Post on 30-Dec-2019
Hornsea Offshore Wind Farm
Project One
Environmental Statement
Volume 6 – Onshore
July 2013
ii
SMart Wind Limited
Hornsea Offshore Wind Farm
Project One – Environmental Statement
Volume 6
Annex 6.9.1 – Electromagnetic Fields Study
SMart Wind Limited
11th Floor
140 London Wall
London
EC2Y 5DN
Tel 0207 7765500
Email info@smartwind.co.uk
Copyright © 2013
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 7.6.9.1
Report Number UK04-050700-REP-0071
Date July 2013
Client Name SMart Wind Limited
Client contact(s)
Chris Jenner
Penny Pickett
Rachael Mills
Rosemary Tingle
Liam Leah
Sheelagh Guilmartin
Ditte Bilde
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 3 x 335 MW circuit arrangement. ...........................................................................3
Figure 2.2 4 x 300 MW circuit arrangement. ...........................................................................4
Figure 2.3 2 x 600 MW HVDC circuits arrangement. ..............................................................5
Figure 2.4 3 x 335 MW + 5 x 360 MW HVAC circuits arrangement. .......................................6
Figure 2.5 2 x 600 MW + 3 x 600 MW circuit arrangement. ....................................................7
Table of Graphs
Graph 2.1 Magnetic field density due to 3 x 335 MW circuits. ................................................4
Graph 2.2 Magnetic field density due to 4 x 300 MW circuits. ................................................5
Graph 2.3 Magnetic field density due to 2 x 600 MW circuits. ................................................6
Graph 2.4 Magnetic field density due to 3 x 335 MW circuits + 5 x 360 MW circuits. .............7
Graph 2.5 Magnetic field densities due to 2 x 600 MW + 3 x 600 MW circuits. .......................8
Table of Tables
Table 2.1 Magnetic field densities due to 3 x 335 MW HVAC circuits. ...................................4
Table 2.2 Magnetic field densities due to 4 x 300 MW HVAC circuits. ...................................4
Table 2.3 Magnetic field densities due to 2 x 600 MW HVDC circuits. ...................................5
Table 2.4 Magnetic field densities due to 3 x 335 MW + 5 x 360 MW HVAC circuits. ............6
Table 2.5 Magnetic field densities due to 2 x 600 MW + 3 x 600 MW circuits. .......................7
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 will be the subject of 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 One (1.2 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 2.1.
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:
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
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:
2
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 One 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:
3 x 335 MW HVAC circuits – Project One*
4 x 300 MW HVAC circuits – Project One
2 x 600 MW HVDC circuit – Project One
3 x 335 MW HVAC circuits + 5 x 360 MW HVAC circuits – Projects One and Two
combined
2 x 600 MW HVDC circuit + 3 x 600 MW HVDC circuit - Projects One and Two
combined
*whilst it is recognised that the total capacity (1 GW) is lower in this scenario, each cable
will have a higher current loading at the peak output than in the alternative 4 x 300 MW
scenario and has been studied to assess which case produces the highest magnetic
field densities.
2.2.5 The arrangement of the cables is assumed as flat formation which provides the
highest magnetic field densities.
2.2.6 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.
3 x 335 MW HVAC Circuits – Project One
2.2.7 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.
2.2.8 The expected cable arrangement is shown below in Figure 2.1.
0.7
m
3m
1m
Profile extends
up to 25 m
away from
trench
335 MW
220 kV
HVAC
0.25m
Profile extends
up to 25 m
away from
trench
3m
3 x 335 MW Circuits – Project One
335 MW
220 kV
HVAC
335 MW
220 kV
HVAC
Figure 2.1 3 x 335 MW circuit arrangement.
2.2.9 In this arrangement the current through each conductor at peak loading will be
approximately 900 A. Table 2.1 below shows the densities across the profile studied:
4
Table 2.1 Magnetic field densities due to 3 x 335 MW HVAC circuits.
Magnetic Field Densities (μT) at Distance from Centre Line of Trenches
0 m (centre)
3.25 m*
4.25 m*
8.25 m*
13.25 m*
18.25 m*
23.25 m*
28.25 m*
1 m above ground
18.12 22.00 18.80 4.20 1.45 0.73 0.44 0.30
* 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.
2.2.10 The magnetic field density across the profile studied is also shown below in Graph 4.1.
Graph 2.1 Magnetic field density due to 3 x 335 MW circuits.
2.2.11 The maximum calculated magnetic field density (at 1 m above ground level) is 22.29
μT, which occurs above the centre of the outer two circuits.
4 x 300 MW HVAC Circuits – Project One
2.2.12 The expected cable arrangement is shown in Figure 2.3.
0.7
m
3m
1m
Profile extends
up to 25 m
away from
trench
300 MW
220 kV
HVAC
300 MW
220 kV
HVAC
300 MW
220 kV
HVAC
0.25m
3m
4 x 300 MW HVAC Circuits – Project One
300 MW
220 kV
HVAC
Profile extends
up to 25 m
away from
trench
Figure 2.2 4 x 300 MW circuit arrangement.
2.2.13 In this arrangement the current through each conductor at peak loading will be
approximately 806 A. Table 2.2 shows the magnetic field densities across the profile
studied.
Table 2.2 Magnetic field densities due to 4 x 300 MW HVAC 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
0.23 19.27 17.00 4.09 1.48 0.78 0.48 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.
2.2.14 The maximum calculated magnetic field density (at 1 m above ground level) is 19.70
μT, which occurs above the centre of the outer two circuits. The magnetic field density
across the profile studied is also shown below in Graph 2.2
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 Resultant Magnetic Field Density
5
Graph 2.2 Magnetic field density due to 4 x 300 MW circuits.
2 x 600 MW HVDC Circuits – Project One
2.2.15 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
600 MW circuits, each carrying a 2,000 A current. The arrangement of the conductors
is shown below in Figure 2.3. Table 2.3 shows the maximum magnetic field densities
calculated in this arrangement.
Figure 2.3 2 x 600 MW HVDC circuits arrangement.
0.7
3m
0.5m
1m
Profile extends up to
25 m away from
trench
600 MW
2000 Amps
Profile extends up to
25 m away from
trench
2 x 600 MW Circuits – Project One
600 MW
2000 Amps
Table 2.3 Magnetic field densities due to 2 x 600 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
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.
0.00
5.00
10.00
15.00
20.00
25.00
-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
6
2.2.16 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
2.3.
Graph 2.3 Magnetic field density due to 2 x 600 MW circuits.
3 x 335 MW HVAC circuits + 5 x 360 MW HVAC circuits – Projects One and Two combined
2.2.17 As shown in sections 0 and 0 the 3 x 335 MW circuit arrangement produces a greater
maximum magnetic field density than the 4 x 300 MW arrangement. To consider the
worst case scenario in Project Two, the 3 x 335 MW arrangement has been taken
forward for the Project Two calculations. The expected arrangement is shown below in
Figure 2.4.
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
220kV 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 2.4 3 x 335 MW + 5 x 360 MW HVAC circuits arrangement.
2.2.18 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 2.4 below shows the magnetic field densities across the profile studied.
Table 2.4 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.
2.2.19 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 2.4.
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
7
Graph 2.4 Magnetic field density due to 3 x 335 MW circuits + 5 x 360 MW circuits.
2 x 600 MW HVDC circuits + 3 x 600 MW HVDC circuits – Projects One and Two combined
2.2.20 The arrangement of the conductors is shown below in Figure 2.5.
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 MW
2000 Amps
600 MW
2000 Amps
2 x 600 MW Circuits + 3 x 600MW Circuits – Projects
One and Two
600 MW
2000 Amps
600 MW
2000 Amps
3m 3m600 MW
2000 Amps
Figure 2.5 2 x 600 MW + 3 x 600 MW circuit arrangement.
2.2.21 In this arrangement the maximum current would be 2,000 A in the conductors
associated with Project One and Project Two. Table 2.5 shows the densities across
the profile studied.
Table 2.5 Magnetic field densities due to 2 x 600 MW + 3 x 600 MW 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 – cable only
37.91 54.42 48.95 12.34 4.64 2.49 1.57 1.08
1 m above ground – North-South
86.32 97.48 71.34 40.63 45.90 47.74 48.57 49.01
1 m above ground –East-West
86.32 103.55 83.20 43.30 46.40 47.93 48.66 49.06
* 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.
2.2.22 The maximum calculated magnetic field density is 103.7 μT (at 1 m above ground
level). The magnetic field density across the profile studied is also shown in Graph 2.5.
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
8
Graph 2.5 Magnetic field densities due to 2 x 600 MW + 3 x 600 MW circuits.
0
20
40
60
80
100
120
-40 -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