Electromagnetic Fields Modeling Using GIS
Kent W. K. Lam,Sandra Z. W. Au
Department of Land Surveying and Geo-Informatics
The Hong Kong Polytechnic University,HungHorn, Kowloon,Hong Kong
email : lskent@polyu.edu.hk
Abstract
Overhead transmission lines emit both electric and magnetic fields and they are called the
extremely-low-frequency electromagnetic fields (ELF-EMF). Some researches believed that
these fields would induce biological effects in human. However, research results are still
inconclusive and further investigations are required before a definite conclusion can be drawn.
However, it is important to have some measurement on the ELF-EMF of the environment for
precaution. Following The International Radiation Protection Association and The International
Non-Ionizing Radiation Committee (IRPA/INIRC) Guidelines, a prototype system is set up using
GIS software. Equivalent charges’ method is used to determine the strength of the radiation in
the area nearby the overhead transmission lines. The results are overlaid with the zoning map.
Areas with radiation higher than the values suggested in the guidelines are identified. Results are
conclusive with the Electricity Networks Ordinance in Hong Kong.
Introduction
Hong Kong’s population has recently reached a record high of more than six million. As the
growing rate is not going to decrease after 1997, the population density will become higher and
higher. As a result, it is becoming more difficult for engineers and planners to plan the route of
overhead power transmission systems to supply power for various newly developed districts in
Hong Kong. Recently, there was a dispute between a power supply company and a group of
village people. They complained that the overhead power transmission system under
construction is too close to their village which would affect their health and their property value.
Environmentalists suggest that power transmission system is a very serious and the dominant
source of ELF-EMF radiation to humans and the environment. Some districts in Hong Kong, the
overhead power lines are very near to the residential areas. Some epidemiological studies have
suggested that a link may exist between exposure to power-frequency electric and magnetic
fields (EMFs) and certain types of cancer, primarily leukemia and brain cancer. Other studies
have found no such link. Currently, laboratory researchers are still studying how such an
association is biologically possible. At this point, there is no scientific consensus about this issue.
A national EMF research effort is under way, and major study results are expected in the coming
few years.
With the increase in public awareness of the possible biological effects caused by radiation from
overhead power transmission systems, the Electrical and Mechanical Service Department
(EMSD) in Hong Kong is now starting to analyze the emission of ELF-EMF from the power
230.lines and towers in urban areas. Besides, Hong Kong Advisory Environmental Council also
formed a working group on EMFs to observe and respond to the changes and update of the
results from the International Radiation Protection Association (IRPA) and other countries.
With the availability of digital base map data in Hong Kong, a prototype system is set up to
examine the possibility of using Geographic Information System (GIS) to facility the route
planning of power transmission systems. The system is developed based on the guidelines
produced by the International Radiation Protection Association and the International Non-Ionizing
Radiation Committee (IRPA/INIPC). Modeling the ELF-EMF emission would be done
by the incorporation of GIS in this project. The ELF-EMF emission model will be incorporated
in a GIS and results are presented in 2.5-dimension. ELF-EMF radiation from an overhead power
transmission system is analyzed together with land use and building coverages to identifj
residential areas which might be in danger and allow to claim for compensation.
Characteristics of Extremely-Low-Frequency Electromagnetic Field
(ELF-EMF) From Overhead Power Lines
Biological and environmental effects caused by the extremely-low-frequency electromagnetic
field (ELF-EMF) have been under investigation for the last twenty years (Goodland, 1973, Smith
and Best, 1989, Carpenter and Ayrapetyan, 1994, Ueno, 1995). There is still no scientific
consensus about this issue. The first mention of a possible association between ELF-EMF and
cancer was published in Russia during 1970 (Wertheimer and Leeper, 1979). High correlation
was detected between “high-current configurations”, i.e. proximity of houses to ELF-EMF
sources such as transmission lines, transformers and large size wires, with cancer, especially
childhood cancer (Ahlbom et al, 1987). Laboratory studies conducted by the National Institute
of Environmental Health Sciences and U.S. Department of Energy in 1995 suggest that there
may be a link between exposure to power-frequency electric and magnetic fields and certain
types of cancer, primarily leukemia and brain cancer. However, other studies find that such link
does not exist. Over the past few decades, many studies were conducted to examine the possible
health effects from EMFs and they oflen produced conflicting results. A number of independent
and authoritative review panels have found no concrete scientific evidence that there is a health
hazard from EMFs.
Electromagnetic fields (EMFs) are a compound of two different kinds of fields : electric fields
and magnetic fields. Normally, these two fields occur simultaneously anywhere electricity is in
use. These two fields are usually analyzed separately. Electric field refers to the electrical
charge surrounding a charged object and a measure of the electric force a charged object exerts
on other objects in the region. Electric field is described with the symbol E, a vector, in units of
volts per meter (V/m). Magnetic field refers to an object’s magnetic force which a moving
electric charge produces on other moving objects. Magnetic field can be described with either
symbol H, a vector, in units of ampere per meter (A/m) or magnetic flux density with the symbol
B, a vector in units of Tesla (T) as used by the EMFs researchers.
ELF-EMF radiation exists in the range of 30 Hz to 300 Hz in the electromagnetic spectrum and
is classified in the non-ionizing radiation range. The ELF-EMF radiation from overhead power
lines has a wavelength of 5000 km and a frequency of 50 Hz. At the very low frequency range of
231.the spectrum, slowly changing electric and magnetic fields can be treated as if they are static or
no change. In addition, a power frequency field with a wavelength of more than 5000 km has a
very low energy level that does not cause heating or ionization. However, alternative current
(AC) fields do create weak electric currents in conduction objects, including humans and
animals. This is the reason why there is a potential for EMFs to cause biological effects.
One of the major factors which affect the magnitude of ELF-EMF emitted from overhead power
lines is the distance separation between a point of interest and the power lines. This is the factor
which should be modeled in a GIS together with the use of a proper ELF-EMF emission model.
