lamps are dark; then, while the lamps are still dark, close  the  main  circuit  breaker  and  turn  off  the synchronizing  switch. After the main breaker has been closed, check and adjust the load distribution by adjusting the governor speed  control.  Maintain  approximately  one-half  load on   the   master   machine   by   manually   adding   or removing the load from the slave machine(s). The master  machine  will  absorb  all  load  changes  and maintain   correct   frequency   unless   it   becomes overloaded or until its load is reduced to zero. The operator also must ensure that all generating sets operate at approximately the same power factor (PF). PF is a ratio, or percentage, relationship between watts (true power) of a load and the product of volts and amperes (apparent power) necessary to supply the load. PF is usually expressed as a percentage of 100. Inductive  reactance  in  a  circuit  lowers  the  PF  by causing the current to lag behind the voltage. Low PFs can be corrected by adding capacitor banks to the circuit. Since the inductive reactance cannot be changed at this  point,  the  voltage  control  rheostat  has  to  be adjusted on each generator to share the reactive load. This adjustment has a direct impact on the generator current,  thus  reducing  the  possibility  of  overheating the generator windings. Emergency Shutdown 3-10 PF adjustment was not discussed in the “Single Plant  Operation”  section  because  a  single  generator has to supply any true power and/or reactive load that may be in the circuit. The single generator must supply the correct voltage and frequency regardless of the power factor. INFINITE  BUS  OPERATION.—Paralleling generator sets to an infinite bus is similar to the isolated bus procedure with the exception that all sets will be slave machines. The infinite bus establishes the grid frequency; therefore,   the  governor  of  each  slave machine has to have speed droop to prevent constant load  changes. In the event of engine overspeed. high jacket water temperature, or low lubricating oil pressure, the engine may shut down automatically and disconnect from the main load by tripping the main circuit breaker. In addition, an indicator may light or an alarm may sound to indicate the cause of shutdown. After an emergency shutdown  and  before  the  engine  is  returned  to operation,   the   cause   of   shutdown   should   be investigated and corrected. NOTE: It is important to check the safety controls at regular  intervals  to  determine  that  they  are  in  good working  order. Basic Operating Precautions The  order  that  you  post  in  the  station  for  the guidance  of  the  watch  standers  should  include  a general list of operating rules and electrical safety precautions.  BE SURE YOU ENFORCE THEM! The important operating rules are relatively few and simple. They are as follows: 1.    Watch  the  switchboard  instruments.  They  show how  the  system  is  operating;  and  they  reveal  overloads, improper division of kilowatt load or reactive current between generators operating in parallel, and other abnormal operating conditions. 2.   Keep the frequency and voltage at their correct values. A variation from either will affect, to some extent  at  least,  the  operation  of  the  electrical  equipment of  the  base.  This  result  is  especially  true  of  such equipment as teletypewriters or electrical clocks. An electrical clock and an accurate mechanical clock should be installed together at the generating station so that the operators can keep the generators on frequency. 3. Use good judgment when reclosing circuit breakers after they have tripped automatically; for example, generally the cause should be investigated if the circuit breaker trips immediately after the first reclosure.  However,  reclosing  of  the  breaker  the  second time may be warranted if immediate restoration of power  is  necessary  and  there  was  no  excessive interrupting disturbance when the breaker tripped. It should be kept in mind, however, that repeated closing and tripping may damage the circuit breaker as well as the overload vault area, thus increasing the repair or replacement work. 4. Do not start a plant unless all its switches and breakers are open and all external resistance is in the exciter field circuit. 5.  Do  not  operate  generators  at  continuous overload. Record the magnitude and duration of the overload in the log; record any unusual conditions or temperatures observed. 6. Do not continue to operate a machine in which there is vibration until the cause is found and corrected. Record the cause in the log.