PRINCIPLES OF NAVAL ENGINEERING 



The ship's service generators and distribu- 

 tion switchboards are interconnected by bus ties 

 so that any switchboard can be connected to feed 

 power from its generator to one or more of the 

 other switchboards. The bus ties also connect 

 two or more switchboards so that the generator 

 plants can be operated in parallel (or the switch- 

 boards can be isolated for split-plant operation). 



In large installations, power distribution to 

 loads is from the generator and distribution 

 switchboards or switchgear groups to load cen- 

 ters, to distribution panels, and to the loads, 

 or directly from the load centers to some loads. 



On some ships, such as large aircraft car- 

 riers, a system of zone control of the ship's 

 service and emergency power distribution is 

 provided. Essentially, the system establishes a 

 number of vertical zones, each of which con- 

 tains one or more load center switchboards 

 supplied through bus feeders from the ship's 

 service switchgear group. A load center switch- 

 board supplies power to the electrical loads 

 within the electrical zone in which it is located. 

 Thus, zone control is provided for all power 

 within the electrical zone. The emergency 

 switchboards may supply more than one zone, 

 depending on the number of emergency genera- 

 tors installed. Figure 20-23 shows the ship's 

 service and emergency power distribution sys- 

 tem in a large aircraft carrier. 



In smaller installations (fig. 20-24) the dis- 

 tribution panels are fed directly from the 

 generator and distribution switchboards. The 

 distribution panels and load centers (if any) are 

 located centrally with respect to the loads they 

 feed to simplify installation. This arrangement 

 also requires less weight, space, and equipment 

 than if each load were connected to a switch- 

 board. 



At least two independent sources of power 

 are provided for selected vital loads through 

 automatic bus transfer equipment. The normal 

 and alternate feeders to a common load run from 

 different ship's service switchboards and are 

 located below the waterline on opposite sides of 

 the ship to minimize the possibQity that both 

 will be damaged by a single hit. 



The lighting circuits are supplied from the 

 secondaries of 450/115-volt transformer banks 

 connected to the ship's service power system. 

 In large ships, the transformer banks are in- 

 stalled in the vicinity of the lighting distribution 

 panels, at some distance from the generator 

 and distribution switchboards. In small ships, 

 the transformer banks are located near the 



generator and distribution switchboards and 

 energize the switchboard buses that supply the 

 lighting circuits. 



EMERGENCY POWER 



The emergency power distribution system is 

 provided to supply an immediate and automatic 

 source of electric power to a limited number of 

 selected vital loads in the event of failure of the 

 ship's service power distribution system. The 

 emergency power system, which is separate and 

 distinct from the ship's service power distribu- 

 tion system, includes one or more emergency 

 distribution switchboards. Each emergency 

 switchboard, supplied by its associated emer- 

 gency generator, has feeders which run to the bus 

 transfer equipment at the distribution panels or 

 loads for which emergency power is provided. 



The emergency generators and switchboards 

 are located in separate spaces from those con- 

 taining the ship's service generators and dis- 

 tribution switchboards. As previously noted, the 

 normal and alternate ship's service feeders 

 are located below the waterline on opposite 

 sides of the ship. The emergency feeders are 

 located near the centerline and higher in the 

 ship (above the waterline). This arrangement 

 provides for horizontal separation between the 

 normal and alternate ship's service feeders 

 and vertical separation between these feeders 

 and the emergency feeders, thereby minimizing 

 the possibility of damaging all tluree types of 

 feeders simultaneously. 



The emergency switchboard is connected by 

 feeders to at least one and usually to two dif- 

 ferent ship's service switchboards. One of these 

 switchboards is the preferred source of ship's 

 service power for the emergency switchboard 

 and the other is the alternate source. The 

 emergency switchboard and distribution system 

 are normally energized from the preferred 

 source of ship's service power. If both the pre- 

 ferred and the alternate sources of ship's serv- 

 ice power fail, the diesel-driven emergency 

 generator starts automatically and the emer- 

 gency switchboard is automatically transferred 

 to the emergency generator. 



When the voltage is restored on either the 

 preferred or the alternate source of the ship's 

 service power, the emergency switchboard is 

 automatically retransferred to the source that 

 is available (or to the preferred source, if volt- 

 age is restored on both the preferred and the 

 alternate sources). The emergency generator 



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