appendix

Entering Loads
Definition of Terms
APPENDIX A
Rev. Jan 2011
Application Manual – Liquid Cooled Generator Sets
A minimum of 10 percent overload capability is available for prime power ratings per
engine rating standards BS 5514 and DIN 6271. Not every generator set configuration is
available for prime duty.
When generator sets are paralleled with a utility service for an extended period of time,
they should not be operated in excess of their base load rating. Generally the base load
rating of a generator set is significantly lower than its prime power rating. Base load
ratings for generator sets are available from the factory or your local Cummins Power
Generation distributor.
Voltage
Available voltage choices are a function of selected frequency. Default values are
277/480, Series Wye.
The next and most important step in sizing a generator set is identifying every type and
size of load the generator set will power. As with most operations in GenSize, the loads
can be entered either from the menu under Projects, Add New Load, or from the icons
located on the tool bar. After selecting a load type, the load entry form will appear. Each
load form will open with load characteristic defaults which can all be changed. Enter all of
the required information. If you are unsure what any of the items are, check the online
Help for an explanation. As each load is entered, they will appear in a list on the left side
of the screen under the project you are working on. Selecting (with a mouse click) one of
the loads in the list will display the load operating characteristics on the right of the
screen. Double clicking a load icon will open the load entry form for that load and you
can edit the load from here. The following is intended to help you understand load
parameters and the way they are calculated by GenSize.
Identify all of the different type and size loads the generator set will need to support. If
you have more than one load of a given size and type, you only need to enter it once,
unless you want each of the loads to carry a different description. The quantity of each
load can be set when you enter the load in the step starting sequence. As described later
in this section
Cummins Power Generation has researched the starting and running characteristics of
many of the common loads and have included defaults for these load characteristics in
GenSize. You can choose to use the defaults or, if you know the characteristics of your
load are different, change the load characteristic. If you have a load type other than what
is identified in GenSize, use a miscellaneous load to define the load starting and running
requirements.
Based on the load characteristics, GenSize calculates values for running kW (RkW),
running kVA (RkVA), starting kVA (SkVA), starting kW (SkW), starting power factor (SPF),
peak kVA (PkVA), peak kW (PkW), and running amps (RAmps). When non–linear loads
are present, it may be necessary to over–size the alternator, and GenSize calculates a
value for the alternator kW (AkW) for the load.
Note that when entering single–phase loads on a three–phase generator set, GenSize
assumes that all three phase loads will be balanced among the three phases. Therefore,
the single–phase loads are converted to an equivalent three–phase load for sizing
purposes. This results in the single–phase load current being distributed across the three
phases so the single–phase load current is divided by 1.73. When a single phase load is
entered for a three phase set application, the actual single phase current will be displayed
in the load entry form, but when the load is entered into a step (the step load is the
balanced load applied to the generator), the step load current is converted to the
equivalent three phase current.
The following abbreviations are used in GenSize for calculating individual load running
and starting requirements, step load requirements, and transient surge load
requirements. These abbreviations are used on load forms and reports in the application
and in the following discussion intended to document some of the calculations performed
in GenSize.
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