UFC 3 -520-01
June 10, 2002
13-4
UPS SYSTEMS .
13-4.1
Introduction.
13-4.1.1 UPS systems are intended to provide stable power and minimize the effects
of electric power supply disturbances and variations. Although momentary voltage
disturbances can often be accommodated by other design features such as voltage
regulators or ferroresonant transformers, longer duration disturbances beyond a
momentary duration will usually require some form of UPS system to ensure
uninterrupted power to critical loads.
13-4.1.2 A UPS syste m must be capable of providing a reliable, regulated, and filtered
source of uninterrupted power to critical loads. A properly selected UPS system will
provide continuous power to its loads throughout most disturbances encountered by the
power source.
13-4.1.3 For long duration outages, additional backup by an engine generator might be
required. The purpose of the engine generator is to provide ac power before the UPS
battery becomes depleted. An engine generator is not alone a suitable alternative to a
UPS system if uninterrupted power is a design requirement; a UPS system will still be
necessary.
13-4.1.4 Several industry standards are available to assist with the selection and
specification of UPS systems. The key standards include:
IEEE 241--provides a detailed overview of UPS design and application
considerations.
IEEE 446--provides detailed information regarding backup power systems, including
design considerations for UPS systems.
IEEE 944, IEEE Recommended Practice for the Application and Testi ng of
Uninterruptible Power Supplies for Power Generating Stations--covers application
criteria for UPS systems.
NEMA PE 1, Uninterruptible Power System --provides guidance regarding the
design of static UPS systems.
13-4.2
Selection and Performance.
13-4.2.1 Table 13-1 provides a summary of selected UPS designs. There is not
necessarily a single design that is ideal for all situations; each design has advantages
and disadvantages that require evaluation for the specific application. Also, evaluate
system cost as part of any design evaluation process. The double -conversion UPS
design provides the best isolation between the input and the output. The term Input
Power Quality in Table 13 -1 refers to how the UPS design affects the electrical system
13-7
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