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
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.
27 July 2011
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Puketoi Wind Farm Technical Report
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
Authorised
Revision
Revision Date
Details
Name/Position
A
27 July 2011
27-Jul-2011
Consent Issue
J Schwaderer
Manager T&D
Signature
AECOM
Puketoi Wind Farm Technical Report
Table of Contents
Executive Summary
1.0
Introduction
1.1
Scope of Investigation
2.0
Overhead Lines
2.1
Line Route Selection
2.1.1
Line Design Methodology
2.2
Line Modelling
2.2.1
Survey Data
2.2.2
Conductor Modelling
2.3
Line Loading
2.3.1
Maximum Wind
2.3.2
Snow & Ice
2.3.3
Conductor Temperatures
2.4
Clearances
2.4.1
Crossings
2.5
Conductor Selection
2.5.1
220kV OHL
2.5.2
33kV OHL
2.5.3
Conductor Tensions
2.6
Insulators and Hardware
2.7
Structure Selection
2.7.1
220kV OHL Structures
2.7.2
33kV OHL Structures
2.8
Structural Analysis
2.9
Foundations
3.0
Collection System
3.1
General
3.2
Unit Sub Station
3.2.1
Step Up Transformer
3.2.2
33 kV RMU
3.2.3
Low Voltage Cabling
3.3
33kV Collection Circuits
3.3.1
Cable Trenches
3.3.2
33 kV Cables
4.0
220/33 kV Substation
4.6
Oil Drainage and Interception System
4.6.1
Description
4.6.2
Oil Volume and Stormwater Criteria
4.6.3
Operation
4.6.4
Transformer Bund Area & Wall Height
4.6.5
Discharge
5.0
Earthing System
5.1
Overview
5.2
Summary
5.3
Soil Resistivity Test and Modelling
5.4
Earth Fault Levels & Clearance Times
5.5
Structure Earth Grid Resistances
5.6
Substation Earth Grid Resistance
5.7
Calculations
6.0
Electromagnetic Field Strength (EMF)
7.0
Preliminary Constructability Review
7.1
Planning and Materials
7.2
Vegetation Management
7.3
Access
7.4
Construction
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8.0
Puketoi Wind Farm Technical Report
7.4.1
Road or Rail Protection
7.4.2
Reinstatement
7.4.3
Line Maintenance
Conclusion & Recommendations
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List of Figures and Tables
List of Figures
Figure 1 Proposed Wind Farm Site
Figure 2 Unit Sub Station Schematic
Figure 3 Electric field strength of the 220kV transmission line
Figure 4 Magnetic flux density of the 220kV and 33kV lines.
1
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List of Tables
Table 1 Line Characteristics
Table 2 Conductor Temperatures
Table 3 OHL Conductor Clearances
Table 4 33kV OHL Existing Crossing Details
Table 5 220kV OHL Existing crossing Details
Table 6 Typical Soil Resistivity Profile derived for Puketoi area
Table 7 Worst case future bus earth fault levels
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Puketoi Wind Farm Technical Report
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
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1.0
Puketoi Wind Farm Technical Report
1
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:
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Updated contour data.
-
Subtle changes made due to landowner discussions surrounding structure types and locations.
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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
Puketoi Wind Farm Technical Report
3
Line Design Methodology
The methodology adopted for determining line design for each line was as follows:
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Revise / develop the PLS-CADD model minimising the extent of turn off angles wherever feasible.
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Make any relevant changes to the model based on information received from MRP.
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Check clearances along the proposed line route.
-
Eliminate any design constraints by relocating structures or altering structure heights.
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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
1330MVA (1330MW at unity power factor)
326MVA (326MW at unity power factor)
Lattice Towers, single and double poles
structures
Single, double and triple pole structures
Concrete Pile
Direct embedment
Composite
Composite
Generation Rating
Structure Types
Foundations
Insulators
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 70002010.
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
Conductor Temperature (°C)
Weather Case
33kV OHL
220kV OHL
10.8
10.8
Everyday Temperature
10
10
Max. Operating Temperature (nil wind)
90
75
Maximum Wind (1532Pa)
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
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
Description
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:
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Vertical clearance under maximum operating temperature, no wind.
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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-PKT5111
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):
2.5.3
6
131.9
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:
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33kV Steel single pole:
direct embedment
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33kV Steel double/triple Pole:
direct embedment
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220kV Steel single pole:
concrete pile
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220kV Steel double pole:
concrete pile
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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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RMU
Figure 2 Unit Sub Station Schem atic
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.
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4.0
220/33 kV Substation
4.1
Introduction
9
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
2
The Substation building has been conceptually designed to be 40m by 15m (600m ), to allow sufficient space for
the following items:
-
Control room to house Protection Relays, Metering, Communications, Remote Equipment Interfaces (RTU
2
and SCADA), and batteries. An area of approximately 20m by 10m (200m ) is required.
-
Switchgear room to allow for the possibility that the outdoor 33 kV switchgear is replaced by indoor
2
equipment at some time in the future. An area of approximately (100m ) is required.
-
Offices, Rest room facilities, and Workshop areas, allowing for 300m .
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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
2
catchment area for the bunding is approximately 300m . 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 300m 2, a volume of approximately 22m3 would
be required for the rainfall event.
3
Therefore, the sump volume required for the plate separator system is 50m (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
3
230m 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.
2
Assuming a 150m 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
2
grid spacing of 5m and covers an area of approximately 11,000m .
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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14
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)
Top
1500
Bottom
300
Thickness
2
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
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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.
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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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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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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.
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