TM 5-6115-593-12 TO 35C2-3-463-1 lighting PARALLEL indicator lamp DS7 (K23 is held energized by self-latching contacts 5 and    6).    With    K23    energized,    power    is applied (through K23 contacts 9, 10, 11, and 12) from power transformers T101 and T102 to the frequency paralleling circuit K106, DS 101,  DS102,  and  K106  is  a  synchronizing check relay which only allows the AC power CKT BKR (CB2) to close to a dead bus or to a "synchronized" energized bus, SYNCHROSCOPE     M109.          K106     is     a synchronizing check relay which only allows the AC power CKT BKR (CB2) to close to a dead  bus  or  to  a  "synchronized"  energized bus. Power   transformer   T102   senses   the   bus voltage, and power transformer T101 senses the output of the incoming generator.   SYNC light DS101 is connected from the output terminal T101 to the output terminal    of    T102.        DS102    is    similarly connected   across   the   remaining   outputs. The greater the frequency difference of the generator    sets,    the    greater    the    voltage across the SYNC lights and the greater the rate of which they will blink on and off.  As the sets approach a zero frequency difference, the lights dim and finally extinguish. SYNCHROSCOPE M109 performs  essentially  the  same  function  and also   indicates   relative   frequency   between the   generators   to   be   paralleled.      When SYNCHROSCOPE M109 points to 12 O'clock,  the  generator  is  in  sync  with  the energized   buss.      If   the   droop   (regulation) characteristics   of   the   separate   generators involved  in  parallel  operation  are  different, their   ability   to   equally   share   the   load   is diminished.        To    compensate    for    these inherent   differences   in   droop,   REACTIVE LOAD  COMPENSATION  CONTROL  R104 allows   the   operator   to   offset   the   output voltage   of   a   particular   generator.      When connected   to   a   load,   this   generator   will droop   to   a   voltage   level   that   will   enable equal load sharing. Similar readings of each generator  set's  AMMETER  will  reflect  this equal load sharing. d. Generator   Faults.      As   a   means   of   either protecting the generator set and/or the load, various   fault-sensing   devices   have   been wired   into   the   AC   generator   and   control circuit.      All   of   the   generator   fault   circuit relays K32 through K36 and indicator lamps DS32     through     DS36,     respectively,     are selflatching, that is, they will stay energized even though the fault which caused them to operate  will  no  longer  manifest  itself  when the  main  contactors  open.  Therefore,  when a   fault   does   occur,   the   crew   should   note which   fault   indicator   lamp   is   lit   prior   to operating the ANNUNCIATOR RESET switch  S14.    Also  when  any  fault  occurs, alarm  horn  Al  will  sound  when  relay  K26 energizes   and   its   normally   open   contacts complete  the  24-volt  return  of  Al.    Current transformers    are    used    in    many    of    the generator fault sensing circuits.  The faults, how they are monitored, and how damage is prevented   are   described   in   the   following paragraphs: (1) Overvoltage    Protection.        If    engine speed  were  to  become  excessive  or voltage  regulator  VR101  malfunction, the   generator   output   voltage   might rise  to  a  level  harmful  to  either  the load, the generator, or engine controls.  To prevent this, overvoltage relay  K102  (connected  across  one  of the generator output windings) senses when   this   occurs,   and   activates   to initiate   the   following   sequence:   K32 energizes  (OVERVOLTAGE  indicator lamp   DS32   lights);   the   engine   fault circuit opens; fuel solenoid L1 deactivates (shutting down the engine);  and  K1  deenergizes  opening the   AC   POWER   CKT   BKR   (CB2) (disconnecting the load). (2) Undervoltage Protection. It is possible that voltage regulator VR101 could  malfunction  in  such  manner  as to   create   an   undervoltage   condition capable of damaging the load. Connected across one of the generator   output   windings,   relay   Kill senses if the output voltage becomes too 1-28