ELECTRICAL/MECHANICAL CHARACTERISTICS TESTING AND ADJUSTING SUBJECT: Caterpillar SR 4 Generators - Electrical/Mechanical Characteristic BUSINESSES: Building Services, Material Handling, Marine, Agriculture PRODUCT: Generator Sets General Description Construction The SR 4 brushless generator is a single bearing, salient pole,  revolving  field  alternator  of  drip-proof  construction built  to  U.S.    NEMA  (National  Electrical  Manufacturers Association) specifications.  The stator frame is bolted to the  engine  flywheel  housing  and  the  rotor  is  connected by  a  flexible  plate  type  coupling  to  the  engine  flywheel. The  generator  shaft  has  an  extension  into  the  flywheel pilot  bore  to  assure  optimum  alignment.    The  pilot  also assures  positive  rotor  support  in  the  unlikely  event  of coupling   looseness   or   fracture.      The   stator   core   is constructed of laminated electrical steel with semiclosed skewed slots. The  rotor  consists  of  an  integral  pole  laminated  steel assembly  keyed  directly  to  the  shaft.    The  pole  faces contain  complete  amortisseur  windings.    Rotating  speed is either 1500 rpm for 50 Hz, or 1800 rpm for 60 Hz. Windings and Insulation All SR 4 generators use Class F insulation on both rotor and stator. NEMA     allows,     for     Class     F     insulation,     a     1050C temperature  rise  (measured  by  resistance)  over  a  40°C inlet air temperature for  continuous  full  load,  24  hour  per day  operation.    A  130°C  temperature  rise  (above  400C) is  allowed  for  standby  operations.  At  prime  power  and standby  kW  ratings,  SR  4  Generators  will  not  exceed allowable   NEMA   temperature   rises.      Actual   operating temperatures are lower than allowable NEMA temperature rises. Stator,  rotor  and  exciter  windings  are  impregnated  with 100%  epoxy  varnish,  and  the  rotor  and  stator  have  an epoxy-asphalt overcoat   which   resists   abrasion   and   fungus   growth. Windings  are  10-wire  wye,  connectable  for  high  or  low voltage.      Multiple   line   leads,   (parallel   wires)   assure maximum line lead flexibility. Cooling The   SR   4   Generator   is   self-ventilated   with   air   entry through   louvers   at   the   rear   end   of   the   generator   and discharge    through    screened    openings    at    the    drive coupling   end.      Air   is   directed   by   two   axial   flow   shaft mounted  fans  and  a  centrifugal  fan  which  is  mounted  to the   flywheel.      The   centrifugal   fan   also   serves   as   a pressure ring for the coupling plates. Regulator Assembly and Terminal Box The  louver  ventilated  steel  cabinet  houses  the  regulator assembly and the generator line leads. SR  4  Generators  have  solidly  mounted  cabinet  with  an independently  shock  mounted  regulator  assembly.    This construction provides vibration isolation for the regulation unit as well as a solid cabinet to which flexible electrical conduit may be attached. Leads may be brought out of the cabinet from either the top   or   side   of   the   upper   right-hand   quadrant   of   the cabinet   (facing   the   rear   of   the   generator   set).      An optional  extension  terminal  box  is  available  on  all  SR  4 Generators   for   improved   ease   of   connections   of   load leads   to   generator   leads,   or   for   mounting   a   circuit breaker or link board. Rotating Brushless Exciter The   rotating   brushless   exciter   is   mounted   within   the generator stator frame.  The stationary exciter field is a 6 pole distributed winding on a core that is integral with the generator end bracket.  The three- 81