Dear Aidan,

 

Thank you for your Official Information Act request where you have
requested confirmation of any feasibility studies Transpower has
commissioned related to voltage upgrades to lower costs as opposed to
constructing new lines. We will respond to your request as soon as
possible and in any event by the statutory time limit of 28 March 2023.

 

If you have any queries please contact us on this email address.

 

 

Kind regards,

 

Transpower Official Information Act Team

 

 

Hello Aidan,

Do you have some time this afternoon for a quick discussion on your request? I'd like to ensure we are answering your question correctly.

Kind regards,
Vanessa

VANESSA HEAD (she/her)
General Management Advisor
Transpower New Zealand Ltd
Waikoukou, 22 Boulcott Street, Wellington, 6011, PO Box 1021
 
DDI: 04 590 8690
M: 021 347 997
www.transpower.co.nz 
 

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Dear Aidan,

Following up on my email below; you have requested the following information: Other utilities internationally have implemented voltage upgrades to existing lines with potentially lower costs and/or impacts than constructing new lines, along with potentially better usage of existing equipment. Could you confirm what feasibility studies transpower has commissioned or carried out in this area, or what reasons it has been found impractical for?

As currently framed, your request will be very difficult to answer due to its wide scope and the substantial collation required because it encapsulates a very high number of studies that could be classified as 'feasibility studies'. The current request may result in us refusing it (section 18(f) of the Official Information Act) or require a charge to supply it due to the complexity and volume of work required. We would like to avoid either of these options and are keen to assist you with providing information that is of value to you.

We will be better able to respond to your request if you clarify more exactly what information you require.

We understand the rationale for making maximum use of an existing asset before building new, and you have focused on voltage upgrades. Are you interested in just voltage upgrades? If so, over what time period are you interested in and would this be within a specific part of the country? We ask as we have also considered current upgrades we have undertaken where we increased the current-carrying ability as a more cost effective upgrade than increasing the voltage with required insulation replacement and other works.

Are you able to refine your request please?

We are very happy to discuss this with you further if you require.

Kind regards,
Vanessa

VANESSA HEAD (she/her)
General Management Advisor
Transpower New Zealand Ltd
Waikoukou, 22 Boulcott Street, Wellington, 6011, PO Box 1021

DDI: 04 590 8690
M: 021 347 997
www.transpower.co.nz

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Hello Aidan,

I'm following up on my email below, have you had a chance to consider this?

Kind regards,
Vanessa

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Hi Aidan,

Thank you for refining your questions, we are now collating the information in order to respond.

Kind regards,
Vanessa

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Hi Aidan,

Thank you again for refining your question, we are underway with collating the documents. Given the dates specified we are checking through older archives, and therefore I am confirming that we will respond to you at the latest by Wednesday, 19 April.

Kind regards,
Vanessa

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Kia ora Aidan,

 

On 8 March we received your OIA request regarding:

 

Other utilities internationally have implemented voltage upgrades to
existing lines with potentially lower costs and/or impacts than
constructing new lines, along with potentially better usage of existing
equipment. Could you confirm what feasibility studies transpower has
commissioned or carried out in this area, or what reasons it has been
found impractical for?

 

On 21 March this request was then refined:

 

I'd be particularly interested in the WUNI 220kV grid backbone. The
current long-term forecasts show the option of using the 400kV Brownhill
Rd line as essentially a standalone link with a bank of 220:400
transformers at either end. I was wondering if Transpower had considered
upgrading this and other lines to a lower voltage (perhaps 300-330kV)
allowing for a larger interconnection at that voltage, rather than a
single very-high-capacity link. Post 2010 documentation? I'd also like to
see any 'big-picture' information Transpower has showing which tower types
(e.g. single-circuit horizontally spaced, or the double-circuit pylons)
are best suited to an upgrade, if such a thing exists.

 

We have considered your request in two different parts; firstly on
feasibility studies applicable to the WUNI 220 kV backbone and secondly on
tower types.  

 

Feasibility studies applicable to WUNI 220 kV backbone

To respond to this query we have provided information relating to the
North Island Grid Upgrade Project (NIGUP).

 

Transpower’s major transmission voltages are 220 kV AC, 110 kV AC and 350
kV DC.

 

Transpower considered a range of transmission and non-transmission options
that included generation north of Auckland (for example, a Gas Turbine
near Helensville) when considering the future central North island to
Auckland transmission corridor and the capacity required.

 

The range of transmission options included various combinations of
upgrading the existing lines to higher capacity, installing more
conductors to raise the operating voltage, as well as the use of HVDC.  In
terms of raising the operating voltage, different voltages were considered
for both existing and new lines including 275kV-330kV-400kV and higher.
This was informed by earlier work that considered options between the
220kV, 330kV, 400kV and 500kV. When evaluated over their operating life
each has their own advantages and disadvantages from a technical,
economic, and construction perspective. These are summarised in the
various reports submitted to the then Electricity Commission (now
Electricity Authority and Commerce Commission ) for approval of the
project. Of the options considered the one with the lowest whole of life
cost was designing and constructing the BHL-WHN A at 400kV but operating
it at 220kV. This is because any option to raise the voltage from 220kV to
something higher requires the extra equipment such as transformers,
switchgear and longer insulator strings on towers, but the additional cost
is offset by the extra power transfer. At the time of evaluation and
construction the extra costs of 330kV and 400kV equipment were quite
similar but the amount of energy transferred was either a 50% more or 80%
more.

 

The documentation attached is from 2000 onwards, which is when the
investigation and analysis needed to be completed so that assets can be
constructed in time whilst managing all the uncertainty in terms of extra
demand coming online sooner but not getting to a point where we were
unable to take existing assets out of service for maintenance or
reconfigure while new ones are built. We expect there to be many reports
that contain information on the NIGUP so have provided these as the most
appropriately linked to your query, please let me know if you would like
to see any further reports.

 

For more recent information you may also be interested in the [1]2022
Transmission Planning Report, Chapter 6 contains a chapter on the Grid
Backbone and shares our views on the future.

 

Tower types

Regarding your second question; we don't have the 'big picture'
information as each of our lines are unique and the towers are site
specific so we cannot form a general view on the feasibility of voltage
upgrades without doing some high level assessments. For decisions around
line upgrades we assess it on a case by case basis which is informed by
engineering assessment and a high level cost benefit analysis. For
example; lines traverse relatively unique landscapes with different
topology, flat ground of Canterbury Plains, rugged hills through the King
Country. Each with different environmental factors such as high winds
around Wellington and snow in the south, views etc. Therefore to be as
cost effective as possible each line has its own ‘family’ of customed
structures (poles and towers). These start from generic designs but are
iterated based on their location and the loads applied to them to minimise
the amount of materials, maximise their ability to support the conductors
while trying to have as few as possible to minimise construction costs and
ongoing maintenance costs. When complete the family of towers is mostly
unique to the line and the topography it crosses and is confirmed and the
line and materials put out to tender. For that reason, although in theory
any structure can be upgraded, it depends on how much residual structural
capacity it has from the beginning of its life, which normally has been
tried to be minimised. This means we always look at upgrading and if the
required capacity is relatively small then the strengthening or tower
raising costs might be modest but if large capacity is required then it
may be cheaper to construct new.

 

Please let me know if you would like any further information or if you
would like to discuss directly any of the information we have provided
here.

 

Thanks

Vanessa

 

 

VANESSA HEAD (she/her)
General Management Advisor

Transpower New Zealand Ltd

Waikoukou, 22 Boulcott Street, Wellington, 6011, PO Box 1021

 

[2]www.transpower.co.nz 

 

 

References

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1. https://tpow-corp-production.s3.ap-south...
2. http://www.transpower.co.nz/