Document Type:Technical Results
This Product is publicly available
Magnetic fields from power lines and other electrical facilities can
interfere with sensitive electronic equipment such as computer
monitors, electron microscopes, medical diagnostic and monitoring
equipment, and air traffic control displays. Appropriate shield design
to reduce magnetic field strength in an area of interest requires
identification of the sources, selection of proper shielding materials
and design and installation of the actual shield. This report takes the
reader step-by-step through this process.
BackgroundResearch on 60-Hz magnetic field shielding was originally started to
provide options for reducing magnetic field strength near electrical
facilities when health concerns arose. Recently, however, interference
issues between magnetic fields and sensitive electronic equipment have
become more prevalent. The concern over adverse health effects of 60-Hz
magnetic fields resulted in research to develop options that could be
used to reduce field strength adjacent to power lines and other
electrical facilities. One important area of this research dealt with
shielding with materials. Although much as been learned over the years
about shielding rooms and equipment from radio frequency
electromagnetic fields, little was known about how to design effective
shields for power frequency magnetic fields. Traditional methods for
shielding power frequency magnetic fields were both very expensive and,
in many cases, marginally effective. Research has shown that the only
widely used shielding material for 60-Hz magnetic fields was an
expensive, high-permeability steel-nickel alloy called mumetal.
ObjectiveTo prepare a practical guide for designing 60-Hz magnetic field shields
incorporating recent research results to aid engineers and technicians
assigned this task.
ApproachInvestigators took results of research on magnetic field shielding and
developed a practical guide for designing shielding structures. Four
basic ingredients were included: information on source identification,
data on material properties needed to design a proper shield,
analytical techniques and design calculations needed to specify shield
performance, and installation details and economic considerations.
Research showed that copper sheeting commonly used for roofing could be
used along with sheet steel to make an effective and economic shield.
Tests and experiments along with the design of several shields used in
actual practice formed the basis for this guide.
ResultsThis Guide represents the end result of extensive research that has
added new knowledge to our understanding of shielding mechanism and
material properties. Information on sources, instruments, material
properties, and design techniques are described. Researchers provide
examples of practical shield designs and methods for verifying shield
performance. Offering a new approach, the techniques documented in the
report for shielding 60-Hz magnetic fields represent a new branch of
electrical engineering not previously included in college courses or
text books. The research results, contrary to common belief, reveal
shields made from conductive materials such as copper and aluminum are
very effective in shielding 60-Hz magnetic fields from electric power
facilities. As to cost, overall results provide savings over previously
used shield construction.
EPRI PerspectiveProduction of this Magnetic Field Shielding Design Guide represents a
major accomplishment in EPRI's Magnetic Field Management efforts.
Techniques for evaluating edge effects, shield thickness, joints and
other important features of the shield are now available. The new
knowledge that has been gained from the research on shielding with
materials can now be used to produce both effective shields and
economic savings over traditional methods. This design guide should be
a valuable source of information for utility engineers when
electromagnetic interference problems arise.
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