Environmental Statement

Volume 6 – Onshore

Annex 6.10.1

Electromagnetic Fields Study

PINS Document Reference: 7.6.10.1

APFP Regulation 5(2)(a)

January 2015

ii

SMart Wind Limited

Hornsea Offshore Wind Farm

Project Two –Environmental Statement

Volume 6 - Onshore

Annex 6.10.1 – Electromagnetic Fields Study

SMart Wind Limited

11th Floor

140 London Wall

London

EC2Y 5DN

Tel 0207 7765500

Email info@smartwind.co.uk

Copyright © 2015

All pre-existing rights reserved.

Liability

This report has been prepared by SKM and RPS, with all reasonable skill, care and diligence within the terms of their contracts with SMart Wind Ltd or their subcontractor to RPS placed under RPS’ contract with SMart Wind Ltd as the case may be.

Document release and authorisation record

PINS document reference 7.6.10.1

Report Number UK04-050700-REP-0071

Date January 2015

Client Name SMart Wind Limited

iii

Table of Contents

1 Introduction ........................................................................................................... 1

1.1 Scope of Report .................................................................................................... 1

1.2 Sources of EMF .................................................................................................... 1

1.3 Cable Configuration .............................................................................................. 2

2 Calculations and Results ....................................................................................... 3

2.1 Approach ............................................................................................................... 3

2.2 Cases Studied ....................................................................................................... 3

Table of Figures

Figure 1.1 Magnetic field produced by current in conductor. ................................................... 1

Figure 2.1 5 x 360 MW circuit arrangement. ........................................................................... 3

Figure 2.2 2 x 900 MW HVDC circuits arrangement. .............................................................. 4

Figure 2.3 3 x 335 MW + 5 x 360 MW HVAC circuits arrangement. ....................................... 5

Figure 2.4 2 x 600 MW + 2 x 900 MW circuit arrangement. .................................................... 6

Table of Graphs

Graph 2.1 Magnetic field density due to 5 x 360 MW circuits. ................................................ 4

Graph 2.2 Magnetic field density due to 2 x 900 MW circuits. ................................................ 5

Graph 2.3 Magnetic field density due to 3 x 335 MW circuits + 5 x 360 MW circuits. ............. 6

Graph 2.4 Magnetic field densities due to 2 x 600 MW + 2 x 900 MW circuits. ....................... 7

Table of Tables

Table 2.1 Magnetic field densities due to 5 x 360 MW HVAC circuits. ................................... 4

Table 2.2 Magnetic field densities due to 2 x 900 MW HVDC circuits. ................................... 4

Table 2.3 Magnetic field densities due to 3 x 335 MW + 5 x 360 MW HVAC circuits. ............ 5

Table 2.4 Magnetic field densities due to 2 x 600 MW + 2 x 900 MW circuits. ....................... 6

iv

Glossary

Term Definition

Project One

With a maximum capacity of 1.2 Gigawatts (GW) or 1,200 MW, Project One is the first offshore wind farm project within the Hornsea Round 3 Zone and includes all necessary offshore and onshore infrastructure required to connect to the existing National Grid substation located at North Killingholme, North Lincolnshire. Project One is the first of a number of wind farm projects planned for the Hornsea Zone to meet a target Zone capacity of 4 GW by the year 2020. Project One has been submitted as a single application to PINS for a DCO under the Planning Act 2008.

Project Two

With a maximum capacity of 1.8 Gigawatts (GW) or 1,800 MW, Project Two is the second offshore wind farm project within the Hornsea Round 3 Zone and includes all necessary offshore and onshore infrastructure required to connect to the existing National Grid substation located at North Killingholme, North Lincolnshire. Project Two is the second of a number of wind farm projects planned for the Hornsea Zone to meet a target Zone capacity of 4 GW by the year 2020. Project Two will be the subject of a single application to PINS for a DCO under the Planning Act 2008.

Round 3

Round 3 was announced by The Crown Estate in 2008 with nine development zones. The successful bidders were announced in January 2010 with a potential generating capacity of 32 GW. The Crown Estate announced the first round of UK offshore wind farm development in December 2000 and the second round of larger sites in July 2003.

Cable circuit and phase

A cable or cables that make up an entire electrical circuit. Usually used in reference to export cables. Where the cables are AC, a circuit could consist of a single three-core cable or three single-core cables. Each core carries one phase of electrical power. Where the cables are DC, the circuit could consist of a single two-core cable or two single-core cables. Typically, offshore AC cables are three-core and onshore cables are single-core. Typically, both offshore and onshore DC cables are single-core.

Acronyms

Acronym Full term

A Amperes

DCO Development Consent Order

EMF Electromagnetic Field

GW Gigawatt

H Henrys

HVAC High Voltage Alternating Current

HVDC High Voltage Direct Current

MW Megawatt

OFTO Offshore Transmission Operator

PINS The Planning Inspectorate

RMS Root Mean Squared

T or µT Tesla (more commonly µT – microtesla – due to magnitude)

1

1.1.1 SMart Wind has been awarded a licence by The Crown Estate to develop

approximately 4,000 MW of wind capacity off the coast of East Yorkshire known as

Zone 4 under the Round 3 Offshore Wind Licensing Arrangements.

1.1.2 As part of the initial design process, SMart Wind has requested that SKM studies the

electromagnetic field (EMF) densities produced by each of the cable connection

arrangements that are being considered for the first two stages of the development

zone (1.2 GW + 1.8 GW), Project One and Project Two respectively. The cable sheath

material will fully shield the electric field at ground level. Therefore only the magnetic

field has been assessed. This note covers the following arrangements:

The HVDC onshore connection between the onshore transition pit at the landfall

and the OFTO converter station; and

The HVAC onshore connection between the onshore transition pit at the landfall

and the OFTO substation.

1.1.3 Calculations of the maximum expected magnetic field strength in the vicinity of the

cable trench have been made which include the combined effect of the cables

operating in parallel. The connections will be made in two stages. Results have been

provided for both Project Two (1.8 GW) and when Project One and Project Two (3

GW) are connected.

1.2.1 When a current passes through a conductor a magnetic field is produced around the

conductor. The direction of the field depends on the direction of current flow in the

conductor as shown below in Figure 1.1.

Current

Conductor

Direction of EMF

produced

Figure 1.1 Magnetic field produced by current in conductor.

1.2.2 With an AC current source the density and direction of the field will vary with the

current. With a DC source the field will have a constant magnitude (providing the

current stays constant) and will be in a constant direction.

1.2.3 The density of the magnetic field is proportional to the current flowing through the

conductor and the distance between the conductor and point of measurement. The

magnitude of the field density is calculated using the Biot-Savart law, from which the

following equation can be derived:

𝑩 = µ𝟎 𝐈

𝟐 𝛑 𝐫

Equation 1 Magnetic flux density.

1.2.4 Where:

B = Magnetic flux density (T)

μ0 = Permeability of free space = 4 x x 10-7 (H m-1)

I = Current through conductor (A)

r = Distance from centre of conductor (m)

1.2.5 An additional source of EMF is the natural static magnetic field produced by Earth

which has a (relatively) constant strength and direction at any specific location. For DC

cables this will interact with the magnetic field produced by the cables and is therefore

considered in the calculations. The interaction with the Earth’s magnetic field depends

on the direction of the cable. Two cable directions have been studied; the HVDC

cables running in a North-South direction and the cables running in an East-West

direction. This study uses typical data for magnetic field strength and direction for the

2

part of the UK in which the project is located. The typical characteristics of the Earth’s

magnetic field in the region are shown below:

Magnitude of magnetic field density = 50 μT;

Inclination of magnetic field = 68 degrees; and

Declination of magnetic field = -2 degrees.

1.2.6 For the purposes of this study, declination has not been considered as a -2°

declination will only have a negligible effect on the total resultant field.

1.2.7 The oscillating magnetic field from the AC cables does not interact with the Earth’s

static field in the same manner.

1.2.8 Other power cables and overhead lines which may exist in the area may also interact

with the EMF produced from the Hornsea cables if they are in close proximity. Details

of these cables and overhead lines are not known and will not be considered in the

calculations.

1.3.1 The detailed arrangement of the cables within the cable corridors is shown for each

arrangement considered, along with the calculated results in Section 2. Some general

assumptions that apply to all arrangements are detailed below.

Cable Screen Bonding

1.3.2 When a cable screen is bonded to the earth grid at both termination ends, an AC

current flowing through the conductor will induce a circulating current in the cable

screen. This current will flow in the opposite direction to the current in the conductor.

This will therefore produce an EMF in the opposite direction to the EMF produced by

the conductor, reducing the resultant EMF of the cable. If the sheath is bonded at one

end only (or cross-bonded) then the circulating current does not occur and no

reduction occurs.

1.3.3 The sheath bonding arrangements depend on a number of factors and the length of

the cable is often the main factor. For the purposes of this study it has been assumed

that the HVAC cables are not bonded at both ends, therefore no reduction in EMF

occurs due to circulating currents. This is a worst case assumption as this

arrangement produces the greatest EMF.

1.3.4 The DC current associated with the HVDC cables does not induce any circulating

currents in any sheath bonding arrangements.

3

2.1.1 Calculations of the expected maximum magnetic field densities have been carried out

for Project Two and for Project One and Project Two together, with AC or DC cables.

In each case the magnetic field density profile is plotted to a distance of 25 m either

side of the cable corridor.

2.1.2 The current in each conductor is based on the expected current at the peak rating of

the wind farm. Magnetic field densities have been calculated at 1 m above ground

level. This height is specified by the DECC Code of Practice for assessing compliance

of power lines and underground cables with EMF exposure guidelines; it represents a

typical height at which the field interacts with the human body.

2.2.1 The actual arrangement of the cables has not yet been finalised and a number of

options are still being considered. The arrangements that will provide the greatest

magnetic field density have therefore been studied.

2.2.2 Magnetic field density is directly proportional to the current in the cables. Only the

cases that provide maximum current have been studied. If the rating of the wind farm

is reduced from those in this study then the magnetic field density will reduce

accordingly.

2.2.3 The number of circuits is also yet to be finalised on the project. If the sum of the

current in each circuit is constant then the highest EMF densities occur when fewer

cables are used to provide the capacity. For example, three circuits each carrying 800

Amps will produce a higher total EMF density than four circuits each carrying 600

Amps. This is due to the fact that the circuits will be physically separated and therefore

the magnetic field produced by each cable will have some element of cancellation at

the point where the peak occurs. The cases reported here are the minimum number of

cables that could be used to provide the 1.2 GW and 1.8 GW capacities associated

with Project One and Project Two respectively.

2.2.4 The cases studied are:

5 x 360 MW HVAC circuits – Project Two

2 x 900 MW HVDC circuits – Project Two

3 x 335 MW HVAC circuits + 5 x 360 MW HVAC circuits – Projects One and Two

combined

2 x 600 MW HVDC circuit + 2 x 900 MW HVDC circuit - Projects One and Two

combined

2.2.5 Whilst it is recognised that the total capacity (1 GW) for Project One in this scenario is

lower than the 1.2 GW maximum expected project generating capacity, each 335 MW

cable would have a higher current loading at peak output than in an alternative 4 x 300

MW scenario, and the 335 MW scenario has therefore been assessed as it would

produce the highest magnetic field density.

2.2.6 The arrangement of the cables is assumed as flat formation which provides the

highest magnetic field densities.

2.2.7 The current for each case is calculated from the maximum power load carried, in the

relationship I = P / V, where I is the current in amps, P is the power in watts, and V is

the potential difference (voltage) in volts.

5 x 360 MW HVAC Circuits – Project Two

2.2.8 For the onshore section of the circuit it is expected that the cables will be laid in a flat

formation. For the purposes of this study it is assumed that the relative phase

arrangement is the same for each circuit.

2.2.9 The expected cable arrangement is shown below in Figure 2.1.

1m

Measurement Profile

Profile extends

up to 15m away

from trench

Profile extends

up to 15m away

from trench

5 x 360MW HVAC Circuits – Project 2

3m 3m 3m 3m360MW

245kV HVAC

360MW

245kV HVAC

360MW

245kV HVAC

360MW

245kV HVAC360MW

245kV HVAC

0.7

m

Figure 2.1 5 x 360 MW circuit arrangement.

2.2.10 In this arrangement the current through each conductor at peak loading will be

approximately 967 A. Table 2.1 below shows the densities across the profile studied:

4

Table 2.1 Magnetic field densities due to 5 x 360 MW HVAC circuits.

Magnetic Field Densities (μT) at Distance from Centre Line of Trenches

0 m (centre)

6.25 m*

7.25 m*

11.25 m*

16.25 m*

21.25 m*

26.25 m*

31.25 m*

1 m above ground 15.87 22.79 20.50 5.17 1.94 1.04 0.66 0.45

* These values represent a distance of 0 m, 1 m, 5 m, 10 m, 15 m, 20 m and 25 m from the edge of the cable corridor.

2.2.11 The magnetic field density across the profile studied is also shown below in Graph 2.1.

Graph 2.1 Magnetic field density due to 5 x 360 MW circuits.

2.2.12 The maximum calculated magnetic field density (at 1 m above ground level) is

23.43 μT, which occurs above the centre of the outer two circuits.

2 x 900 MW HVDC Circuits – Project Two

2.2.13 The voltage, number of circuits, and current for the HVDC option have not yet been

finalised. As a worst-case assumption, this report calculates the magnetic field for two

900 MW circuits, each carrying a 2,000 A current. The arrangement of the conductors

is shown below in Figure 2.2. Table 2.2 shows the maximum magnetic field densities

calculated in this arrangement.

Figure 2.2 2 x 900 MW HVDC circuits arrangement.

0.7

3m

0.5m

1m

Profile extends up to 25 m away from

trench

900 MW 2000 Amps

Profile extends up to 25 m away from

trench

2 x 900 MW Circuits – Project Two

900 MW 2000 Amps

Table 2.2 Magnetic field densities due to 2 x 900 MW HVDC circuits.

Magnetic Field Densities (μT) at Distance from Centre Line of Trenches

0 m (centre)

1.75 m*

2.75 m*

6.75 m*

11.75 m*

16.75 m*

21.75 m*

26.75 m*

1 m above ground – Cable Only 13.16 58.58 47.03 9.28 2.97 1.44 0.85 0.56

1 m above ground: North-South 62.39 103.23 73.91 43.23 47.40 48.70 49.22 49.48

0

5

10

15

20

25

-40 -30 -20 -10 0 10 20 30 40

Mag

ne

tic

Fie

ld D

en

sity

(μ

T) R

MS

Distance From Centre of Trenches (m)

Total ResultantMagnetic Field Density

5

Magnetic Field Densities (μT) at Distance from Centre Line of Trenches

1 m above ground: East-West 62.39 108.35 84.84 45.39 47.77 48.82 49.28 49.51

* These values represent a distance of 0 m, 1 m, 5 m, 10 m, 15 m, 20 m and 25 m from the edge of the cable corridor.

2.2.14 The maximum calculated magnetic field density (at 1 m above ground level) is

108.35 μT. The magnetic field density across the profile studied is also shown below

in Graph 2.2.

Graph 2.2 Magnetic field density due to 2 x 900 MW circuits.

3 x 335 MW HVAC circuits + 5 x 360 MW HVAC circuits – Projects One and Two combined

2.2.15 Worst case arrangement for Project Two and Project One combined is shown below in

Figure 2.3.

0.7

m

3m 3m

1m

Measurement Profile

Profile extends

up to 15m away

from trench

Profile extends

up to 15m away

from trench

3 x 335MW + 5 x 360MW HVAC Circuits – Project 1 & 2

Combined

335MW

245kV HVAC

335MW

245kV HVAC

3m 3m 3m 3m 3m335MW

245kV HVAC

360MW

245kV HVAC

360MW

245kV HVAC

360MW

245kV HVAC

360MW

245kV HVAC360MW

245kV HVAC

Figure 2.3 3 x 335 MW + 5 x 360 MW HVAC circuits arrangement.

2.2.16 In this arrangement the current through each conductor at peak loading will be

approximately 900 Amps in the Project One cables and 967 Amps in the Project Two

Cables. Table 2.3 below shows the magnetic field densities across the profile studied.

Table 2.3 Magnetic field densities due to 3 x 335 MW + 5 x 360 MW HVAC circuits.

Magnetic Field Densities (μT) at Distance from Centre Line of Trenches

0 m (centre)

10.75 m*

11.75 m*

15.75 m*

20.75 m*

25.75 m*

30.75 m*

35.75 m*

1 m above ground

8.26 23.28 20.41 4.75 1.65 0.83 0.49 0.33

* These values represent a distance of 0 m, 1 m, 5 m, 10 m, 15 m, 20 m and 25 m from the edge of the cable corridor.

2.2.17 The maximum calculated magnetic field density is 35.86 μT (at 1 m above ground

level) which occurs between the cable trenches of Project One and Project Two (a

worst case assumption regarding the phase arrangements of the cables of the two

projects has been assumed). The magnetic field density across the profile studied is

also shown below in Graph 2.3.

0

20

40

60

80

100

120

-30 -20 -10 0 10 20 30

Mag

ne

tic

Fie

ld D

en

sity

(μ

T)

Distance From Centre of Trenches (m)

Total Resultant Magnetic Field Density

Total from Cable Only Total with Cable E-W Total with Cable N-S

6

Graph 2.3 Magnetic field density due to 3 x 335 MW circuits + 5 x 360 MW circuits.

2 x 600 MW HVDC circuits + 2 x 900 MW HVDC circuits – Projects One and Two combined

2.2.18 The arrangement of the conductors is shown below in Figure 2.4.

0.7

m

3m

0.5m

3m

1m

Measurement Profile

Profile extends up to 25m away from

trench

Profile extends up to 25m away from

trench

600 MW2000 Amps

600 MW2000 Amps

2 x 600 MW Circuits + 2 x 900MW Circuits – Projects One and Two

900 MW2000 Amps

900 MW2000 Amps

3m

Figure 2.4 2 x 600 MW + 2 x 900 MW circuit arrangement.

2.2.19 In this arrangement the maximum current would be 2,000 A in the conductors

associated with Project One and Project Two (a worst case assumption regarding the

phase arrangements of the cables of the two projects has been assumed). Table 2.4

shows the densities across the profile studied.

Table 2.4 Magnetic field densities due to 2 x 600 MW + 2 x 900 MW circuits.

Magnetic Field Densities (μT) at Distance from Centre Line of Trenches

0 m (centre)

4.75 m*

5.75 m*

9.75 m*

14.75 m*

19.75 m*

24.75 m*

29.75 m*

1 m above ground – cable only

84.45 62.55 45.93 6.92 1.69 0.67 0.33 0.19

1 m above ground – North-South

98.14 108.19 76.27 45.31 48.56 49.41 49.70 49.83

1 m above ground –East-West

113.12 103.67 64.56 43.45 48.30 49.34 49.67 49.82

* These values represent a distance of 0 m, 1 m, 5 m, 10 m, 15 m, 20 m and 25 m from the edge of the cable corridor.

2.2.20 The maximum calculated magnetic field density is 129.90 μT (at 1 m above ground

level). The magnetic field density across the profile studied is also shown in Graph 2.4.

0

5

10

15

20

25

30

35

40

-40 -30 -20 -10 0 10 20 30 40

Mag

ne

tic

fie

ld D

en

sity

(μ

T) R

MS

Distance From Centre of Trenches (m)

Total Resultant Magnetic Field Density

7

Graph 2.4 Magnetic field densities due to 2 x 600 MW + 2 x 900 MW circuits.

0

20

40

60

80

100

120

140

-30 -20 -10 0 10 20 30 40

Mag

ne

tic

Fie

ld D

en

sity

(μ

T)

Distance From Centre of Trenches (m)

Total Resultant Magnetic Field Density

Total from Cable Only Total with Cable E-W Total with Cable N-S