DIESEL-DRIVEN  GENERATORS Practically all Navy ships are equipped with diesel-driven  emergency  generators.  Diesel  engines are  particularly  suited  for  this  application  because of   their   quick   starting   ability.   Emergency generators  furnish  power  directly  to  the  radio, radar,  gunnery,  and  vital  machinery  equipment through  an  emergency  switchboard  and  automatic bus  transfer  equipment. The  typical  shipboard  plant  consists  of  two diesel  emergency  generators,  one  forward  and  one aft,  in  spaces  outside  engine  rooms  and  firerooms. Each  emergency  generator  has  its  own  switch- board and switching arrangement. This controls the  generator  and  distributes  power  to  certain vital  auxiliaries  and  a  minimum  number  of lighting fixtures in vital spaces. The  capacity  of  the  emergency  units  varies with the size of the ship. Regardless of the size of  the  installation,  the  principle  of  operation  is the same. You   may   obtain   detailed   information   con- cerning the operation of diesel-driven generators from   appropriate   manufacturers’   technical manuals. MOTOR  GENERATORS Aboard Navy ships, certain weapons, interior communications,  and  other  electronics  systems require   closely   regulated   electrical   power   for proper  operation.  Special,  closely  regulated  motor generator (MG) sets supply this power (usually 400 Hz). Any given ship has several MGs to provide power  to  specific  loads.  These  MGs  are  often  of different ratings. The rating of an MG set can be less than 1 kW or as large as 300 kW. MGs can also  be  used  to  provide  electrical  isolation. Isolation  is  required  when  certain  loads  cause distortion of the power and adversely affect the operation  of  other  equipment. The  MG  set  (fig.  12-5)  is  generally  a  two- bearing   unit.   (Older   units   often   consist   of   a separate motor and generator connected together and mounted on a bedplate.) The frame is of one- piece   construction.   The   stationary   component parts  of  the  motor  and  generator  are  press  fit into a welded steel frame. The rotating elements are  mounted  on  a  single  one-piece  shaft.  The MG   is   usually   deck   mounted   horizontally   on its  own  integral  feet;  however,  some  specially designed,   vertically   mounted   units   are   also provided.  MGs  with  100-kW  power  and  larger  are usually cooled by a water-air cooler mounted on top  of  the  MG. Solid-state   voltage   and,   often,   frequency regulating systems are provided on MGs. They are mounted either in a control box, which is directly mounted on the MG for forced-air cooling, or in bulkhead-mounted   control  panels.  The  voltage Figure  12-5.—Motor  generator. 12-5


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