Schedule of the nominal capacity of the HVDC link over time from the beginning to the current day.
Nicky McLean made this Official Information request to Transpower New Zealand Limited
The request was partially successful.
From: Nicky McLean
Dear Transpower New Zealand Limited,
The link started in 1965 as 300MW via ±250KV and 1,200 amps, for both pole 1 and pole 2. Then there came adjustment to the mercury valves, allowing a different voltage and current capacity (270KV and 2,000 amps, though 1,600 amps was the preferred upper bound), then the introduction of southward power flow (with its own capacity), then operational constraints due to a Cook Strait cable failure, etc. then repairs, then pole 1 was stood down "indefinitely", then it wasn't, then some mercury valves were removed and others replaced by silicon-based thyristors and a new voltage and current capacity allowed except that was not for both poles, and later was (?), and it is all confusing since PR releases reported in the news media are rarely specific, and alas, I haven't kept a folder full of clippings over the years.
So, I am requesting a schedule of the nominal capacities as they varied over time, both for pole 1 and pole 2, both northwards and southwards, and regarding "pole 3" as being the new name for pole 1. This would be with specific dates (not just "in 1965") and specific voltages/currents/capacities, made more complex by changes to the capacity of the undersea cables and the use of the "ground return" should one pole (which?) be unavailable for an extended period. Planned outages for maintenance, etc. would be included, but not half-hourly data on actual usage. This is for nominal capacities as the link's abilities are changed from time to time.
To reduce puzzlement, is it the case that the switches selecting a Cook Strait cable for pole 1 and for pole 2 at each end of the undersea cables are used always to maintain parity over the whole link, or can the parity be swapped? That is, suppose one faces north from Benmore and finds pole 1 on the left of the power pylons and pole 2 on the right (which is it?), will this parity be the same on arrival at Haywards? This is particularly relevant when the poles are operated at different voltages.
Yours faithfully,
Nicky McLean
From: Lisa Holland
Transpower New Zealand Limited
Hi Nicky, thank you for your email, I acknowledge receipt and we will be back to you once the information has been compiled.
Have a great weekend
LISA HOLLAND
EA to Alex Ball, CFO and David Knight, General Counsel & Company Secretary
Transpower New Zealand Limited
22 Boulcott Street, PO Box 1021, Wellington
DDI: +64 4 590 7330
MB: +64 21 569 738
www.transpower.co.nz
CAUTION: This message and any attachments contain information that is CONFIDENTIAL and may be LEGALLY PRIVILEGED.
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show quoted sections
From: Dan Twigg
Transpower New Zealand Limited
Nicky, this email is a response to your Official Information Act request
received on 18^th October 2018 (the contents of your request are set out
below).
Part 1 of your request.
You have asked for detailed outage information and the effect on capacity
back to 1965. We do not have such data prior to 1993.
What is provided in the following table are the general maximum ratings
through time, as major changes occurred, with approximate dates. Note:
this does not include every single time HVDC ratings changed but captures
the major changes. You requested “specific dates (not just "in 1965")
and specific voltages/currents/capacities”; the table below may not
literally meet that description, but we think it may be information
sufficient for your purposes. To provide the information of changes on
specific dates would require considerable work – the information does not
actually exist, but can be calculated – and we would likely impose a
charge for its production. Doubtless you will advise me if anything
further is required.
Year Range Pole 1 Pole Pole 1 Pole 2 Pole Pole 2 Pole 3 Pole Pole 3 Bipole Comment
Technology 1 Voltage/Current Technology 2 Voltage/Current Technology 3 Voltage/Current Power
Power Power Power Limit
1965-1973 12 pulse 300MW +250kV/1200A 12 pulse 300MW -250kV/1200A - - - 600MW Original
Mercury Arc North North Mercury North North North HVDC link.
Valve utilising Arc Valve Cook Strait
two 6 pulse 0MW utilising 0MW 0MW Cables 1, 2,
valve groups in South two 6 South South 3 installed.
series pulse
valve
groups in
series
1973-1992 12 pulse 300MW +250kV/1200A 12 pulse 300MW -250kV/1200A - - - 600MW Southflow
Mercury Arc North North Mercury North North North controls
Valve utilising Arc Valve modification
two 6 pulse 300MW -250kV/1200A utilising 300MW +250kV/1200A 400MW performed.
valve groups in South South two 6 South South South*
series pulse
valve
groups in
series
1992-1996 12 pulse 540MW +270kV/2000A 12 pulse 700MW -350kV/2000A - - - 1240MW Hybrid HVDC
Mercury Arc North North Thyristor North North North project
Valve utilising Valve upgrade.
four 6 pulse 540MW -270kV/2000A 666MW +333kV/2000A 600MW Cook Strait
valve groups in South South South South South* Cables 4, 5,
series/parallel 6 installed.
(limited to
2000A by
transmission
line)
1996-2007 12 pulse 540MW +270kV/2000A 12 pulse 500MW -350kV/1430A - - - 1040MW Last
Mercury Arc North North Thyristor North North North original
Valve utilising Valve Cook Strait
four 6 pulse 540MW -270kV/2000A 489MW +342kV/1430A 600MW cable fails.
valve groups in South South South South South*
series/parallel
(limited to (limited by
2000A by single Cook
transmission Strait cable)
line)
2007-2012 12 pulse 200MW +270kV/741A 12 pulse 700MW -350kV/2000A - - - 1040MW Half of Pole
Mercury Arc North North Thyristor North North North 1
Valve utilising Valve permanently
two 6 pulse 0MW 666MW +333kV/2000A 600MW shut down.
valve groups in South South South South* Remaining
series half pole
made
temporarily
available
for 200MW
northflow
only.
2012-2013 - - - 12 pulse 700MW -350kV/2000A - - - 700MW Pole 1
Thyristor North North North permanently
Valve shut down.
666MW +333kV/2000A 666MW
South South South
(limited by
single Cook
Strait cable)
2013-Present - - - 12 pulse 500MW -350kV/1430A 12 pulse 700MW +350kV/2000A 1200MW Pole 3
Thyristor North North Thyristor North North North project
Valve Valve completed.
489MW +342kV/1430A 700MW -350kV/2000A 850MW
South South South South South*
(limited by
single Cook
Strait cable)
* South power limits are generally determined by AC system constraints,
not HVDC system constraints
Part 2 of your request.
With regard to your question relating to switching, some background will
be helpful. Cable 4 is permanently connected to Pole 2 and Cable 6
permanently connected to Pole 3. Only Cable 5 can be switched between
poles. However, Transpower does not have switchgear for this action. To
switch Cable 5 requires a piece of buswork to be removed and replaced at
each cable station. For practicability reasons this can only be carried
out during a bipole outage, something which is undertaken only
occasionally.
Assuming your reference to “parity” is in fact to ‘polarity’ we confirm
the polarity is switched on each pole/cable whenever a power direction
change is required. A 5 minute discharge period is required before the
polarity is swapped, to allow the space charge in the Cook Strait cable
insulation to dissipate. Changing polarities in a timeframe faster than 5
minutes can damage the cable insulation. Further, the polarity on each
pole is the same at Haywards and Benmore – the voltage will just be
slightly lower at the receiving end due to voltage drop over the
line/cable (which is dependent on current loading).
In the South Island, the Pole 2 conductor is on the westward side of the
towers and the Pole 3 conductor is on the eastward side of the towers. In
the North Island, the Pole 2 conductor is on the eastward side of the
towers and the Pole 3 conductor is on the westward side of the towers.
Section 28 of the Official Information Act provides you a right of review
by the Ombudsman (if desired) of any decision by Transpower’s relating to
this response to your request.
Yours sincerely
Dan Twigg
Governance and Administration Manager
Transpower New Zealand
Waikoukou
22 Boulcott Street
PO Box 1021
Wellington 6011
021 380 123
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Dear Transpower New Zealand Limited,
The link started in 1965 as 300MW via ±250KV and 1,200 amps, for both
pole 1 and pole 2. Then there came adjustment to the mercury valves,
allowing a different voltage and current capacity (270KV and 2,000 amps,
though 1,600 amps was the preferred upper bound), then the introduction of
southward power flow (with its own capacity), then operational
constraints due to a Cook Strait cable failure, etc. then repairs, then
pole 1 was stood down "indefinitely", then it wasn't, then some mercury
valves were removed and others replaced by silicon-based thyristors and a
new voltage and current capacity allowed except that was not for both
poles, and later was (?), and it is all confusing since PR releases
reported in the news media are rarely specific, and alas, I haven't kept a
folder full of clippings over the years.
So, I am requesting a schedule of the nominal capacities as they varied
over time, both for pole 1 and pole 2, both northwards and southwards, and
regarding "pole 3" as being the new name for pole 1. This would be with
specific dates (not just "in 1965") and specific
voltages/currents/capacities, made more complex by changes to the capacity
of the undersea cables and the use of the "ground return" should one pole
(which?) be unavailable for an extended period. Planned outages for
maintenance, etc. would be included, but not half-hourly data on actual
usage. This is for nominal capacities as the link's abilities are changed
from time to time.
To reduce puzzlement, is it the case that the switches selecting a Cook
Strait cable for pole 1 and for pole 2 at each end of the undersea cables
are used always to maintain parity over the whole link, or can the parity
be swapped? That is, suppose one faces north from Benmore and finds pole 1
on the left of the power pylons and pole 2 on the right (which is it?),
will this parity be the same on arrival at Haywards? This is particularly
relevant when the poles are operated at different voltages.
Yours faithfully,
Nicky McLean
From: Nicky McLean
Dear Dan Twigg,
Thank you for your reply clarifying the orientation of the connections of the HVDC link, and that the Cook Strait cable connections require a spanner to adjust. By parity I really do mean the left/right east/west alignment of the power lines, and I'm surprised that they are swapped along the way. Since you mention pole 3 in this context, one wonders if this situation applied from the start, before pole 1 became called pole 3. As for polarity, I had read earlier that when the polarity is to be changed, time has to be allowed for the Cook Strait cable's insulation to discharge and recharge lest damage result, though this isn't a problem with AC lines whose voltage is never sustained. I wonder if, were the cable connections easily juggled, their connections could be swapped instead so that the cables remained at the same voltage. But not by hand!
Your information on the capacities of the HVDC link in its various conditions looks to be useful and contains numbers, but alas, what appears to have been an attempt at a table of some sort has had its layout thoroughly scrambled by the workings of the FYI website. Despite staring at the mess for a while, I can't make out details that can definitely be attributed to pole one (or three) as distinct from pole two, or north versus south transfer.
Below is the schedule that I am trying to fill out. It comes form a file NominalGenerationCapacity.txt and contains some longish lines that the FYI interface wraps. It looks a lot better with a fixed-spacing typeface (such as Courier) rather than the usual variable spacing that spoils attempts at alignment. And I see from the preview that the FYI interface converts multiple spaces into a single space, thus further damaging an attempt at alignment. The layout is a name entry (the first line below) followed by lines that each start with a date (and possibly, a time), a value in KW, and then some remark. Then comes another name entry (a line not starting with a date, which starts with a number, which starts with a digit not a letter) and so on.
The information came from some texts on the history of the NZED system plus news reports, though it doesn't contain mention of the dramatic occasion when a few transmission towers were blown over by a breeze, and that not in Wellington either!
Nominal.HVDC.North.Pole1 High Voltage Direct Current transmission link, Benmore - Haywards, pole 1. Later, refurbishad and called pole 3.
1/4/1965 300000 Single pole operation. Each line is run at ±250KV, up to 1200 amps.
2/1992 540000 Mercury valves reconfigured to run +270KV and 2000 amps, though 1600 is the preferred limit.
10/2004 386000 One Cook Strait cable failed, limiting the whole to 886MW; I'll finger pole 1 as suffering.
3/2005 540000 Repaired. Details would be good.
21/ 9/2007 0 Declared "stood down indefinitely" with fuss over mercury vapour possibly contaminating the country...
12/2007 270000 Revised as "warm standby", but one half of the parallel set of mercury valves were removed: half current presumably. Full current on the other, with earth balance?
1/ 7/2009 200000 Declared restrictions: only between 100 and 200MW, or presumably, zero.
11/11/2009@5am 0 Planned outage.
16/11/2009@5am 200000 Planned resumption.
1/8/2012@10:00 0 As per the words of Robbie Christillo (duty energy co-ordinator, Wellington): "It is with a heavy heart I issue this final instruction, 'Stop Pole One!'." Decommissioned, to be revived as pole "3".
12/2013 700000 Designed claim. 350KVx1430A. 1,000MW for half an hour (Cook Strait cable insulation now solid plastic: no oil cooling) Supposed completion in March slipped somewhat.
Nominal.HVDC.North.Pole2 High Voltage Direct Current transmission link, Benmore - Haywards, pole 2.
6/1965 300000 Third Cook Strait cable recovered and repaired in May 1965; both lines operational.
1993 700000 Mercury valves moved to pole 1 (for parallel use) and replaced by thyristors running -350KV.
1997 500000 Cook Strait cable problems. Fixed when?
1/ 7/2009 700000 Declared capacity.
11/11/2009@5am 0 Planned outage.
16/11/2009@5am 700000 Planned resumption.
Nominal.HVDC.South.Pole1 High Voltage Direct Current transmission link, Haywards - Benmore, Pole 1.
1975 200000
1/ 7/2009 0 Declared incapable.
12/2013 700000 Designed claim.
Nominal.HVDC.South.Pole2 High Voltage Direct Current transmission link, Haywards - Benmore, Pole 2.
1975 200000
1/ 7/2009 666000 An odd choice of current for this, chosen by Ranil DaSilva (prime suspect) for transpower's engineers.
11/11/2009@5am 0 Planned outage.
16/11/2009@5am 666000 Planned resumption.
Yours sincerely,
Nicky McLean
From: Nicky McLean
Dear Lisa Holland,
While the response from Dan Twigg has clarified the nature of the power line connections, his response to the main part of the query has been so thoroughly scrambled in its presentation that I can't be sure that I can find definite answers in it. This is described in my reply to his response, and you can view this for yourself via the log of messages maintained by the FYI system.
Thus, could the information please be re-supplied in an uncluttered form? This can be checked via the "preview" facility offered by the FYI system.
And I am puzzled that your organisation seems to retain only vague recollections as to what are significant changes to the operational capacity to an important part of the national grid, but perhaps the future is what occupies the mind.
Yours sincerely,
Nicky McLean
From: Lisa Holland
Transpower New Zealand Limited
Thank you for your email, I will discuss with Dan
Have a great day
LISA HOLLAND
EA to Alex Ball, CFO and David Knight, General Counsel & Company Secretary
Transpower New Zealand Limited
22 Boulcott Street, PO Box 1021, Wellington
DDI: +64 4 590 7330
MB: +64 21 569 738
www.transpower.co.nz
CAUTION: This message and any attachments contain information that is CONFIDENTIAL and may be LEGALLY PRIVILEGED.
If you are not the intended recipient any use, disclosure or copying of this email message or attachments is strictly prohibited.
If you have received this message in error, please notify immediately and erase all copies of this message and attachments.
show quoted sections
From: Dan Twigg
Transpower New Zealand Limited
FW Schedule of the nominal capacity of the HVDC link over time from the beginning to the current day.pdf
1.6M
Download
View as HTML
Nicky. Here is my earlier email as PDF. This should ‘unscramble’ the
chart I had included in my earl;ier mail.. I hope this is what you need.
Best wishes
Dan Twigg
From: Dan Twigg
Sent: Wednesday, 31 October 2018 4:25 PM
To: '[FOI #8904 email]'
<[1][FOI #8904 email]>
Subject: Schedule of the nominal capacity of the HVDC link over time from
the beginning to the current day.
Nicky, this email is a response to your Official Information Act request
received on 18^th October 2018 (the contents of your request are set out
below).
Part 1 of your request.
You have asked for detailed outage information and the effect on capacity
back to 1965. We do not have such data prior to 1993.
What is provided in the following table are the general maximum ratings
through time, as major changes occurred, with approximate dates. Note:
this does not include every single time HVDC ratings changed but captures
the major changes. You requested “specific dates (not just "in 1965")
and specific voltages/currents/capacities”; the table below may not
literally meet that description, but we think it may be information
sufficient for your purposes. To provide the information of changes on
specific dates would require considerable work – the information does not
actually exist, but can be calculated – and we would likely impose a
charge for its production. Doubtless you will advise me if anything
further is required.
Year Range Pole 1 Pole Pole 1 Pole 2 Pole Pole 2 Pole 3 Pole Pole 3 Bipole Comment
Technology 1 Voltage/Current Technology 2 Voltage/Current Technology 3 Voltage/Current Power
Power Power Power Limit
1965-1973 12 pulse 300MW +250kV/1200A 12 pulse 300MW -250kV/1200A - - - 600MW Original
Mercury Arc North North Mercury North North North HVDC link.
Valve utilising Arc Valve Cook Strait
two 6 pulse 0MW utilising 0MW 0MW Cables 1, 2,
valve groups in South two 6 South South 3 installed.
series pulse
valve
groups in
series
1973-1992 12 pulse 300MW +250kV/1200A 12 pulse 300MW -250kV/1200A - - - 600MW Southflow
Mercury Arc North North Mercury North North North controls
Valve utilising Arc Valve modification
two 6 pulse 300MW -250kV/1200A utilising 300MW +250kV/1200A 400MW performed.
valve groups in South South two 6 South South South*
series pulse
valve
groups in
series
1992-1996 12 pulse 540MW +270kV/2000A 12 pulse 700MW -350kV/2000A - - - 1240MW Hybrid HVDC
Mercury Arc North North Thyristor North North North project
Valve utilising Valve upgrade.
four 6 pulse 540MW -270kV/2000A 666MW +333kV/2000A 600MW Cook Strait
valve groups in South South South South South* Cables 4, 5,
series/parallel 6 installed.
(limited to
2000A by
transmission
line)
1996-2007 12 pulse 540MW +270kV/2000A 12 pulse 500MW -350kV/1430A - - - 1040MW Last
Mercury Arc North North Thyristor North North North original
Valve utilising Valve Cook Strait
four 6 pulse 540MW -270kV/2000A 489MW +342kV/1430A 600MW cable fails.
valve groups in South South South South South*
series/parallel
(limited to (limited by
2000A by single Cook
transmission Strait cable)
line)
2007-2012 12 pulse 200MW +270kV/741A 12 pulse 700MW -350kV/2000A - - - 1040MW Half of Pole
Mercury Arc North North Thyristor North North North 1
Valve utilising Valve permanently
two 6 pulse 0MW 666MW +333kV/2000A 600MW shut down.
valve groups in South South South South* Remaining
series half pole
made
temporarily
available
for 200MW
northflow
only.
2012-2013 - - - 12 pulse 700MW -350kV/2000A - - - 700MW Pole 1
Thyristor North North North permanently
Valve shut down.
666MW +333kV/2000A 666MW
South South South
(limited by
single Cook
Strait cable)
2013-Present - - - 12 pulse 500MW -350kV/1430A 12 pulse 700MW +350kV/2000A 1200MW Pole 3
Thyristor North North Thyristor North North North project
Valve Valve completed.
489MW +342kV/1430A 700MW -350kV/2000A 850MW
South South South South South*
(limited by
single Cook
Strait cable)
* South power limits are generally determined by AC system constraints,
not HVDC system constraints
Part 2 of your request.
With regard to your question relating to switching, some background will
be helpful. Cable 4 is permanently connected to Pole 2 and Cable 6
permanently connected to Pole 3. Only Cable 5 can be switched between
poles. However, Transpower does not have switchgear for this action. To
switch Cable 5 requires a piece of buswork to be removed and replaced at
each cable station. For practicability reasons this can only be carried
out during a bipole outage, something which is undertaken only
occasionally.
Assuming your reference to “parity” is in fact to ‘polarity’ we confirm
the polarity is switched on each pole/cable whenever a power direction
change is required. A 5 minute discharge period is required before the
polarity is swapped, to allow the space charge in the Cook Strait cable
insulation to dissipate. Changing polarities in a timeframe faster than 5
minutes can damage the cable insulation. Further, the polarity on each
pole is the same at Haywards and Benmore – the voltage will just be
slightly lower at the receiving end due to voltage drop over the
line/cable (which is dependent on current loading).
In the South Island, the Pole 2 conductor is on the westward side of the
towers and the Pole 3 conductor is on the eastward side of the towers. In
the North Island, the Pole 2 conductor is on the eastward side of the
towers and the Pole 3 conductor is on the westward side of the towers.
Section 28 of the Official Information Act provides you a right of review
by the Ombudsman (if desired) of any decision by Transpower’s relating to
this response to your request.
Yours sincerely
Dan Twigg
Governance and Administration Manager
Transpower New Zealand
Waikoukou
22 Boulcott Street
PO Box 1021
Wellington 6011
021 380 123
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Dear Transpower New Zealand Limited,
The link started in 1965 as 300MW via ±250KV and 1,200 amps, for both
pole 1 and pole 2. Then there came adjustment to the mercury valves,
allowing a different voltage and current capacity (270KV and 2,000 amps,
though 1,600 amps was the preferred upper bound), then the introduction of
southward power flow (with its own capacity), then operational
constraints due to a Cook Strait cable failure, etc. then repairs, then
pole 1 was stood down "indefinitely", then it wasn't, then some mercury
valves were removed and others replaced by silicon-based thyristors and a
new voltage and current capacity allowed except that was not for both
poles, and later was (?), and it is all confusing since PR releases
reported in the news media are rarely specific, and alas, I haven't kept a
folder full of clippings over the years.
So, I am requesting a schedule of the nominal capacities as they varied
over time, both for pole 1 and pole 2, both northwards and southwards, and
regarding "pole 3" as being the new name for pole 1. This would be with
specific dates (not just "in 1965") and specific
voltages/currents/capacities, made more complex by changes to the capacity
of the undersea cables and the use of the "ground return" should one pole
(which?) be unavailable for an extended period. Planned outages for
maintenance, etc. would be included, but not half-hourly data on actual
usage. This is for nominal capacities as the link's abilities are changed
from time to time.
To reduce puzzlement, is it the case that the switches selecting a Cook
Strait cable for pole 1 and for pole 2 at each end of the undersea cables
are used always to maintain parity over the whole link, or can the parity
be swapped? That is, suppose one faces north from Benmore and finds pole 1
on the left of the power pylons and pole 2 on the right (which is it?),
will this parity be the same on arrival at Haywards? This is particularly
relevant when the poles are operated at different voltages.
Yours faithfully,
Nicky McLean
References
Visible links
1. mailto:[FOI #8904 email]
From: Nicky McLean
Dear Dan Twigg,
Thanks, the table is intelligible now!
Yours sincerely,
Nicky McLean
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