CIRCULATING CURRENTS TESTING AND ADJUSTING Operating  conditions  as  just  described  are  not  always possible  over  the  entire  load  range  of  the  generators. Electrical and mechanical variations in generators cause a small difference in ampere or kVA division.  Neither is exactly proportionate to kW load division.  The difference shows up in the panel ammeter indications:   the sum of individual    generator    line    currents    exceeds    the    load current. Acceptable   levels   of   circulating   current   result   if   the published   procedures   are   followed   for   voltage   level, regulator  gain,  and  voltage  droop  on  SRCR  and  SR  4 generators.    These  adjustments  are  always  made  with the generator at or near operating temperature.  When a "cold"  unit  is  paralleled  to  the  bus,  circulating  currents may   be   noted.      However,   these   will   decrease   as   the incoming  generator  reaches  its  operating  temperature. These  currents  are  seldom  cause  for  concern.    Where excessive   circulating   currents   do   exist,   the   cause   is generally  found  to  be  error  in  the  adjustment  procedure or in operating procedure. When  different  sizes  of  generators  are  used,  or  where different  types  of  voltage  regulators  are  used,  the  best adjustment   results   from   using   the   actual   plant   load. Voltage   droop   levels   should   be   established   from   a reference voltage level, and at a reference frequency. It  is  generally  desirable  to  have  the  same  voltage  droop on   all   generators.      This   means   that   each   generator should reduce its voltage an equal amount (3% to 5%X) between no-load and expected full load.  Where different size  generators  are  involved,  it  may  be  impractical  to make   the   full   load   droop   adjustment   on   the   larger generators.      A   close   approximation   can   be   made   by considering the droop system as a linear device.  Select a plant load equal to at least three-fourths of the smaller generator   capacity.      Set   the   required   droop   on   this smaller  unit  (example  5%).    Transfer-parallel  this  same load  to  the  larger  generator  and  establish  the  reference frequency.    Set  the  droop  proportionate  to  the  capacity. Example:  5%  was  set  on  the  smaller  unit  with  full  load. That load is one-half the larger generator capacity.  Set the droop on the larger generator at 2.5%.  The resulting adjustment will be quite adequate. Operating     errors     can     cause     very     high     circulating currents.        These    generally    occur    where    indicating instruments are limited to voltmeters and ammeters.  It is entirely  possible  to  have  one  generator  set    absorbing power from the system, and have the ammeters showing "correct"  currents.    To  avoid  this,  the  operator  should always  have  the  incoming  generator  set  running  slightly fast, as shown by synchronizing light brilliance at 6 to 10 times per minute prior to closing the circuit breaker.  This will  assure  that  the  incoming  generator  supplies  power (kW) to the load at the time of breaker closure.  Load is then  added  to  the  incoming  generator  set  by  increasing the   setting   of   its   governor   control,   or   decreasing   the setting of the on-line generator set governor controls. Operating refinements to regulator adjustment are easily made on installations equipped with VAR meters, power factor  meters,  or  wattmeters  and  line  ammeters.    (If  the system  includes  only  ammeters,  regulator  adjustments must  be  made  with  a  single  unit  on  the  line.)  Where power   factor   or   VAR   meters   show   equal   indications, each generator is supplying its share of the load current reactive    amperes,    and    circulating    current    between generators is at a minimum.  Example: load power factor is  0.8.    Generator  No.    1  indicates  0.7  P.F.    Generator No.  2 indicates 0.85 P.F.  These meter readings tell the operator  that  Generator  No.    1  is  supplying  too  much magnetizing    current    to    the    load,    and    possibly    to Generator No.  2.  The magnetizing current of Generator No.    1  can  be  reduced  simply  by   lowering  its  voltage level.      Or,   if   desired,   by   raising   the   voltage   level   of Generator  No.    2,  the  operating  power  factors  can  be equalized.  Circulating current is then at a minimum. Wattmeters  and  ammeters  can  provide  the  information necessary   to   accomplish   operating   or   on-line   voltage level adjustments. Example: Load kW 500, Load Line Amperes 750, Voltage 480 Generator No.  1, Load kW 250, Line Amperes 350 Generator No.  2, Load kW 250, Line Amperes 450 These  meter  readings  indicate  that  Generator  No.    2  is supplying  more  than  its  share  of  magnetizing  current. This  is  true  because  Generator  No.    1  is  operating  at  a power factor of 0.86 which is higher than the load power factor  of  0.80,  and  generator  No.    2  is  operating  at  a power  factor  of  0.67  which  is  lower  than  the  load  power factor.  Decreasing the voltage level setting of Generator No.    2  will  reduce  its  magnetizing  current  and  increase the   power   factor.      At   the   same   time   the   magnetizing current   from   Generator   No.      1   will   increase,   and   its power factor will decrease. When loads are not equal, the calculated power factor of each generator can be used 124