UNDERGROUNDING
TRANSMISSION
LINES
IN
URBAN AREAS
APRIL 2013
CONTENTS
Page
01 1. The issue
02 Why do we need transmission lines?
02 Why were the lines erected over
built-up areas?
03 Can buildings still be erected under
high voltage lines?
03 What is the impact of overhead
transmission lines in urban areas?
04 How extensive is underbuild?
05 2. Undergrounding
08 But aren’t underground cables more
reliable, and cheaper to maintain?
08 Won’t these lines be replaced over
time anyway as they age?
08 Are there alternatives to
undergrounding?
10 How can undergrounding
(or relocation) of existing
lines be funded?
10Who are the beneficiaries?
11 3. Transpower’s view
12 Our current approach
13 The future
02
1.
THE
ISSUE
1.
THE ISSUE
We have some 400 km of overhead
transmission lines running through
built-up areas in New Zealand cities.
These are visually unattractive and
can constrain what landowners do
with the underlying land. So can
these existing lines be undergrounded?
If so, who should foot the bill?
2.
UNDERGROUNDING
3.
TRANSPOWER’S VIEW
01
1
Why do
we need
transmission
lines?
Transmission lines are an integral and essential part of
electricity supply. They are the system’s arteries.
Most of New Zealand’s electricity comes from power stations
located remote from our major cities. Much of our generation
is located in the South Island, but we use the most electricity
in the Upper North Island. Our high voltage transmission lines
carry it from the generation plants to major substations in,
and around, our cities. From there, local lines companies
(like Vector) distribute it to our businesses and houses.
Auckland, New Zealand’s major consumer, has nine Transpower
substations: smaller cities like Gisborne have just one.
Transmission lines in Auckland in 1963.
Why were the lines erected
over built-up areas?
With a few exceptions dating back decades, they weren’t!
However, over the years, cities have grown out and – in some
cases – under transmission lines which were built years before
over open land. This development under high voltage lines
is called ‘underbuild.’ The photos below show two examples.
The lines through South Auckland (below left) were built on
open farmland, and the city boundaries have grown out to
encompass them. The tower in Onehunga (below centre) was
constructed in the sea bed, before reclamation brought the city
out to meet it.
We do not build transmission lines over built-up areas. All new
transmission lines within urban areas are placed underground.
02
Residential
Commercial
Educational
Facilities
Cultural
Health
Public green areas
Can buildings still be erected
under high voltage lines?
Since the 1950s and 1960s, when the Government built many
of our transmission lines, the terms under which they occupy
private land have been defined by legislation (The Electricity
Act). This does not prevent underbuild.
Very recently, the Government has enacted the National Policy
Statement on Electricity Transmission, which is helping us work
with councils and developers to restrict further underbuild of
the older transmission lines.
1.
THE ISSUE
When we build an overhead line today, we buy easements
beneath the line to ensure inappropriate development
cannot occur.
Any existing dwellings are removed. So underbuild is not an
issue for our newer lines, like the 400 kV line recently completed
through the Waikato. For existing transmission lines, the new
legislation should prevent underbuild getting any worse.
2.
UNDERGROUNDING
What is the impact of overhead
transmission lines in urban areas?
Most people understand the need for transmission lines but,
understandably, nobody wants them in their neighbourhood.
For the landowner, they can restrict development. For the
neighbourhood, they usually aren’t viewed as a piece of art.
3.
As neighbourhood land values rise, these impacts increase.
TRANSPOWER’S VIEW
Undergrounding
a transmission
line costs
$5-15 million
a kilometre.
Underbuild also impacts Transpower. Overhead transmission
lines require ongoing maintenance. This requires ready access
to towers. Access problems caused by underbuild increase the
difficulty of regular maintenance, and can make major
maintenance, like replacing corroded conductors (wires),
extremely difficult, if it can be done safely at all.
Maintenance difficulties aside, we would prefer nobody lived
beneath our lines. While we operate and maintain them well
within international guidelines for electromagnetic fields,
residents still raise concerns. We understand that.
03
How extensive is underbuild?
The principal areas of underbuilt urban transmission lines are
shown on the map below. Key areas include the west and south
of Auckland, suburban Tauranga, and Christchurch, but there
are pockets across the country.
The absence of underbuild in some cities reflects, in part,
different topographies: Wellington City is surrounded by steep,
undeveloped hills, along which the transmission arteries run.
In contrast, in Auckland, all the lines must pass through the
narrow, fully developed isthmus.
The historic policies of local councils are also an influence.
Some councils controlled underbuild through their planning
processes, while others allowed development (despite counsel
against doing so).
PRINCIPAL AREAS OF UNDERBUILT TRANSMISSION LINES
Auckland
tauranga
Christchurch
04
2.
UNDERGROUNDING
1.
THE ISSUE
New lines are undergrounded within
urban areas – clearly, a solution is to
underground the existing ones too?
This is technically possible and
would resolve most landowners’ and
neighbourhoods’ concerns!
2.
UNDERGROUNDING
Unfortunately, undergrounding is very expensive. In fact,
it is prohibitively expensive on a widespread basis. As a rule
of thumb, undergrounding a transmission line costs $5 to
$15 million a kilometre. Overall, undergrounding our 400 km
of urban lines could cost around $4 billion.
3.
TRANSPOWER’S VIEW
To understand why it is so expensive, we need to do some
elementary engineering.
Two things are important – insulation and heat.
We insulate a transmission line so that the electricity won’t take
a short cut and jump to earth – and electrocute anyone in its
path (the electricity on our higher voltage lines will jump up to
2 metres through air, just as forked lightning will jump to earth).
Heat, on the other hand, is generated when we send electricity
along a conductor. Feel your extension cord after it has been
powering the vacuum cleaner for a while – it will be warm.
05
5
When a conductor is suspended high up on our overhead lines,
it is surrounded by air, which both insulates and cools it. So the
conductor can just be a bare wire, strung between insulators.
These bare wire conductors are usually made of aluminium.
When transmission lines are buried in the ground, they have
to be coated with insulation material (special plastics), in the
same way as your electrical wiring – and your extension cord
– is insulated in your house. As you can see from the diagram,
this specialized insulation is thick.
The cable
costs
about
$750/metre
– 50 times
more than
the bare wire
conductor.
Getting rid of the heat (to stop the cables overheating) is also a
major problem underground, as we don’t have the cooling effect
of air to carry the heat away like overhead conductors. So we use
more costly metals (usually copper) which don’t heat up so
much, and bigger conductors which generate less heat.
As a result, underground electricity cables, especially the very
high voltages ones that we need to use, are bigger, heavier and
more expensive than equivalent overhead wires.
UNDERGROUND CABLE AND OVERHEAD CONDUCTOR
15 cm
4 cm
The diagram shows equivalent underground cable and overhead
wire. The cable costs about $750/metre – up to 50 times more
than the bare wire conductor.
Underground cables do not, of course, need transmission towers
and other hardware, but the total equipment cost is still much
lower than for underground cable.
Further, the cost of laying high voltage underground cable is
high. High voltage cables have to be protected from accidental
damage – not least, so people don’t get hurt or killed. They must
also be located away from other services, like metal water pipes,
gas lines and telecommunication cables, because of the effects
of the high voltages and currents.
Usually, the roadway must be used: our two recent underground
circuits from Brownhill to Pakuranga in Auckland are an
example (see photo opposite). Each circuit consists of three
150 mm diameter power cables, which are laid in a 1 metre
wide, 2 metre deep trench – one trench for each circuit.
The trenches are then backfilled with special, heat conducting
cement, before the road is resurfaced.
06
Residential
Commercial
Educational
Facilities
Cultural
Health
TRENCH FOR BROWNHILL TO PAKURANGA CABLES
1.
THE ISSUE
Underground cables often need to be longer (and therefore
more costly) than overhead lines: the transmission line shown
below takes the direct route across the gully (as shown below),
while an underground cable would need to take a longer route.
2.
UNDERGROUNDING
TRANSMISSION LINE CROSSING A GULLY
3.
TRANSPOWER’S VIEW
On average, we plan on an underground line being at least ten
times more costly than the equivalent new overhead line.
07
But aren’t underground cables more
reliable, and cheaper to maintain?
Yes, cable failures are uncommon. But they do occur, and they
take a couple of weeks – or longer – to fix, which can mean
longer power outages for residents and businesses. For critical
lines, this risk means we may need another back-up
transmission line, adding to the cost!
Underground
cables are
neither
cheaper
nor more
reliable
long-term.
Overhead lines have more frequent faults, but we can fix them
very quickly. Cables are less susceptible to cyclones (and
lightning, in most cases), but can suffer long-term damage in
earthquakes, unlike overhead lines. On balance, an overhead
system can be more resilient over time.
High voltage underground cables don’t cost a lot to maintain
– but they don’t last forever, cannot be modified once laid,
and are very expensive to replace.
Overhead lines do need to be maintained regularly, including
painting the towers and renewing conductors. But, maintained
properly, they will last forever.
Overall, underground cables are neither cheaper nor more
reliable long-term.
Won’t these lines be replaced
over time anyway as they age?
No. Overhead lines are like the farmer’s wagon: many parts are
replaced over time, but the wagon lives on. Properly maintained,
they can last forever.
Very occasionally, older lines become redundant, often because
a bigger line is required to meet increased electricity demand.
Recently, an 8.2 kilometre long overhead line between
Pakuranga and Penrose (in Auckland) was taken down in this
way. But this is the exception.
Are there alternatives to undergrounding?
In some cases, yes. The line can be re-routed or redesigned
at a much lower cost.
The case study on the next page demonstrates a successful
project undertaken between Transpower and a developer.
The 107 hectare Highbrook subdivision in Auckland invested
$22.7 million to both move and underground existing lines a
decade ago. They used a combination of undergrounding and
innovative redesign and re-routing to achieve a striking
outcome. The redesigned overhead line is built higher than
normal, so that native trees can grow unencumbered below.
One issue is where the line can be moved to. Nobody but
the affected landowner is keen to see it moved closer to
their backyard.
08
SOME OF
THE LARGEST
MONOPOLES
IN NEW ZEALAND
In August 2005, Transpower and Highbrook Development Limited
entered into an agreement whereby Highbrook paid to underground,
or realign, existing transmission lines. This was to facilitate their
development of a high class business park on their land in East
Tamaki, while allowing Transpower to maintain the capacity of their
existing lines located on the site.
1.
THE ISSUE
The project involved cabling 2.6 km of the Otahuhu–Penrose A
and B 110 kV lines and realigning 2.6 km of the Otahuhu–Penrose
C 220 kV line onto nine steel monopoles. The new lines were
commissioned in May 2008. Redundant towers and conductors
were removed.
2.
UNDERGROUNDING
The monopoles are some of the largest 220 kV double circuit
monopoles installed in New Zealand. Pole 8 is the largest with a
height of 48 metres, a base diameter of just under 3 metres and
weighs just under 60 tonne. The monopoles were fabricated in
South East China. The average cost for an installed monopole at
Highbrook is approximately $540,000.
The monopole option was chosen due to cost; they are cheaper to
install than underground cable of equal capacity and Highbrook
considered monopoles to be less intrusive than a conventional
lattice tower.
3.
TRANSPOWER’S VIEW
09
The lines
have to run
somewhere,
just as
motorways, ports
and prisons (to
name just some
infrastructure)
affect a few
communities
to serve all.
How can undergrounding (or relocation)
of existing lines be funded?
This is the thorny question.
It is impossible to underground all of the existing urban
transmission lines. As noted, the bill would be around $4 billion,
and New Zealand simply does not have the wealth to fund that
– whoever picks up the bill.
But, if more lines in urban areas are undergrounded or moved,
who can or should share the cost?
The economist will say the beneficiary should bear the cost.
We’ll explore that more in a moment.
Others cite fairness: “why should I have all the towers in my
neighbourhood, when it is serving the leafy suburbs across the
city?” That is a completely understandable view, but not one that
helps us find a solution. The lines have to run somewhere, just
as motorways, ports and prisons (to name just some
infrastructure) affect a few communities to serve all.
Who are the beneficiaries?
Individual landowners benefit directly. The value of properties
hosting towers and lines increases if they are removed, due to
the removal of development restrictions.
A secondary benefit is the removal of the ‘stigma’ associated
with the lines for all landowners in their vicinity.
The community – the landowners, residents, retailers and
visitors – are also beneficiaries to the extent that the
neighbourhood is improved.
Transpower is sometimes a beneficiary through lower ongoing
costs. Unfortunately, this is usually only a small part of the
total cost.
10
Residential
Commercial
Educational
Facilities
Cultural
Health
Public green areas
3.
TRANSPOWER’S
VIEW
1.
THE ISSUE
We support undergrounding. Economics
aside, we would prefer not to be the
‘ugly duckling’ in a community. We will
always attempt to help those who
seek ways to lessen the impact of
overhead transmission lines. However,
we are rarely a material beneficiary of
undergrounding the lines.
2.
UNDERGROUNDING
The lines are operated well within international limits for
public safety; they are legally established (and in most
– not all – cases, were there before the current owner
purchased the property); and they have the right to remain
there indefinitely. Occasionally, we face significant one-time
expenditure to maintain an overhead line. Replacing
corroded wires – which might happen after 50 years – is an
example. Avoiding costs such as these by undergrounding
is a benefit, which we do contribute to offset the cost of the
undergrounding. However, even for the most difficult task
on the most difficult line, this avoided expenditure will only
be a small part of the cost for a new underground line.
3.
TRANSPOWER’S VIEW
11
Transpower’s income comes from electricity consumers
nationwide, through their monthly electricity bill. All of our costs
are subject to review by the Commerce Commission to ensure
we are achieving our goal of keeping these bills as low
as possible. If we spend money which is unnecessary, or for
which we cannot show a benefit to the electricity consumer,
we cannot include it in our charges.
Put simply, electricity users in, say, the South Island do not
expect to pay increased electricity bills for underground existing
lines in Auckland, when those existing lines are doing their job well.
Ultimately,
that is a
policy
decision for the
Government,
not Transpower,
and must
be prioritised
with other
public spending.
Were we to spend the money, the cost will fall to our owner
– the Government, and therefore the New Zealand taxpayer.
The effect is the same as the Government funding the
undergrounding directly.
Ultimately, that is a policy decision for the Government, not
Transpower, and must be prioritised with other public spending.
Our current approach
Our policy is to support and encourage undergrounding or
relocation of an overhead transmission line provided the
beneficiary meets the costs that cannot be justified by Transpower.
Over $40 million of undergrounding has been funded in this way
since 2000. Major examples are Highbrook (see earlier case
study) and the undergrounding of 2.4 kilometres of line to allow
development of the new Westgate development in Auckland
(see photo, below).
WESTGATE DEVELOPMENT – AUCKLAND
Almost exclusively, this undergrounding has been funded by
a single landowner developing a large block of land.
Undergrounding short sections of less than a kilometre or two
can seldom be justified by smaller landowners: the ‘fixed costs’
(including providing joints at each end of the cable) make small
projects very expensive. So it is really only a viable option for
large landholders.
For Transpower’s own projects and works, we have a policy
of undergrounding any new lines required in urban areas.
12
The benefits of
undergrounding
(or relocating)
a single line
is greatest
when it
is the only
line, and
when land
is being developed.
The future
Discrete undergrounding funded by landowners will continue.
From time to time, we will remove redundant lines. Neither will
address many of the existing underbuilt areas.
If a community really wants to underground existing transmission
lines through their community, who could foot the bill? If the
benefits do stack up for the community as a whole, one
candidate is the local authority. Perhaps there are situations
where this is appropriate, but the challenges in large cities like
Auckland are obvious: the competition from core infrastructure
needs, like transport and sewage, is high and councils face
tough choices about where they spend their money.
1.
THE ISSUE
We mentioned fairness earlier. We hear – and empathise with
– the argument that the Government should (directly or by
foregoing dividends from its investment in Transpower) fund part
of undergrounding since the overhead lines affecting individual
neighbourhoods are there for the greater good? That is a matter
of policy for Government, not Transpower, but we would be
remiss not to point out that this is not an argument unique to
existing urban transmission lines. What about the rural landowners
where transmission towers limit irrigation development? Or the
landowners near the major motorway from which the noise and
disturbance has grown over the years, or those near prisons, and
airports – and the list goes on.
2.
UNDERGROUNDING
Inevitably many of the mature and developed communities
most impacted are likely to be at the back of the queue in any
prioritisation. The benefits of undergrounding (or relocating)
a single line is greatest when it is the only line, and when land
is being developed.
3.
TRANSPOWER’S VIEW
With new lines being undergrounded in urban areas, and
with corridor management legislation in place to limit further
underbuild of overhead transmission lines, the problem is at
least not growing.
For existing underbuild, we are conscious we have not provided
a solution: there simply isn’t an easy one. But hopefully we have
left everybody better informed.
13
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