appendix

Detailed Load
Calculations
APPENDIX A
Rev. Jan 2011
Application Manual – Liquid Cooled Generator Sets
• Effective Surge kW – the Cumulative Peak kW times a multiplier to account for the
reduced load effect due to sustained reduced output voltage during the transient
surge load.
• Effective Surge kVA – the Cumulative Peak kVA times a multiplier to account for the
reduced load effect due to sustained reduced output voltage during the transient
surge load.
The following documents all of the individual load requirements calculations. Load
running, starting and peak surge requirements are calculated for each load based on
assumed default operating characteristics as displayed on the individual load entry forms.
Light Load Calculations
Three different light load types can be entered:
Fluorescent – A low–pressure mercury type discharge lamp where most of the light is
emitted by an excited layer of fluorescent material. The same load characteristics are
used for ballast or electronic types. Both are non–linear loads, but GenSize ignores the
non–linearity for this load type since this is usually a small part of the total connected
load.
Incandescent – Standard bulb type lamp assemblies, which use a filament to create light.
Discharge (HID) – Lamps that produce light by passing a current through a metal vapor;
includes high pressure sodium, metal halide, and mercury vapor discharge lighting.
RkW If kVA entered: RkW = kVA x RPF
If Ramps entered: 1∅ RkW = (Ramps x voltage x RPF) ÷ 1000
3∅ RkW = (Ramps x voltage x RPF x 1.73) ÷ 1000
RkVA If RkW entered: RkVA = RkW ÷ RPF
If Ramps entered: 1∅ RkVA = (Ramps x voltage) ÷ 1000
3∅ RkVA = (Ramps x voltage x 1.73) ÷ 1000
RPF Running power factor as entered or default
SkW SkW = RkW for incandescence and florescence
SkW = 0.75 x RkW for HID
SkVA SkVA = SkW ÷ SPF
SPF SPF = RPF, except for HID where default SPF = 0.85
AkW AkW = RkW
Ramps 1∅ Ramps = (RkW x 1000) ÷ (voltage x RPF)
3∅ Ramps = (RkW x 1000) ÷ (voltage x RPF x 1.73)
Air Conditioner Load Calculations
GenSize simply converts tons to horsepower for sizing air conditioning loads at 2 HP/ton
as a conservative estimate of the total load for a lower efficiency unit. If you want a more
exact size and know the individual component motor loads in the A/C equipment, enter
them individually and come up with a demand factor for what loads are likely to start
simultaneously.
RkW RkW = AC Tons x 2 x 0.746
RkVA RkVA = RkW ÷ RPF
RPF Running power factor as entered or default from database
SkW High Inertia SkW = SkVA x SPF
Low Inertia SkW = SkVA x SPF x 0.6
SkVA SkVA = HP x (LRkVA/HP) x SkVA factor, where
LRkVA/HP is the average kVA/HP for the NEMA Code letter of the motor,
and SkVA factor is 1.0 for full voltage starting, or from reduced voltage
starting table (see Reduced Voltage Starting Method)
SPF As entered, or default values from database by HP and starting method
For loads that are designated to automatically cycle on and off:
A–9