Sten Bohlin, Kjell Eriksson, Gunnar Flisberg
ABB Power Systems A.B
A more effective use of the world's considerable
potential of renewable energy resources is an alternative
to decrease pollution. Electrical transmission has
to be used since electric power must be transported.
It is not practical to store electric energy in
large quantities. Furthermore, the production place
is fixed for renewable energy resources such as hydro,
tidal and geothermal power. As production and consumption
places in most cases are separated, the only possibility
to make use of the power is to build transmission
lines. The use of more renewable energy resources
such as hydropower can be a powerful tool in the battle
for a better environment as it can reduce the green
house effect and man-made carbon dioxide and other
gases. The potential of renewable power resources
still not used is enormous.
From a technical point of view, a considerable amount
of power can be transported on ac. and dc. transmission
lines over very long distances. Also between areas
separated by long distances of water, the use of a
dc. system gives the possibility to transmit the energy
by submarine cables.
Environmental effects from transmission lines can
be found only close to the line. Biological effects
from electrical and magnetic fields around the line
have been intensively discussed during the last couple
Certain research studies show marginal adverse health
effects on human beings. Other studies do not confirm
these effects. Ongoing ambitious field studies in
Europe and North America will give further valuable
information in this area.
The active use of transmission to replace polluting
energy sources by renewable energy sources could eliminate,
in 10 to 15 years, about:
- 1500 million tonnes/year of CO2
- 5 million tonnes/year of NOX
- 15 million tonnes/year of SO2
Transmission of electric energy is the task of bringing
energy from one place to another, from the point of
generation to the point of consumption. Originally,
when electric energy was first used but not available
at the point of consumption and a distant generation
source could be used, a transmission line was built
to connect the two points. Many times the available
generation could produce more than the consumer needed
and more consumers were connected to the transmission.
Thereby the generation installation could be used
more efficiently. The capital spent on the generation
installation could be more efficiently utilized thus
giving a faster pay-off and a lower energy price to
1. Why transmission
Transmission of electric energy is still today a
means to carry out the above two tasks -- bringing
electric energy from distant generation and sharing
the electric energy between several consumers. To
fulfill these tasks the electrical intermeshed and
interconnected networks of today were developed, thereby
striving towards a maximum utilization of the
available generation sources and to provide a safe
supply to the consumers. As will be shown here transmission
could be used to improve also the environmental effects
of the electric energy production.
Running a generation source at high and stable load
not only gives the best economy in relation to the
resources invested but it also keeps the ambient impact
at a lower level, compared with several generation
sources of the same type operating at different load
levels at different times depending on the need of
their specific loads. These circumstances are particularly
valid for thermal generation stations which are more
economical and which produce lower ambient impact
if operating at a constant load.
One of the challenges arises when we try to supply
the electric energy required by the market at the
same time as we try to protect the environment. Global
warming or the greenhouse effect, is currently seen
as the most significant environmental issue now facing
us. Thermal power stations releasing man-made carbon
dioxide and other gases are increasing this effect.
On the other hand, available potential of renewable
resources such as hydro, wave, tidal and geothermal
power are still enormous. A typical weakness with
many of the best renewable power resources in the
world is chat they are located far from the load centre
and the transmission systems have to be expanded if
we want to use these sources.
I am not declaring that the use of available renewable
resources such as hydro and geothermal power together
with an expanded transmission system will solve all
environmental problems. A more intensive use of, e.g.
hydro power and long transmission will help to reduce
the greenhouse effect but may contribute to other
environmental effects of a local nature.
2. Characteristics of transmission
The type of transmission used depends on the type
of generation and distances involved. In the case
of thermal generation a "fuel transmission line" could
be an alternative to transmission of electric energy
and the generation could be closer to loads if this
gives other advantages in the specific case. As not
all consumers are located in the same place transmission
of electric energy is needed in almost all cases.
For hydro power the generation locations are fixed
and an electric transmission line is the only alternative.
Let us concentrate on transmission and take a look
at the type of system available. By transmission we
define today systems with voltages from 69 kV and
above. At lower voltages we use the terminology distribution.
Today's interconnected and meshed networks use threephase
alternating current, ac, with a frequency of 50 or
60 Hz as the commonly used technique taking advantage
of the easy use for transformation between voltage
levels. Direct voltage, HVDC, is used especially for
long transmission lines where it gives the advantage
of the same power level being transmitted to/on comparatively
small lines. This in turn results in lower losses
and economical advantages. But, HVDC can also b* used
for special applications when it is possible or difficult
to connect the two networks by an ac transmission,
e.g. for stability reasons.
The capacity of an 800 kV ac line is around 2000
14W and an anticipated figure for future 1200 kV lines
is 5000 MW. A realistic maximum distance for
an ac transmission is around 1200 km.
The most powerful HVDC transmission used today has
a capacity of around 3000 kW, but an increase by a
factor of 2 at least is within the existing technology.
There are no practical limitations of line length
for an HVDC overhead line.
Water crossings can be included and the existing
technique when using HVDC gives possibilities for
cable routes of several hundreds of kilometers.
The above characteristics of transmission lines
for transmission of electric energy means that there
is a possibility of using long transmission lines
to a larger extent than is the case today. Thereby
the proportion of the renewable and cleaner types
of generation of electricity is increased and reduces
the amount of generated green house effect gases.
Such bulk power transmissions over long distances
can be built at moderate cost. A transmission of 2000
MW over 1000 km would cost less than 1 cent/kWh.
3. Environmental advantages with transmission
An example of a replacement to cover additionally
needed energy or replacement of high-pollution sources
has been presented by the use of Norwegian hydro power
in Central Europe. Assuming that 15 TWh could be exported
from Norway per year this could reduce the pollution
in Central Europe by:
- 24 million tonnes of CO2
- 45,000 tonnes of NOx
- 110,000 tonnes of SO2
It has also been concluded that the transmission
across Skagerrak between Norway and Denmark in the
15 years it has been in operation has given a net
transmitted power of 31 TWh Norwegian hydro energy
to Denmark. The corresponding environmental results
for Denmark is a relief of pollution by 22.5 million
tonnes of CO2, 85,000 tonnes of NOx and 185,000 tonnes
4. Environmental effects of transmission lines
Environmental effects from transmission lines have
been reported and discussed and will shortly be referred
to here. It is obvious that an overhead line has visual
effects on the landscape which in many cases are unwanted
and the required right-of-way contributes to the deforestation.
Considerations have to be taken to avoid the most
sensitive areas from a visual point of view.
Environmental impact such as soil erosion in connection
with transmission lines is in most cases limited,
but can occur in particularly sensitive areas. The
risk of damage can be avoided if planning and working
methods in connection with line work have been arranged
in a proper manner. Another effective method to avoid
harmful influence is to use selective clearing of
the vegetation in the line area. Trees that can reach
tall dimensions will be cut but other vegetation in
the area can remain intact.
All other side effects from transmission lines are
basically due to the electric and magnetic fields
and the ionization emanating from the electric field.
Although concluded and ongoing investigations have
not proven that these effects can be damaging to humans,
they have caused public concern, and power companies
are finding it increasingly difficult to get permission
to build new overhead transmission lines.
The electric field is caused by the voltage applied
to the line and proportional to the voltage level.
The magnetic field is caused by and proportional to
the current actually passing through the line. Both
types of fields decrease rapidly with the distance
from the transmission line.
Not only transmission lines but also installations
in buildings and e.g. household appliances such as
vacuum cleaners, TV sets, electric stoves etc., generate
electric and magnetic fields of power frequency, 50
or 60 Hz. While the magnetic field from a transmission
line with two or more phases decreases with the square
of the distance, the field from a household appliance
decreases still more pronounced, approximately as
the cube of the distance.
The electric field close to the high voltage conductors
can give rise to corona causing ionization leading
to generation of ozone and oxides of nitrogen, possible
radio and TV interference, and audible noise.
Corona discharges generate small quantities of ozone
(O3) and oxides of nitrogen (NO and NO2). These gases
are also generated by many other sources such as industries
and traffic. The natural level of ozone can vary within
wide limits, e.g. concentrations in connection with
thunderstorms of 0.05-0.15 ppm have been measured.
Normal values outside polluted areas fall between
Investigations show that the highest value from
power lines occurring in practice can reach 0.001
ppm with the highest voltage levels and that no ozone
contributions to background levels could be measured
even from high voltage ac transmission lines
From an HVDC line corona, air molecules are separated
into positively charged ions, O2 and N2, and free
electrons. A small part of these positive and negative
ions are then converted to ozone and nitrogen gases.
In case of a wind, say laterally to the line, they
create a plume, which can still be detected a few
hundred metres from the line. According to investigations,
the total production of ozone over a year, as well
as the peak production, is less than for a corresponding
ac line. It is concluded that no effects could be
found. The production of nitrogen gases emanating
from HVDC transmission lines is so small, that it
cannot be distinguished from the ambient gas level.
Corona effects on transmission line conductors will
result in audible noise at high voltage levels. The
noise will increase under rain and smog conditions.
For ac lines and voltages above 400 kV noise levels
between 50-60 dB (A) at the edge of 'right of way'
can be inconvenient.
For dc lines different measurements indicate that
up to +/- 600 kV, the audible noise level 40 m from
the centerline will seldom go above 40 dB (A). Even
if the audible noise during very heavy rain can amount
to 50 dB (A) this effect is considered insignificant.
It is a widespread consensus that the electric field
effects cause no adverse health effects to human beings
The magnetic field and its effects and influence
on biological life has been debated since the beginning
of the 1980's. In 1979, a reputed American journal
published a report by a psychologist Wertheimer from
Denver, USA indicating a connection between childhood
cancer and high current distribution lines. A number
of epidemiological studies has then examined the association
of the risk for cancer to exposure of magnetic fields
from power lines.
In the absence of objective, and reliable measures
of exposure suitable for use in epidemiological studies,
indirect measures have generally been used. Such measures
included job titles for occupational exposures and
the configuration of and distance from overhead wiring
systems for residential exposures. These measures
have been criticized because they do not take into
account temporal variations, nor do they necessarily
reflect the extent or intensity of past exposures.
Also few of the published studies have addressed
'confounding factors" adequately, and the differing
end points and populations studied make it difficult
to draw general conclusions.
Thus from the epidemiological studies published
to date, it is very difficult to conclude if there
is a connection between the risk of human cancer and
the exposure to magnetic fields from electrical power
lines, installations and equipment.
As a consequence of the above weak indications a
number of research projects to try to find the physiological
mechanism for the possible connection between risk
of cancer and fields were carried out.
Within the research projects the effects of magnetic
fields on molecules, cells, tissues and animals have
been investigated in laboratory experiments. Individual
investigations have indicated increases in the frequency
of chromosome damage and deformation of embryos of
chicken, mice, rats etc. The effects seem to be limited
to certain windows both in frequency and amplitude
of the exciting magnetic field.
Another effect of magnetic fields that has been
indicated is the influence on secretion of pineal
melatonin hormone in the brain. Melatonin affects
the need of rest and sleep, perception etc. There
are some indications that low nighttime production
of melanin correlate with an increased frequency of
otherwise rare male breast cancer.
From the aggregate of studies that has so far been
presented, it is not possible to prove if there is
a health risk from magnetic fields of power frequency
or not. Neither has it been possible to establish
a physiological mechanism by which the influence of
magnetic field could pose health risks to human beings.
If 50-60 Hz magnetic field exposure poses health risks,
these risks seem to be small compared to many other
hazards of normal life.
While waiting for a clearer picture which could
explain the possible risks and alleviate the public
concern or establish reasonable limit values many
utilities have adopted the principle of prudent avoidance,
i.e. reduce the field exposure where the cost is low.
Today several ambitious investigations are underway
both on the epidemiological side and on the experimental
side. Thus it is hoped that a more clear picture will
emerge in a few years.
The environmental impact from HVDC transmissions
is quite different from ac transmissions. Reference
to results from ac investigations are therefore, in
general, not relevant for dc. The electromagnetic
dc field at earth level is basically determined by
the conductor configuration and its distance to the
earth surface. The field distribution will however,
also be influenced by the ion distribution in the
air. The ions are mainly produced by the corona at
the surface of the conductors, and the ion flow between
the conductors and the earth corresponds to a dc current
of less than 0,5 mA/m2 at earth level.
The magnetic dc field, measured at the earth level
under the conductor has for a line carrying 1000 A,
about half the magnitude as compared with the natural
earth magnetic field and decreases proportionally
to the distance from the conductors.
It is therefore a consensus among experts that there
is no reason to expect any harm due to the magnetic
field from dc lines.
The environmental effects from transmission lines
as shown in this paper are all local to the close
vicinity of the line route and do not contribute in
an additive way to global effects in the same way
as pollution of e.g. green house effect gases.
5, Use transmission to reduce pollution
By using transmission to a larger extent the type
of pollution improvement as described above for the
Norwegian - Central Europe transmission could be adopted
in practically all regions of the world. On the other
hand in industrial countries with mature transmission
systems, internal need for increased interconnection
should in many cases be possible to solve without
building new lines. Power flow on the existing lines
could be increased and better controlled than today
by use of already existing or emerging transmission
technologies. This includes upgrading of lines within
a certain ROW to considerably higher power levels.
Of the available global hydro energy potential,
roughly 15,000 TWh/year, only around 2000 TWh/year
is exploited, generating somewhat above 20% of the
installed electricity. The potential hydro energy
would then be sufficient to cover both to replace
the existing polluting electric energy sources and
provide for the necessary expansion in the world for
the next couple of decades. Probably it would not
be practically possible to eliminate all high pollution
generation and probably some of the available hydro
power is not feasible for various reasons such as
flooding of large areas or necessity to relocate large
populations. However, it would be possible to use
a considerably larger part of potential hydro resources.
One example is Central and Western Europe which
today have exploited almost all its hydro resources
but which could receive hydro power from Central Africa
and/or Eastern Soviet Union, two regions with abundant
amount of potential hydro power.
Even with a conservative approach it could be assumed
that another 2000 TWh/year of hydro power can be developed
to replace existing fossil generation if transmission
is more actively used thereby replacing more polluting
sources. The annual reduction in greenhouse effect
gases obtained through this conversion per year would
- 1500 million tonnes CO2
- 5 million tonnes NOX
- 15 million tonnes SO2
By such measures taking place during a 10-15 year
horizon, roughly one third of today's total pollution
by electrical generation can be eliminated.