Figure 2-6.—Typical pole-mounted feeders, primary mains, transformers, and secondaries.system. It provides the best service reliability to thethrough fused or automatic cutouts. Figure 2-6 showsdistribution transformers or load centers, particularlywhen the system is supplied from two or moredistribution substations. Power can flow from anysubstation to any distribution transformer or load centerin the network system. The network system is moreflexible about load growth than the radial or loopsystem. Service can readily be extended to additionalpoints of usage with relatively small amounts of newconstruction. The network system, however, requireslarge quantities of equipment and is, therefore, moreexpensive than the radial system.Primary MainsPrimary mains are connected to the primary feeders.In overhead installations, these mains are alwaysinstalled below the feeders on a pole. The distributiontransformers are connected to the primary mainsthe primary main to which the transformer is tapped.The cutouts, one on each primary line, contain the fusesthat protect the transformer against overload and shortcircuits.Distribution TransformersMost electrical equipment in the Navy uses 120/208volts. The primary voltage on Navy shore installations,however, is usually 2,400/4, 160 volts. For this reason, adistribution transformeris required to reduce (stepdown) the high primary voltage to the utilization voltageof 120/208 volts. Figure 2-6 shows one of variousdifferent types of transformer arrangements andinstallations. Regardless of the type of installation orarrangement, transformers must be protected by fusesor circuit breakers and lightning protection.2-4
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