UFC 3 -520-01
June 10, 2002
on the input. For example, the double -conversion type tends to reflect harmonic
distortion back to the source.
Table 13-1. Performance of Selected UPS Designs
Input
Power
Disturbance
Dynamic
Energy
UPS Type
Power
Suppression
Response
Efficiency
Quality
Off-line
Fair
Fair
Fair
Excellent
Excellent
Double-Conversion
Excellent
Excellent
Excellent
Fair
Fair
Line- Interactive
Very Good
Fair
Excellent
Very Good
Very Good
Rotary
Good
Good
Fair
Excellent
Fair
13-4.2.2 The UPS selection process also depend s on the types of loads to be
supplied. As part of the UPS selection process, categorize the types of critical loads as
follows:
Loads that cannot withstand a sustained loss of voltage.
Loads that cannot withstand voltage or frequency fluctuations beyond specified
limits.
Loads that cannot withstand harmonic distortion beyond specified tolerances.
13-4.2.3 UPS selection should also be based on past operating experience. Even
when two UPS system designs are based on the same technology, they might not be
equal. For example, some UPS systems are designed such that the batteries are
virtually inaccessible during operation. This sort of maintenance-proof design almost
guarantees a future UPS system failure; dead batteries will be detected only when the
system is needed.
13-4.3
Sizing.
13-4.3.1 Size the UPS to be large enough to power the total expected connected load
during normal and abnormal conditions. UPS systems are rated in kVA at a given
power factor. The UPS system loads will usually set the required system size. Obtain
the following load data:
Total continuous load.
Load power factor.
Short-duration or momentary loads that add to the continuous loads.
Inrush current requirements of the loads.
13-8
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