FIGURE   4-10.   Brushless   Generator   Schematic

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ARMY  TM  9-6115-644-24 AIR  FORCE  TO  35C2-3-446-12 MARINE  CORPS  TM  09249A/09246A-24/2 GENERATOR STATOR EXCITER FIGURE   4-10.   Brushless   Generator   Schematic To  energize  the  field,  DC  excitation  must  be  applied  to  the  generator  field  coils.  The  excitation  current  is  supplied   from  a brushless exciter mounted on the generator shaft. The  brushless  exciter  is  actually  an  AC  generator  with  its  output  rectified  through  a  full  wave  bridge  circuit.  This  type  of brushless  exciter  will  provide  the  necessary  excitation  current.  The  generator  set  field  flash  circuit,  activated  during  each engine  start,  applies  voltage  to  the  exciter  stator  to  begin  the  voltage  build-up  process  to  energize  the  generator  field. The  generator  output  voltage  is  controlled  by  controlling  the  alternating  field  current.  This  is  accomplished  by regulating  the  exciter  field  coil  voltage.  The  exciter  field  coil  voltage  is  regulated  with  a  solid-state-type  voltage  regulator. 4-16-2  Damper  Bars  are  inserted  through  the  field  laminations  and  welded  at  the  end  to  a  solid  copper  plate. The  damper  windings  provide  stable  parallel  operation,  reduce  damping  current  losses,  and  limit  the  increase  of  third  har- monic  voltage  with  increase  in  load. 4-16-3   Brushless Exciter  The brushless exciter consists of an armature with a three-phase AC winding and rotating rectifi- er assembly within a stationary field. The stationary exciter field assembly is mounted in the main generator frame. The exciter armature is press fit and keyed  onto  the  shaft  assembly.  The  rotating  rectifier  assembly  slides  over  the  bearing  end  of  the  generator  rotor  shaft  and is secured with bolts and washers to an adapter hub which is shrunk on the generator shaft. 4-16-4 Rotating Rectifier Bridge. The rotating rectifier bridge consists of rectifying diodes mounted on a brass heat sink which  is  in  turn  mounted  on  an  insulating  ring.  The  entire  assembly  bolts  to  the  adapter  on  the  generator  shaft.  Therefore, the rotating rectifier assembly will rotate with the exciter armature eliminating the need for any sliding contacts between the  exciter  output  and  the  alternator  field. 4-16-5 Exciter Field. The  exciter  field  on  the  high  frequency  exciter  consists  of  laminated  segments  of  high  carbon  steel which are fitted together to make up the field poles. The field coils are placed into the slots of the field poles. 4-16-6  Exciter  Field  Coil  Voltage  Source.  Field  coil  DC  voltage  is  obtained  by  rectifying  the  voltage  from  a  phase  to  neutral line  of  the  generator  output,  or  other  appropriate  terminal  to  provide  the  needed  voltage  reference. The rectifier bridge is an integral part of the static regulator. The static regulator senses a change in the generator output and automatically regulates current flow in the exciter field coil circuit to increase or decrease the exciter field strength. An external adjust  rheostat  sized to be compatible with the regulator  is used  to provide adjustment  to the regulator sensing  circuit. 4-31


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