8
Technical Data TD00405018E
Effective August 2009
Generator Sizing Guide
EATON CORPORATION www.eaton.com
UPS - GENERATOR COMPATIBILITY
Passive (also referenced as standby or off-line) and Line-
Interactive
These technologies are most common for personal workstations and
point of sale applications. They are typically single phase equipment
with size ranges of 350 VA - 2000 VA for passive and 500 VA to 5000
VA for line-interactive.
Passive UPS’s are the simplest type. Under normal conditions AC
power passes straight through to the UPS load. When the input
power supply goes outside of specifications, the UPS transfers
the load from input power to the internal DC to AC power inverter.
Passive UPS’s do not correct for voltage or frequency deviations
under “normal” operation.
Line-interactive is similar to the passive technology except it has
circuitry that attempts to correct for standard voltage deviations.
Frequency deviations under “normal” power operation are not cor-
rected.
Equipment Notes:
These devices tend to be electrically / harmonically very noisy. A
single small UPS is not a significant concern, but applications with
multiple UPS’s can be problematic.
Passive UPS technology typically has normal tolerances of 10-25% on
voltage and 3 hertz on frequency. If the input source goes outside of
these tolerances, the UPS will switch onto the UPS battery source.
Some line-interactive units may have frequency tolerances factory set
to 0.5 hertz. These units will need to have their frequency tolerance
increased to a minimum of 2 hertz.
Generator Sizing Recommendation:
•
Limit the total UPS loading to 15% - 20% of the generator
capacity.
Double-Conversion
This technology is most common for critical load applications. Double-
conversion UPS’s constantly rectify AC to DC and then invert the DC
back into AC. This configuration results in an output that corrects for
voltage and frequency deviations.
There are single and three phase models covering small through large
applications. Most UPS applications larger than 5000 VA use double
conversion technology. This approach is also the preferred technology
for generator applications.
Equipment Notes:
Double-conversion UPS’s that are single phase or unfiltered three
phase models tend to create a significant level of electrical/ harmonic
noise. This is illustrated by harmonic current distortions that are great-
er than 35%. Minuteman UPS products could have current distortion
of 8%. When three phase models are supplied with harmonic filters
(current distortion less than 10%), this concern is no longer an issue.
Generator Sizing Recommendation:
•
Single phase models: Limit the total UPS loading to 25% of the
generator capacity.
•
Single phase Minuteman UPS models: Limit the total UPS
loading to 50% of the generator capacity.
•
Three phase models without filters (current distortion > 30%):
Limit the UPS loading to 35% of the generator capacity.
•
Three phase models with filters (current distortion < 10%):
Limit the UPS loading to 80% of the generator capacity.
Supplier(s) Passive (Standby) Line-Interactive Double-Conversion
Powerware 3000 series 5000 series 9000 series
Minuteman UPS Enspire Enterprise Plus Endeavor
APC Back-UPS Series Smart-UPS Series Symmetra Series
Liebert PowerSure PST & PSP PowerSure PSA & PSI UPStation & Nfinity
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