scatec solar 132kv new lines - cape eaprac re capital 3/ba grid... · sans 10280: 2013 - 01, in...

PROJECT

ENGINEERING

Preliminary Design Report

Job ID: P1902-3829/04/01

Job Name: Scatec solar 132kV DCt Lines

Author: Trans-Africa Projects

Date: July 2015

Revision: 0

Scatec Solar 132kV Line

Preliminary design Document

Document Number Revision No Date

P1902-3829/04/01 0 July 2015

Table of Contents

1. INTRODUCTION ............................................................................................................................................ 4

1.1 GEOGRAPHICAL LOCATION.................................................................................................................................. 5 1.2 ROUTE PLANS .................................................................................................................................................. 6

2 DESIGN PHILOSOPHY .................................................................................................................................... 7

2.1 SALIENT ASPECTS OF THE LINE ............................................................................................................................. 8 2.2 ENVIRONMENTAL CONSIDERATIONS ..................................................................................................................... 9

2.2.1 Structure Types ........................................................................................................................................ 9 2.2.3 Enviromental Impact ............................................................................................................................. 10

2.3 ACCESS ......................................................................................................................................................... 11 2.4 LIST OF CROSSINGS ......................................................................................................................................... 12

3 STATUTORY REQUIREMENTS ....................................................................................................................... 13

4 CONDUCTORS .............................................................................................................................................. 13

4.1 CONDUCTOR SELECTION ................................................................................................................................... 13 4.2 PHASE CONDUCTORS ....................................................................................................................................... 14 4.3 SHIELD WIRE .................................................................................................................................................. 14

5 INSULATION AND HARDWARE ..................................................................................................................... 15

5.1 PHASE CONDUCTOR ........................................................................................................................................ 15 5.2 B.I.L ............................................................................................................................................................ 15 5.3 OPGW FIBRE OPTIC DESIGN ............................................................................................................................. 15 5.4 HARDWARE ................................................................................................................................................... 17 5.5 STRAIN ASSEMBLY .......................................................................................................................................... 17 5.6 CLOSING SPAN ASSEMBLY ................................................................................................................................ 17 5.7 SHIELD WIRE HARDWARE .................................................................................................................................. 18 5.8 VIBRATION CONTROL ...................................................................................................................................... 18 5.9 POSITION OF VIBRATION DAMPERS ON THE PHASE CONDUCTOR .............................................................................. 18

6 DESIGN LOADS ............................................................................................................................................. 18

6.1 WIND PRESSURE ............................................................................................................................................ 18 6.2 CONDUCTOR TENSION CRITERIA ........................................................................................................................ 19

7 TOWER TYPES .............................................................................................................................................. 19

8 FOUNDATIONS ............................................................................................................................................. 23

8.1 SOIL RESISTIVITY / EARTHING ................................................................................................................................... 24

9 LABELLING ................................................................................................................................................... 25

9.1 LINE DESIGNATION.......................................................................................................................................... 25

10 DESIGN RELATED MAPS ............................................................................................................................... 26

10.1 ICE LOADING IN SOUTH AFRICA .......................................................................................................................... 26 10.2 VULTURE ELECTROCUTION ................................................................................................................................ 26 10.3 LIGHTINING FLASH DENSITY .............................................................................................................................. 27 10.4 RAINFALL ...................................................................................................................................................... 27 10.5 CORROSION ................................................................................................................................................... 28

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1. INTRODUCTION

Scatec Solar has been awarded three solar PV (Photovoltaic) projects as part of round 4 group of renewable energy

projects in Siyanda District within the jurisdiction area of Khai Garib Local Municipality in the Northern Cape. All

the three farms are located approximately 22km south west of Upington and 15km north of Keimos. Each plant

will have a generation capacity of 75MW. The total power that will be evacuated from the three solar farms will be

225MW. The three solar farms shall be called Dyasonsklip 1, Dyasonsklip 2 and Sirius 1.

Dyasonsklip 1 and 2 will share a substation, called Dyasonsklip Substation and evacuated generated power to Sirius

substation by means of a single circuit (SCt) Twin Tern line. From Sirius substation the power shall be evacuated by

means of a SCt Twin Tern line to the new Upington MTS. Eskom planning has opted for the use of Twin Tern to

accommodate future generating plants planned in the area*.

Trans Africa Projects (Pty) Ltd has been commissioned for the design of both 132kV single circuit lines to facilitate

the connection of Dyasonsklip 1, Dyasonsklip 2 and Sirius 1 to the Eskom grid through the new Upington MTS

substation. Two options are considered in this design, the first being a Twin Tern SCt guyed monopole solution and

the second option, a SCt Twin Tern self-supporting solution.

The guyed solution shows a considerable cost saving. However, the Northern Cape Operating Unit (NCOU) has

expressed slight reservation over the use of guyed structures. The following report aims to address these as well

and other design constraints and considerations for both options.

*This heavy configuration was agreed to by the developer in lieu of a lighter fit for purpose solution involving the use of single Kingbird and

twin Chicadee line. The developer has stated an intention to construct the solution with guyed structures to accommodate the increased cost

of this heavy configuration.

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1.1 Geographical Location

SCATEC Solar has planned 5 solar farms adjacent to each other in the area. The approved and planned

solar farms are located 22km south west from Upington, a major city in the province, and are within an

approximate 10 km radius from the Orange River. Land usage at the solar farm site is partially used for

grazing and can be described as mostly flat land, with a slight natural slope towards the Orange River.

The figure below shows the solar farms’ location relative to Upington and the Orange River.

Figure 1.1.1: Shows geographic map of all three farms

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1.2 Route Plans

Two routes have been proposed for the line connections between the three substations. The figure

1.2.1 shows the preferred route in green. The route follow Dyasonsklip 1 and 2 and Sirius 2 solar farm

boundaries, crossing over a dirt access road, to connect to Sirius substation. From Sirius substation it

follows a straight trajectory towards McTaggerts 132kV Line where it makes an underpass crossing. The

line then bends in a south-east direction towards the existing Oranje-Oasis 132kV wood pole line where

it crosses over at approximately midsapn and heads towards its final bend before termination at the

new Upington MTS.

The corridor adjacent to McTaggerts 132kV Turn-in Lines has been earmarked as a 400kV line crorridor

to the new Upington MTS. In addition to this, the corridor will host a planned access road to the planned

Eskom CSP plant located on the eastern side of !Khi Solar CSP Plant. The underpass crossing at the

McTaggerts 132kV Turn-in Line will be made such that clearance to the planned 400kV line and access

road is maintained.

The second route option, marked in yellow in the image below, also follows the solar farm boundaries of

Dyasonsklip 1 and 2 and bends toward the existing Oranje-Oasis 132kV line where is runs parallel until

turning into Sirius 1 substation. The line exists Sirius 1 substation in a southernly direction towards the

existing wood pole line, where it crosses over at approximately midspan and bends to again follow

parallel to the existing 132kV line. The last two bends allows it to turn and terminate at the new

Upington MTS.

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Figure 1.2.1: Line location relative to major suburbs and land features (Google Earth Imagery).

2 DESIGN PHILOSOPHY

Self-supporting steel monopoles and guyed steel monopoles were considered in obtaining a

recommended concept for the Dyasonsklip - Sirius 132kV line and Sirius - Upington MTS 132kV Line. The

design philosophy adopted in generating each option incorporated a balance between performance

optimisation and cost. As recommended by design standard SANS 10280: 2013-01, a reliability level of 1

was used to model each design. A reliability level of 1 implies a wind load factor of 1 which in turn

corresponds to a return period of 50 years. SANS 10280: 2013 - 01, in accordance with IEC60826,

stipulates a minimum reliability level of 1 for lines up to 132kV.

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2.1 Salient Aspects of the Line

Conductor: Twin Tern Conductors (ungreased)

Shield wire: OPGW with 2 X 48-cores rated for 20kA at 0.5 second fault withstand (or

equivalent). (Total rating 40kA)

Insulators: Insulator type to be used on this line shall be as per IEC 60815 specifications.

Composite long rod insulators for 132kV applications shall be used. The

creepage shall be 20mm/kV as specified for inland regions.

Earthing: Footing resistance values shall be adopted from the Eskom Distribution (DX)

Earthing standard (SCSASABF9 - line earthing) where earthing is necessary. For

132kV lines the maximum acceptable footing resistance is 20Ω. These values

shall be measured during construction and additional earthing installed if

required.

Corona & Audible

Noise:

The selected conductor, Tern, satisfies Eskom’s requirements in terms of

corona and noise parameters with sufficient margin of safety.

Hardware: Standard hardware components have been used.

Towers : Self-supporting monopoles and guyed monopoles.

Foundations: Standard pad and plinth foundations for the self-supporting towers.

Dead-man anchor/stay plate anchor foundations for stays and a central plinth

for tower mast will be used for the guyed monopoles.

Corrosion

protection:

Standard galvanizing as per SANS 121 and ISO 9223 for C2 corrosion

categories.

Length: Dyasonsklip - Sirius 132kV line is approximately 6km and Sirius - new Upington

MTS is approximately 3km.

Line Profile: Lines templated at 70°C maximum operating temperature.

Route: Between Dyasonsklip-Sirius-Upington MTS substations about 22km south west

of Upington in the Northern Cape.

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2.2 Environmental Considerations

2.2.1 Structure Types

The EA (Environmental Assessment) stipulates that poles to be used as support structures, therefore

lattice structures were not considered as a support option.

Aspect Appendix A Design Consideration

Coastal/Inland The line is located inland.

Snow Probability Figure 9.1 The 132kV line does not fall within an ice-

loading risk area. The line has therefore

not been designed for ice-loading.

Altitude

-

The altitude of the proposed site ranges

from approximately 815-845m above sea

level.

Birds

Figure 9.2 On the basis of figure 5.2, the line will be

away from the vulture electrocution risk

area. No special design considerations will

be needed regarding vulture

electrocution.

Lightning Flash Density

Figure 9.3 The lightning ground flash density for the

area is 1-2 flashes per square kilometre

and is regarded as low risk.

Rainfall Figure 9.4 The rainfall in the Upington area is given

as greater than 350mm per annum as

shown in figure 5.4.

Corrosion Figure 9.5 The corrosion category for the Upington

area is C2 (Inland/Rural).

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2.2.3 Enviromental Impact

As per the Environmental Authorisation (EA) document (KAI1231.14), the potential environmental

constraints that were identified to date are Flora and Fauna, main drainage lines and seasonal washes.

The required buffer zones on all seasonal washes/streams shall be maintained. This design also caters

for any possible replantation of protected plant species should they be identified within the line

corridors.

The EA document also stipulates the possible conductor collusion and electrocution of Eagles, Vultures

and Flamingos. To deter nesting, all structures shall be fitted with anti-nesting’s devices as shown below.

In addition, bird perches will be fitted to all structure tops of all intermediate poles to prevent earthwire

collusions. OPGW will be fitted with bird flight diverters.

Figure 2.2.1 shows anti-bird nesting above the post insulator

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2.3 Access

The proposed site can be accessed through National Road N14 and the farm dirt roads and possible

access roads from the neighbouring projects. However it would be after the preliminary line walk down

the chosen route the necessity for additional new access roads. However, the necessity for additional

access roads would be verified once a site visit and line walk down on the selected route is done. The

following image shows the existing roads that can be used as access roads during construction.

Figure 2.3; Shows the access roads around the solar farms

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2.4 List of Crossings

Crossing Description Special

Precautions

Responsible Authority

Power line Crossing

Mc Taggerts 132kV Line

(underpass)

132kV Cruciform towers Eskom

Power line crossing

Orange-Oasis 132kV line

132kV Live line nets Eskom

Seasonal water streams - Department of

Environmental Affairs

Secondary Road Crossing

(access road to !Khi Solar

CSP Plant)

Corner of Dyasonsklip 2

solar farm

Dirt road crossing Traffic goal posts Local Traffic Authority/

relevant persons from !Khi

Solar

Secondary Road crossing Planned Eskom access

road to planned

Eskom CSP Plant

Erosion control

measures, e.g.

gabions

Eskom

*Other crossings shall be confirmed after the preliminary line walk down.

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3 STATUTORY REQUIREMENTS

The clearances with which the line will be profiled are stated below in Table 3.1. Note: an additional

clearance buffer of 0.3m will be included to clearances in all areas in the final design.

Table 3.1: Table of Minimum Clearances (SANS 10280-1:2013)

Description Clearances (m)

Electrical Clearances:

Phase to Phase 1.68

Phase to Earth 1.45

Vertical Clearances

Ground clearance all areas 6.3

Roads in townships or proclaimed roads, railways, tramways 7.5

To buildings, poles, structures not part of power lines and vegetation 3.8

To telecommunication lines and between power lines 2

4 CONDUCTORS

4.1 Conductor selection

During interaction with Eskom planners and Developer, two solutions were considered. These possible

solutions are influenced by number of planned developments and capacity that the chosen conductor

can handle. These solutions are based on “Rate A” for probabilistic ampacity as per Eskom Standard

EST32-319. The best possible solution was the Long-term solution and Fit for purpose solution (Lean

solution). Both Eskom and developer chose the long-term solution as the best solution because of the

current carrying capacity and future planned projects around this area. The long term solution consists

of Twin Tern throughout the lines. This solution will make possible to evacuate power from the planned

projects in the area. The following tables shows how conductor bundles were determined, where table

4.1 shows the preferred option (long term solution) and table 4.2 shows the lean solution.

Table 4.1.1: Shows Long Term Solution.

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Table 4.1.2: Lean Solution

4.2 Phase Conductors

Conductor choice has a significant impact on the line design, governing the tower series selection and

influencing the overturning moments experienced by the structure, which subsequently affects the

structure foundation choice; a design component with a significant cost contribution to the line project.

The following table gives conductor information for the conductor Tern, selected by Network Planning,

which has influenced the structure choice alternatives and their respective wind and weight span

capabilities in carrying this conductor.

Table 4.2.1: Electrical/Mechanical Properties of Conductors

Conductor

Code name

Stranding

(mm)

Area

Al.

(mm2)

Total

Area

(mm2)

Overall

Diameter

(mm)

Mass

(kg/km

at 20°°°°C)

UTS

(kN)

Final

Modulus

of

Elasticity

(N/mm2 x

104)

Coeff. of

Linear

Expansion

(10-6

/°°°°C)

Tern 45/7 403.77 431.77 27.00 1340 101.92 6.66 21.12

4.3 Shield wire

The main function of any shield wire is the control of fault conditions, which presumes a short circuit at

any point of the line or substation busbar. Hence, the shield wire must be chosen such that when it is

loaded with the anticipated high current it retains its mechanical and electrical properties without

degradation.

Based on interaction with Western Cape Operating Unit, ungreased 2*24 core, 0.5 second fault

withstanding OPGW is to be used. The line’s OPGW is to cater for worst-case fault levels. Eskom’s

planning department provided the following assumptions for the forecasted fault levels.

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Table 4.2.2: Fault level at the Busbars

CONFIGURATION STATUS

Fault levels at Busbar (kA)

1 PH 3 PH

Upington MTS 132kV Planned 39.9 32.5

Sirius 132KV Planned 21.6 24.2

Dyasonsklip 132kV Planned 10 14.8

*Smaller OPGW is possible between Dyasonsklip SS and Sirius SS, however a standard solution was

adopted for both lines, given the short distances involved.

5 INSULATION AND HARDWARE

5.1 Phase Conductor

Insulator options have been determined as per Eskom Standard 34-510 Rev 0. This Standard allows for

use of silicon post insulators and silicon long rod insulators. The type of insulator to be used on this line

shall be as per IEC 60815 specifications. For this project, the creepage shall be 20mm/kV as specified for

inland regions. It is proposed that insulators with standard ratings for 132kV be implemented. The

insulating material shall be silicon rubber and the dry arcing distance to be a minimum of 1200mm for

132kV. No steel pipes or railway lines know as yet, however this will be verified during line walk down.

5.2 B.I.L

The minimum basic insulation level required for 132kV line equipment is 650kV for the lightning

impulses withstand at sea level. The 60 seconds power frequency withstands is 275kV (as per DSP 34-

540 Rev 0).

5.3 OPGW Fibre optic design

Ungreased 2*24 core OPGW rated 40kA, 05s fault will be installed from the gantry at Dyasonsklip

substation to gantry at Sirius substation. Another 2*24 core OPGW rated at 40kA, 05s fault withstand

rating will be installed from gantry at Sirius to the gantry at Upington MTS substation.

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5.4 OPGW Schematic diagram

Figure 5.4.1: OPGW schematic diagram

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5.5 Hardware

Assemblies must comply with the Code of Practice for overhead power lines for conductors prevailing in

South Africa, SANS 10280-1: 2013. Insulated shield wire assemblies have been catered for on terminal

towers. Standard hardware based on Eskom DX standards was chosen as far as possible. All OPGW

hardware shall conform to the provided specification. All OPGW hardware shall conform to the NRS 061-

2:2004.

5.6 Strain Assembly

According to SANS 10280-1:2013, the strain assembly should have a strength value of at least the

breaking point of the conductor or the shield wire. For Tern conductor (98.7kN) this means that a

strength rating of 120kN is sufficient.

5.7 Closing Span Assembly

The closing span assemblies make use of bolted connections at the gantry and compression assemblies

on the terminal tower. Provision for the connection of droppers to the closing span should be made and

completed by the relevant substation contractor.

Figure 5.7.1: Closing span assembly outline

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5.8 Shield wire hardware

Standard OPGW hardware, including those needed for insulated towers, will be used on the line. OPGW

hardware with spare parts and material available on the National Contract for Eskom should be used.

5.9 Vibration Control

To minimize vibration on the phase conductors, multi-frequency vibration dampers will be installed on

the line according to Distribution standard DSP 34-1204 Rev 0. Note, no vibration dampers are required

on the closing/slack spans. Non-bolted dampers must be used on the OPGW, as per supplier’s

instructions.

5.10 Position of Vibration Dampers on the Phase Conductor

The number and position of the vibration dampers on the phase conductor is determined by making use

of the following table (extracted from Eskom Distribution Specification: 34-1204).

Table 5.10.1 Number and Placing of Dampers on a Span

Conductor Span

(m)

NO of dampers

per span per

conductor

Arrangement of dampers

per conductor

Damper placement*

Tern 0 to 369 4 2 damper at each end 0.97m from ends

* To be confirmed by supplier

6 DESIGN LOADS

6.1 Wind Pressure

The wind pressure used for this line was calculated based on the SANS 10280-1:2013 loading philosophy

and is based on several factors as shown below:

Line Reliability Level: 1

Reference (10min) wind speed at 10m of height: 29m/s

Return period for maximum wind speed: 50 year

Terrain Category: B

Topography Type: General

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6.2 Conductor Tension Criteria

All conductor tensions were calculated based on the formula C = T/M, where C = 1800m for the

Conductor and 2100m for the OPGW shield wire at EDT creep condition.

M is the mass of the conductor in kg/m.

T is the horizontal tension in kg.

In addition, the tensions are limited to the following values from the table below.

Table 6.2.1 Cable Tension Limits - Damped conductors

Conductor condition Phase conductor Shield wire

After creep condition at -5 °C C limit: 2 450 m C limit: 2 750 m

After creep at EDT C limit: 1 800 m C limit: 2 100 m

Ultimate wind/Ice load 70% of UTS

7 TOWER TYPES

The design has considered self-supporting and guyed monopoles as structure options to carry the

selected conductor Twin Tern. Lattice options were excluded in the analysis as the EA stipulated

monopoles should be used. In addition, lattice structures are not preferred in the region as bird nesting

poses a serious maintenance and operational problem.

The 2-WT/1294 and 2-WT/1295 structure series considered was designed for Twin Bearsfort and Tiger

EW (Earth Wire). The series allows for planted self-supporting suspension structures and guyed strain

structures. To present a fully self-supporting and fully guyed option, the design team has conceptually

designed and estimated structural capacities and steel weights for a guyed heavy suspension to carry

Twin Tern as well as self-supporting strain structures for the bend points and terminal positions at the

substation.

The probability of theft of stays, the need for re-tensioning of stays and corrosion of stay anchors,

possibly leading to the collapse of structures, are some of the larger concerns highlighted by the region.

Self-supporting structures in this regard, provides an option which requires fewer maintenance and

operational effort.

Where guyed structures may pose a potentially more costly maintenance option, the cost saving on the

capital investment still remains large. An approximate 27% cost saving may be achieved with the use of

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guyed structures as opposed to self-supporting towers. This compared to the projected maintenance

costs and probability of structure collapse in the life time of the asset, remains a greater advantage.

The following images are examples of self-supporting and guyed structure types proposed.

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Figure 7. 1. Shows example of self-supporting suspension and strain structures

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Figure 7.2. Shows example of guyed suspension and strain structures

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8 FOUNDATIONS

A geotechnical test will be done all accessible structure positions to evaluate the soil strata. The results

are useful in determining the foundation type structures that will need to be used. The results are also

useful in deciding on any soil stabilising (e.g. gabions) and appropriate foundation types (e.g Drilled

foundations). Experience has shown that both soil stabilising and blasting can have significant cost

implications if not catered for early in the design stages. Soil nomination shall be performed by TLB to

ascertain the soil profile.

Foundations have been designed according to the following geotechnical classification:

Type 1 – Hard engineering strong granular soil

Type 2 – Less competent soil, stiff clay or dense sand

Type 3 – Very incompetent soil i.e. loose sand or soft clay

Type 4 – Saturated or submerged soft ground below the seasonal water table

Hard rock – Solid continuous moderately fractured

Soft rock – Very fractured, weathered or decomposed rock

Load safety factors have been incorporated for the designs allowing for variations in geotechnical

conditions, construction inconsistencies and long-term performance

The contractor however, must perform a soil investigation exercise during construction, at which point

the prevailing sol or rock type classification is performed, and a suitable foundation system is selected

for various type of structures.

Should stay plates be used for guyed monopole solution, and should it be declared that the soil of the

selected corridor be acidic or aggressive, bitumastic tape shall be used to wrap the stay plates to

prevent the plates from corroding.

All stay rods shall be encased with PVC pipe up to 100mm above the ground level to prevent any

possible contact with the soil.

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Figure 7.1 Pad and Plinth Foundations

8.1 Soil Resistivity / Earthing

Earth resistance measurements will be carried out to decide on the type of earthing required for

particular steel towers. This should be performed once the towers have been erected, but before

stringing is performed. If additional earthing is required, it will be done in accordance with Eskom’s

standard SCSASABF9. The tower footing resistance of all structures on 132kV lines shall be less than

20Ω.

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9 LABELLING

9.1 Line Designation

The designation labels for the Dyasonsklip-Sirius lines will be (CIRCUIT #) DYS-SIR # and for Sirius-

Upington MTS will be (CIRCUIT #) SIR-ESP #. Labelling on both lines will be according to the Standard for

the labelling of Substations and Networks (DISAAN0 Rev 2).

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10 DESIGN RELATED MAPS

10.1 Ice loading in South Africa

Figure10.1: Ice-loading map of South Africa

10.2 Vulture Electrocution

Figure 10.2: Vulture electrocution risk map of South Africa

Line Position

Line Position

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10.3 Lightining Flash Density

Figure10.3: South African lightning ground-flash density map (CSIR 2007)

10.4 Rainfall

Figure10.4: South Africa annual rainfall

Line Position

Line Position

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10.5 Corrosion

Figure10.5: South Africa corrosion map

Line Position

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