ELECTRICAL VOLTAGES AVAILABLE TESTING AND ADJUSTING SR   4   Generators   directly   meet   these   requirements. Single-phase  loads  should  be  distributed  equally  from the   three   lines   to   the   neutral   giving   230   volts   single- phase   (at   400   volts,   three-phase).      Industrial   50   Hz three-phase   loads   in   the   range   of   480   volts   can   be directly   supplied   by   the   480   volt   50   Hz   generators. However,   if   single-phase   voltage   in   the   range   of   220 volts   is   also   required   from   a    480    volt    three-phase system,   single-phase   step   down   transformers   will   be required. Larger  60  Hz  industrial  loads  are  generally  three-phase in  the  range  of  460  to  480  volts.    Single-phase  120  volt, 120-240    volt    or    240    volt    loads    are    almost    always supplied from transformer banks, operating from the 460 to  480  volt  three-phase  service.    The  480  volt  60  Hz  SR 4 Generators  match  this  requirement  directly.    With  the stator  coils  parallel  connected,  this  range  of  generators will  directly  match  large  industrial  three-phase,  230-240 volt loads. Other  60  Hz  commercial  service  supplies  power  in  the range   of   120/208Y   to   125/216Y   volts   in   a   4-wire   "Y" connected single-phase/three-phase system. The nominal 120/208Y 60 Hz generator is directly applicable. Motor  starting  ability  compares  to  the  nominal   240   volt generator   operating   at   240   volts.      The   broad   voltage range  5N43,  5N46,  5N48,  5N56,  and  5N58  Generators connected  for  low  voltage  will  also  directly  meet  these application,  as  the  voltage  level  control  has  adequate range. When these broad range generators are operated in the 208-416  volt  range,  motor  starting  ability  is  good,  but  of course,   less   than   when   operating   at   the   240-480   volt range.    The  expected  voltage  dip  at  the  208-416  setting will  approximate  35%  when  starting  0.5  hp  of  motor  per kW of generator prime power rating. Another    common    60    Hz    commercial    power    service distribution  comes  from  Delta  connected  transformers, which will simultaneously supply 240 and 120 volt single- phase.        Such    systems    can    be    quite    satisfactorily supplied from the 60 Hz, 120/208Y volt SR 4 Generator, since   connected   equipment   readily   accepts   a   ±10% voltage   tolerance.      When   the   prospective   installation demands     voltages     exactly     equal     to     the     original, transformers will be necessary, as 120 and 240 volts can not  be  obtained  simultaneously  from  a  "Y"  connected generator. In     any     installation,     single-phase     loads     should     be distributed   as   equally   as   possible   around   the   three- phases to avoid generator derating or excessive heating. Single-phase loads,  balanced  within  10%,  are  considered  acceptable within present engineering practices.  In any combination of  single-and  three-phase  loads,  individual  line  current should   not   exceed   the   generator   nameplate   ampere rating. Voltage Modifications There are areas where existing commercial 50 Hz power systems  will  eventually  be  converted  to  60  Hz.    These areas require a  generator  which  will  presently  produce  a given voltage at 50 Hz and later be capable of producing the    same    voltage    at    60    Hz.        Suitable    generator application depends on present voltage. If the present required 50 Hz three-phase voltage is 240 or 480, and the future system will be 60 Hz, 240 or 480 volts,  the  50  Hz  240-480  volt  generator   is   suggested. This   generator   will   produce   300-600   volts   at   60   Hz. However,   the   exciter-regulator   system   can   easily   be reconnected to lower generated voltage to 240-480 at 60 Hz when the change in commercial frequency occurs. As    originally    constructed,    this    50    Hz,    240-480    volt generator   has   the   voltage   regulator   and   exciter   field tapped  into  the  three  generator  coils  forming  the  center "Y".    These  coil  taps  terminate  at  terminals  20,  22,  and 24  of  the  regulator  terminal  board.    Remove  the  wires from the terminal board, and carefully insulate each wire to avoid any possible connection or ground.  Install new No.    14  gauge,  600  volt  insulated  flexible  wires  from  the terminal board to the generator line leads as follows: From Terminal Board To Line Lead No.  20 T-9 No.  22 T-7 No.  24 T-8 The  generator  will  now  produce  240  or  480  volts  at  60 Hz.  The modified generator has the same kVA rating at 60  Hz  as  it  did  originally  at  50  Hz.    Parallel  operation  is not  affected.    Since  the  modified  excitation  system  is running  at  a  reduced  excitation  level,  the  ability  to  start very large motors will be reduced.  The range of voltage level control is also slightly reduced. If  the  application  presently  requires  three-phase  50  Hz voltage  at  400  volts,  and  the  future  60  Hz  three-phase voltage will  also  be  400  volts,  the  200-400  volt  50  Hz generator  is  a  good  choice.    Without  modification,  this generator  would  produce  240  or  480  volts  at  60  Hz.    A special connection of the 96