Kohler 14EKOZD Installation Manual page 71

Step Potential Cause
Fault: Bus Frequency Out of Spec
1 The generators which
are connected to the
paralleling bus are
overloaded
Fault: Failure to Synchronize
1 Varying load
requirements drive
generator frequency
unstable
2 Fuel variations or other
environmental factors
cause the generator
frequency regulation to
suffer
3 Different sized units or
units of different fuel
types
Fault: Generator Voltage Average Line to Line: High Warning
1 Metering calibration
issue
2 Voltage drop on
generator connection
leads
3 Attempting to operate a
generator in base-load
mode while it is
connected to a variable
load
Fault: Generator Voltage Average Line to Line: Low Warning
1 Metering calibration
issue
2 Attempting to operate a
generator in base-load
mode while it is
connected to a variable
load
TP-7045 3/18c
Explanation
When the generators which are supplying a
load are overloaded, their engine speed will
decrease, resulting in a decrease in output
voltage. Sometimes this decrease in output
voltage is sufficient to allow the generators
to recover.
Heavy variations in the load on a generator
will cause the speed of the generator to
vary significantly. It can be difficult to
synchronize with a generator with
continuously changing frequency.
When the frequency regulation is impeded
by atmospheric conditions or fuel quality,
the ability to synchronize may be affected.
Not only is the bus varying more than
normal, but it is more difficult for the
generator to control speed while synching.
The factory synchronizing gains were
calibrated for equal-sized units. The
response of a large unit to a small one is
slightly different than two small units. A diesel
generator has significantly better frequency
regulation than a natural gas generator.
All the generators on the paralleling bus
attempt to control to the same voltage. If
one has incorrect calibration, it may see
this voltage as a much higher level than the
other generators, resulting in a protective
relay trip.
If the generator is sourcing high current
through too small of output leads, the
voltage drop in these cables may require
the generator to run at an increased
voltage to supply the necessary current to
the paralleling bus.
The speed bias and voltage bias control
real and reactive load in base-load mode
against a source with a nearly constant
frequency and voltage (such as a utility
source). If the generator is disconnected
from the utility source, the speed and
voltage will deviate to either extreme of the
bias range, depending on the target load
and the actual load.
All the generators on the paralleling bus
attempt to control to the same voltage. If one
has incorrect calibration, it may see this
voltage as a much lower level than the other
generators, resulting in a protective relay trip.
The speed bias and voltage bias control
real and reactive load in base-load mode
against a source with a nearly constant
frequency and voltage (such as a utility
source). If the generator is disconnected
from the utility source, the speed and
voltage will deviate to either extreme of the
bias range, depending on the target load
and the actual load.
Troubleshooting
Verify the load requirements are met by a
single generator. If not, it may be
necessary to connect several low priority
loads to load shed outputs from the
paralleling generators to avoid overloading
a single generator.
Adjustment of synchronizing dwell time or
synchronizing gains may improve ability to
synchronize.
It may be necessary to adjust the
synchronizing gains.
It may be necessary to adjust the
synchronizing gains.
Verify the controller is measuring voltage
accurately. If not, re-calibrate it.
Install oversized connecting leads for the
generator to minimize voltage drop
between the generator and the paralleling
bus.
Install contacts in series with the base-load
mode input to the controller which are
disconnected when the utility source is
disconnected from the paralleling bus.
Verify the controller is measuring voltage
accurately. If not, re-calibrate it.
Install contacts in series with the base-load
mode input to the controller which are
disconnected when the utility source is
disconnected from the paralleling bus.
Section 9 Paralleling Generator Sets 71