appendix

Application Manual – Liquid Cooled Generator Sets
• The surge kVA exceeds generator set capacity. The surge kVA requirement is similar
to the surge kW requirement except that there is no derating for altitude or ambient
temperature. GenSize uses the greater of cumulative kVA and Peak kVA (if any) to
determine the load surge kVA requirement.
• The alternator kW required exceeds the alternator capacity, which may be derated for
altitude and ambient temperature by the project parameters. The altitude knee for
alternators, however, is 1000m (3280 ft) and the temperature knee 40° C (104° F).
Alternator kW will be derated 3% per 500m (1640 ft) of altitude above the knee and
3% per 5° C (9° F) of ambient temperature over the knee.
• The alternator kVA required exceeds alternator capacity, which can be derated by
altitude and temperature in the same way as the alternator kW.
• The total non–linear load requirement exceeds 25 percent of the total load requirement.
This will exclude shunt–excited generators where PMG excitation is not available.
The total non–linear load requirement is the sum of the Alternator kW values of
all of the non–linear loads.
• The calculated voltage and frequency dips exceed the limits set in the current project
parameters.
• Starting voltage dip is calculated using the higher of two values: dip based on the
maximum Step kW or on the maximum step kVA.
• Peak voltage dip is calculated only if loads in the project exhibit a running surge
(cyclic loads or loads like medical imaging that have a high peak power requirement
when they are operated.
• Frequency dip is calculated using the higher of two values: maximum Step kW or
Peak kW from loads which exhibit running surge.
• The message, “No generator set is available that meets your running load requirements”
usually means that something in the New Project Parameters has been
changed after having specified the running load. For instance, you will get the message
if you change from diesel to natural gas fuel or from no sound attenuation to
Quite Site and the running load you had specified exceeds the capacity of the largest
natural gas or Quite Site generator set available. It may also mean that your project
falls into a “gap” in the Cummins Power Generation product line. At this point, lowering
the minimum percent rated load in the project parameters could allow a recommended
set. If this is the case, contact your local Cummins Power Generation distributor
for help.
• The message, “No generator set is available which meets your frequency or voltage
dip requirements” generally means that the surge requirement of some load step is
forcing selection of such a large generator set that the steady state running load falls
below 30 percent of the generator set capacity. Since Cummins Power Generation
does not recommend running at less than 30 percent of rated capacity, no set can be
recommended. At this point, you may have several choices:
• Increase the allowable voltage or frequency dip.
• Reduce the minimum percent rated load to less than 30 percent.
• Apply loads in more steps to lower the individual step surge load.
• Provide reduced–voltage motor starting.
• Parallel generator sets.
• Add loads that do not have a high starting surge (lights, resistive loads, etc.).
A–20 APPENDIX A
Rev. Jan 2011