Proposed Thurso South 275kV / 33kV Substation

Project Background

The driver for transmission network reinforcement in Caithness is renewable generation to the north of Beauly including the marine generation in the Pentland Firth and Orkney Waters, as presented in the graph and maps below.

A key part of the reinforcement plan is the replacement of the existing 132 kilovolt (kV) infrastructure between Dounreay, Thurso and Mybster with a new 275kV double circuit overhead line from Dounreay, via a new substation at Thurso. This will terminate at a new High Voltage Direct Current (HVDC) converter station at Spittal. An upgrade is also required to the 4km section of existing 132kV overhead line between Spittal and Mybster.

The proposals for the upgrades required to the existing overhead lines between Dounreay, Thurso and Mybster are still at the development stage and a formal consultation process will be carried out over the coming months. This is one of several elements of reinforcement work that includes a new HVDC link between Spittal and Blackhillock substation in Moray.

This poster presentation is in relation to the proposed substation to the south of Thurso.

Growth in Renewable Energy Generation Offshore Renewable Generation

Onshore Renewable Generation

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Proposed Thurso South 275kV / 33kV Substation

Project Description

The aim of the project is to strengthen the high voltage network in Caithness and involves replacing / upgrading the existing 132kV overhead line (OHL) between the substations at Dounreay, Thurso and Mybster with new higher capacity infrastructure. The main elements of the project are as follows:

Construction of the proposed Thurso South 275kV / 33kV substation and associated cabling works to connect the new 275kV OHL to the existing 33kV distribution infrastructure.

Construction of a new double circuit 275kV OHL from the Dounreay substation to the proposed HVDC converter station at Spittal, via a new substation near Thurso. The proposed route corridor is presented below in the Project Overview Map in Amber.

Connection to the new 275kV / 132kV substation at Dounreay, which is currently under construction.

Construction of 275kV infrastructure at the proposed HVDC converter station at Spittal.

Upgrade the existing 132kV OHL between the Spittal HVDC converter station and the existing Mybster substation. An extension to the Mybster substation may also be required. The proposed route corridor is presented below in the Project Overview Map in Green.

Consultation Process

This project is still in the early stage. No decisions have been finalised about the location for the substation or the precise route for the overhead lines, however we have commenced engineering and environmental studies to identify potential locations and suitable corridors. We firmly believe that early and regular communication and consultation with those likely to be affected by the proposal forms a critical part of its development.

As a result, no final decisions will be made until full consideration has been given to the comments, views and suggestions provided by statutory and key consultees, elected representatives, landowners, communities likely to be affected by the proposals and any other interested parties.

The current programme of the project is shown below: Have Your Say Develop and compare site / route options Ongoing

This exhibition is your opportunity to comment on and ask questions about our proposals Identify proposed site / OHL route February / March 2012 so far. We would greatly appreciate it if you would take the time to fill out our short

questionnaire and post it in the comments box.

Publish consultation document May 2012

Complete Environmental Impact Assessment October 2012 Alternatively, you can write to:

Apply for consents November 2012 Lisa Kelly

Scottish Hydro Electric Transmission Ltd Submit Planning Application for Substation November 2012 10 Henderson Road,

Receive Consent Approval November 2013 Inverness,

IV1 1SN Start Construction Early 2014

Please submit your comments by 1st March 2012.Completion and commissioning 2016 - 2017

Project Overview Map

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Proposed Thurso South 275kV / 33kV Substation

Development Process

Thurso South Substation

SHETL identified four possible sites for the substation, sites A - D (see figure below). These were selected through a process of high level screening giving due consideration to known environmental constraints, technical feasibility (including proximity to the River Thurso and other watercourses, and the railway), proximity to the existing network, and cost.

Initial discussions were held with landowners and statutory consultees, including The Highland Council, Scottish Natural Heritage, and the Scottish Environment Protection Agency in order to gain a greater understanding of the key factors likely to influence development at the site. These discussions, as well as further assessment of the technical issues, have led us to our preferred site, however full consideration will be given to all the comments received through this stage of consultation.

The new Thurso South substation will be approximately 205m x 230m and will connect the 275kV transmission network to the existing 33kV distribution network, via new underground cabling. The indicative layout of the new Thurso South Substation is presented below.

The reinforcement of the overhead lines from 132kV to 275kV and the installation of the new Thurso South substation will not only enable the connection of the numerous generation schemes north of Beauly but will also provide greater security of supply to electricity users in the area.

Dounreay to Mybster Overhead Lines

An initial high level screening of baseline information has been carried out for potential overhead line routes from the Dounreay Substation to the Mybster Substation. This identified the main 2km wide corridor (as shown on Poster 2) that is currently the subject of extensive survey work to determine a viable route within the corridor.

The overhead lines are assumed to be of lattice tower construction between Dounreay and Mybster and the options for the upgrades are under technical review. The locations of the towers along the corridor will be determined from extensive technical and environmental studies and discussions with landowners, developers and statutory and key consultees. There will be approximately 29.5km of new overhead line required for this project.

Thurso South Substation Site Options A - D Thurso South Substation Indicative Site Layout

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Proposed Thurso South 275kV / 33kV Substation

Substation sites in detail

Following initial discussions with statutory authorities and key consultees, four possible substation sites were selected for further assessment and comparison. This includes detailed environmental studies, further baseline information gathering and continued consultation.

The following sections highlight some key considerations currently identified for each of the four sites. The visualisations shown for each site are only preliminary and have been produced to give an indication of the scale of the development within the surrounding landscape only. These will be updated as further information becomes available and detailed design is undertaken. The detailed design will refine the following aspects that are likely to affect the visual impact:

Technical specification Orientation of site Access arrangements Opportunity for landscaping (e.g. earth bunding and screen planting) Height of the infrastructure Route of the new overhead lines

Site A - Approximately 2.5Km south of Thurso, adjacent to the A9

Considerations

Environment Highly visible from Thurso and users of the A9

Open landscape with no existing screening, therefore potential impact to the landscape character of the area.

Close proximity to residential housing

Medium risk of flooding from adjacent watercourse during storm events.

Technical The existing infrastructure needs to remain ‘live’ during

construction to maintain supply to customers, requiring significant arrangements during construction and commissioning including crossings of the A9.

Significant technical and health & safety constraints during construction due to ‘live’ infrastructure.

Suitable existing site access directly off the adjacent A9. Abnormal loads could come via Scrabster Harbour.

Relatively flat site requiring minimal earthworks.

Site B - Approximately 1.9Km south of Thurso to the west of the River Thurso

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Considerations

Environment Open landscape with no existing screening, therefore

potential impact to the landscape character of the area.

Close proximity to the edge of Thurso will increase the visual impact of the substation and the towers.

Medium risk of flooding from adjacent watercourse during storm events.

Potential to adversely impact the River Thurso SSSI / SAC during construction.

Technical Site accessed from B874 and requires upgrading of

existing tracks and improvement of restricted visibility.

Restricted access for construction and operation by the crossing of the railway.

Poor connection to existing infrastructure due to location on the west side of the River Thurso, requiring multiple directional drilled cables below the river.

Permitting requirements to cross the railway with the new overhead lines.

Crossing of the existing overhead lines will require additional temporary towers and advance diversion works.

New substation can be constructed off-line, thereby reducing construction and operation constraints

Relatively flat site requiring minimal earthworks

Proposed Thurso South 275kV / 33kV Substation

Site C – Approximately 4km south of Thurso to the west of the River Thurso

Considerations

Environment Undulating ground profile provides limited

screening, limiting the potential impact to the landscape character of the area. Existing hedgerow along the B874 provides screening from the road.

Lessen visual impact with removal of several spans of existing overhead line which crosses the A9.

Existing towers close to Thurso will be removed.

Minimal risk of flooding from adjacent watercourse during storm events.

Technical Poor connection to existing distribution

infrastructure due to location to the west of the River Thurso, requiring multiple directional drilled cables crossing the river and the railway.

New substation can be constructed off line, thereby reducing construction and operation constraints.

Considerable earthworks required to create the construction platform, increasing site traffic.

Access from the B874 to be created to provide sufficient visibility.

Reduced number of crossings of the existing 132kV overhead lines.

Site D – Approximately 3.3km south of Thurso to the east of the River Thurso

Considerations

Environment

Undulating ground profile provides limited screening, limiting the potential impact to the landscape character of the area. Existing hedgerow along the A9 and plantation provide screening from the road.

Lessen visual impact with removal of several spans of existing overhead line which crosses the A9.

Existing towers close to Thurso can be demolished.

Minimal risk of flooding from adjacent watercourse during storm events.

Technical

Good connection to the existing distribution infrastructure with only the overhead lines crossing the River Thurso and the railway.

New substation can be constructed off line, thereby reducing construction and operation constraints.

Relatively flat site requiring minimal earthworks to create platform.

Site is approximately 250m from the A9 and requires a new access road.

Based on environmental and engineering studies, as well as cost estimates undertaken to date we consider that Site D is our preferred location for the Thurso South 275kV/33kV substation.

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