10
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 corrected.
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.
Minuteman UPS input tolerance is
closer to 10-36%. 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.
Minuteman UPS products are close to
5 Hertz and not 0.5 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 greater 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.
UPS - Generator Compatibility
Supplier(s)
Passive (Standby)
Line-Interactive
Double-Conversion
Minuteman UPS
Enspire
Enterprise Plus
Endeavor
APC
Back-UPS Series
Smart-UPS Series
Symmetra Series
Liebert
PowerSure PST & PSP
PowerSure PSA & PSI
UPStation & Nfinity
Powerware
3000 series
5000 series
9000 series
Note: Ferrups and Delta-Conversion UPS technologies not included in discussion
UPS Information
2 x kVA rating for a filtered system
3 – 5 x kVA rating for an unfiltered system
It is recommended you refer to the Honeywell UPS Generator Compatibility sheet
(Pg 10) and contact the manufacturer of the UPS system to assist in your installation.
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