UFC 3 -520-01
June 10, 2002
application. Reactors use energy or consume power in proportion to their impedance,
and will decrease overall efficiency because of these added losses.
12-5.5.2.3 The filter design depends on the equipment and where it is installed. If the
equipment is changed, the filter might no longer be effective for its intended purpose.
Also, the filtering characteristics are strongly influenced by the source impedance, which
is not always known accurately and varies with the system configuration. For this
reason, filters should be carefully selected for the application and location. Filters can
be relatively expensive on a per-kVA basis and they can cause more problems than
they solve if they are applied improperly.
12-5.5.2.4 The filters described in this section are called passive filters. Active filters
have been developed that act as current sources to nonlinear inductive loads to cancel
current harmonics. These products are still new to the market and require professional
design assistance in their selection and application.
12-5.5.3 Shielded Isolation Transformers. Shielded isolation transformers provide a
filtering function by separating the harmonic frequencies between the source and the
load. These transformers can be used for retrofit applications to address existing facility
problems, but should not be arbitrarily used in new facilities because of the high per-
kVA cost.
12-5.5.4 K-Factor Transformers. Transformers are available for high harmonic-
content power distribution systems without derating, often referred to as k-factor
transformer selection.
12-5.5.5 Phase Shifting Transformers. Phase shifting transformers are intended to
cancel harmonic currents produced by nonlinear loads. These transformers can be
used for retrofit applications to address existing facility problems, but should not be
arbitrarily used in new facilities because of the high per-kVA cost.
12-5.5.6 UPS Systems. UPS systems provide protection from many power quality
problems. Refer to Chapter 13 for additional information regarding UPS design
considerations.
12-5.5.7 Power Conditioners. Power conditioners are available in a variety of
designs. As the name implies, these devices pro vide a power conditioning function to
achieve a pre-defined result. The design of each type of power conditioner varies and a
detailed evaluation of equipment specifications is necessary to ensure that the desired
result will be achieved.
12-5.5.8 Grounding. Grounding is not necessarily a power quality design feature.
However, many power quality problems can be traced back to poor wiring and
grounding practices. For this reason, any power quality evaluation must consider the
grounding system design.
12-7
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