Offshore Substation
Earthing, Bonding and Lightning Protection
technical standards
ETS-04 Rev. 3
Document no. 56361/10, Case 10/4054 - ETS-04 v. 3
Revision survey
Document title
Earthing, Bonding and Lightning Protection
Document no.
56361-10
Target group
Fabrications Contractors and Designer for Offshore substations.
Revision
1
2
Document
status
Approved
Approved
after review
Writer
Init
N/A
xomo
Reviewer
Date
Init
12.10.09 N/A
POD,XBOH,
26.10.12
SGH, POB, JEJ
Approver
Date
Init
12.10.09
SGH
26.10.2012
SGH
Date
18.09.12
Minor alterations, type errors, rephrases' e.t.c where the meaning of the text is left
unchanged are not shown.
Appendix no. and description
None
Document no. 56361/10, Case 10/4054 - ETS-04 v. 3
Revision
Table of contents
1.
Scope
4
2.1
2.2
References
Statutory Regulations
Codes and Standards
4
4
4
3.1
3.2
Definitions and Abbreviations
Definitions
Abbreviations
4
4
5
2.
3.
4.
Technical Requirements
4.1
Earthing and bonding
4.1.1
General
4.1.2
Earth electrode
4.1.3
Earthing
4.1.4
Equipotential Bonding
4.2
Lightning
4.2.1
General
4.2.2
Lightning damage protection
4.2.3
Equipment requiring protection
5.
5
5
5
5
8
9
10
10
10
11
5.1
Certificates / Data books
General
11
11
6.1
6.2
Appendix
A: Overall earthing and bonding principles LV systems
B: Bonding principles for structure and equipment
12
12
13
6.
Document no. 56361/10, Case 10/4054 - ETS-04 v. 3
1.
Scope
This technical standard specifies the basic requirements for the earthing, bonding
and lightning protection to be established on an offshore located transformer
platform (Substation) for offshore wind power farms established in the Danish
offshore sector.
2.
References
2.1
Statutory Regulations
2.2

2006/95/EC
Low Voltage Directive (LVD).

2004/108/EC
EMC Directive.
Codes and Standards



DS/EN 50164
IEC 60092
IEC 60364





IEC 61000
IEC 61892
IEC 62305
DNV-OS-J201
DEFU Recommendations Nr. 25
Lightning Protection Components.
Electrical installations in ships.
Low voltage electrical installations - Protection for safety
and protection against electric shock.
Electromagnetic compatibility (EMC).
Mobile and fixed offshore units – Electrical installations.
Protection against lightning.
Offshore Substation for Wind Farms.
Lightning protection of wind turbines.
3.
Definitions and Abbreviations
3.1
Definitions

Shall:
Verbal form used to indicate requirements to be strictly followed in
order to conform to the standard and from which no deviation is
permitted, unless accepted by all parties.

Should:
Verbal form used to indicate that among several possibilities one is
recommended as particularly suitable, without mentioning or
excluding others, or that a certain course of action is preferred but
not necessarily required.

May:
Verbal form used to indicate a course of action permissible within the
limits of the standard.
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
3.2
Can:
Verbal form used for statements of possibility and capability, whether
material, physical or casual.
Abbreviations









ABA
CCTV
HVAC
LEMP
LPS
LPZ
SCADA
PE
UPS
“Automatisk Brand Alarm system” Automatic fire alarm system
Closed Circuit Television
Heating, Ventilation and Air Conditioning
Lightning electromagnetic impulse
Lightning protection system
Lightning protection zone
Supervisory control and data acquisition
Protective earth
Uninterruptible Power Supply
4.
Technical Requirements
4.1
Earthing and bonding
The earthing and bonding shall comply with the Low Voltage Directive 2006/95/EC,
IEC 60364, IEC 61892 and DEFU 25.
Further, ref. clause 4.2.1, IEC 62305 shall be adhered to.
4.1.1
General
To ensure safety of personnel and apparatus in case of electrical equipment failures,
and to prevent fires, mechanical damage or malfunction resulting from lightning or
static electricity, proper earthing and equipotential bonding shall be made.
The earthing system shall comprise main earth electrodes, main earth bus, branch
conductors and connectors.
If the unit has separate modules, every single module shall have its own individual
main earth electrodes, main earth bus, branch conductors and connectors.
Extraneous conductive parts of all the modules shall be tied together by means of
connections to the common equipotential bonding system. The bonding shall be such
as to give a substantially equal potential and a sufficiently low earth-fault loop
impedance to ensure correct operation of protective relays.
4.1.2
Earth electrode
Platform support structure (jacket) can be made of concrete or steel. Both models
can be assumed to establish a solid and effective earth electrode which applies to
grounding and protection against lightning on the platform. Bonding using 95 mm2
copper wire shall be performed at bolted connections.
If the foundation is made as a steel jacket, it will together with its piles into the
seabed act as a solid and efficient earth electrode.
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If the foundation is made as steel mono piles, as figure 1, the steel tube is
considered as a huge earth rod, and it is only necessary to make sufficient
conductive and corrosion resistant connections between the pile and the tower
bottom.
As the monopole and the transition section is not directly connected, an
equipotential bonding directly between the two sections in the bottom of the
tower should be performed.
For flexible connections between
monopole and transition tower section,
equal to least 95 mm2 Cu
Corrosion and mechanical protection must
be considered, e.g. use stainless steel.
Fig. 1
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If the foundation is made as a concrete structure (fig. 2a + 2b), reinforcement shall
be performed as a continuous electrical network, and can be welded, bolted or
securely tied together all the way from top to bottom. The connection point to the
foundation earth shall be fixed earthing terminals of stainless steel located in the top
of the structure.
Concrete
caissons
Connections of
Reinforcement in
meshes, size 3-5 m,
in top and bottom of
foundation by
welding or clamping
Concrete
caissons
Tower flange bolt
connected to the
reinforcement bars
Fig. 2a
Tower flange bolt
connected to the
reinforcement bars
Connections of
Reinforcement in
meshes, size 3-5 m,
in top and bottom of
foundation by welding
or clamping
Fig. 2b
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The connecting conductor from the foundation earth electrode to the steel bottom of
the platform shall be installed at min. 4 connection points at the bottom of the lower
deck. Each of these connections must be performed through copper wire 95 mm2
and be removable test connections to support structure (jacket).
4.1.3
Earthing
Requirements and recommendations for system earthing, i.e. an intentional
connection of the neutral point of the electrical power system to the structure are
specified according to IEC 61892-2, Clause 5.
The selection of methods of treating the neutral for a specific power system shall be
based on technical and operational factors.
The selection of neutral earthing method shall be based on one of the following
methods:

Directly earthed (TN-S system).

Impedance earthed (IT system)

Isolated (IT system)
A summary of principal features of the neutral earthing methods are listed according
to IEC 61892-2, Table 1.
The earth reference points shall be earth bars. The earth bar for protective earth
(PE) shall be located in all relevant technical rooms. The main earth bars shall be
solidly earthed via connections to a minimum of two earth bosses for each earth bar,
welded to the main platform structure. Earth cables for these connections shall at
least be 95mm2 Cu.
The earthing of the platform shall be designed for a short circuit current of at least
16kA for 1 sec. Exact level of short circuit current shall be established in detailed
design.
Earth bars shall be fabricated from copper and shall be prepared with suitable drilled
holes for the required size and number of connections.
The PE bar or the earth boss shall act as the main connection point for the following
equipment:

On site standby generator neutral point

33/0,4kV transformers neutral point

UPS systems neutral point

Earth bars in HV/MV and LV switchgear

PE earth bars in instrument panels
All other electrical equipment and electrical consumers shall be earthed via earth
core in the supply cables.
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The PE earth bar shall act as the connection point for the individual instrument panel
PE bars.
The instrument panel PE bars shall act as earthing point for instrument cable screens
and for spare/unused instrument cable cores.
See section 6 appendix for further details.
4.1.4
Equipotential Bonding
Bonding shall be made locally in close proximity to the items which require bonding.
Normally bonding connections shall be made by bolted connections to steel pads
(earth bosses) which shall be welded to the steel deck or structure.
Every bonding connection to earth shall be of copper or other corrosion resistant
material and shall be securely installed and protected where necessary against
damage and also against galvanic corrosion. Connections shall be secured against
becoming loose due to vibration.
All equipment bonding connections shall be made with suitable compression cable
lugs.
Equipment and items to be bonded shall include:








All metallic components of the structure which is not welded to the platform
main structure
Metallic enclosures of electrical equipment
Metallic doors
Stairs, ladders and railings
Steel cable ladders and trays
Piping systems
Tanks and vessels
Packaged units
Not insulated earthing connections (connectors/ bolts) shall be sealed in such a way
that corrosion is avoided.
Minimum cross section in the local earthing shall be copper wire 10 mm2 due to
mechanical strength.
Consumers can be earthed either through supply cable or through local cable
earthing. Local earthing is preferred.
See section 6 appendix for further details.
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4.2
Lightning
Lightning protection shall be made in accordance with IEC 61892 and lightning
protection components shall be in accordance with DS/EN 50164.
Although the IEC 62305 primarily concerns buildings and structures on shore, it shall
be used for the transformer platform as the basis for the assessment of the lightning
zones and protective devices.
4.2.1
General
As the platform will be exposed to lightning, precautions shall be made to prevent
damage to the structures and the equipment on the platform.
Earthing and bonding are important means to reduce the impact of lightning, hence
the relevant recommendations of IEC 62305-4 clause 5 shall be taken into
consideration for the design and implementation of earthing and bonding in clause
4.1 of this standard.
4.2.2
Lightning damage protection
When evaluating the requirements for lightning damage protection, the worst case
scenarios shall be used as the design basis.
The platform shall be divided into lightning protection zones (LPZ) as described in
IEC 62305-1.
Where an LPZ is defined, bonding shall be provided for all metal parts and services
(e.g. metal pipes/conduits, cable ladders/trays, bridges between modules etc.)
penetrating the boundary of the LPZ.
The lightning protection systems (LPS) shall be designed in order to ensure that no
major equipment is exposed to a direct lightning flash. This can be achieved either
by designing the main and secondary structure in a way so that it protects the
equipment, or by installing air-termination systems.
As the lightning electromagnetic impulse (LEMP) can be very damaging to electrical
and electronic systems, protection against LEMP shall also be provided. It shall be
ensured that the LEMP severity in a particular lightning protection zone will not
exceed the LEMP withstand level of the equipment to be protected.
The protection of electrical and electronic equipment located in equipment rooms
should be a combination of the following:



Bonding of all metallic components (i.e. pipes and cable armouring) which
enters from an outer zone to an inner zone
Installation of surge protective devises on all cables entering an inner zone from
the roof of the platform.
Equipment enclosures acting as magnetic shields
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Outdoor cable installations and equipment for lighting, small power, navigation aids
e.t.c shall, as far as practicable, be installed in areas where there is no risk of the
cables and equipment to be hit by direct flashes. Furthermore, the formation of cable
loops, or metallic loops such as pipe work, in proximity to down conductors shall be
avoided. Cables in close proximity to down conductors shall be installed in metal
pipes.
4.2.3
Equipment requiring protection
The equipment that needs protection against lightning damage is:
Electrical:










132/33/33kV main transformer
132kV switchgear
33kV switchgear
33/0.4kV utility transformers
400V main utility switchgear
400V on site standby generator
400V emergency switchgear
Lighting and small power distribution board
AC/DC UPS systems and distribution boards
HVAC systems
Electronic:









SCADA panels
Communication panels
ABA system
Antennas
Weather station
Navigation aids
CCTV system
VHF radio communication
Navigation aids control panel and power package
5.
Certificates / Data books
5.1
General
N/A
Document no. 56361/10, Case 10/4054 - ETS-04 v. 3
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6.
Appendix
6.1
A: Overall earthing and bonding principles LV systems
Document no. 56361/10, Case 10/4054 - ETS-04 v. 3
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6.2
B: Bonding principles for structure and equipment
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