lamps are dark; then, while the lamps are still dark,
close the main circuit breaker and turn off the
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
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.
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
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
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
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
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
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.