems and may be overhead or underground. RADIAL DISTRIBUTION SYSTEM. A schematic example of a radial distribution system is shown in figure 2-3. In this system, primary feeders take power from the distribution substation to the load areas by way of subfeeders and lateral-branch circuits. This is the most common system used because it is the simplest and least expensive to build. It is not the most reliable served by the system.Service on this type of system can be improved by installing automatic circuit breakers that will reclose the service at predetermined intervals. If the fault continues after a predetermined number of closures, the breaker will be locked out until the fault is cleared and service is restored.PRIMARY LOOP (OR RING) DISTRIBUTION SYSTEM. The loop (or ring) distribution system is one that starts at a distribution substation, runs through or around an area serving one or more distribution transformers or load centers, and returns to the same substation. The loop system (fig. 2-4) is more expensive to build than the radial type, but it is more reliable and may be justified in areas where continuity of service is requiredat a medical center, for example.In the loop system, circuit breakers sectionalize the loop on both sides of each distribution transformer connected to the loop. A fault in the primary loop is cleared by the breakers in the loop nearest the fault, and power is supplied the other way around the loop without interruption to most of the connected loads. If a fault occurs in a section adjacent to the distribution substation, the entire load can be fed from one direction over one side of the loop until repairs are made. NETWORK SYSTEM. The network system (fig. 2-5) is the most flexible type of primary feeder
Figure 2-5.Network distribution system.
Figure 2-6.Typical pole-mounted feeders, primary mains, transformers, and secondaries. system. It provides the best service reliability to the 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. |
 
|
|
|
||
