considerations are important key factor in UPS selection.
Efficiency and reliability often depend on the type of unit, the
load, and the environment. The higher a unit's efficiency, the
lower the operating cost. The type of load being protected is an
important consideration, too. Microprocessor-based equipment may
require a different type of UPS unit than other loads. For
example, switching power supplies, found in most computers,
react differently to certain types of UPS systems. Today's
UPS units should be capable of supplying non-linear type loads
without derating or degradation in total harmonic distortion
(THD). Load size determines what size UPS is needed. Systems
usually are sized in kilovolt-ampere ratings. Before selecting
UPS capacity, a profile of critical electrical loads should be
computed, listing the power requirements of each piece of
equipment to be protected.
UPS manufacturers also recommend allowing for a 25 to 30 percent
future expansion factor. Systems generally are available in both
single-phase and three-phase models to suit the application.
Consideration should be placed on the application of the UPS.
Computer-room UPS components are more densely packaged to create
a smaller footprint. Many times, isolation transformers are
removed from the front end of a computer type UPS
rectifier/battery charger. Although this usually is acceptable
in most office/computer-room environments, it can be a problem
in an industrial facility due to the presence of large equipment
that may cause disturbances during starting. Noise emitted by an
UPS can be a factor, depending on the surrounding environment.
In most cases, UPSs placed in computer centers, control rooms,
or office-type environments need to operate as quietly as
possible. Noise levels vary according to the type of system. UPS
manufacturers' specifications generally include noise-level
questions must be asked about the UPS manufacturer's service
capabilities; depending on how critical your computers are for
day-to-day and hour-to-hour business, depot repair services and
express delivery of replacement UPSs may not be enough. A
manufacturer who has 7-day-a-week, around the clock dispatch
capabilities, and offers on-site support by factory-trained
service specialists, can prove invaluable, particularly in
emergency situations. A mature service organization also speaks
to a UPS manufacturer's understanding of the need for systems
availability and commitment to deliver highest levels of
US Army Corp of Engineers
- National Power Corporation
- Tri-State Generation and Transmission Association, Inc.
- The cartoon is from Ron Leishman