Download Richard Turner Annexure E

EMF aspects of the
proposed Trustpower Waverley
wind farm 110 kV Transmission line
Report 2016/144
This report was prepared for:
Trustpower Ltd
Private Bag 12023
Tauranga Mail Centre
Tauranga 3143
Report prepared by: Martin Gledhill
Finalised: 10 February 2017
About EMF Services and the author of this report
EMF Services is a division of Monitoring and Advisory Services NZ Ltd (MAASNZ), and
provides professional measurement and advisory services related to possible health
effects of non-ionising radiation, including electromagnetic fields (EMFs), lasers and
ultraviolet radiation.
Martin Gledhill has an MA degree in Natural Sciences (Physics) from Cambridge University
and an MSc in Medical Physics from the University of Otago. He is a member of the
Australasian Radiation Protection Society and of the Bioelectromagnetics Society. Before
forming MAASNZ he was head of the non-ionising radiation section at the National
Radiation Laboratory of the New Zealand Ministry of Health. In this position he provided
advice to central and local government, the public and industry on the health effects of
EMFs, and carried out measurement and assessment services in this area. This work
included providing policy advice to the Ministries of Health and the Environment,
preparation of public information material, presenting expert evidence at local authority
and Environment Court hearings, and assessing exposures to EMFs by both measurements
and calculations.
EMF Services
P O Box 17
Clyde 9341
New Zealand
EMF aspects of proposed Trustpower Waverley wind farm 110 kV line
EMF Services report 2016/144
[email protected]
www.emfservices.co.nz
+64 27 545 4217
EMF aspects of the proposed
Trustpower Waverley wind farm
110 kV transmission line
1
Introduction and summary
This report discusses electric and magnetic field (EMF) aspects of the proposed 110 kV
transmission line which will carry electric power from the Waverley wind farm to the
Transpower Waverley substation. In particular it discusses the differences between a
100 MVA line (construction of which is permitted under the District Plan) and a 130 MVA
line, which requires a Resource Consent.
Electric and magnetic fields produced around the proposed line will be well below limits
recommended by the World Health Organisation and the New Zealand Ministry of Health.
The fact that the line has a capacity of 130 MVA rather than 100 MVA means that magnetic
fields are 30% higher than they would be for a 100 MVA line, but this makes no difference
to compliance of the line with the recommended limits. The difference in line capacity
makes no difference to the electric fields.
2
Qualifications and experience
I have an MA degree in Natural Sciences (Physics) from Cambridge University and an MSc
in Medical Physics from the University of Otago, and am a member of the Australasian
Radiation Protection Society and of the Bioelectromagnetics Society. Between 1990 and
2011 I worked at the National Radiation Laboratory of the New Zealand Ministry of
Health, where I was head of the non-ionising radiation section. In this position I provided
advice to central and local government, the public and industry on the health effects of
EMFs, and carried out measurement and assessment services in this area. This work
included providing policy advice to the Ministries of Health and the Environment,
preparation of public information material, presenting expert evidence at local authority
and Environment Court hearings, and assessing exposures to EMFs by both measurements
and calculations.
After the Ministry of Health divested itself of the National Radiation Laboratory in 2011, I
formed my own company to carry on providing similar services for a similar range of
clients (including the Ministry of Health). I regularly attend scientific meetings on the
health effects of EMFs and maintain an overview of the research literature in this area.
3
Electric and magnetic fields
The voltages and currents on electrical equipment or cables produce extremely low
frequency (ELF) electric and magnetic fields around them. ELF fields are found around
high voltage electricity transmission lines, low voltage electricity distribution lines, wiring
in the home, and electrical equipment and appliances.
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The strengths of these fields depend on a wide range of factors. For transmission lines,
one of the factors affecting the strength of the electric field depends is the voltage of the
line, while the magnetic field depends on the current it carries. The electric and magnetic
fields also depend on the spacing between the conductors, how they are arranged on the
poles, and the height of the conductors above the ground. The strengths of the fields
decrease rapidly with increasing distance from the line.
3.1
Electric fields
Electric fields present around transmission lines are readily shielded by trees and most
building materials. In addition, they are dependent only on the voltage of the line, but not
on the current it carries1. As the key difference between a 110 kV transmission line
carrying 100 MVA and 130 MVA is in the amount of current it is capable of carrying (the
voltage stays the same) electric fields will not be considered in any detail in this report.
3.2
Magnetic fields
Magnetic fields produced around a transmission line depend (all other things being equal)
on the current flowing through the line. The strength of the magnetic field (referred to as
the magnetic flux density) is proportional to the current. As a 130 MVA line is capable of
carrying 30% more current than a 100 MVA line, the highest magnetic field that might be
found around a 130 MVA line is 30% higher than the highest magnetic field found around
a 100 MVA line2 operating at the same voltage. 3
It is important to note, however, that while the voltage on a transmission line is constant
however much load it carries, the current varies in proportion to the load. Normally the
load, and hence the current, varies over the day and between seasons. With regard to this
particular line, the current will vary depending on how much power is being generated by
the wind turbines. This will obviously vary according to the wind conditions, and the
demand.
The graph below shows the magnetic field one metre above the ground, as a function of
distance from the line, when a 100 MVA and 130 MVA line carry their maximum current.
It assumes that the lowest conductor is at the minimum legal height of 6.5 m above the
ground4, and that the other two conductors are 1.814 and 3.628 m above it, as shown on
the drawing of a standard pole proposed for this line.
Strictly, there may be a very small increase in the electric field when a line carries higher current
because the temperature of the line may increase very slightly which results in it sagging a little
more. However, this should be taken into account at the design stage, so that the line never sags
below the minimum legal clearance distance set in the Electricity Regulations.
2 As discussed above in connection with electric fields, there may also be a very small effect related
to the greater sag of a line carrying a higher current.
3 Another factor which affects the strengths of magnetic fields found around a line is the spacing
and arrangement of the conductors on the support poles. For a given voltage of line, the spacing
and arrangement is not affected by the load carried by the line.
4 This is the minimum legal clearance in the road corridor, where there is a possibility of vehicles
passing underneath.
1
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Magnetic flux density (microtesla)
10
8
130 MVA
100 MVA
6
4
2
0
-50
-40
-30
-20
-10
0
10
20
30
40
50
Distance from point below conductors (m)
The plot shows the magnetic flux density, in units of microtesla, one metre above the
ground as a function of distance from a point directly beneath the conductors. (Distances
greater than zero are on one side of the line, distances less than zero are on the other
side.) The blue curve shows the magnetic flux density for a 100 MVA line carrying its
maximum current, and the red line the magnetic flux density for a 130 MVA line carrying
its maximum current.
In practice, magnetic field levels will almost always be lower than these values, as the line
would very rarely carry its maximum possible current. Based on the maximum capacity
and the anticipated annual electricity output, I estimate that the average magnetic field
below the line will be about 3.7 T.
In addition, the current design has the conductors at a greater height above the ground
than the minimum legal clearance. This will have the effect of reducing the magnetic flux
density.
4
Magnetic fields in relation to recommended limits
4.1
Recommended limits
The Ministry of Health recommends the use of exposure Guidelines published by the
International Commission on Non-Ionizing Radiation Protection (ICNIRP). ICNIRP is a
scientific body, recognised by the World Health Organisation (WHO) for its independence
and expertise in this area. Their Guidelines are based on a careful examination of the
research data on the health effects of exposure to ELF fields, and include margins for
safety. ICNIRP periodically reviews its Guidelines to take account of new research data.
The most recent revision was published in December 20105 and is largely based on a
comprehensive review of the relevant research data published by the WHO6. The
5
6
International Commission on Non-Ionizing Radiation Protection. Guidelines for limiting
exposure to time-varying electric and magnetic fields (1 Hz – 100 kHz). Health Physics, 99 (6),
818 – 836. Available at: www.icnirp.org.
WHO. Environmental health criteria 238. Extremely low frequency fields. WHO, Geneva, 2007.
Available for download at: www.who.int/peh-emf/publications/elf_ehc/en/index.html
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underlying basis for the Guidelines has remained unchanged for more than twenty years.
The ICNIRP guidelines have been adopted by a number of overseas health bodies.
A National Policy Statement on Electricity Transmission (NPSET) published in 2008 under
the Resource Management Act requires that planning provisions dealing with ELF fields be
based on the previous (1998) version of the ICNIRP Guidelines7 and subsequent revisions,
as well as recommendations in the WHO review. A National Environmental Standard
issued in 2009, which applies to changes to existing transmission lines and cables, also
references the 1998 ICNIRP guidelines8. It is expected that both the National Policy
Statement and the National Environmental Standard will be updated at some stage to refer
to the latest version of the ICNIRP Guidelines. While both these legal instruments strictly
apply only to transmission lines forming part of the national grid operated by Transpower,
it seems reasonable to take them into account when considering the construction of a
transmission line such as the one proposed by Trustpower.
At the frequency of 50 Hz used by mains electricity, the limits recommended in the 2010
ICNIRP Guidelines for continuous exposures of the public are 5 kilovolts per metre (kV/m)
for the electric field and 200 microtesla (T) for the magnetic field.
The highest magnetic field expected beneath the proposed line, when carrying the
maximum current, is 3.6 T. This is well below the recommended limit of 200 T.
I have not calculated the highest electric field expected near the line. Based on
measurements around over one hundred 100 kV and 220 kV transmission lines around
New Zealand, however, I would not expect the highest electric field to exceed 3 kV/m.
4.2
Minimising exposures
In addition to compliance with limits of the type recommended by ICNIRP, the WHO also
recommends taking low cost measures to reduce exposure when constructing new
electrical infrastructure. The Ministry of Health supports this recommendation, which has
effectively been taken up in the NPSET.
The reasoning behind this recommendation from the WHO and the Ministry of Health is
the existence of open questions with regard to childhood leukemia. Epidemiological
studies (ie population-based observational studies) find a weak but relatively consistent
association (correlation) between long term exposure to relatively strong low frequency
magnetic fields and childhood leukemia. On the other hand, it is also recognised that the
way these studies were carried out could have artificially contributed to this apparent
correlation. Laboratory studies under carefully controlled conditions do not suggest that
there could be any effect at these levels.
For those reasons, the WHO review concluded that the data did not justify implementing
more stringent exposure limits, but it was worth taking simple, low-cost measures to
reduce exposures where this was possible. These measures should not compromise the
health, social and economic benefits of electric power.
7
8
International Commission on Non-Ionizing Radiation Protection. Guidelines for limiting
exposure to time-varying electric, magnetic, and electromagnetic fields (up to 300 GHz). Health
Physics, 74 (4), 494 – 522. Available at: www.icnirp.org.
The limits for set for the public in the ICNIRP 1998 Guidelines and the National Environmental
Standard are 100 T for magnetic fields and 5 kV/m for the electric fields.
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The types of measures anticipated to reduce or avoid exposures are generally simple, and
could include, for example:



Where there are options for route selection, choosing the one which avoids or
reduces exposures, all other things being equal;
Arranging the conductors so as to maximise the self-cancellation of fields from the
individual phases (this is most effective for double circuit lines, rather than single
circuit lines of the type under consideration here);
Considering the possibility of preventing new housing or other developments
directly beneath a line.
In many situations, such measures might be taken anyway as they would bring other
advantages.
In the context of this proposal, I note that an objective in identifying a route was to locate
the transmission corridor in a manner that avoided dwellings, and either using existing
road and rail corridors or a 30 m wide transmission corridor. I also note that the
proposed pole design holds the conductors higher above the ground than the legal
minimum. Hence it appears as though a number of decisions taken for other reasons have
also resulted in helping reduce the magnitude of the EMFs.
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