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Mighty River Power Ltd 27 July 2011 Document No. 60214865-001

Puketoi Wind Farm Technical Report Transmission Line, Sub Station and Collection System

AECOM Puketoi Wind Farm Technical Report

27 July 2011

Puketoi Wind Farm Technical Report Transmission Line, Sub Station and Collection System

Prepared for

Mighty River Power Ltd

Prepared by AECOM New Zealand Limited Unit H, 1 Brynley Street, Hornby, Christchurch 8042, P O Box 710, Christchurch MC, Christchurch 8140, New Zealand T +64 3 363 8500 F +64 3 363 8501 www.aecom.com

27 July 2011

60214865

AECOM in Australia and New Zealand is certified to the latest version of ISO9001 and ISO14001.

This report has been prepared by AECOM New Zealand Limited on the specific instructions of Mighty River Power Limited as our Client. It is for our Client’s use for the purpose for which it was intended, being the resource consent application for the Puketoi Wind Farm, in accordance with the agreed scope of work and information provided. Any use or reliance by any person contrary to the above, to which AECOM New Zealand Limited has not given its prior written consent, is at that person’s own risk.


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Quality Information Document Puketoi Wind Farm Technical Report

Ref 60214865

Date 27 July 2011

Prepared by I Bilbrough, K James, G Urban, K Maddumarachchi, S Kendrick, B Flavall, H Porter

Reviewed by Rodney Urban

Revision History

Revision Revision Date Details Authorised

Name/Position Signature

A 27-Jul-2011 Consent Issue J Schwaderer Manager T&D


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Table of Contents Executive Summary iii 1.0 Introduction 1

1.1 Scope of Investigation 2 2.0 Overhead Lines 2

2.1 Line Route Selection 2 2.1.1 Line Design Methodology 3

2.2 Line Modelling 3 2.2.1 Survey Data 3 2.2.2 Conductor Modelling 3

2.3 Line Loading 3 2.3.1 Maximum Wind 3 2.3.2 Snow & Ice 4 2.3.3 Conductor Temperatures 4

2.4 Clearances 4 2.4.1 Crossings 4

2.5 Conductor Selection 5 2.5.1 220kV OHL 5 2.5.2 33kV OHL 5 2.5.3 Conductor Tensions 6

2.6 Insulators and Hardware 6 2.7 Structure Selection 6

2.7.1 220kV OHL Structures 6 2.7.2 33kV OHL Structures 6

2.8 Structural Analysis 7 2.9 Foundations 7

3.0 Collection System 7 3.1 General 7 3.2 Unit Sub Station 7

3.2.1 Step Up Transformer 8 3.2.2 33 kV RMU 8 3.2.3 Low Voltage Cabling 8

3.3 33kV Collection Circuits 8 3.3.1 Cable Trenches 8 3.3.2 33 kV Cables 8

4.0 220/33 kV Substation 9 4.6 Oil Drainage and Interception System 12

4.6.1 Description 12 4.6.2 Oil Volume and Stormwater Criteria 12 4.6.3 Operation 12 4.6.4 Transformer Bund Area & Wall Height 12 4.6.5 Discharge 13

5.0 Earthing System 13 5.1 Overview 13 5.2 Summary 13 5.3 Soil Resistivity Test and Modelling 14 5.4 Earth Fault Levels & Clearance Times 14 5.5 Structure Earth Grid Resistances 14 5.6 Substation Earth Grid Resistance 14 5.7 Calculations 14

6.0 Electromagnetic Field Strength (EMF) 15 7.0 Preliminary Constructability Review 16

7.1 Planning and Materials 16 7.2 Vegetation Management 16 7.3 Access 16 7.4 Construction 17


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7.4.1 Road or Rail Protection 17 7.4.2 Reinstatement 17 7.4.3 Line Maintenance 17

8.0 Conclusion & Recommendations 18

List of Figures and Tables List of Figures

Figure 1 Proposed Wind Farm Site 1 Figure 2 Unit Sub Station Schematic 8 Figure 3 Electric field strength of the 220kV transmission line 15 Figure 4 Magnetic flux density of the 220kV and 33kV lines. 16

List of Tables

Table 1 Line Characteristics 3 Table 2 Conductor Temperatures 4 Table 3 OHL Conductor Clearances 4 Table 4 33kV OHL Existing Crossing Details 5 Table 5 220kV OHL Existing crossing Details 5 Table 6 Typical Soil Resistivity Profile derived for Puketoi area 14 Table 7 Worst case future bus earth fault levels 14


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Executive Summary

Mighty River Power Ltd is currently proposing to build a new wind farm in the Puketoi Ranges approximately 40kms south east from Palmerston North. The proposed wind farm is to contain up to 53 turbines, each with up to 6.15 MW generating capacity. Electricity generated will be collected by combinations of 33kV overhead lines and underground cables and then fed into the national grid via a 220kV overhead transmission line.

AECOM has been engaged by MRP to provide details of the transmission system to be used to connect the Puketoi Wind Farm to the Turitea Wind Farm and the national grid.

Transmission line and internal reticulation design has taken into consideration line capacity, transmission voltage, clearance height of wires from the ground, structural loading, electrical earthing, electrical field and magnetic field levels.

A 39km long 220kV overhead line is proposed between the Puketoi Wind Farm and the Turitea Wind Farm Plantation Substation. It has been designed to provide for a single transmission solution for the Puketoi Wind Farm and other generation projects in the wider Puketoi area in order to reduce costs and environmental effects. The proposed 220kV overhead line comprises two circuits supported by both steel lattice structures and single or double steel pole structures with a combined total of 111 structures with a maximum structure height of approximately 52m.

Electricity generation from the proposed wind turbines is collected using a system of both underground and aerial cables at a voltage of 33kV. The aerial 33kV collection system lines comprise single, double and triple pole structures supporting single, double and triple circuits, and will extend for approximately 23kms. The proposed 33kV line routes comprise of 166 structures, with a maximum height of 22m.

A new 33/220kV on site substation is to be located below the summit of the Puketoi range in order to connect the 33kV collection circuits and to step the voltage up to 220kV for connection to the national grid.


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Glossary of Terms

A Amps

AC Alternating Current

Al Aluminium

CB Circuit Breaker

cct Circuit

CDEGS Integrated Software for Power System Grounding/Earthing, Electromagnetic Fields and Electromagnetic Interference

CT Current Transformer

Cu Copper

DC Direct Current

DIS Disconnnector

EEA Electrical Engineers' Association

EF Earth fault

EGVR Earth Grid Voltage Rise

EMF Electromagnetic Field Strength

EPR Earth Potential Rise

FE Finite Element

HDCu Hard-drawn copper

HV High Voltage

IEC International Electrotechnical Commission

kA kilo-Amp

kV kilo-Volts

kVA kilo-Volts-Ampere

LV Low Voltage

MEWP Mobile Elevated Work Platform

MRP Mighty River Power Limited

MVA Mega-Volt-Ampere

NCT Neutral Current Transformer

NER Neutral Earthing Resistor

NZECP New Zealand Electrical Code of Practice

OC Overcurrent


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OD Overall Diameter

ODJB Outdoor Junction Box

OHEW Overhead Earth wire

OHL Overhead Line

OLTC On Load Tap Changer

PLS-CADD Power line Systems Computer Aided Design and Drafting

PSCAD EMTP PSCAD, an Electromagnetic Transients Program

RMU Ring Main Unit

RS Ruling Span

SA Surge Arrestor

SCADA Supervisory Control and Data Acquisition

SLD Single Line Diagram

VT Voltage Transformer

WTG Wing Turbine Generator

XLPE Cross-linked Polyethylene

AECOM Puketoi Wind Farm Technical Report 1

1.0 Introduction Mighty River Power (MRP) has proposed to develop a wind farm on agricultural land in the Puketoi Range, located approximately 40km south east of Palmerston North.

Figure 1 Proposed Wind Farm Site

The wind farm is proposed to contain up to 53 turbines, each with up to 6.15 MW generating capacity. Electricity generated will be collected by combinations of 33kV overhead lines and underground cables and then fed into the National Grid via a 220kV overhead transmission line. The purpose of this report is to provide information for the wind farm consent application.

MRP is cognisant of other potential generation projects (both consented and in consent processes) in the wider Puketoi area, and wishes to ensure that environmental effects associated with more than one transmission line between the existing 220kV infrastructure near Palmeston North and the Puketoi area are avoided. Accordingly, MRP wishes to ensure that the capacity of the proposed 220kV transmission line is sufficient to accommodate all Puketoi-area generation, if this proves to be the most environmentally and commercially sensible outcome. The total Puketoi area potential generation is understood to sum to around 1332MW, which has driven the selection of the conductor. Sufficient infrastructure is to be provided at the Puketoi substation on the 220kV side to allow for other projects to connect.

This report covers 220kV infrastructure from the proposed Turitea plantation substation on the Tararua Range, to the proposed Puketoi substation. The Turitea substation and the 220kV line between the Turitea Plantation Substation and the National Grid at Linton are addressed in the resource consent applications for the Turitea project.

This report provides details on the following aspects of the transmission network associated with the proposed wind farm and covers the design methodology in order to complete the developed design of the Puketoi Wind Farm:

- 220kV overhead transmission line (OHL)

- 33kV overhead transmission line (OHL)

- 33kV underground cable routes

- 33/220kV substation layout and conceptual design

- Environmental effects of the transmission system including;


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Earth potential rise (EPR)

Electromagnetic Field Strength (EMF)

1.1 Scope of Investigation The scope of work for the developed design for the Puketoi Wind Farm connection into the national grid was determined following preliminary work carried out by AECOM in 2010. In brief, the scope of this investigation included the following tasks: - 220kV transmission line design

Identify structure sites on preferred route (commenced in 2010 investigation).

Identify prefered conductor types (commenced in 2010 investigation).

Refine tower site locations.

Recommend structure types for single and double circuits.

Provide 3D models and drawings of structures.

- 220kV substation design.

Prepare 3D model of Puketoi substation.

Provide simplistic schematic diagrams.

Additional tasks that were requested and were included in the scope of works are listed below:

Design the 33kV on site collection system.

Undertake overhead line EMF calculations.

Identification of potential EPR sites of concern for telecommunication plant for future investigation.

Identifying the clearances to the KiwiRail asset in span 78-79 of the 220kV OHL.

Prepare a developed design report.

This report does not include any design work for the Turitea substation.

2.0 Overhead Lines

2.1 Line Route Selection MRP has led a detailed multi-criteria analysis using constraint mapping to develop and select the preferred line route.

Further to the earlier work carried out by MRP and AECOM in 2010, the 220kV OHL route was revised to take into consideration the following:

- Updated contour data.

- Subtle changes made due to landowner discussions surrounding structure types and locations.

- Further advice from the project landscape architect, ecologist, civil and geotechnical engineer.

The 33kV collection system (which incorporates the underground cable from each turbine and the OHL connection to the new substation) was designed to provide a “backbone” alignment that would provide some flexibility for connection into the wind farm turbines. Several underground connections to the backbone have been designed to allow flexibility in the electrical design which will ultimately be dependent on final turbine choice.


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2.1.1 Line Design Methodology

The methodology adopted for determining line design for each line was as follows:

- Revise / develop the PLS-CADD model minimising the extent of turn off angles wherever feasible.

- Make any relevant changes to the model based on information received from MRP.

- Check clearances along the proposed line route.

- Eliminate any design constraints by relocating structures or altering structure heights.

- Change structure types to landowner and landscape architect preferences.

The preliminary line characteristics for the 33kV and 220kV OHL’s are shown below: Table 1 Line Characteristics

220kV OHL 33kV OHL

Total Line Length 39km 23km

Line Description Double Circuit 220kV Single, Double and Triple Circuit 33kV

Earth Wire Twin OPGW 7/3.71 SC/AC

Conductor Duplex Chukar ACSR/AC Simplex Zebra ACSR/AC

Generation Rating 1330MVA (1330MW at unity power factor) 326MVA (326MW at unity power factor)

Structure Types Lattice Towers, single and double poles structures Single, double and triple pole structures

Foundations Concrete Pile Direct embedment

Insulators Composite Composite

Line route layout is depicted in drawings MRP-PKT-5101 and MRP-PKT-4220 to MRP-PKT-4227.

2.2 Line Modelling All OHLs have been modelled using PLS-CADD software. This is currently the most widely used OHL design software and forms the basis of the line design. All structure loads, line clearances and conductor swing calculations were exported directly from the PLS-CADD models.

2.2.1 Survey Data

All survey data was supplied by MRP and consisted of contours with 2m and 5m intervals, an assortment of aerial photographs and topographical maps.

2.2.2 Conductor Modelling

The conductors modelled in PLS-CADD use the ruling span (RS) method for calculating conductor loads but use the finite element (FE) analysis method for calculating conductor position. The line is modelled to take into consideration long term creep and clearances are based on the maximum elongated condition.

2.3 Line Loading The load combinations, weather conditions and factors used in the model are in accordance with AS/NZS 7000-2010.

2.3.1 Maximum Wind

MRP provided site-specific wind loads for the substation site at Puketoi. These were then compared to velocities taken from AS/NZS 1170.2. A basic non-directional wind speed of 46m/s was selected for the calculation of the design wind speed, with a final general wind speed of 50m/s (1532Pa) used for all areas. This selection was based on the Structural Design Wind Action part 2 (ASNZ 1170.2). This wind speed was used to calculate the indicative over turning moments for the foundation designs.


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It is noted the lower levels of farm land adjacent to Pahiatua are relatively flat and sheltered when compared to the more undulating hill country where the Turitea and Puketoi substations are located. More consideration of this topography will form part of the detailed design phase.

2.3.2 Snow & Ice

As sections of the lines are within the N1 snow loading zone, some structures on the lines will require snow loading evaluation during detailed design. Snow loads should be calculated in accordance with line loading standard AS/NZS 7000:2010.

2.3.3 Conductor Temperatures

Table 2 lists the conductor temperatures used for the appropriate weather cases based on Overhead Line Detailed Design procedures ASNZ 7000.2010: Table 2 Conductor Temperatures

Weather Case Conductor Temperature (°C)

33kV OHL 220kV OHL

Maximum Wind (1532Pa) 10.8 10.8

Everyday Temperature 10 10

Max. Operating Temperature (nil wind) 90 75

2.4 Clearances The minimum safe electrical distance requirements have been considered in accordance with NZECP 34-2001 and AS/NZS 7000-2010. Table 3 displays all the clearances considered in this report: Table 3 OHL Conductor Clearances

Description Required Clearance 33kV (m)

Required Clearance 220kV (m)

Minimum vertical distance to ground 6.0* 8.0*

Minimum side slope distance to ground 2.0 4.5

Minimum distance from Railway lines 7.0* 8.0* *To allow for design and construction tolerances, an additional 0.50m has been considered for all clearances.

For determination of preliminary structure heights and positions in the design the following clearance checks were carried out:

- Vertical clearance under maximum operating temperature, no wind.

- Horizontal clearance under Max Wind for blow out clearances. Conductor swing has been calculated based on AS/NZS 7000:2010, which is the applicable standard used for OHL design in Australia and New Zealand.

2.4.1 Crossings

A review of the OHL routes to identify any existing under crossings (includes major river crossings, sealed road crossings, rail crossings and distribution line crossings) was carried out and compiled. This information will form part of the scope of works for the detailed design phase of the project. Table 4 and

Table 5 identify the under crossings found on the 33kV and 220kV OHL routes.


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Table 4 33kV OHL Existing Crossing Details

33kV OHL Existing Crossings

Spans: C26-C27 Distribution Line Undercrossing – assumed low voltage (LV)

A53-A54 Road crossing – Pahiatua Pongaroa road

Table 5 220kV OHL Existing crossing Details

220kV OHL Existing Crossings

Spans: 8-9 Road crossing – Ongaha road.

19-20 Road crossing – Woodville Aohanga road

42-43 Road crossing – Pahiatua Pongaroa road

48-49 Road crossing – Hinemoa Valley road

51-52 Road crossing – Mangaone Valley road

70-71 Road crossing – State Highway 2 (SH2)

75-76 Road crossing – Scarborough Konini road

75-76 River crossing – Mangatainoka river

78-79 Rail crossing – Wellington Woodville railway

79-80 Distribution Line Undercrossing – assumed low voltage.

80-81 Road crossing – Ridge road

83-84 River crossing – Mangahao River

89-90 Road crossing – Makomako road

Further detail regarding the KiwiRail crossing in span 78-79 of the 220kV OHL is provided in drawing MRP-PKT-5111

2.5 Conductor Selection 2.5.1 220kV OHL

Three conductors were identified for use on the 220kV line based on the overall 1330MVA rating (zebra ACSR/AC, Chukar ACSR/AC and a 42/19 AACSR). The conductor chosen based on its load carrying capacity is the Chukar ACSR/AC in duplex configuration. Zebra ACSR/AC in duplex configuration would not have sufficient load carrying capacity.

This conductor has the following characteristics:

Diameter (mm): 40.7

Mass (kg/m): 3.077

Ultimate Tensile Strength (UTS) (kN): 233

2.5.2 33kV OHL

Based on the collection system layout and the expected electrical loading a Zebra ACSR/AC conductor was selected for use on all circuits of the 33kV OHL circuits. The Zebra ACSR/AC conductor in simplex configuration is proposed based on the overall 326MVA required capacity rating.

This conductor has the following characteristics:

Diameter (mm): 28.62

Mass (kg/m): 1.621


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Ultimate Tensile Strength (UTS) (kN): 131.9

2.5.3 Conductor Tensions

The maximum allowable tension and the vibration limit criteria from CIGRE 273 and ENA C (b) 1 was identified and a suitable tension selected. A basic horizontal tension of 20% of the UTS under everyday conditions was selected. From experience on many NZ and Australian line design projects, a starting basic tension of 20% of the conductor UTS is common. This may vary during the detailed design and construction phases, but provides good clearances without excessive structure loading for the initial design and is consistent with tensions used on other recent MRP projects.

2.6 Insulators and Hardware All insulators were assumed to be composite providing minimal visual impact. Further investigation will be undertaken during the detailed design phase to verify the suitability of composite insulators.

2.7 Structure Selection The design consists of both steel poles and steel lattice type structures. The structure types selected for specific sites were identified with direct input from MRP and the project landscape architect.

2.7.1 220kV OHL Structures

The 220kV OHL utilises steel single poles, double poles and steel lattice tower structures. All structures are double circuit in configuration. A brief outline of these structures is detailed below:

a) Steel single pole, approximate ground line diameter of 2000mm, maximum height of 48.5m, with 6 crossarms.

b) Steel double pole, approximate ground line diameter of 900mm, maximum height of 48.5m, with 6 crossarms.

c) Steel single/double pole, stayed, maximum height of 48.5m, with 6 crossarms, using steel wire rope to ground anchors offset from the centre line. Such structures are predominantly for heavy angles to offset the transverse loads.

d) Lattice towers with 6 crossarms, a maximum base width of 13m and a maximum structure height of 52m (depending upon topography and span lengths).

e) All structures are equipped with twin OPGW earth wires for lightning protection and communication purposes.

f) No accurate assessment of structure strength has been carried out. An indicative weight of structures ranges from 3 tonne to 50 tonne, depending on design loading. The weights are proportional to strength and the number of conductors being supported.

2.7.2 33kV OHL Structures

Each 33kV OHL utilises steel pole structures in Single pole, Double Pole and Triple pole configuration. The Double Pole structures carry a mix of double and triple circuits depending on which part of the wind farm they are connecting.

A brief outline of these structures is detailed below:

a) Steel single pole, approximate ground line diameter of 900mm, maximum height of 19 m, with 2 crossarms.

b) Steel double pole, approximate ground line diameter of 600mm, maximum height of 21.35m, 2-3 crossarms.

c) Steel triple pole, approximate ground line diameter of 600mm, maximum height of 14.0m, and no crossarms. These structures are used as termination structures near the cable riser locations at the line OHL ends. These may have steel wire stays connected to ground anchors in line with the conductors to offset the termination loads.

d) The 33kV OHL is equipped with OHEW/COMMS wires for lightning protection, control of earth potential rise and communication to WTGs. In the worst case it will be a combination of one SC/AC earth wire and one OPGW.


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The proposed structures are depicted in drawings MRP-PKT-5501 to MRP-PKT-5504 and in MRP-PKT 5514.

2.8 Structural Analysis No detailed structural analysis has been carried out on the proposed line routes. During the detailed design phase of the project, site specific loading will be used to determine the capacity requirements for the structures and the appropriate steel structures will be sourced based on this data.

2.9 Foundations Preliminary foundation design has been proposed based on the ground line (GL) overturning moments (OTM) extracted from PLS-CADD. These indicative foundations are being designed by Tonkin and Taylor.

The following preliminary foundation types are proposed:

- 33kV Steel single pole: direct embedment

- 33kV Steel double/triple Pole: direct embedment

- 220kV Steel single pole: concrete pile

- 220kV Steel double pole: concrete pile

- 220kV Lattice Tower concrete pile

The above foundation types were used for assessing the effect of Earth Potential Rise (EPR).

Preliminary investigation results favour the use of a rock anchor design for the 220kV foundations in hilly terrain. This may reduce concrete volumes by up to 50% at each tower. Further investigation is however required to confirm the feasibility of this type of foundation.

Further investigation is therefore required at the detailed design phase, including consideration of geotechnical investigations once final structure heights, widths and geometries are established.

3.0 Collection System

3.1 General A 33kV collection system will be required to connect each wind turbine generator (WTG) to the interconnecting 33kV Switchyard. The overall collection system comprises a unit substation at the base of each WTG unit, 33kV underground cables and 33kV overhead transmission lines along the route ( as shown in overview drawings MRP-PKT-4220 to 4227 ).

Collection circuits (underground cables) are designed to collect power from up to five 6.15 MW WTG units and feed onto a 33kV transmission line via a cable riser structure. The overall collection system will comprise of 14 separate collection circuits (cabled) that will connect to the 33kV transmission lines via eight cable riser structures. Refer drawing MRP-PKT-4102 for the overall Puketoi Single Line Diagram (SLD).

This section outlines the unit substations, collection circuits and connection to the overhead lines. An outline of the 33kV overhead lines and the riser pole structures is given in section 2.1.1 and 2.7.2.

Should a smaller capacity wind turbine be selected for detailed design, the sizing of the transformer and the cable will have to be reduced accordingly; the concepts used for equipment selection and their layout are still applicable.

3.2 Unit Sub Station It is proposed the unit substation will comprise of a dry type 0.66/33kV, 6.5MVA step-up transformer and a Ring Main Unit (RMU) rated for outdoor applications. An indicative layout of the WTG base layout plan including the step-up transformer, cable ducts and the RMU is given in drawing MRP-PKT-4501. The layout design is based on the tower base dimensions of a 6.15 MW WTG available in the market.


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Figure 2 Unit Sub Station Schematic

3.2.1 Step Up Transformer

A transformer may be required at the base of each turbine. Some turbines have a transformer internally. The transformer is required to step up the WTG output voltage (output voltage could range between 660V-20 000V) to the reticulation voltage (33kV). We have assumed the generator output voltage to be 660V for a 6.15MW WTG as the worst case design. The Transformers will be of a cast resin (oil free) type transformer for environmental and maintenance reasons. By using a cast resin transformer in place of a standard oil-filled type transformer, the fire and pollution risks associated with standard oil-filled type transformers are avoided. In addition, the selection of oil-free transformers will avoid high maintenance costs associated with standard oil-filled type transformers given the terrain and the number of transformers scattered across the site.

3.2.2 33 kV RMU

A 33 kV RMU is required to connect the WTG to the collection system. Each RMU will have three cubicles, one with a vacuum circuit breaker to connect the transformer high voltage (HV) output and two with cable switches for connection of the incoming and the outgoing cables as shown in Figure 2. The utilisation of an RMU will enable each generator unit and step up transformer to be isolated for maintenance purposes. Similarly, a section of a collection circuit, including the WTGs, can be isolated for maintenance if required.

3.2.3 Low Voltage Cabling

Up to twelve 150mm diameter PVC ducts are proposed for the installation of low voltage cables between the WTG and the step-up transformer. This will accommodate four cables with an overall diameter (OD) up to 44mm per duct (total of 48 cables) or three cables with an OD up to 51mm per duct (total of 36 cables) (refer Olex Cable Catalogue).

The size, type and number of cables required and the installation arrangement is to be determined and confirmed during detailed design.

3.3 33kV Collection Circuits 33kV XLPE cables are laid underground between WTGs with connections to the RMU and step-up transformer units to form the 33kV collection circuits. The collection circuits (underground cabling) are designed to collect power from up to five 6.15 MW WTG units and feed into a 33kV transmission line via a cable riser structure.

3.3.1 Cable Trenches

To assist the ease of installation, 300mm wide cable trenches will be dug to allow the 33 kV cables to be laid at a depth of 1200mm. The trenches will be laid under the wind farm roads to minimise environmental impacts. The cables will have a thermally stable cable backfill for initial cover of the cables.

Cables are to be laid in trenches in a trefoil touching configuration. This involves a triangular arrangement with two of the three cables on the bottom of the trench touching each other and the last laid on top of the two cables (refer drawing MRP-PKT-4307).

3.3.2 33 kV Cables

Cables laid between turbine towers progressively increase in size to accommodate the increase in capacity as the number of turbines in each cluster increases before connection to the transmission lines. The cables used furthest away from the 33kV riser pole structures will start at 95mm² single core Aluminium XLPE (OD - 38mm). The size of the next cable used in the cluster would be 300mm² single core Aluminium XLPE (OD – 48.4mm). Refer drawing MRP-PKT-4102 which details the various cable sizes determined for connections between RMUs. Cable sizes are chosen to minimise losses in the collection system.

RMU


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4.0 220/33 kV Substation

4.1 Introduction A substation is required to collect the 33kV circuits from the wind turbines, and step up the voltage to 220kV for the high voltage transmission circuits connecting the Wind Farm to the National Grid. The design also allows for the connection of other generation facilities in the area. There are three main components to the substation:

- 220 kV Switchyard, containing:

33/220 kV outdoor Transformer units, to step up the voltage from 33kV to 220kV

220 kV outdoor switchgear, to join together the supplies from the transformers, potentially neighbouring wind farms, and allow switching on/off of the various 220kV circuits

- 33 kV Switchyard, containing:

33 kV outdoor Switchgear, to join together and allow switching on/off of the various 33kV circuits

33 kV outdoor Capacitor Banks,

- Building for control equipment, offices, and workshop area

4.2 220 kV Switchyard 4.2.1 Overview

A double circuit transmission line connecting the Puketoi Substation to the Turitea Wind Farm substation is proposed using two electrical circuits strung along one set of towers. The Puketoi substation has been designed to allow separation of these two circuits to enable maintenance to be undertaken on one circuit with the other circuit still in service.

The Puketoi 220 kV switchyard contains a single 220 kV Bus, with two bus sections and one bus section Circuit Breaker and includes:

- Two sets of switchgear equipment for the transmission line circuits to Turitea

- Allowance for four sets of switchgear equipment for transmission line circuits to potential neighbouring Wind Farms

- Two sets of switchgear equipment for the step up Transformers

- One set of switchgear equipment for the Bus Section

In general, a switchgear bay includes the following equipment:

- A Circuit Breaker, to break the current

- Current Transformers and Voltage Transformers, to measure the current flow and the voltage

- High Voltage Switches/Disconnectors, to switch open the circuit and make safe for maintenance

- High Voltage conductors to connect the equipment.

4.2.2 Equipment and Structures

The equipment and structures proposed for the 220kV switchyard include:

- The 220 kV Transmission lines will terminate onto concrete/steel ‘H pole’ structures, which are two poles and a beam in an H shape. The termination structures will include earthing spikes to help protect the substation equipment from direct lightning strikes.

- Nine 220 kV three phase Circuit Breakers (CB) are required. One with a 3000A rating for the Bus Section, and eight with 2500A ratings for the transmission circuits and the transformers.

- Nine sets of 220 kV single phase combined Current Transformers/Voltage Transformers are required. Note that these are single phase rather than three phase units, and a total of 27 individual units are required. These will be installed alongside the Circuit Breakers.


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- Sixteen 220 kV three phase Disconnectors are required. Two are required for the Bus section bay with a 3000A rating, twelve are required for the six transmission circuits each with a 2000A rating, and the two to the transformers will have a 1250A rating. These are installed between the 220 kV Bus and the circuit breaker, and for the transmission lines there is an additional disconnector between the CT/VT and the outgoing line.

- The step-up in voltage will be achieved by installing two 220/33 kV 160 MVA transformers. The transformer will require an ONAN rating of 100 MVA and an ONAF rating of 160 MVA. The transformer will be able to handle throughput of up to 160 MVA. As the transformer will be lightly loaded for a large portion of the time, the design of the transformer can be optimised for this lower loading to reduce the cost, size, and weight of the transformer.

- The 220 kV Bus will be constructed using Aluminium tube; typically this would be 200mm in diameter.

4.2.3 Safety

The following considerations have been given with regard to safety:

- For safety of the public, the switchyard compound will be kept secure using security fencing and gates

- The conceptual layout of the 220 kV Switchyard meets NZ requirements (New Zealand Electrical code of Practice for Electrical Safe Distances (NZECP 34) and Safety Manual- Electricity Industry (SM-EI)).

- The switchgear has been set out to allow sufficient access around the high voltage equipment for maintenance using a mobile working platform, and to achieve a minimum vertical work safety clearance of 4540mm and a minimum horizontal work safety clearance of 5900mm, as per NZECP 34 table 6 on page 16.

- The switchgear and fencing has been set out to allow sufficient vehicle access around the interior perimeter of the switchyard. This layout provides sufficient room available for a vehicle 2500mm wide by 3100mm high with an outside turning circle radius of 10m.

- A double vehicle entrance gate will be located in line with the 220/33 kV transformers as the trailers for transporting the transformers are wider and have increased turning circles

4.3 33 kV Switchyard 4.3.1 Overview

The 33 kV outdoor switchyard will link together the wind turbines, the Capacitor Banks, and connection to the step-up transformers. The Puketoi 33 kV switchyard contains a single 33 kV Bus, with two bus sections and one bus section Circuit Breaker and includes:

- Six sets of switchgear equipment for the incoming feeds from the Wind Turbines

- Two sets of switchgear equipment for four 20 MVar Capacitor Banks

- Two sets of switchgear equipment for the step up Transformers

- One set of switchgear equipment for the Bus Section

Split levels of the 220 kV and 33 kV switchyards are proposed up the hill, allowing physical separation of the switchyards and reducing the earthworks required. As there is an overhead tie between the switchyards for the transformers, they should be kept alongside each other, separated as required only for the slope between the levels. The overhead tie would be high enough for safe electrical clearances for work from ground level only.

4.3.2 Equipment and Structures

The equipment and structures for the 33kV switchyard include:

- The 33 kV overhead lines from the Wind Turbines will terminate onto concrete/steel ‘H pole’ structures, which are two poles and a beam in an H shape. The termination structures will include earthing spikes to help protect the substation equipment from lightning strikes.

- For any 33 kV underground cables from the Wind Turbines, a stand will be installed to support the cables to bring them up from the ground to the 33 kV equipment. For underground cable circuits, an H pole termination structure will not be required.


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- Eleven 33 kV Dead Tank Circuit Breakers are required. These contain Current Transformers on the bushings of the Circuit Breaker, and avoid the need for additional stands and space for separate Current Transformers. Three Circuit Breakers (CBs) with a 3000A rating are required for the Bus Section and Transformers, and eight CBs with a 2000A rating are required for the overhead/underground generator circuits.

- Two sets of 33 kV single phase Voltage Transformers are required, one for each of the 33 kV Buses. These will be located underneath the 33 kV Bus.

- Eighteen 33 kV three phase Disconnectors are required. Four with a 3000A rating are required for the Bus section bay and the transformer bays, and fourteen are required for the generator circuits and the capacitor banks.

- Four 33 kV ‘Switches’ designed for on-load interruption of Capacitive loads will be installed to switch in and out the Capacitor Banks. These are of lower cost than the Circuit Breakers and are intended to be replaced more regularly than the Circuit Breakers

- Four 33 kV Capacitor Banks, each with a rating of 20 MVar are to be installed, and will provide reactive power to help compensate the reactive power that is drawn by the Wind Turbine generators. Installing these on the 33 kV side reduces cost, and will minimise the reactive power flowing through the transformers.

- The 33 kV Bus will be constructed using Aluminium Tube; typically this would be 200mm in diameter to achieve the Current rating of 3000A.

- A 100kVA indoor local service transformer will be installed to provide low voltage supplies to the building

4.3.3 Safety

The following considerations have been given with regard to safety:

- For safety of the public, the switchyard compound will be kept secure using security fencing and gates

- It is impractical to mount the 33 kV Capacitor banks above head height to allow adequate clearance for personnel to walk below. This equipment will be installed closer to ground level, so each of the Capacitor Banks will be inside a separately fenced area, with opening of the gate only possible once the equipment is de-energised and safe to approach.

- The conceptual layout of the 33 kV Switchyard follows NZ requirements (NZECP 34 and SM-EI). The conceptual layout of the switchyard is based on electrical clearances required for 66 kV. 33 kV switchyards in New Zealand have historically used shorter clearances, however this has resulted in difficulty in maintaining older equipment as the required safety distances for maintenance have increased beyond those allowed during design. The conceptual layout has been set out to allow sufficient access around the high voltage equipment for maintenance using a mobile working platform, and achieve a minimum vertical work safety clearance of 3070mm and a minimum horizontal work safety clearance of 4430mm.

- The switchgear and fencing has been set out to allow sufficient vehicle access around the interior perimeter of the switchyard – there is sufficient room available for a vehicle 2500mm wide by 3100mm high with an outside turning circle radius of 10m. In addition signage and barriers will be installed underneath the 33 kV transformer connections from the 33 kV switchyard to the 220 kV switchyard to prevent vehicles from getting too close to the lines.

4.4 Building The Substation building has been conceptually designed to be 40m by 15m (600m2), to allow sufficient space for the following items:

- Control room to house Protection Relays, Metering, Communications, Remote Equipment Interfaces (RTU and SCADA), and batteries. An area of approximately 20m by 10m (200m2) is required.

- Switchgear room to allow for the possibility that the outdoor 33 kV switchgear is replaced by indoor equipment at some time in the future. An area of approximately (100m2) is required.

- Offices, Rest room facilities, and Workshop areas, allowing for 300m2.


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4.5 Hazardous Substances The following electrical equipment makes use of hazardous substances:

- Each of the two power transformers will contain approximately 50,000 litres of di-electric insulating oil

- The Outdoor Current Transformers (CTs) and Voltage Transformers ( VTs) will contain a minimal amount of insulating oil

- The 220 kV and 33 kV switchgear will contain Sulfur Hexafluoride (SF6 ) gas, which is a greenhouse gas.

The management and containment of the transformer oil is explained in the next section of this report.

The substation layout is depicted in drawings MRP-PKT-4303, MRP-PKT-4305 and MRP-PKT-4306.

4.6 Oil Drainage and Interception System 4.6.1 Description

To manage potential spills of oil, both transformers will be placed within separate bunded areas designed to contain the total volume of all transformer oil and stormwater generated from an extreme rainfall event. The total catchment area for the bunding is approximately 300m2. Each transformer bund will have a sump connected to oil catch tanks via a gravity fed pipe. The outlet from the catch tanks is connected to an oil plate separator to remove any oil that may be contained in storm water. Any oil separated out can then be removed from site for appropriate disposal. If there are any issues with high ground water level on site, the catch tanks may require holding down arrangements or ballast to prevent tanks from emerging out of the ground when empty.

4.6.2 Oil Volume and Stormwater Criteria

The following was taken into consideration in the oil plate separator with catch (storage) tank system concept design:

- The capacity of the sump tank required for a plate separator system is typically based on a volume equivalent to the greater of the largest oil filled equipment (50,000 litre of oil in the transformer) OR a 1 in 10 year rainfall event of 6 hours duration falling into all of the transformer bunded areas

- Based on NIWA high intensity rainfall system data for Makuri, a 1 in 10 year rainfall event of 6 hours duration corresponds with 72.8mm of rain with a total bunded area of 300m2, a volume of approximately 22m3 would be required for the rainfall event.

Therefore, the sump volume required for the plate separator system is 50m3 (being the volume of oil in one transformer).

4.6.3 Operation

For an oil plate separator system, the oil that is separated goes to a separator waste oil tank which will have a high level alarm with SCADA connections to the main control centre. Maintenance personnel will be dispatched to site for removal of oil. If the separator waste oil tank were to fill completely causing the oil separator to stop processing the contents of the storage tank, the system (sump and bunded areas) could hold approximately 230m3 before overflowing the bund walls into the environment. This is more than the volume of oil held inside both transformers plus the volume of a 1 in 100 year storm rainfall over 72 hours (308.3mm of rainfall).

The separator waste oil tank high level is alarmed to SCADA and 6 hours is considered sufficient time for the maintenance contractor to respond on site.

4.6.4 Transformer Bund Area & Wall Height

The bund surrounding the transformer is to be sufficient to contain 110% of oil volume of the transformer, and be sufficiently large around the transformer to include radiators, and allow cubicle doors to be opened. Allowance should be made for rainfall should the outlet valve be inadvertently left closed.

Assuming a 150m2 bund area,

- 110% of oil volume (55,000 litres) corresponds to a height of 367mm

- 1% Annual Expected Precipitation (AEP) corresponds to 218.9mm of rain for 24 hour rainfall


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Thus the bund wall requires a minimum height of 586mm. A 600mm bund wall height (three standard concrete blocks) will be adequate and provide greater than 10% buffer.

4.6.5 Discharge

SEPA oil plate separators have been installed around New Zealand substation sites and are used to provide low concentrations of oil in their effluent discharge. These typically come with a SEPA standard performance warranty with the following performance:

1) 15 mg/l total oil content for effluent (for influent < 1000 ppm oil)

2) 50 mg/l total oil content for effluent (for influent with up to 1,000,000 ppm oil)

The proposed system will include a SEPA oil plate separator. It is recommended that the “separated” effluent from the plate separator be diverted to a soak pit if practical, which will discharge to land. All discharges will be at least 10 m from any river, lake or wetland.

5.0 Earthing System

5.1 Overview The earthing system for the Puketoi wind farm involves the earthing systems associated with the following:

- 220 kV transmission line – double circuit line using Chukar ACSR/AC type conductor, with lattice tower, double pole, single pole arrangements all with twin overhead earth wire (OHEW) for the whole length of the line;

- 33 kV collection system

33 kV Ring Main Units (RMU)

33 kV cables

Connections between RMUs at each turbine

Connection to main 33 kV transmission line from each cluster of wind turbines;

- Wind Turbine Generators with reinforced concrete foundations

- Puketoi substation (220/33 kV site)

Substation earth grid buried underneath the substation makes use of 20x4 mm HDCu with a minimum grid spacing of 5m and covers an area of approximately 11,000m2.

The current splits and earth grid voltage rise at the various structures in the system is determined using PSCAD EMTP software and the extent of the EPR hazard zones around the various structures are determined by CDEGS calculation.

5.2 Summary The system comprises up to 53 turbines along a single ridge. The earth grid resistance of each turbine foundation plus step-up transformer will be less than 10 . These will be interconnected in clusters via 33kV cables with double point bonded cable screens and then reticulated to a single 220/33kV substation. The substation earth grid is connected to each turbine cluster via double point bonded cable screens and/or double overhead earth wires. The tower footing resistance of each 33kV aerial feeder pole will be less than 30 , the design value required to meet lightning performance and system reliability requirements. The generation will then be dispatched to the National Grid via a 39km long double circuit 220kV transmission line with continuous double overhead earth wires between the wind farm substation and National Grid. This line will tie into Linton substation via a line from the Turitea wind farm. Only the transmission line connection between Puketoi and Turitea is considered in the earthing assessment. The tower footing resistance of each 220kV aerial feeder pole will be less than 20 , being the design value required to meet lightning performance and system reliability requirements.


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5.3 Soil Resistivity Test and Modelling Soil resistivity testing has not been conducted in the area for the developed design. Test data is however available near the National Grid connection point and also for similar wind farm developments in the area (specifically Tararua and Te Rere Hau wind farms). Using this available data, the soil resistivity in the area is characterised by a two layer profile, comprising a very high resistivity (±1500 m) top layer with nominal thickness of 2m and a high resistivity (<300 m) bottom layer for the underlying shale and rock. The following soil resistivity profile to be used for the earthing system design is summarised in Table 6.

Table 6 Typical Soil Resistivity Profile derived for Puketoi area

Layer Resistivity ( -m) Thickness

Top 1500 2

Bottom 300

It is recommended that soil resistivity tests be carried out during the detailed design stage along the proposed transmission lines, wind turbine installations and substation sites. This will confirm the soil profiles to be used for the detailed design.

5.4 Earth Fault Levels & Clearance Times The 220kV earth fault level at the grid connection at Linton substation is 4kA, which was obtained from the Electricity Authority centralised data set. The 33kV earth fault level will be limited to less than about 250A using an earthing transformer and Neutral Earth Resistor (NER). The typical 220kV aerial transmission line primary and backup fault clearance times have been assumed for the line. These are 0.12s and 0.5s respectively, as per the Electrical Engineers' Association (EEA) recommendations.

The worst case earth fault current levels used in the assessment are summarised in Table 7. Table 7 Worst case future bus earth fault levels

Fault Current [kA]

220 kV bus earth fault @ Turitea end (grid connection point) 4.0

33 kV bus earth fault @ Puketoi substation 0.25

5.5 Structure Earth Grid Resistances The extensive reinforced turbine foundation (>10m) will achieve a grid resistance of 10 or less. Additional counterpoise conductors can be buried in the 33kV cable trenches if required to achieve the design value (although this is not considered likely). The 33kV line structure earth grids achieve a calculated earth resistance of between 51 and 68 . Additional vertical earth rods will therefore be added at these structures to reduce the footing resistance to below the 30 design value. The 220kV line structure earth grids achieve a nominal earth resistance at least less than 20 , below the design value. All values are calculated in the MALT module of CDEGS.

5.6 Substation Earth Grid Resistance The substation earth resistance is 2.3 for a standard horizontal mesh with 5mx5m mesh elements. It is not necessary to reduce this further given that the local earthing system is distributed to all turbines via multiple cable screens and earth wires.

5.7 Calculations The extended earthing system comprising turbines, cable sheaths, earth wires, substation grid and structure (tower and pole) earths are modelled in the EMTP software package within PSCAD in order to determine the current split and grid voltage rise at each electrode for both 220kV and 33kV earth fault scenarios. The EGVR values are then input into the CDEGS model and the extent of the 2500V, 650V and 430V EPR contours are


calculated. The structure locations and EPR contours are plotted on the contour maps to assist in locating these areas with respect to the Telecom network. EPR contour radii along the 220kV transmission line route are depicted in drawings MRP-PKT-5121 to MRP-PKT-5126. The EPR is below 430V for all collection system structures and turbines and therefore only the 220kV structures between the substation and grid connection point are included.

6.0 Electromagnetic Field Strength (EMF) As part of the EMF assessment, the Electric Field Strength (EFS) and Magnetic Flux Density (MFD) are calculated along the 220kV transmission line and 33kV line routes at 1m above ground in areas that are reasonably accessible to the public below and next to the line. The calculations consider normal operating conditions only. The calculated maximum values are then compared to the ICNIRP reference levels. Areas in which the calculated maximum values are below the reference levels are then deemed to be safe in that there is no risk of adverse health effects associated with long term EMF exposure in those areas.

The highest EFS in public access areas below and next to the line is 4.95kV/m at 1m above the normal standing position of a person. This is below the 5kV/m reference level for public exposure. The EFS of the 220kV transmission line is depicted in Figure 3.

Figure 3 Electric field strength of the 220kV transmission line

Similarly, the highest MFD in public access areas below and next to the 220kV transmission line is 32 T at 1m above ground level for the normal standing position of a person. This value is based on 1330MVA of power transmitted on the transmission line. The MFD of the 220kV and 33kV lines are depicted in Figure 4.


Figure 4 Magnetic flux density of the 220kV and 33kV lines.

7.0 Preliminary Constructability Review

7.1 Planning and Materials The planning of a new transmission line requires the co-ordination of the following main activities,

a) Bulk purchase of materials;

b) Access preparation;

c) Foundation installation;

d) Tower construction; and

e) Stringing of the conductors.

Each activity is dependent on the other to maintain progress in an orderly manner. Therefore foundation installation cannot begin until the access has been prepared, the structures cannot be installed until sufficient foundations (maybe 30%) are complete and the stringing cannot begin until complete strain sections are built.

The construction would be organised so that materials are fabricated and delivered to site on time so that damage to property is kept to a minimum and that landowners are kept well informed of any changes.

7.2 Vegetation Management The lines are generally located to avoid most large trees, and conductors are generally suspended high above valleys with native scrub. However, it will be necessary to fell willow (or other fast growing vegetation) trees at river and road crossings.

7.3 Access Generally, access across flat paddocks in pasture is acceptable, unless working during the winter months, when a formed track with compacted chips or river metal may be necessary. The use of existing farm tracks in the hills will be such as to allow a 20 or 30 tonne tracked digger to get to the sites. Access will be upgraded as the diggers complete one site and move to the next. Generally a digger can travel from one ridge system to another, depending upon landowner co-operation and their expectations. An access track which travels along or near to the line is an advantage for maintenance inspections.


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7.4 Construction The use of helicopters overcomes difficult access areas where slips and erosion are a hazard. Helicopters can be used for all activities on hill sites, including the daily carriage of construction crews to site, the lifting of reinforcing steel and concrete for foundations, the cartage of structure steel and its assembly, and the initial phases of stringing. Track access can be achieved to all or most tower sites so helicopters will be used only where relevant.

The structures are fabricated in sections suitable for the crane or helicopter’s lifting capacity, each structure section being fitted together progressively, using standard procedures based on safe work methods. The lattice towers will be bolted together using plates and cleats and the poles use a compressive jointing system.

It is anticipated that steel pole structures will be slip jointed (sometimes bolted plate connections are also used) allowing small lighter sections to be lifted into place with a helicopter or crane.

Safety of line construction crews on the job is paramount and all construction activities will follow an approved procedure.

The stringing of the conductors is completed using the tension stringing method, where all conductors are kept up off the ground and pulled by a large winch at one end with tensioning equipment at the other end. Helicopters are often used to pull through a pull rope. This then allows the conductor to be attached to the pull rope and pulled along the line under a desired tension. A typical stringing length for high voltage heavy conductor is 5-6km.

The large drums of conductor are usually set up every 5-6kms along the line, and in an area which is relatively flat and accessible for a rough terrain type crane. The cables and conductors are suspended above the ground as the drums unwind, and pulled up to final tension once correctly sagged. Each section of conductor is pulled out through running blocks on each of the structures, jointed to the end of the previous section, before being clamped to the insulators. The process is then repeated; leap frogging from one area to the next.

The construction of the 33/220kV substation will require additional large plant for installing substation equipment which is often very heavy. Helicopters are generally not utilised for such works and therefore the area around the substation will be frequently accessed by large cranes, concrete trucks etc.

Access tracks to the substation site will be required to be of a condition to with stand the large amount of heavy plant traffic expected.

7.4.1 Road or Rail Protection

All public roads are generally protected with hurdling (usually made from a timber H structure either side of the road) providing protection for vehicles using the road during the stringing phase of construction. The same protection is installed for the crossing of low voltage (LV) distribution lines and temporary undergrounding of the LV asset can also be used.

7.4.2 Reinstatement

The final activity is reinstatement which includes a general tidy up of all structure sites including any outstanding fencing or roading issues to the satisfaction of each landowner.

7.4.3 Line Maintenance

The rate of regular inspections of a transmission line increases as the age of the line increases. Most steel structures have a minimum design life of 50 years, and are expected to be relatively free of maintenance problems for the first 20 years.

Generally, an inspection would involve a lineman climbing the structure to check for loose steel or damage. The lineman would gain access by motorbike or 4X4 vehicle.

Typical maintenance duties resulting from adverse weather and vandalism include replacement of damaged insulators or the installation of repair sleaves for conductors. A landowner would not expect to be visited more than twice in 3-5 years, unless adverse weather has been prevalent.


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8.0 Conclusion & Recommendations In order to connect the new MRP Puketoi wind farm into the National Grid approximately 23km of 33kV OHL and 39km of 220kV OHL will be required. This will traverse from the foot hills of the Puketoi ranges, across valleys and onto flat agricultural land, before climbing back up into the hills to the south west of Pahiatua where it will connect into the National Grid.

The lines will consist of single, double and triple circuit multiple steel pole structures on the 33kV OHL and single, double steel poles and steel lattice towers on the 220kV OHL.

To accommodate the electricity generated from the 53 turbines on the Puketoi range and to step the voltage up from the 33kV OHL to the 220kV OHL a new 33/220kV substation is to be constructed in the foothills of the Puketoi ranges.

During the construction phase there will be several road crossings and distribution line under crossings that will require protection in the form of timber hurdling or similar. There is also a rail crossing (owned by KiwiRail) that will need to be protected.

In order to access the substation construction site, access tracks will be required for the transportation of large plant.

Puketoi Wind Farm Technical Report - pncc.govt.nz. Transmission.pdf · National Grid via a 220kV...

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Transcript of Puketoi Wind Farm Technical Report - pncc.govt.nz. Transmission.pdf · National Grid via a 220kV...