
60 SEBU8088-06
Operation Section
Generator Operation
If derating for
the block load is required, refer to ISO
3046 Standards or SAE J1349 Standards. Also,
reference Engine Data Sheet, LEKX4066, “Loading
Transient Res
ponse” and Engine Data Sheet,
LEKX4067, “Block and Transient Response”.
Note: ISO sta
nds for International Standards
Organization.
Power Factor
The power fac
tor represents the efficiency of t he
load. Power factor is the ratio of apparent power
to total power. The power factor is expressed as a
decimal. The
power factor represents that portion of
the current which is doing useful work. The portion of
current which is not doing useful work is absorbed
in maintain
ing the magnetic field in motors or other
devices.
In most appl
ications, electric motors and transformers
determine the power factor of the system. Induction
motors usually have a 0.8 or smaller power factor.
Incandesc
ent lighting is a resistive load of about 1.0
power factor, or unity.
The power f
actor of a system may be determined by
a power factor meter or by calculations. Determine
the power requirement in kW by multiplying the power
factor by
thekVAthatissuppliedtothesystem.As
the power factor increases, the total current supplied
to a constant power demand will decrease. For
example,
a 100 kW load at a 0.8 power factor will
draw more current than a 100 kW load at 0.9 power
factor. High power factor will result in full engine load
at less t
han the rated amperage of the generator.
A lower power factor increases the possibility of
overloading the generator.
Note: Caterpillar generators are designed for a 0.8
power factor unless otherwise specifi ed.
Excitation Systems
Self-E xcited G enerators
Self-ex
cited (SE) generators receive power for
excitation and voltage sensing for the regulator from
the output of the main armature of the generator.
The vol
tage regulator senses the generator output
voltage. The voltage regulator provides the regulated
output to the exciter of the generator. The exciter
then p
rovides power to the main rotating field. As the
main field rotates, a voltage is induced into the main
armature. This voltage is a generator output voltage.
Note: The main armature is also called the stator.
Themainrotatingfield is also called the rotor.
Permanent Magn
et Pilot Excited
Generators
Permanent Mag
net Pilot Excited (PMPE) generators
receive power for the voltage regulator from a pilot
exciter, rather than the main armature. The pilot
exciter cons
ists of a permanent magnet rotor and a
permanent magnet stator. The pilot exciter operates
independently from the generator output voltage.
Constant exc
itation during a large load application
is possible because the irregularities that occur in
generator output voltage are not fed back into the
exciter. Su
ch irregularities can be caused by load
conditions. The independent operation also allows
the generator to better sustain an overload for a
short durat
ion. The pilot exciter also ensures that the
generator will start properly even if the rotating field
becomes completely demagnetized.
Low Idle Adjustm ent
Generator sets normally have a higher low idle
setting than industrial engines. Low idle will be
approxima
tely 66% of the full load speed of 60 Hz
units. Low idle will be approximately 80% of the full
load speed of 50 Hz units.
There is no low idle stop on generator sets with
electronic governors. On generator sets with
mechanic
al governors and natural gas generator
sets, the low idle is set at the factory. The low idle
should only be adjusted by your Caterpillar dealer
if adjust
ment is required.
Note: Operating the generator set at low idle speed
for an ex
tended time will cause some voltage
regulators to shut off. The generator set must be
completely shut down. Then, the generator set must
be resta
rted. This will allow the voltage regulator to
again produce an output.
Standby Generator S ets
Most st
andby units are installed with controls that
will start the unit automatically. Standby units start,
pick up the load, run, and stop without an operator
in atte
ndance.
Standby units can not change the governor (speed)
contro
l, or change the voltage level settings
automatically. The governor speed and voltage level
must be preset for the proper operation of the standby
unit.
Whenever the set is operated manually, be
sure that the governor speed and voltage levels are
correct for automatic operation. Check all switches
for th
e proper setting. The start select switch should
be in the AUTOMATIC position. Emergency Stop
Switches should be in RUN position.