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INDUSTRIAL GENERATOR SETS — APPLICATION & INSTALLATION MANUAL — REV. #4 (09/07/07) — PAGE 21
GENSET SIZING
Generator Set Sizing Calculations (Continued)
Step 5. Select a Generator Set
a. Establish the minimum size required
i. At this point the addition of future loads should be
considered. The RkW and RkVA values that were
highlighted or circled in Step 4 (previous page)
should be multiplied by a factor representing your
best judgement.
ii. Referring to the genset specification sheets, pick
the generator set model having a kW/kVA rating
that meets the highest RkW and RkVA totals
highlighted or circled in Step 4. Use the values
calculated for RkW and RkVA in sub-step i above if
the future addition of load was factored in.
iii. In addition to the specification sheet, the motor
starting curve should be referenced. Make sure to
take into account any derating factors such as high
altitudes or ambient temperature.
b. In applications where it is necessary to limit transient
voltage dip to approximately 10 to 20 percent of nominal
voltage, multiply the SkVA highlighted or circled in Step
4 by at least 1.25. Repeat the selection steps above.
A transient voltage dip of approximately 20 to 40% can
be expected when the genset selected is only slightly
greater than the maximum SkVA. The actual transient
voltage dip is a function of several factors and is difficult
to determine accurately.
c. In applications where GkW has been determined (Step
4) and where GkW is greater than the kW rating of the
generator set that has been selected, an alternator (AC
generator) must be picked for the set which has a kW
rating equal to or greater than GkW.
i. See the alternator data sheet for the alternator
temperature rise. Compare GkW to the alternator
kW rating at the appropriate voltage. The greater
the voltage, the greater the kW rating.
ii. If GkW is too high for the alternator selected to meet
the temperature rise specifications (if any), find the
alternator data sheet for the alternator specified for
the next lower temperature rise. Compare GkW to
the alternator kW rating at the appropriate voltage.
Repeat the procedure with any other models. If there
are no generator temperature rise specifications that
have to be met, consider comparing GkW to the
kW rating at the higher temperature rise rating of
125°C.
iii. If none of the alternators available for the generator
set has a kW rating sufficient to meet GkW, refer to
the specification sheet for the next larger size
generator set and repeat the selection process.
NOTE
The running load should not be
less then 30 percent of the
generator set rating.