Kohler EKOZD Series Service page 259

94kW
Generator
(99kW rating)
Figure 14-5 Example System With Increased Critical
Load and Increase Priority 1 Load
Although the 99 kW generator is only producing
94 kW, this lies dangerously close to the maximum
capacity of the generator. Any sudden increases in
load may result in the generator being overloaded,
potentially causing the critical load to receive
voltage and frequency that are outside of normal
operating parameters.
The Generator Overloaded Percent for the
example system is set to the default (85%) while
the generator is actually producing 95% of its rated
capacity. At this difference, Load Management will
begin counting to shed priority 6.
Figure 14-6 Load Shed Timing Based on Generator
Output Power
(Generator Overload Percent = 85%,
Base Over Load Shed Time = 30 seconds)
TP-6953 7/19
35kW 21kW 8kW 3kW 10kW 12kW 5kW
Load
Critical Most Least
Shed
loads important important
Panel
non- Additional
critical non-critical critical
loads loads
Figure 14-6 indicates that at 95% of rated capacity,
Load Management will wait for 30 seconds before
shedding a priority. Because priority 6 is the first
priority to shed from a stable state, the shed timing
Load
is identical to what is indicated by Figure 14-6.
Shed
Panel
Shedding priority 6 decreases the load on the
generator by 5 kW, but it is still at 90% of rated
capacity. Figure 14-6 provides a time reference for
90% load at 120 seconds (2 minutes), but Load
non-
Management will accelerate the shed timing as the
loads
overload condition was already present and was
not cleared by priority 6 shedding. The acceleration
factor for overload shed is 0.4, hence priority 5 will
shed in 120 – (120* 0.40) = 72 seconds.
The generator output power will drop to 78 kW
(79% capacity) when priority 5 sheds, allowing
sufficient margin above the working load of the
generator that small increases/fluctuations in the
requirements of the load should be easily handled
by the generator.
Priorities 5 and 6 will not add again until the
generator output power drops below 55 kW for long
enough for the loads to add.
4. Underfrequency Shed. In order to maintain
acceptable power quality, loads must be shed if the
frequency of the generator dips, even if the
generator is not producing enough power to
indicate that it is overloaded and cause an overload
shed. This can occur if the engine has a dirty fuel
filter or air filter, the intake air temperature is
significantly warmer than the generator operating
temperature, the generator is located at a high
elevation, the fuel system has a restriction or
improperly sized lines, or the engine is damaged or
near end of life.
Even without a failure on the engine, the
Underfrequency Shed logic is active any time the
generator
Underfrequency Shed Level below the generator
nominal operating frequency. Depending on the
configuration of the engine, the Underfrequency
Shed timing may cause a priority to shed before the
Overload Shed timing.
frequency is less
Section 14 Load Management
than the
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