The electrical plant in general follows the design incorporated in type IX-C40 vessels except for the following:  
          (a)  Battery voltage for main electric machines has been tripled.  
          (b)  Electrically operated torpedo handling gear has been introduced.  
          (c)  Creeping motors have been added for use in lieu of the main electric machines during slow speed silent operation.  
          (d)  The size of the hydraulic plant has been materially increased.  Planes and rudder are operated hydraulically instead of electrically.  
          (e)  An air conditioning plant and a deep freeze unit have been added.  
          Auxiliary power voltage is the same as on type IX C/40 vessels (110-170 V. D.C.)  
March, 1946
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  REPORT 2G-21
  1.  Introduction  
          Reference should be made to Report 2G-9C-S60 on the type IXC vessels regarding the electrical plant installed on type XXI vessels.  The scope of this report is concerned only with the differences in the two plants.  
  2. Description  
          Two main electric machines are installed in this type vessel, one port and one starboard.  These serve as motors for propulsion and when energized from the battery or as generators for charging the batteries.  
          Split main control cubicles are installed for control of the main electric machines.  
          Two creeping speed motors each connected to its respective propulsion shaft, Port or Starboard, with multiple V-belts, are installed for use when operating under evasive tactics.  Split control cubicles provide for power connection either to the related main control cubicle or the related auxiliary power switchboard.  When connected to the control cubicle, the power supply voltages vary between 110 and 170 D.C.  
          Two batteries are installed, each consisting of 186 cells from which voltages of 330 to 510 may be obtained.  One is considered as a port and one as a starboard battery.  These are not normally connected together, but provision is made for a parallel connection by means of a suitable rotary type switch in the Maneuvering Room.  
          Each battery is divided into 3 groups of 62 cells which are installed in separate watertight tanks.  The corresponding groups of each battery are located in tanks one above the other.  An air circuit breaker is installed between the battery and the main control cubicle in the positive leg only.  
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  REPORT 2G-21
          Auxiliary power loads are arranged to be connected to either the port or starboard auxiliary power switchboards.  Auxiliaries in the Engine Room and Aft are connected to the Port board, forward of the Engine Room are connected to the Starboard board.  Power supplies are obtained for the port board from the upper battery and for the starboard from the lower battery.  Provision is made in the Control Room to apply disconnect blocks for the connecting each board to the opposite battery.  
          Auxiliary power supply voltages vary between 110 - 170 volts D.C. and power is obtained by providing each board with a transfer switch to connect the load to any of the three groups of 62 cells of its respective battery.  
          Regulated 110 V. D.C. for lighting, I.C. equipments and various other purposes is obtained thru use of voltage sensitive relay actuated regulators incorporated as part of the auxiliary power switchboards.  
          In order to meet the hydraulic power requirements due to changing from electric to hydraulic control of the steering and diving plane systems, a second hydraulic plant is installed.  
          One electric motor driven air compressor is installed.  
  3. Conclusions  
          The same conclusions as are contained in report 2G-9C-S60 on type IX-C40 vessels apply to the type XXI vessels with the addition that a wider use of hydraulic power is observed.  
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