part iii - attachment b - technical report rev 1

NORTH AUCKLAND AND NORTHLAND GRID

UPGRADE PROJECT

ATTACHMENT B

TECHNICAL REPORT

Revision 1 – May 2008

Attachment B: Technical Report – May 2008 Revision

Grid Upgrade Plan 2007 Instalment 1, Part III – North Auckland and Northland Investment Proposal – May 2008 Revision © Transpower New Zealand Limited 2008. All rights reserved.

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Executive Summary A number of transmission development options were considered for providing a secure power supply to North Auckland and Northland. This report presents analysis of four options from the preliminary long list of options. These are the options which remained as viable options after a high level analysis of the long list.

With some minor upgrades, the existing transmission system reaches its capacity by 2016 and a major new investment is required to be in place before then. The long list of options included building new transmission assets, upgrading the existing lines, providing generation north of the constriction, distributed generation or load control in the North Auckland-Northland region.

The four options analysed in detail in this report include: • Installing a single new 220 kV cable circuit across Auckland from Penrose to Albany,

with a second circuit installed if and when required; • Upgrading the existing 220 & 110 kV networks by replacing existing conductor with

high temperature conductor of equal dimensions; • Installing a new 220 kV cable circuit from Penrose to Mount Roskill and a 220/110 kV

interconnection at Mount Roskill; • New generation in the area north of Auckland.

Option 1: Single 220 kV cable circuit from Penrose to Albany

This option involves a single 220 kV cable circuit from Penrose to Hobson Street via an existing tunnel, then from Hobson Street to Wairau Road using cable buried along the roading system and attached to the Harbour Bridge, and a section from Wairau Road to Albany mostly buried in a new busway currently under construction.

The new 220 kV cable circuit is assumed to have a capacity of 630 MVA in winter. The cable circuit will include a series reactor to balance power flow north between this circuit and existing overhead lines. A new 220kV cable connection is also installed between Pakuranga and Penrose substation.

The augmented transmission system into Northland is expected to reach its n-1 capacity by 2036,1 requiring an additional 220 kV cable circuit to be installed.

Option 2: High Temperature Conductor

This option includes replacing the conductor on the 220 kV HEN-OTA line and on the 110 kV OTA-MNG-ROS-HEP-HEN lines as n-1 capacity is exceeded. The type of conductor used is assumed to be of similar dimension to the existing conductor to avoid any change in the physical appearance of the lines.

Eventually a new circuit from Penrose to Mount Roskill will be required as the n-1 capacity of the upgraded circuits is exceeded.

Option 3: Single 220 kV cable circuit from Penrose to Mount Roskill

This option involves installing a 220 kV cable from Penrose substation to Mount Roskill substation and initially a single 220/110 kV transformer at Mount Roskill.

The new circuit has a rating of 630 MVA and is approximately 10 km in length. This will be installed before the Henderson-Otahuhu overhead circuit exceeds n-1 capacity, and will increase supply capacity to the Northland region by increasing power flow north on the 110 kV circuits across Auckland. A new 220kV cable connection is also installed between Pakuranga and Penrose substation.

1 Note that the n-1 analysis in this attachment was carried out on the basis of the security criteria set out at section 2.7 of this attachment.



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A second interconnecting transformer is installed at Mount Roskill when required to increase power flow north on the 110 kV system. The second transformer increases the 220-110 kV total n-1 transfer capacity and delays further major investment by four more years. Ultimately a cross-harbour cable as in Option 1 will be installed.

Option 4: Installing new generation north of the Auckland

A technical analysis of this option is provided for information only. A discussion on the status of this option is provided in the proposal document.

This option includes installing new generation north of Henderson substation. For the purposes of this work, it is assumed that the new generation is connected into the 220 kV Huapai-Marsden circuit. The maximum amount of reliable generation assumed to be available is 240 MW.

The new generation delays the requirement to reinforce the supply into Northland. The 110 kV system is reinforced as its n-1 capacity is exceeded, by installing a 220 kV Penrose-Mount Roskill circuit and an interconnection at Mount Roskill. Eventually under this option a cross-harbour cable will be installed including new GXP’s at Hobson Street and Wairau Road

Reactive support is planned to meet reactive power losses and ensure voltage stability of the power system. Dynamic reactive power support is planned such that there are sufficient reserves to cover the worst transmission contingency, whether the Ngawha power station new generation (15 MW) is in service or not



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Contents

EXECUTIVE SUMMARY.......................................................................................2

1 INTRODUCTION ............................................................................................6

2 EXISTING SYSTEM........................................................................................9

2.1 Transmission .....................................................................................................................................9

2.2 Voltage Support ..............................................................................................................................12

3 ASSUMPTIONS AND METHODOLOGY......................................................13

3.1 General Assumptions......................................................................................................................13

3.2 Demand Forecast ............................................................................................................................13

3.3 Generation .......................................................................................................................................14

3.4 Component Ratings ........................................................................................................................15

3.5 Description of Modelled New Circuits ..........................................................................................15

3.6 Distribution System ........................................................................................................................15

3.7 Security Criteria..............................................................................................................................17

3.8 Planning Horizon ............................................................................................................................17

3.9 Methodology for Analysis...............................................................................................................17

4 COMMON AUGMENTATIONS.....................................................................19

4.1 North Island Grid Upgrade Project ..............................................................................................19

4.2 Other Projects .................................................................................................................................20

4.3 Voltage Support Plan......................................................................................................................21

4.4 Penrose 110 kV Reinforcement......................................................................................................22

5 PROJECT ALTERNATIVES.........................................................................24

5.1 Option 1 – Cross Harbour Cables .................................................................................................25

5.2 Option 2 – High Temperature Conductor ....................................................................................28

5.3 Option 3 – New interconnection at Roskill ...................................................................................31

5.4 Option 4 – New generation north of Auckland.............................................................................34



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6 DISCUSSION ON REACTIVE PLANS .........................................................37

6.1 Static Reactive Requirements ........................................................................................................37

6.2 Dynamic Reactive Requirements...................................................................................................37

7 SUMMARY ...................................................................................................41

APPENDIX A – EXISTING CIRCUIT RATINGS .................................................42

APPENDIX B - INTERCONNECTION TRANSFORMER RATINGS...................43

APPENDIX C - PARAMETERS OF NEW COMPONENTS USED......................44

APPENDIX D - SUBSTATION CODES...............................................................46

APPENDIX E - FORECAST LOAD DATA..........................................................48

APPENDIX F - CHARACTERISTIC OF NAAN LOAD........................................49

APPENDIX G - CHARACTERISTIC OF PENROSE LOAD................................50



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1 Introduction For the purposes of this report, the North Auckland and Northland (NAaN) region includes the loads at Hepburn and Henderson, and everything north of that. The peak load of this region was about 839 MVA in 2006 and is expected to be in excess of 850 MVA in 2007. The historical average annual increase over the past five years is approximately 3%.

This report describes the technical assessment of alternatives for augmenting the transmission capacity across Auckland and into the NAaN area, to ensure adequate security of supply out to 2039. The results of the analysis are summarised in the form of a timed development plan for each transmission alternative. The timings of the planned transmission developments are based on Electricity Commission’s prudent demand forecast as of August 2007, adjusted by Transpower and as used for the 2008 Annual Planning Report.

The scope of this report is limited to: • steady state analysis of the Auckland and Northland power system to ensure that it

would remain in a satisfactory state following any single credible contingency event occurring on the core grid. This assumes that Ngawha generation is 10 MW, which allows for an outage of 15 MW of Ngawha generation (due to be commissioned).

• analysis of the power transmission system across Auckland and into the NAaN area. It does not address security issues into the Auckland area from the south. For security of supply into Auckland (specifically into Otahuhu and Pakuranga), the analysis assumes the development plans as described in the North Island Grid Upgrade Project (NI GUP) – Amended Proposal, Option 2.

The reactive power support plan is developed to ensure stable operation of the power system. The plan for each development option ensures the set voltage (1.02 pu for this study) can be maintained at each controlled bus, under n-1 conditions, to a demand level of the forecast peak demand in each year. Sufficient dynamic support is planned so that no capacitor switching is required post-contingency.

The reactive plan from Otahuhu south is as developed for the NI GUP, and it is assumed that the voltage at Otahuhu is maintained at 1.02 pu under all contingencies.

Four transmission options were analysed in detail for enhancing the security of supply into the NAaN area as follows:

1. Installing a 220 kV cross-harbour cable, from Penrose to Albany, connecting into new grid exit points (GXPs) along the route at Hobson Street and Wairau Road.

2. Upgrading existing transmission circuits using high temperature conductor, avoiding as far as possible constructing any new lines

3. Installing a new 220 kV cable circuit from Penrose to Mount Roskill with a 220/110 kV interconnection at Mount Roskill. This would be followed by a cross harbour cable as per option 1 but deferred by 10 years.

4. New generation in the Northland region – modelled as being connected into the 220 kV Huapai-Marsden circuit.

Table 1-1 below summarises the development plans for the four options considered in detail.



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Table 1-1 Summary of Development Plans for the Four Preferred Options

Year* Option 1

Cross harbour cable Option 2 HTC

Option 3 Reinforce Mt Roskill

Option 4 Northern generation

2009 2nd 220/110 kV transformer at PEN in parallel with PEN T10

2nd 220/110 kV transformer at PEN in parallel with PEN T10



2010

2011

2012

2013

2014

2015

2016 1st PEN-HOB-WRU-ALB cable

New HOB and WRU

GXP's One 220 kV PAK-PEN

circuit

High Temp conductor on 220 kV HEN-OTA

circuits

One 220 kV PAK-PEN circuit

New 220 kV transformer feeder at ROS (one 220 kV PEN-ROS cable) and a ROS

220/110 kV interconnecting

transformer (ICT)



120 MW new generation at Rodney connected to

220 kV MDN-HPI 1 circuit

2017

2018 Upgrade HEN 220/110 kV

transformers with 2 x 250 MVA 7% units

Replace existing HEN 220/110 kV

transformers with 2 x 250 MVA 7% units

2019 Install a second ICT at ALB

2020 Second 220/110 kV transformer at ALB

Install a second ICT at ALB

New 220 kV transformer feeder at ROS (one

220 kV PEN-ROS cable & one ROS 220/110 kV

transformer)

2021 High Temp conductor on 110 kV MNG-ROS

circuits

Upgrade 200m of ALB-HEN 3 to duplex zebra

conductor

2022 Install a second ICT at ROS

2023 Second 220/110 kV transformer at HOB

One series reactor in the PAK-PEN 1 circuit

2024 2nd supply transformer at WRU

Third 220/110 kV transformer at OTA in parallel with T3 & T5

High temp conductor on

Upgrade HEP-ROS 1 & 2 circuits



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Year* Option 1 Cross harbour cable

Option 2 HTC



110 kV OTA-ROS 1 & 2

2025 Series reactor in OTA-PEN 2 circuit

2026 2nd 220 kV PAK-PEN circuit

Install first cross-harbour cable PEN-HOB-WRU-ALB plus

GXPs at HOB and WRU

Install a second supply transformer at WRU

Install a second PAK-PEN cable and a series

reactor

2nd 220 kV PAK-PEN circuit

2027

2028 Series reactors In 220 kV PAK-PEN

circuits

New 220 kV transformer feeder at ROS

(one 220 kV PEN-ROS cable & one ROS

220/110 kV transformer)

High temp conductor on 110 kV MNG-OTA 1 & 2

120 MW additional generation at Rodney

2029 High temp conductor on ALB-HEN-HPI circuits

2030 Series reactor on OTA-PEN 2 circuit

Third 220/110 kV transformer MDN


2031 Third 220/110 kV transformer MDN


2032

Install a series reactor on OTA-PEN 2 circuit

Install a second ICT at ROS

Install series reactors in PAK-PEN 1 & 2 circuits

2033

2034

2035

2036 2nd 220 kV ALB-PEN cable, this one not

connected into HOB or WRU GXP's

New 220 kV transformer feeder at ROS

(one 220 kV PEN-ROS cable & one ROS

220/110 kV transformer)

Series reactors in 110 kV ALB-HEN 1&2

circuits

High temp conductor on HEP-ROS 1&2 circuits

2nd 220 kV PAK-PEN circuit

Second 220/110 kV transformer at HOB

1st PEN-HOB-WRU-ALB cable

New HOB and WRU GXP's, two ICT’s at

HOB

Install second HOB ICT

Instal second WRU supply transformer



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Year* Option 1 Cross harbour cable

Option 2 HTC



2037

2038 Upgrade PAK-PEN circuits from 667 MVA to

985 MVA

2039

2040 High temperature conductor on HEN-WEL

1 & 2 circuits

Upgrade PAK-PEN circuits from 667 MVA to

1100 MVA

2nd 220 kV ALB-PEN cable, this one not

connected into HOB or WRU GXP's

* Year in which development is required, e.g. 2013 = development required to be commissioned by winter (May)

of 2013

These four options were short-listed for further detailed analysis because they: • represent different strategic approaches which could potentially improve the supply

security to the NAaN area • are considered to provide similar benefits

Other transmission options that were studied during the preliminary phase, but not short listed are discussed in the document “Assessment of Options”. These options are listed in Table 1-2.

Table 1-2: Options Not Considered Description Type

Deep tunnel Hobson Street – Albany Transmission

Deep tunnel Penrose - Henderson Transmission

Central corridor 110 kV to 220 kV line replacement Transmission

Distributed generation Supply side

Ripple Control Demand side

Huntly – Huapai cables via harbour Transmission

Deep tunnel Hobson Street – Henderson Transmission

HVDC light from Penrose to Albany (two terminal) Transmission

HVDC light Pakuranga – Penrose – Albany (three terminal) Transmission

Huntly – Henderson overhead / underground Transmission

Huntly to Huapai 220 kV double circuit overhead line Transmission

2 Existing System 2.1 Transmission

The transmission system across Auckland supplying the North Auckland and Northland (NAaN) area is composed of two branches:



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1. A double circuit 220 kV line from Otahuhu to Henderson, with Southdown power station connected into one of these circuits just north of Otahuhu.

2. Two 110 kV lines from Otahuhu to Mount Roskill (with one double-circuit line going via Mangere) then to Hepburn Road and on to Henderson. This system is presently split for operational reasons between Mount Roskill and Hepburn Road. The split is due to be closed in 2008 following the installation of new secondary equipment.

Figure 2-1: Existing transmission System in the Auckland and Northland Region



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Table 2-1 below gives the ratings of the existing circuits supplying the NAaN area, including conductor ratings and limiting components. Refer to Appendix A for a full list of circuit ratings in the NAaN area.

Table 2-1: Existing circuits supplying NAaN area

Circuit Line Conductor V (kV)

Conductor Rating (MVA)

Branch Rating (MVA)

Notes on limiting component

HEN-HEP 1 to 4

HEN-ROS A Simplex Wolf 75oC

110 92/101 92/101

HEN-OTA 1 HEN-OTA A Duplex Zebra 120oC

220 938/985 915/915 Disconnector

HEN-SWN 1 HEN-OTA A Duplex Zebra 120oC

220 938/985 915/915 Disconnector

HEP-ROS 1&2

HEN-ROS A 2 bonded Wolf 75oC

110 184/202 114/114 Disconnector at 114 MVA then single span at 174/191 MVA

MNG-OTA 1&2

MNG-OTA A Duplex Zebra 75oC

110 355/390 305/305 Disconnector

MNG-ROS 1&2

MNG-ROS A Simplex Wolf 75oC

110 92/101 92/101

OTA-ROS 1&2

OTA-PEN B & PEN-ROS A

Simplex Wolf 75oC

110 92/101 92/101

OTA-SWN 1 HEN-OTA A Duplex Zebra 120oC

220 938/985 912/912 Transducer

The capacity of the transmission system into Northland is presently equal to the n-1 capacity of the 220 kV HEN-OTA line. This is a double-circuit line, each circuit being duplex zebra conductor with a temperature rating of 120oC. The resulting n-1 rating is 938/985 MVA summer/winter.



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Figure 2-2: Reduced network between Otahuhu and Henderson

Figure 2-2: shows the transmission system supplying the NAaN area.

Consent to operate the 220 kV HEN-OTA line at 120°C during forced outages has been attained, however this is subject to an appeal. The appeal is expected to be heard some time in mid to late 2008, but until then Transpower are permitted to make use of the consent that has been granted.

The split shown in the 110 kV system at Mount Roskill is to be normally closed by late 2008. Closing this split will increase the transfer limit to Northland. While there is very little power flow from Mount Roskill to Hepburn when the system is operating normally, an outage of one 220 kV Henderson-Otahuhu circuit does result in power flow north via the 110 kV system, reducing load on the remaining 220 kV circuit.

The balance of load flow between the 110 kV and 220 kV systems has a significant effect on the transfer limit to the NAaN area. This is determined mainly by the impedance of the circuits and interconnecting transformers at Otahuhu and Henderson, as well as loads on the 110 kV system and in particular at Mount Roskill.

Under this configuration, n-1 transmission capacity into Northland is more difficult to quantify, and is dependant on various factors including the load at Mount Roskill substation. With the present load distribution, closing the 110 kV split adds the equivalent of about four years average load growth capacity to the Northland transmission system, or about 100 MVA. The Penrose 110 kV bus must be reinforced due to the recent load shift.

From Henderson, the region is supplied by parallel 220 and 110 kV systems as far north as Marsden, and a 110 kV system north to Kaitaia. There are 220/110 kV interconnections at Henderson, Albany and Marsden.

2.2 Voltage Support

Table 2-2 lists the existing and planned voltage support in the NAaN region. Dynamic support at Marsden is contracted as an ancillary service by the System Operator to maintain a specified voltage during outages and other times it may be required.



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Table 2-2: Planned and Existing Voltage Support in the NAaN Region

Location Size Dynamic/Static

Notes

Kaikohe 20 Mvar S Existing

Albany 110 Mvar S Existing

Henderson 135 Mvar S Existing

Marsden +60/-20 Mvar D Existing

Hepburn 2 x 50 Mvar S Existing

Albany 100 Mvar S Existing

Albany +/- 100 Mvar D Due to be commissioned 2008

Kaitaia 24 Mvar S Committed Project

Henderson +/- 100 Mvar D Seeking approval – may not be at HEN

3 Assumptions and Methodology The following assumptions are made in the technical analysis.

3.1 General Assumptions

Pakuranga substation will be entirely converted to 220 kV by 2011 and there will be two 220 kV OTA-PAK circuits (on the existing OTA-PAK A line). In addition, as part of this conversion; • The 110 kV ARI-PAK 1 circuit will be decommissioned; • The 110 kV PAK-PEN 1 circuit will be decommissioned; and • 110 kV OTA-PAK 1 & 7 circuits will be converted to 220 kV. • The BOB-GLN interconnection is built by 2015.

All system upgrades south of Otahuhu as defined in the North Island Grid Upgrade Project (NI GUP) are common to all of the alternatives and will be modelled as occurring in the year proposed by the NI GUP – Amended Proposal, Option 2. A complete list of common projects is provided in section 4.

All Upper North Island voltage support projects from Otahuhu south are assumed to be as in the Amended NI GUP. For simplicity the analysis assumes the Otahuhu bus voltage remains at 1.02 pu throughout the studies.

Voltage support in the NAaN area will include dynamic support at Henderson, Albany and Marsden, and the 220 kV buses at these substations will be maintained at 1.02 pu voltage.

3.2 Demand Forecast

The load forecast used is based on the EC prudent forecast August 2007, as adjusted by Transpower for use in the 2008 Annual Planning Report.

The graph below shows the load forecast for the NAaN area as used for the technical assessment. It has been assumed that this forecast takes distributed generation into account. See the Appendix for a summary of Northland and Auckland forecast regional load peaks.



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Figure 3-1: EC Prudent Demand Forecast for Northland and North Auckland 2010-2040

500

750

1000

1250

1500

1750

2000

2010 2015 2020 2025 2030 2035 2040

Year

MW

As the distribution of loads in the EC forecast does not exactly match the distribution of loads that Transpower use in modelling the system, some rearrangement of loads was required. This is detailed below.

The EC loads LST_110A and LST_110B were combined then split as follows: • 52% to LST_110/ROS • 24% to ROS_KING/1 • 24% to ROS_KING/2

The EC loads PEN_110A and PEN _110B were combined then split as follows: • 56% to LST_110/PEN • 22% to PEN_QUAY/1 • 22% to PEN_QUAY/2

PEN_33A and PEN_33B are regarded as PEN22 and PEN33 respectively.

Total PEN110 load for this study is based on a diversity factor of 81% for loads supplied from this GXP. This is the peak region diversity for these loads as in the draft peak demand forecast used. The Penrose 110 kV load includes: Hobson St (LST/PEN), Liverpool St (LST/ROS), Quay St (PEN/QUAY 1 + 2) and Freemans Bay (25% of diversified ROS_KING total).

3.3 Generation

Ngawha is assumed to be generating at 10 MW out of a total capacity of 25 MW, and 8.7 Mvar voltage support controlling the Ngawha 33 kV bus voltage.



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Southdown generating 170 MW with 4 machines, controlling the SWN 220 kV bus voltage at 1.02 pu.

3.4 Component Ratings

a) Percentage loading on transformers refers to the percentage of post-contingency winter rating of the transformer, unless otherwise specified.

b) Loading on circuits is a percentage of the winter conductor rating, unless otherwise specified.

c) For cables, all ratings are assumed to be winter peak capacity, based on typical load profiles. No additional capacity has been assumed for short-term contingencies.

d) For high temperature conductors, the ratings were assumed to be equal to the existing conductor operating at a temperature of 220oC. This approximates the rating of a high temperature conductor that has physical dimensions similar to the existing conductor.

N.B. See Table A-0-1 and Table B-0-1 for a list of line ratings and transformer ratings in the Auckland area. See Table C-0-1 for a list of electrical parameters of the new components used in these studies.

3.5 Description of Modelled New Circuits

PEN-HOB cable • 10.21 km of 1600mm2 trefoil in air (tunnel)

HOB-WRU cable • 1.39 km of 1600mm2 trefoil in air (bridge) • 8.46 km of 2000mm2 trefoil in ducts

WRU-ALB cable • 8.45 km of 2000mm2 trefoil in ducts (busway)

PEN-ROS cable • 10.2 km of 2000mm2 trefoil in ducts

PAK-PEN cable • 8.6 km of 2500mm2 direct buried (forced cooled for upgraded options)

Notes:

1. The 220 kV cross-harbour cables are installed such that the winter cyclical rating for the entire length is 630 MVA.

2. See Table C-0-1 for electrical parameters of new components.

3. The cross sectional areas and ratings provided above are minimums. Installed cross sectional areas (and ratings) may differ from those provided following the detailed design phase of the works.

3.6 Distribution System



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Vector’s distribution system in the Greater Auckland area is assumed to be configured as follows: • Freemans Bay load is approximately 25% of the total Kingsland load, and as of 2007

is permanently transferred from Mount Roskill to Hobson Street. • Quay Street load will be transferred from Penrose to Hobson Street if and when a

new grid exit point (GXP) is built there • If no GXP is built at Hobson Street, Quay Street will be supplied via new 110 kV

cables out of Penrose. • The Mount Roskill-Liverpool Street cable will normally be in standby mode and not

supplying load. All Liverpool St load is transferred to PEN110 via the PEN-LST cables.

• Hobson Street will be supplied from Penrose until a new GXP is built at Hobson Street.

• If no GXP is built at Hobson Street, the Hobson Street load will continue to be supplied via existing (and if necessary additional) 110 kV Penrose-Liverpool Street-Hobson Street cables

• Paralleling of the local lines company’s network with Transpower’s network will be allowed until it causes overloading, at which time Vectors network will be split

• If no new GXP is built at Wairau Road, Vector will reinforce the 110 kV supply from Albany as necessary

Two new grid exit points (GXPs) are proposed as part of upgrade options 1, 3 & 4. These are at Vector’s existing zone substation sites of Hobson Street and Wairau Road. The studies have assumed the following: • The first 220 kV cross-harbour cable will be diverted into each new GXP, giving n-1

security. • The Hobson Street GXP will include a single 250 MVA 220/110 kV transformer

initially, with a second added when required to maintain n-1 security of supply. This generally occurs when the Lines Company’s and Transpower’s systems can no longer be operated in parallel.

• The Wairau Road GXP will include a single 250 MVA 220/33 kV transformer initially, paralleled with existing supply transformers on the 33 kV side. When the load exceeds the combined post-contingency rating of the three existing 110/33 kV supply transformers, a second 220/33 kV transformer will be added, and 110/33 kV transformers taken out of service.

Note: Specifications of the actual supply transformers installed will be decided in discussion with the customer.

3.6.1 Configuration of 110 kV system into CBD

Vector presently supply their Liverpool Street 110kV CBD substation from both Penrose (via two 110kV cables) and Mt Roskill (via a single 110kV cable). Due to Vector concerns over security of sub transmission into the CBD, they have decided to reconfigure their 110kV sub transmission network so that Liverpool Street substation is supplied solely from Penrose, i.e. the ROS 110kV cable will be out of service and all of the CBD 110kV load will be supplied out of PEN.

The consequence of this is an overall increase of load on the Transpower 110kV bus at Penrose (equating to about 90MW in 2007).

Penrose 110kV bus is supplied from: • T10 (220/110kV transformer) • 110kV PAK – PEN circuit • 110kV OTA – PEN circuit



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Prior to Vector’s shifting of load from ROS, PEN will be in need of reinforcement by 2013, this is independent of the installation of the first cross harbour cable, which coincidentally would also occur in 2013. Following the shifting of Vector’s load from ROS, PEN would require reinforcement in 2009 in order to meet increased demand. This reinforcement would include a new 220/110kV transformer at Penrose.

This work can be deferred by switching the ROS cable back into service in 2009, thereby reducing the 110kV load at PEN. Transpower however assume that the Liverpool Street load is now permanently shifted to the PEN 110kV bus, and will not be shifted back in order to manage load peaks at the Penrose 110 GXP.

3.7 Security Criteria

The analysis was carried out on the basis that committed generation from Ngawha is unavailable. It should be noted that the amount of generation at Ngawha is relatively small compared to the NAaN load, and that therefore this assumption does not have a material impact on the results.

3.7.1 Contingencies

In addition to an outage of the Ngawha generation, the following contingencies were considered to determine the development plans for all the options: • Loss of any single 220 kV or 110 kV transmission circuit from Otahuhu to Marsden; • Loss of one of Vectors 110 kV cable connections between Penrose and Liverpool

Street and Hobson Street • Loss of a 220/110 kV interconnecting transformer (from Otahuhu to Marsden).

3.7.2 Steady State Planning Criteria

The planning criteria used in the studies are as follows: • Transmission lines are limited to 100% of their respective winter or summer rating

with no short term overload capability • Cables are limited to 100% of their cyclic rating with no additional short term overload

capability • Existing transformers are limited to their winter or summer 24hr rating, assuming that

the transformers are cyclically loaded • New 220/110 kV 250 MVA interconnecting transformers are equivalent to the existing

Otahuhu T5 transformer, with the same overload ratio (1.27/1.33 summer/winter) • Loading was rounded to the nearest percentage point and anything loaded to 100%

or more was considered to be overloaded

3.8 Planning Horizon

The analysis extends out 32 years to 2040 as follows: • Every second year from 2008 to 2040 • Other years where necessary to determine the accurate timing of the critical

investments

3.9 Methodology for Analysis

This is a steady-state analysis based on load flow calculations. All the plans developed have assumed winter demand and winter component ratings. This is justified by the significantly winter peaking nature of the NAaN area load (see Figure F-0-1), as well as that of all the GXPs in the Auckland area, including Mangere, Pakuranga and Mount Roskill. Penrose loads are less strongly winter peaking and are described in Appendix G - Characteristic of Penrose Load.



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Deterministic grid reliability criteria were assumed for planning the transmission grid. The grid is planned to provide the supply reliability to the loads for an outage of one transmission element together with an outage of a single generating unit in the NAaN area (i.e. n-g-1). The transmission plans developed for all the options satisfy the assumed grid reliability criteria.

Transmission development plans ensure that the system remains stable and the transmission assets remain within their rated capacity for all credible contingencies. Appropriate winter demand and circuit ratings were assumed in determining the loading of the transmission circuits.

Note that summer loadings and ratings were also analysed in order to confirm whether the binding constraints would occur in summer or winter. The analysis shows that even though the ratings of circuits drop in the summer, the nature of the load (refer to appendices F and G) is such that the winter situation remains the most onerous and hence winter ratings and winter peak loads are those that are used in the subsequent analysis.

3.9.1 Reactive Power Support

In planning the reactive power support requirements, outages of the critical transmission components were modelled. Adequate reactive power support ensures that: • acceptable voltages (0.90 pu – 1.1 pu) are maintained at all the 220 kV and 110 kV

buses, and • sufficient reactive reserves are maintained, pre-contingency, in the dynamic reactive

devices (generators, synchronous condensers and SVCs) so that post-contingency switching of capacitors is not required

This analysis has not attempted to optimise the location or the quantity of reactive power support. For the purpose of comparing the transmission options, all the dynamic reactive support is assumed to be located at Henderson, Albany and Marsden. The voltage was maintained at 1.02 pu at all buses that had dynamic support. Switched capacitors at Kaitaia were modelled as an SVC with a 24 Mvar limit. Otahuhu voltage is assumed to remain constant under all contingencies.

3.9.2 Dynamic Analysis

The proposed development plans provide adequate transmission capacity into the NAaN area and maintain steady state voltages within the Electricity Governance Rule limits following a contingency. The plans were developed using steady state analysis (power flow and voltage stability) of the power system.

Transient performance of the connected generators and the loads (especially the motor loads) could affect the stability of the power system following a transmission disturbance and will require more detailed power system simulation.

Past studies2 indicate that additional investment in the form of dynamic reactive power support (e.g. synchronous condensers or SVCs) may be required to ensure power system stability. As the extra dynamic reactive support is mainly dependent on the characteristics of the connected rotating plant, it is assumed that additional reactive power requirements will be similar for all transmission alternatives.

2 NP306 “Auckland Reactive Power Requirements by 2010”, Transpower NZ Ltd, October 2005



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4 Common Augmentations A number of augmentations common to all of the development alternatives have been drawn from the following sources: • North Island Grid Upgrade Project – Amended Proposal – October 2006 • Annual Planning Report

4.1 North Island Grid Upgrade Project

The table below lists the common augmentations that are part of the North Island Grid Upgrade project.

Table 4-1: Common Augmentations that are part of the North Island Grid Upgrade project

Year Augmentation

2009 Decommission the 110 kV ARI-PAK line

Build new 400 kV double circuit line (Triplex AAAC Sulphur conductor) from WKM to BHL, operated at 220 kV

Install two new 220 kV cables from BHL-PAK

Build a new cable transition station at BHL

Build a new 220 kV substation at PAK

2011

Increase operating voltage of the OTA-PAK 1 & 2 circuits (OTA-PAK A transmission line) to 220 kV

2013 Re-conductor 110 kV ARI-HAM 1 & 2 circuits (ARI-HAM B double circuit line) with Nitrogen 75°C conductors.

Install 55% compensation on WKM-BHL 1 and 2 circuits

Install 110 kV OTA-WIR cable

Build new switching station at BHL

2021

Install 1st 220 kV BHL-OTA cable

2023 Install 2nd 220 kV BHL-OTA cable

2026 Re-conductor HAM-BOB 110 kV circuits to Nitrogen Conductors.

2027 Thermally upgrade the 220 kV HAM-HLY-1, HLE-WKM and HAM-WKM-1 circuits ( HLE-HAM-WKM section of the OTA-WKM C double circuit line) to 2xGoat 80°C

2028 Install 20 Ohm reactors on the OTA-WKM 1 & 2 circuits (OTA-WKM A&B lines)

2031 Install forced cooling on the 220 kV BHL-PAK cables

Install forced cooling on the 220 kV BHL-OTA cables

Build new 400 kV substation at Whakamaru

Build new 400 kV substation at Ormiston Road

Increase operating voltage of the WKM-BHL circuits to 400 kV

Install six 400/220 kV, 600 MVA interconnecting transformers at BHL

Install six 400/220 kV, 600 MVA interconnecting transformers at WKM

2033

Reduce series compensation on the 400 kV BHL-WKM circuits to 45%

2037 Install a 75 MVA Phase Shifting Transformer on the 110 kV ARI-BOB circuit



20

4.2 Other Projects

The table below lists the other common augmentations that are not part of the North Island Grid Upgrade project.

Table 3-2: Common Augmentations that are not part of the North Island Grid Upgrade project

Year Common Augmentation

2008 Upgrade the bus protection at Mount Roskill and close the 110kV split between Hepburn Road and Mount Roskill substation.

Thermal upgrade of 220 kV HLY-OTA-1 circuit (HLY-OTA section of OTA -WKM C double circuit line) from 493/404 MVA to 670/614 MVA.

Thermal upgrade of 220 kV WRK-PPI-WKM-1 circuit (WRK- WKM B single circuit line) from 292/239 MVA to 448/421 MVA

Shift half of HAM 33 kV load to new substation at TWH on HLY-TMN 220 kV circuit.

Thermal upgrade of 220 kV BPE-HAY-1 circuit (BPE-HAY A single circuit line) from 247/202MVA to 335/307 MVA

Thermal upgrade of 220 kV BPE-HAY-2 circuit (BPE-HAY B single circuit line) from 247/202MVA to 335/307 MVA

Thermal upgrade of 220 kV TKU-WKM-1 circuit (TKU-WKM section of single circuit BPE- WKM A line) from 281/244 MVA to 335/307 MVA

Thermal upgrade of 220 kV TKU-WKM-2 circuit (TKU-WKM section of single circuit BPE- WKM B line) from 281/244 MVA to 335/307 MVA

Thermal upgrade of 220 kV RPO- WRK-1 circuit (RPO- WRK section of BPE-WRK A single circuit line) from 292/239 MVA to 370/333 MVA

Thermal upgrade of 220 kV BPE-TKU-1 circuit (BPE-TKU section of BPE- WKM A single circuit line) from 246/202 MVA to 335/307 MVA

Thermal upgrade of 220 kV BPE-TKU-2 circuit (BPE-TKU section of BPE- WKM B single circuit line) from 246/202 MVA to 335/307 MVA

Thermal upgrade of 220 kV OTA-WKM-1 circuit (OTA-WKM A single circuit line) from 246/202 MVA to 323/293 MVA

Thermal upgrade of 220 kV OTA-WKM-2 circuit (OTA-WKM B single circuit line) from 246/202 MVA to 323/293 MVA

Bus the 220 kV HAM-HLY-1, HLY-OTA-1 and OTA-WKM-3 circuits (OTA -WKM C double circuit line) at HLE in a breaker-and-a-half configuration

Install second Wilton 100 MVA, 220/110 kV Interconnecting transformer

Shift 40% of Load from HIN to ARI (to compensate for new GXP at Putaruru)

Install new +/- 100 Mvar SVC at ALB

Install new 24 Mvar Capacitors at KTAInstall new +/- 100 Mvar SVC at ALB

Install new 25 Mvar Capacitors at TGA

Reconductor the 220 kV BPE-TKU-1 circuit (BPE-TKU section of BPE- WKM A single circuit line)Install new 24 Mvar Capacitors at KTA

By 2010

Reconductor the 220 kV BPE-TKU-2 circuit (BPE-TKU section of BPE- WKM B single circuit line)Install new 25 Mvar Capacitors at TGA



21

Year Common Augmentation

Reconductor the 220 kV TKU-WKM-1 circuit (TKU-WKM section of single circuit BPE- WKM A line)Reconductor the 220 kV BPE-TKU-1 circuit (BPE-TKU section of BPE- WKM A single circuit line)

Reconductor the 220 kV TKU-WKM-2 circuit (TKU-WKM section of single circuit BPE- WKM B line)Reconductor the 220 kV BPE-TKU-2 circuit (BPE-TKU section of BPE- WKM B single circuit line)

Thermal upgrade of 220 kV BPE-TNG-1 and RPO-TNG-1 circuits (BPE-TNG-RPO section of the BPE-WRK A single circuit line)Reconductor the 220 kV TKU-WKM-1 circuit (TKU-WKM section of single circuit BPE- WKM A line)

Reconductor the 220 kV OHK-WRK-1, ATI-OHK-1 and ATI-WKM-1 circuits (WRK-WKM A single circuit line)Reconductor the 220 kV TKU-WKM-2 circuit (TKU-WKM section of single circuit BPE- WKM B line)

Install two new 220/110kV interconnecting transformers at HHI and operate the HHI-TGA-1 circuit at 220kV.Thermal upgrade of 220 kV BPE-TNG-1 and RPO-TNG-1 circuits (BPE-TNG-RPO section of the BPE-WRK A single circuit line)

Build a third 110kV HAM-WHU CircuitReconductor the 220 kV OHK-WRK-1, ATI-OHK-1 and ATI-WKM-1 circuits (WRK-WKM A single circuit line)

Bus the 220 kV HLY-SFD-1 circuit at TMNInstall two new 220/110kV interconnecting transformers at HHI and operate the HHI-TGA-1 circuit at 220kV.

Add BOB Tee (59% from HLY) to 220 kV GLN-HLY circuit and feed BOB via a new 200 MVA, 220/110 kV interconnecting transformer2Build a third 110kV HAM-WHU Circuit

2011

Install a third 200 MVA, 220/110 kV interconnecting transformer ,at TRKBus the 220 kV HLY-SFD-1 circuit at TMN

2014 Reconductor the WRK-PPI-WKM-1 circuit (WRK- WKM B single circuit line)Add BOB Tee (59% from HLY) to 220 kV GLN-HLY circuit and feed BOB via a new 200 MVA, 220/110 kV interconnecting transformer2

Install a third 200 MVA, 220/110 kV interconnecting transformer ,at TRK 2015

Reconductor the WRK-PPI-WKM-1 circuit (WRK- WKM B single circuit line)

The development plan for the common reactive support requirements is shown in Table 4-3. Reactive support specific to each alternative project is provided in section 5.

4.3 Voltage Support Plan

Table 4-3: Voltage Support Common to all Options

YEAR Location Quantity (Mvar)

Static(S) / Dynamic(D)

2008 ALB 100 S

2008 ALB 100 D

2008 KTA 24 S

2009 HEN 100 D

2009 MDN 60 S

2024 KTA 24 S

2024 MPE 30 S

2025 WKO 30 S

2030 MPE 30 S

2033 WKO 30 S



22

2036 MPE 30 S

2039 HAM 50 S

2039 HAIRINI 100 S

For the purposes of these studies, reactive support at Otahuhu was modelled as a single large SVC of a magnitude no greater than that modelled in the NIGU project.

4.4 Penrose 110 kV Reinforcement

The Liverpool Street load has a forecast 2008 peak of approximately 100 MW. In mid-2007, Vector shifted this load from the Mount Roskill GXP to the Penrose GXP, supplied via the 110 kV PEN-LST cables. Vector now maintain the Mount Roskill-Liverpool Street cable on standby, and will not use this cable to supply load under normal circumstances.

This load shift has an effect on the load flows into the NAaN area, as it removes load from the Mount Roskill GXP, allowing greater capacity for supplying Northland via the 110 kV system. At the same time, the increased load on Penrose and in particular the PEN 110 kV bus, means that the need for reinforcement of this bus is brought forward.

The Penrose and Pakuranga 110 kV loads are supplied from three points; • The Penrose interconnection (PEN T10) • The Otahuhu interconnection (OTA T2 & T4) • The 110 kV ARI-PAK 1 circuit

There is also a 110 kV connection to Bombay but there is virtually no load flow north on this circuit.

In 2009, the ARI-PAK 1 circuit is scheduled to be decommissioned as part of the North Island Grid Upgrade project, leaving the Otahuhu and Penrose interconnecting transformers to supply the Pakuranga and Penrose 110 kV load. By 2009 these interconnecting transformers will not be able to provide sufficient n-1 capacity.

In 2011, the Pakuranga substation will be converted to 220 kV as part of the North Island Grid Upgrade project. This will reduce the 110 kV load in the area (because the PAK 110 kV load is transferred to 220 kV system), but it will also reduce the security of supply into the Penrose 110 kV bus with the removal of the 110 kV PAK-PEN circuit.

Therefore the two issues are: • Not enough n-1 capacity supplying PAK and PEN 110 kV loads from 2009 to 2011 • A loss of n-1 security into PEN110 from 2011

A number of options were investigated to resolve these issues, including • Install another interconnecting transformer at Penrose or Otahuhu • Parallel Vector’s 110 kV network with Transpower’s between Penrose and Mount

Roskill (this will move some of the 110 kV load back to Mt Roskill) • Retain one 110 kV PAK-PEN circuit and either install an interconnecting transformer

at Pakuranga or retain one 110 kV OTA-PAK circuit

The Penrose interconnection option works well if the impedance is chosen to balance flow between the 220 kV and 110 kV OTA-PEN circuits. This will mean that no additional reinforcement will be required prior to the installation of the cross harbour cable until 2016.



23

The option to parallel the Vector network would require two reactors on the 110 kV cables (approximately 20 Ohm each), which would be redundant once the cross-harbour cable was installed. It would also mean that the Vector assets become part of the transmission network and would require monitoring and control capability for the System Operator.

The option to retain the 110 kV PAK-PEN circuit would require additional interconnecting capacity at Otahuhu initially. Then when Pakuranga is converted to 220 kV, either this interconnector is transferred to Pakuranga or alternatively, one of the existing overhead OTA-PAK circuits can be operated at 220 kV with the other retained at 110 kV. The 110 kV PAK-PEN 1 circuit would be retained, and Penrose 110 kV bus would effectively have another circuit connection to Otahuhu via Pakuranga.

The preferred option is to install a second interconnecting transformer at Penrose, parallel to the existing PEN T10. This is a low cost option that allows the PAK-PEN 1 circuit to be removed and means that two OTA-PAK circuits are available for the 220 kV connection. A suitable Penrose interconnecting transformer would be a 15% impedance, 250 MVA unit.



24

5 Project Alternatives Four alternatives have been studied to provide comparisons on cost, effectiveness, build ability and operability.

Alternatives considered are as follows:

1. Installing a single 220 kV cross-harbour cable from Penrose to Albany, followed by a second parallel cable as load growth makes this necessary. 220 kV Pakuranga-Penrose circuits are also installed one at a time as necessary to reinforce Penrose.

2. Upgrading the existing 220 kV overhead double-circuit line from Otahuhu to Henderson, including replacing existing conductor with high-temperature conductor (HTC), and upgrading the existing 110 kV transmission system with HTC as required. Assume no new lines are built until all HTC upgrade options have been exhausted.

3. Reinforcing the 110 kV system across Auckland prior to installing the cross-harbour cable. This involves adding an interconnection at Mount Roskill, supplied at 220 kV from Penrose.

4. New generation in the North Isthmus area, connected into the 220 kV HPI-MDN circuit.

The tables below show the system limitations and recommended augmentations based on forecast load growth. The Year column gives the year at which the limitation will first occur. Therefore to avoid the limitation the recommended augmentation would need to be complete before the winter peak of that year



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5.1 Option 1 – Cross Harbour Cables

This involves Installing a single 220 kV cross-harbour cable from Penrose to Albany, followed by a second parallel cable as load growth makes this necessary. 220 kV Pakuranga-Penrose circuits are also installed one at a time as necessary to reinforce Penrose.

5.1.1 Development Plan

Table 5-1: Option 1 - Cross-harbour cable development plan

Year NAaN load Limitation Augmentation Notes 2009 910 MW OTA T2 & T4 and PEN T10 do

not provide n-1 security to 110 kV loads they supply

Install a 2nd 250 MVA 15% interconnecting transformer at PEN

2013 1025 MW OTA-PEN 5 102% with OTA-

PEN 6 out of service Special protection scheme; take PEN T10 out of service when either 220 kV OTA-PEN cct trips


PEN 6 out of service, with PEN T10 switched out HEN-SWN 1 101% with HEN-OTA 1 out of service

Install one 220 kV PAK-PEN cct Install one 220 kV cable PEN-HOB-WRU-ALB plus HOB and WRU GXPs

Leaving the new PEN interconnecting transformer in service delays the need to split Vector’s HOB-LST connection and therefore delays the second interconnecting transformer at HOB from 2021to 2023

LST-HOB 1(2) o/l with LST-HOB 2(1) out of service LST-PEN 1(2) o/l with LST-PEN 2(1) out of service

Special protection scheme; if one cable trips, its parallel circuit is taken out of service.

Due to new interconnecting transformer at HOB being operated in parallel with the LST-PEN 110 kV cables:

2020 1191 MW OTA-PEN 2 102% with PEN

T10 out of service Special protection scheme; Intertrip OTA-PEN 2 with PEN T10, leaving PEN T12 to take the load

1256 MW LST-PEN 1 & 2 100% with

HOB-PEN 1 out of service Split Vector network between HOB and LST.

One PEN interconnecting transformer may be removed (or the OTA-PEN 2 cct may be removed)

2023

HOB has no n-1 security with the HOB-LST split

Install a second interconnecting transformer at HOB.

2024 1279 MW WRU load approximately equal to total 110 kV supply capacity

Assume 2nd WRU 220/33 kV supply Tx is installed and 110 kV supply taken out of service

Later than in original GUP due to the new assumption that James St Load (about 33 MW) remains shifted to ALB 33.



26

2026 1323 MW HEN-SWN 1 100% with HEN-OTA 1 out of service

Reduce impedance of PEN-HOB cable reactor to 12.4 Ohms

OTA-PEN 6 100% with PAK-PEN 1 out of service

Install second PAK-PEN cable

Brought forward by reduction in PEN-HOB reactor and consequent increase in power flow north out of PEN

2028 1366 MW HEN-HEP 1-4 100% with OTA

T3 or T5 out of service HEN T1 102% with HEN T5 out of service Two of HEN-SWN 1, HEN-OTA 1 & HOB-PEN 1 95% loaded with any one out of service

Install one PEN-ROS 220 kV feeder and 220/110 250 MVA 15% interconnecting transformer at ROS

PAK-PEN 1 100% with PAK-PEN 2 out of service

Install reactors in PAK-PEN cables to balance load flow between these and OTA-PEN 5 & 6 o/h circuits

1.2 Ohm reactance is about right

2031 1435 MW MDN T1 101% with T2 out of

service Install a 3rd interconnecting transformer at Marsden equivalent to the existing T1 & T2

May change as the existing MDN transformers may be replaced in the near future

2036 1554 MW HEN-SWN 1 100% with HEN-

OTA 1 out of service HOB-PEN 1 99% with HEN-SWN out of service

Install 2nd cross-harbour cable direct from Penrose to Albany

2038 1605 MW PAK-PEN 1 101% with PAK-

PEN 2 out of service OTA-PEN 6 98% with PAK-PEN 1 out of service

Increase rating of these circuits by adding forced cooling Bypass PAK-PEN circuit reactors to reduce load on OTA-PEN 5 & 6

2040 1656 MW HEN-HEP 1-4 highly loaded

with PEN-ROS 1 out of service An upgrade of these

circuits (presently 75 wolf) or a second PEN-ROS circuit will be required within 2–3 years

*Note: Upgrading PAK-PEN 1 & 2 in 2038 will involve cooling stations for the cable cooling system.

5.1.2 Reactive Plan

The reactive plan includes the common support shown in Table 4-3 as well as that listed in the table below:

Table 5-2: Option 1 Voltage Support Plan





27

2022 HEN 50 S

2028 ALB 100 S

2034 HEN 50 S

5.1.3 Single Line Diagram

Figure 5-1: Option 1 - Development Plan Single Line Diagram



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5.2 Option 2 – High Temperature Conductor

This option involves upgrading the existing 220 kV overhead double-circuit line from Otahuhu to Henderson, including replacing existing conductor with high-temperature conductor (HTC), and upgrading the existing 110 kV transmission system with HTC as required. Assume no new lines are built until all HTC upgrade options have been exhausted.


Table 5-3: High Temperature conductor development plan Year NAaN load Limitation Augmentation Notes 2009 910 MW OTA T2 & T4 & PEN T10 do

not provide n-1 security to 110 kV loads they supply

Install a 2nd 250 MVA 15% interconnecting transformer at PEN


PEN 6 out of service Special protection scheme; take PEN T10 out of service when either 220 kV OTA-PEN circuit trips


PEN 6 out of service, after PEN T10 is switched out HEN-SWN 1 101% with HEN-OTA 1 out of service

Install one 220 kV PAK-PEN circuit High temperature conductor on HEN-OTA circuits

2018 1144 MW HEN T1 100% with HEN T5

out of service Replace HEN transformers with two 250 MVA 7% interconnecting transformers

2020 1191 MW ALB-HEN 1 & 2 102% with ALB T4 out of service

Install a second interconnecting transformer at ALB equal to existing

2021 1213 MW MNG-ROS 1&2 101% with

HEN-SWN 1 out of service ALB-HEN 3 100% with HEN-HPI 1 out of service

Upgrade MNG-ROS circuits to high temperature conductor Upgrade terminal spans to duplex zebra conductor

2024 1279 MW OTA T5 101% with T3 out of

service HEN-WEL 1 & 2 101% with HPI-MDN 1 out of service

Install a third interconnecting transformer at OTA in parallel with and equivalent to T5 Thermal upgrade of HEN-WEL 1 & 2 from 50oC Coyote to 75oC coyote

OTA-ROS 1 & 2 108% with HEN-OTA 1 out of service

High temperature conductor on OTA-ROS circuits

Brought forward by the lower impedance at OTA due to 3rd interconnecting transformer


T10 out of service Special protection scheme: Trip OTA-PEN 2 with PEN T10

2028 1366 MW MNG-OTA 1 100% with MNG-

OTA 2 out of service High temperature conductor on the MNG-OTA 1 & 2 circuits

2029 1388 MW HEN-HPI 1 100% with ALB- Upgrade HEN-HPI 1 to



29

HEN 3 out of service high temperature conductor


service PEN T12 100% with PEN T10 & OTA-PEN 2 out of service (Special protection scheme)

Install a 3rd interconnecting transformer at Marsden equivalent to the existing

Assume by now PEN T10 has been replaced due to condition with 15% 250 MVA interconnecting transformer. Install reactor on OTA-PEN 2 to balance load flow into PEN110

Pen T10 is 1972, nearly 60 yrs old by this time. If this is not the case, increase T10 impedance with a reactor

2032 1458 MW ALB-HEN 3 100% with HEN-

HPI 1 out of service OTA T4 101% with T2 out of service

High temperature conductor on ALB-HEN 3 Special protection scheme – trip T2 & T4 together. PEN interconnecting transformers take the load

Likely do this at same time as HEN-HPI 1


OTA 1 out of service ALB-HEN 1&2 100% with HEN-HPI 1 out of service

Install PEN-ROS cable and 250 MVA interconnecting transformer at ROS Install 10 Ohm reactors in ALB-HEN 1&2 circuits

PAK-PEN 1 overloads for various outages due to installation of new PEN-ROS circuit HEP-ROS 1&2 overload with HEN-SWN 1 out of service due to new PEN-ROS circuit

Install 2nd 220 kV PAK-PEN circuit Upgrade HEP-ROS circuits to high temperature conductor

2039 1631 MW HEN-WEL 1&2 100% with

HPI-MDN 1 out of service High temperature conductors on HEN-WEL 1 & 2

2040 ALB-HPI 1 101% with ALB-

HEN 3 out of service HEN-OTA 1 96% with HEN-SWN 1 out of service

Upgrade ALB-HPI 1 to high temperature conductor

Likely done at same time as HEN-HPI 1 First ALB-PEN cable will be required within about 2 years

5.2.2 Reactive Plan

The reactive plan includes the common reactive plant shown in table 4-3 well as the reactive plant support listed in the table below.




2016 ALB 50 S

2016 HEN 100 S

2024 ALB 50 S

2026 HEN 100 S

2030 ALB 50 S

2038 ALB 50 S



30

5.2.3 Single Line diagram

Figure 5-2: Option 2 Development Plan – Single Line Diagram



31

5.3 Option 3 – New interconnection at Roskill

This option involves reinforcing the 110 kV system across Auckland prior to installing the cross-harbour cable. This involves adding an interconnection at Mount Roskill, supplied at 220 kV from Penrose.


Table 5-5: New Interconnection at Roskill

Year NAaN load Limitation Augmentation Notes 2009 910 MW OTA-PEN 5 (6) exceeds

branch capacity when cct 6 (5) is out of service OTA T2 & T4 & PEN T10 do not provide n-1 security to 110 kV loads they supply

Remove branch restriction Install a 2nd 250 MVA 15% interconnecting transformer at PEN





Install one 220 kV PAK-PEN cable Install PEN-ROS cable and 250 MVA interconnecting transformer at ROS

2020 1191 MW ALB-HEN 1 & 2 101% with

ALB T4 out of service Install 2nd interconnecting transformer at ALB, equivalent to ALB T4


OTA 1 out of service Install 2nd interconnecting transformer at ROS

HEP-ROS 2 101% with HEN-OTA 1 out of service

Upgrade a single span to get the full capacity of the existing HEP-ROS 1&2 circuits (184/202 MVA)

2023 1256 MW PAK-PEN 1 101% with OTA-

PEN 6 out of service Install a series reactor (1.2 Ohm) in this circuit to balance flow between this and OTA-PEN 5&6

Balancing the power flow delays the cable installation work for ~3 yrs, until the cross harbour cable is installed

2024 1279 MW HEP-ROS 2 102% with HEN-

SWN 1 out of service Upgrade HEP-ROS 1 & 2 from 75oC wolf to 90oC wolf

This delays need for cross-harbour by about 2 years


OTA 1 out of service Vector’s WRU load exceeds the capacity of their 110 kV supply system OTA-PEN 5 & 6 overload with PAK-PEN 1 out of service

Install first PEN-HOB-WRU-ALB cable and HOB and WRU GXPs Install 2nd supply transformer at WRU Install a second 220 kV PAK-PEN cable (including a series reactor)

Assuming that the reinforcement that Vector do in 2010 is removed to allow for installation of the 220 kV ALB-WRU cable



32

OTA-PEN 2 o/l with PEN T10 out of service

Special protection scheme to take OTA-PEN 2 out of service when PEN T10 trips

2028 1366 MW OTA T4 102% with OTA T1

out of service Special protection scheme – inter-trip OTA T4 with OTA T2

PEN interconnecting transformers take the load


service Install a third interconnecting transformer at MDN equivalent to existing


T12 out of service Install a series reactor (10 Ohms) on OTA-PEN 2 to balance flow between this circuit and the two interconnecting transformers.

If T10 hasn’t been replaced by this time, increase it’s impedance using a series reactor (5 Ohms). PEN T10 is circa 1972

2036 1554 MW Vector lose n-1 security on

their PEN-LST cables about this time

Assume 2nd HOB interconnecting transformer is installed at this time, and LST-HOB cables and PEN-QUAY cable are normally open

2040 1656 MW PAK-PEN 1 101% with PAK-

PEN 2 out of service HEN-OTA 1 100% with HEN-SWN 1 out of service HEN-WEL 1 & 2 100% with HPI-MDN out of service

Upgrade these cables to force-cooled, increasing capacity from 660 MVA to 1100 MVA Install the second cross harbour cable, ALB-PEN Reconductor these circuits

Bypass series reactors to reduce load on OTA-PEN 5 & 6 circuits

*Note: Upgrading PAK-PEN 1 & 2 will involve cooling stations for the cable cooling system.

5.3.2 Reactive Plan

The reactive plan includes the common reactive plant shown table 4-3 as well as the reactive plant listed in the table below




2016 ALB 50 S

2018 HEN 50 S

2028 HEN 50 S



33


Figure 5-3: Option 3 Development Plan



34

5.4 Option 4 – New generation north of Auckland

This option involves installation of new generation in the North Isthmus area, connected into the 220 kV HPI-MDN circuit.

This development plan is provided for information only. 5.4.1 Development Plan

Table 5-7: New generation north of Auckland Year NAaN load Limitation Augmentation Notes 2009 910 MW OTA-PEN 5 (6) exceeds

branch capacity when cct 6 (5) is out of service OTA T2 & T4 & PEN T10 do not provide n-1 security to 110 kV loads they supply

Remove branch restriction Install a 2nd 250 MVA 15% interconnecting transformer at PEN





Install one 220 kV PAK-PEN cable Install 120 MW generation at Rodney connected to the HPI-MDN 1 circuit

2018 1144 MW HEN T1 102% with T5 out of

service Replace HEN T1 & T5 with two 250 MVA 7% interconnecting transformers

2019 1167 MW ALB-HEN 1 & 2 100% with

ALB T4 OOS Install a second ICT at ALB equivalent to ALB T4

Not required in other options where the new WRU GXP takes load from ALB 110


OTA 1 out of service Install one ROS interconnecting transformer with a single 220 kV cable feeder from PEN


T10 out of service Install a 9 Ohm series reactor in OTA-PEN 2 cct to balance power flow with PEN interconnecting transformers

2026 1323 MW OTA-PEN 6 100% with PAK-

PEN 1 out of service Install a second 220 kV PAK-PEN cable

2028 1366 MW HEN-OTA 101% with HEN-

SWN out of service Increase ROD generation from 120 MW to 240 MW

A 2nd interconnecting transformer at ROS would overload HEP-ROS


service Install a third interconnecting transformer at MDN equivalent to existing


OTA 1 out of service Install a second interconnecting transformer at ROS

HEP-ROS 1 o/l with HEN- Upgrade HEP-ROS 1 & 2 to Brought forward by



35

SWN 1 out of service PAK-PEN 1 100% with PAK-PEN 2 out of service

90oC wolf Install series reactors on PAK-PEN 1 & 2

the installation of a second interconnecting transformer at ROS

2036 1554 MW HEN-OTA 1 101% with HEN-

SWN 1 out of service and vice versa

Install the first cross harbour cable PEN-HOB-WRU-ALBN, and HOB and WRU GXPs

Vector lose n-1 security on their PEN-LST cables about this time Vector’s WRU load exceeds the capacity of their 110 kV supply system

Assume 2nd HOB interconnecting transformer is installed at this time, and LST-HOB cables and PEN-QUAY cable are normally open Install 2nd interconnecting transformer at WRU

Assuming that three 200 MVA cables supply the CBD from PEN (a new PEN-QUAY is installed by Vector around 2013) Assuming that the reinforcement that Vector do in 2010 is removed to allow for installation of the 220 kV ALB-WRU cable

2040 1656 MW OK

5.4.2 Reactive Plan

The reactive plan includes the common reactive plant shown table 4-3 as well as the reactive plant listed in the table below.




2016 ALB 50 S

2022 HEN 50 S

2024 ALB 50 S

2038 HEN 50 S




36

Figure 5-4: Option 4 - Single Line Diagram



37

6 Discussion on Reactive Plans The reactive power losses in the power system increase quadratically as the loading in the transmission circuits are increased. The reactive power losses in the transmission circuits are supplied from the two ends of each transmission circuit. Generally a higher amount of reactive power needs to be supplied from the receiving end compared to the sending end.

For the cross-Auckland transmission, the sending end reactive power requirements are supplied from the reactive support at Otahuhu. The reactive power available from Otahuhu based on the NI GUP reactive plan Option 2 is sufficient to provide this reactive requirement. Additionally, planned and committed reactive power support in the NAaN area will be sufficient to meet the reactive power losses in the transmission system until at least 2010.

6.1 Static Reactive Requirements

For each modelled option, sufficient reactive power was supplied at the Henderson, Albany and Marsden 220 kV buses to maintain 1.02 pu voltage at these buses at peak load times and with normal operating configuration. The additional static reactive support required in the NAaN area for the four transmission options is shown in Figure 6-1.

Figure 6-1: Reactive Support Requirement in NAaN Area

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900

2010 2015 2020 2025 2030 2035 2040

Year

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R

Option 1

Option 2

Option 3

Option 4

6.2 Dynamic Reactive Requirements

The reactive power loss in the transmission system north of Otahuhu may undergo a significant step change following an outage of a transmission circuit. In a voltage stability constrained system such as the power system supplying the NAaN region, it is not prudent to rely on post-contingency switching of the capacitor banks for ensuring system stability. It is considered good industry practice to carry sufficient dynamic reserves in the system, pre-contingency, to cater for such events. The dynamic reactive power reserves



38

can be maintained in the form of reactive power from synchronous generators, synchronous condensers, SVCs and thyristor switched capacitors.

In analysing the dynamic reactive power reserves required in NAaN region for power transmission north from Otahuhu, the total reactive power supplied to the transmission system from Henderson, Albany and Marsden under the worst contingency is assessed both pre and post-contingency. The reactive power difference between the pre and post-contingency situation represents the minimum level of dynamic reactive reserves required at these substations.

By 2010, it is likely that the dynamic reactive support in the Northland area will be supplied from three sources; synchronous condensers at Marsden and Henderson (1 x 60 Mvar and 2 x 50 Mvar respectively) and an SVC at Albany (100 Mvar). The dynamic reactive power requirements for Option 1, 2, 3 and 4 are shown in Figure 6-2, Figure 6-3, Figure 6-4 and Figure 6-5.

Figure 6-2: Dynamic reactive requirement for Northland for Option 1

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2005 2010 2015 2020 2025 2030 2035 2040

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r

MDN dynamicALB dynamicHEN dynamic



39


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The graphs for each option indicate that the existing dynamic support (at Marsden) plus that already committed (Albany SVC) and under consideration (Henderson condensers) in the NAaN region will be sufficient to maintain a stable power system following the worst likely single transmission contingency.



41

7 Summary The existing transfer limit into the NAaN area is limited by the capacity of the 220 kV HEN OTA circuits. This limit will be reached by winter 2011. One interim measure planned to increase this transfer limit is closing the 110 kV HEP-ROS split.

Under present load growth forecasts and with existing interconnecting transformers in service, the power flow will be well balanced between the 220 and 110 kV systems when the HEP ROS split is closed. This allows the best possible load transfer given the circuit ratings. Where interconnecting transformers are added in the reinforcement plans, 15% impedance is preferred as the standard value except where a variation is required to achieve a higher n-1 transfer limit, or where the new transformer has to match an existing transformer.

To increase the transfer limit into the NAaN area further, four transmission options have been developed and analysed. Each option takes a different approach to supplying the increasing NAaN area load for the next thirty years. The four options are:

1. A new 220 kV cable circuit across Auckland from Penrose to Albany

2. Replacing existing 220 & 110 kV conductors with High Temperature Conductors

3. Additional 220/110 kV interconnection to increase transmission across the existing 110 kV transmission system

4. New generation in the NAaN area used to delay new transmission options

A new 220 kV cable circuit is required to be built by winter 2016 in option 1. The new transmission system reaches its capacity by 2028 when the 110 kV system needs to be reinforced, and then in 2036 the transmission capacity needs to be further augmented by adding a second 220 kV cable.

Option 2 minimises the number of new lines required to be built. Existing circuits are upgraded using high temperature conductor; the first upgrade being required by 2016. The entire 110 and 220 kV systems from Otahuhu to Henderson must be upgraded as the load increases, beginning with the 110 kV MNG-ROS and 220 kV HEN-OTA circuits. Eventually in 2036 an interconnection is required at Mount Roskill to prevent the upgraded lines from overloading.

This option has the highest reactive support requirement of all those studied, being about double that of the other options. By the end of the study period this option has about 800 Mvar of support in the NAaN region, compared to about 400 Mvar for the other options.

Option 4 assumes that new generation is installed north of Auckland, reducing the load on the cross-Auckland transmission system. This generation does not remove the overloading on the 110 kV system, which is relieved by an interconnector at Mount Roskill in 2017. Assuming a maximum of 240 MW of new generation in the Rodney area, the first 220 kV cable is required in 2033.

Reinforcement of the 110 kV system in preference to the 220 kV system is examined in Option 3, where the Mount Roskill interconnection is installed in 2016 when the system reaches its limit. This delays the reinforcement of the 220 kV system until 2025, when the first cross-harbour cable is installed between Penrose and Albany.



42

Appendix A – Existing Circuit Ratings Table A-0-1: Existing Circuits in Upper North Island south of Albany

Circuit Asset Conductor Conductor

Rating (MVA)

Branch Rating (MVA)

Notes

ALB-HEN 1 ALB-HEN A Simplex Wolf 80oC 96/105 96/105

ALB-HEN 2 ALB-HEN A Simplex Wolf 80oC 96/105 96/105

ALB-HEN 3 ALB-HPI A & HEN-MDN A

Duplex Zebra 71oC 680/756 561/617 200m simplex chukar

HEN-HEP 1 HEN-ROS A Simplex Wolf 75oC 92/101 92/101

HEN-HEP 2 HEN-ROS A Simplex Wolf 75oC 92/101 92/101

HEN-HEP 3 HEN-HEP A Simplex Wolf 75oC 92/101 92/101

HEN-HEP 4 HEN-HEP A Simplex Wolf 75oC 92/101 92/101

HEN-OTA 1 HEN-OTA A Duplex Zebra 120oC 938/985 915/915 Disconnector

HEN-SWN 1 HEN-OTA A Duplex Zebra 120oC 938/985 915/915 Disconnector

HEP-ROS 1 HEN-ROS A 2 bonded Wolf 75oC 184/202 114/114 Disconnector at 114 MVA then single span at 174/191 MVA

HEP-ROS 2 HEP-ROS A 2 bonded Wolf 75oC 184/202 114/114 Disconnector at 114 MVA then single span at 174/191 MVA

MNG-OTA 1 MNG-OTA A Duplex Zebra 75oC 355/390 305/305 Disconnector

MNG-OTA 2 MNG-OTA A Duplex Zebra 75oC 355/390 305/305 Disconnector

MNG-ROS 1 MNG-ROS A Simplex Wolf 75oC 92/101 92/101

MNG-ROS 2 MNG-ROS A Simplex Wolf 75oC 92/101 92/101

OTA-PAK 1 OTA-PAK A Duplex Chukar 75oC 561/617 235/235 Earth fault relay

OTA-PEN 2 OTA-PEN A & OTA-PEN B

2 bonded Wolf 75oC 184/202 174/191 Connecting spans of simplex zebra

OTA-PEN 5&6 OTA-PEN C Simplex Zebra 120oC 469/492 455/455 Transducer limit

OTA-PEN 7 OTA-PAK A Duplex Chukar 75oC 561/617 Inactive

OTA-ROS 1 OTA-PEN B & PEN-ROS A

Simplex Wolf 75oC 92/101 92/101

OTA-ROS 2 OTA-PEN B & PEN-ROS A

Simplex Wolf 75oC 92/101 92/101

OTA-SWN 1 HEN-OTA A Duplex Zebra 120oC 938/985 912/912 transducer

PAK-PEN 1 PAK-PEN A 2 Bonded 19/2.57 Cu 50oC 114/140 114/140



43

APPENDIX B - Interconnection Transformer Ratings Table B-0-1: Ratings of Auckland Area 220/110 kV Interconnecting Transformers

IC Transformer

Winding

(for 3 winding transformers )

Continuous Summer Winter Notes

ALB T4 H 200 274 290 Limited to 267 MVA by MV & HV protection settings

M 200 274 290

HEN T1 H 200 254 270

M 200 254 270 Limited to 229 MVA by MV circuit breaker rating

HEN T5 H 200 274 290 Limited to 267 MVA by MV circuit breaker rating

M 200 274 290

MDN T1 H 141 190 201 Limited to 183 MVA by tap changer rating

M 141 190 201

MDN T2 H 141 190 201 Limited to 183 MVA by tap changer rating

M 141 190 201

OTA T2 H 117 158 170

M 100 135 145

OTA T3 H 250 324 338

M 260 337 351

OTA T4 H 200 254 270

M 200 254 270

OTA T5 2-winding 250 318 332

PEN T10 H 206 309 313 Limited to 291 MVA by HV protection settings

M 200 296 300



44

Appendix C - Parameters of New Components Used Table C-0-1: Parameters of New Components used in Studies

Component Length (km) R (Ohms) X (Ohms)

Winter Rating (MVA)

Summer Rating (MVA)

notes

x-harbour cables (ALB-PEN):

ALB-WRU 8.45 0.127 1.463 543 630 cyclic rating

HOB-WRU 9.85 0.152 1.618 543 630 cyclic rating

HOB-PEN 10.21 0.183 1.133 543 630 cyclic rating

Total (ALB-PEN) 28.51 0.462 4.214 543 630 cyclic rating

220 kV PAK-PEN ccts - cable section

8.6 0.085 1.424 667 667 Direct buried

220 kV PAK-PEN ccts - cable section

8.6 0.085 1.424 1115 1115 Force-cooled

220 kV PEN-ROS cable 10.2 0.153 1.766 543 630 cyclic rating

4th ALB-WRU 110 kV cct (cable) 8.5 0.252 1.038 120 120 Vector's

Vector CBD 110 kV cables:

LST-PEN 1&2 8 0.238 0.982 205 205 Vector's

LST-ROS 1 10.2 0.304 2.228 150 150 Vector's

HOB-LST 1&2 1.5 0.070 0.202 150 150 Vector's

Transformers:

HEN ICT1 & 2 0.2% 7% 318 338 Continuous 250 MVA

HOB ICT1 & 2 0.2% 15% 318 338 Continuous 250 MVA

ROS ICT1 & 2 0.2% 15% 318 338 Continuous 250 MVA

WRU T1 & 2 0.2% 15% 250 250 Continuous 250 MVA

High Temperature Conductor

ALB-HPI / ALB-HEN / HEN-HPI 1350 1300 R & X as per existing

HEN-OTA 1350 1300 R & X as per existing



45

HEP-ROS 350 340 R & X as per existing

MNG-OTA 670 660 R & X as per existing

MNG-ROS 180 170 R & X as per existing

OTA-ROS 180 170 R & X as per existing



46

Appendix D - Substation Codes Table D-1: Substation 3-letter Codes

Short Code

Site Short Code

Site Short Code

Site Short Code

Site

ABY Albury HEN Henderson MTR Mataroa TAK Takanini

ADD Addington HEP Hepburn Road NMA North Makarewa TAP Te Apiti

ALB Albany HIN Hinuera NPK National Park TCC Taranaki Combined Cycle

ALD Arnold HKK Hokitika NPL New Plymouth TGA Tauranga

ANC Anchor Products (Te Awamutu)

HLE Huntly East (Ohinewai)

NSY Naseby TIM Timaru

ANI Aniwhenua HLY Huntly OAM Oamaru TKA Tekapo A

APS Arthur’s Pass HOR Hororata OHA Ohau A TKB Tekapo B

ARA Aratiatia HPI Huapai OHB Ohau B TKH Te Kaha

ARG Argyle HTI Hangatiki OHC Ohau C TKR Takapu Road

ARI Arapuni HUI Huirangi OHK Ohakuri TKU Tokaanu

ASB Ashburton HWA Hawera OKE Okere TMH Three Mile Hill

ASY Ashley HWB Halfway Bush OKI Ohaaki TMI Te Matai

ATI Atiamuri IGH Inangahua OKN Ohakune TMK Temuka

AVI Aviemore INV Invercargill ONG Ongarue TMN Taumarunui

BAL Balclutha ISL Islington OPI Opihi TMU Te Awamutu

BDE Brydone KAI Kaiapoi OPK Opunake TNG Tangiwai

BEN Benmore KAW Kawerau OPU Opuha TOB Tokomaru Bay

BLN Blenheim KEN Kensington BHL Brownhill (400 kV Cable-Line interface)

TRK Tarukenga

BOB Bombay KIK Kikiwa ORO Orowaiti Tee TUI Tuai

BPE Bunnythorpe KIN Kinleith OTA Otahuhu TVT Teviot

BRB Bream Bay KKA Kaikoura OTB Oteranga Bay TWH Te Kowhai

BRK Brunswick KOE Kaikohe OTC Otahuhu CC TWI Tiwai

BRR Branch River KPI Kapuni OTG Otahuhu Power Station

TWZ Twizel

BRY Bromley KPO Karapiro OTI Otira UHT Upper Hutt

BWK Berwick KPU Kopu OWH Owhata UTK Upper Takaka

CBG Cambridge KTA Kaitaia PAK Pakuranga WAA Whareroa

CLH Castle Hill KUM Kumara PAL Palmerston WAH Wahapo

CML Cromwell KWA Kaiwharawhara PAP Papanui WAI Waiotahi

COB Cobb LFD Lichfield PEN Penrose WDV Woodville



47

COL Coleridge LIV Livingstone PKE Poike WEL Wellsford

CPK Central Park LTN Linton PNI Pauatahanui WES Western Road

CST Carrington Street MAN Manapouri PPI Poihipi WGN Wanganui

CUL Culverden MAT Matahina PRM Paraparaumu WHE Wheao

CYD Clyde MCH Murchison PTA Patea WHI Whirinaki

DAR Dargaville MDN Marsden RDF Redclyffe WHU Waihou

DOB Dobson MGM Mangamaire RFT Reefton WIL Wilton

DVK Dannevirke MHO Mangahao ROB Robertson Street WIR Wiri

EDG Edgecumbe MLG Melling ROS Mount Roskill WKM Whakamaru

EDN Edendale MNG Mangere ROT Rotorua WKO Waikino

FHL Fernhill MNI Motunui ROX Roxburgh WMG Waimangaroa

FKN Frankton MOK Mokai RPO Rangipo WPA Waipapa

GFD Gracefield MOT Motueka RTR Retaruke WPI Waipori

GIS Gisborne MPE Maungatapere SBK Southbrook WPR Waipara

GLN Glenbrook MPI Motupipi SDN South Dunedin WPT Westport

GOR Gore MRA Moturoa SFD Stratford WPW Waipawa

GYM Greymouth MST Masterton SPN Springston WRA Wairoa

GYT Greytown MTI Maraetai STK Stoke WRK Wairakei

HAM Hamilton MTM Mt Maunganui STU Studholme WTK Waitaki

HAY Haywards MTN Marton SVL Silverdale WTU Whakatu

HBK Highbank MTO Maungaturoto SWN Southdown WVY Waverley



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Appendix E - Forecast Load Data Table E-1: MW Load Forecast for Northland and Auckland as per EC Website April 2007

Year Northland MW Auckland MW

2007 839 1365

2008 870 1424

2009 910 1481

2010 1538

2011 978 1594

2012 1001 1638

2013 1025 1683

2014 1049 1730

2015 1073 1776

2016 1097 1822

2017 1121 1867

2018 1144 1912

2019 1167 1958

2020 1191 2004

2021 1213 2047

2022 1234 2090

2023 1256 2133

2024 1279 2179

2025 1301 2223

2026 1323 2266

2027 1345 2309

2028 1366 2351

2029 1388 2394

2030 1411 2439

2031 1435 2486

2032 1458 2531

2033 1482 2580

2034 1505 2626

2035 1529 2673

2036 1554 2724

2037 1579 2775

2038 1605 2826

2039 1631 2878

2040 1656 2930



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Appendix F - Characteristic of NAaN Load The graph below gives the 2006 load profile of the NAaN area based on half-hourly SCADA logs of the HEN-OTA 1 and HEN-SWN 1 MW circuit loading.

Figure F-0-1: NAaN Area 2006 MW Load Profile

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50

Appendix G - Characteristic of Penrose Load The graphs below indicate the nature of the total load on the Penrose GXP. Data for these graphs comes from half-hourly SCADA data for the 2006 calendar year.

There is occasional load shifting to Penrose from the Mount Roskill GXP. This makes the summer/winter nature of the usual load unclear.

Figure G-0-1: Total 2006 Penrose GXP Load including 22 kV, 33 kV, Liverpool St Feeders and Quay St Feeders

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Figure G-2 below shows the load on the Liverpool St feeders from Penrose. The occasional high peaks indicate periods when the lines company has shifted the Liverpool St load from Mount Roskill to Penrose. Apart from those periods and an apparent step change around August, the load on the Penrose-Liverpool St feeders is seen to be flat across the year.



51

Figure G-0-2: 2006 Liverpool St Feeder Load

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Figure G-3 shows the Penrose GXP load without the Liverpool St feeder load. This graph indicates clearly that the Penrose loads as a whole are winter peaking, if load shifting from Mount Roskill is avoided.

Figure G-3: 2006 Penrose Load without Liverpool St Feeder Load

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Figure G-4 shows the annual load profile at Liverpool St supplied from Mount Roskill. This may be added to the Penrose load under certain upgrade scenarios. The profile indicates that Penrose will remain winter peaking overall if this load transfer occurs.

Figure G-4: 2006 Mount Roskill Liverpool St Feeder Load

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part iii - attachment b - technical report rev 1

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