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 Response” and Engine Data Sheet,
LEKX4067, “Block and Transient Response”.
Note: ISO stands for International Standards
Organization.
Power Factor
The power factor represents the efficiency of the
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
maintaining the magnetic field in motors or other
devices.
In most applications, electric motors and
transformers determine the power factor of the
system. Induction motors usually have a 0.8 or
smaller power factor. Incandescent lighting is a
resistive load of about 1.0 power factor, or unity.
The power factor 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 the kVA that is supplied to the
system. 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 than 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 specified.
Excitation Systems
Self-Excited Generators
Self-excited (SE) generators receive power for
excitation and voltage sensing for the regulator from
the output of the main armature of the generator. The
voltage regulator senses the generator output
voltage. The voltage regulator provides the regulated
output to the exciter of the generator. The exciter
then provides 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.
The main rotating field is also called the rotor.
Permanent Magnet Pilot Excited
Generators
Permanent Magnet Pilot Excited (PMPE) generators
receive power for the voltage regulator from a pilot
exciter, rather than the main armature. The pilot
exciter consists of a permanent magnet rotor and a
permanent magnet stator. The pilot exciter operates
independently from the generator output voltage.
Constant excitation during a large load application is
possible because the irregularities that occur in
generator output voltage are not fed back into the
exciter. Such irregularities can be caused by load
conditions. The independent operation also allows
the generator to better sustain an overload for a short
duration. The pilot exciter also ensures that the
generator will start properly even if the rotating field
becomes completely demagnetized.
Low Idle Adjustment
Generator sets normally have a higher low idle
setting than industrial engines. Low idle will be
approximately 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
mechanical 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
adjustment is required.
Note: Operating the generator set at low idle speed
for an extended time will cause some voltage
regulators to shut off. The generator set must be
completely shut down. Then, the generator set must
be restarted. This will allow the voltage regulator to
again produce an output.
Standby Generator Sets
Most standby 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
attendance.
94
SEBU7125-13
Operation Section
Generator Operation
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