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Dnvgl st 0359 subsea power cables for wind power plants
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STANDARD
The electronic pdf version of this document found through dnvgl is the officially binding version. The documents are available free of charge in PDF format.
DNVGL-ST-0359 Edition June 2016
Subsea power cables for wind power plants
© DNV GL AS June 2016
Any comments may be sent by e-mail to rules@dnvgl
This service document has been prepared based on available knowledge, technology and/or information at the time of issuance of this document. The use of this document by others than DNV GL is at the user's sole risk. DNV GL does not accept any liability or responsibility for loss or damages resulting from any use of this document.
FOREWORD
DNV GL standards contain requirements, principles and acceptance criteria for objects, personnel, organisations and/or operations.
Contents
- Standard, DNVGL-ST-0359 ñ Edition June 2016 Page
- CHANGES ñ CURRENT Contents
- Sec General
- 1 Introduction ...........................................................................................
- 1.1 Scope and application.....................................................................
- 1.1 Alternative methods and procedures.................................................
- 1 References and definitions .....................................................................
- 1.2 General ........................................................................................
- 1.2 Standards ....................................................................................
- 1.2 Guidelines ....................................................................................
- 1.2 Terminology and definitions.............................................................
- 1.2 Abbreviations and symbols
- 1 Introduction ...........................................................................................
- Sec Project life cycle..........................................................................................
- 2 General.................................................................................................
- 2.1 Objective
- 2.1 Application
- 2.1 Dependability and risk based design
- 2 Preliminary design ..............................................................................
- 2.2 Approach
- 2.2 System analysis...........................................................................
- 2.2 Conceptual design........................................................................
- 2 Detailed design
- 2.3 General
- 2.3 Cable system design.....................................................................
- 2.3 Subsea power cables
- 2.3 Cable protection design
- 2.3 Cable interface at fixed offshore units
- 2.3 Landfall
- 2 General.................................................................................................
- Sec Manufacturing and testing
- 3 General.................................................................................................
- 3 Quality assurance and testing ..............................................................
- Sec Transport and installation
- 4 General.................................................................................................
- 4 Cable storage .......................................................................................
- 4 Cable load-out ......................................................................................
- 4 Cable transport
- 4 Cable installation..................................................................................
- 4.5 Jointing
- 4.5 Cable pullñin to offshore unit
- 4.5 Landfall
- 4.5 Cable protection
- 4 Infrastructure crossings.......................................................................
- 4 As-built survey .....................................................................................
- 4.7 General
- 4.7 Survey requirements
- 4 Termination..........................................................................................
- Sec Commissioning
- 5 General.................................................................................................
- Standard, DNVGL-ST-0359 ñ Edition June 2016 Page
- 5 Testing after installation ...................................................................... Contents
- Sec In-service....................................................................................................
- 6 General.................................................................................................
- 6 Operation planning...............................................................................
- 6 Maintenance and monitoring requirements ..........................................
- 6 Repair work..........................................................................................
- 6.4 General
- 6.4 Repair planning and execution
- Sec Decommissioning
- 7 General.................................................................................................
- 7 Removal process ..................................................................................
- App. A Documentation
- A General................................................................................................
- A Preliminary design
- A Detailed design
- A Manufacturing and testing...................................................................
- A Transport and installation
- A Commissioning
- A In-service............................................................................................
- A Decommissioning
Standard, DNVGL-ST-0359 ñ Edition June 2016 Page 7
1.1 Alternative methods and procedures.................................................
Methods and procedures alternative to those described in this standard may be used, provided that they
meet the overall objectives, safety and quality levels specified herein and are suitable for the respective
application. This shall be evaluated and agreed in each individual case.
1 References and definitions .....................................................................
1.2 General ........................................................................................
The following documents include provisions which, through specific reference in the text, constitute
provisions of this standard essential for its application.
Where reference is made to documents other than DNV GL service documents, the valid revision shall be
taken as the revision which was current at the date of issue of this standard.
1.2 Standards ....................................................................................
Table 1-2 Overview on referenced standards
Standard no. Title IEC 60183 Guide to the selection of high-voltage cables IEC 60502 Power cables with extruded insulation and their accessories for rated voltages from 1 kV (Um = 1,2 kV) up to 30 kV (Um = 36 kV) IEC 60840 Power cables with extruded insulation and their accessories for rated voltages above 30 kV (Um = 36 kV) up to 150 kV (Um = 170 kV) - Test methods and requirements IEC 60228 Conductors of insulated cables IEC 60287-1-1 Electric cables - Calculation of the current rating - Part 1-1: Current rating equations (100% load factor) and calculation of losses - General IEC 60287-2-1 Electric cables - Calculation of the current rating - Part 2-1: Thermal resistance - Calculation of thermal resistance IEC 60287-3-2 Electric cables - Calculation of the current rating - Part 3-2: Sections on operating conditions - Economic optimization of power cable size IEC 60300-1 Dependability management - Part 1: Dependability management systems IEC 60793 Optical fibres IEC 60794 Optical fibre cables IEC 61400-3 Wind turbines - Part 3: Design requirements for offshore wind turbines IEC 62067 Power cables with extruded insulation and their accessories for rated voltages above 150 kV (Um = 170 kV) up to 500 kV (Um = 550 kV) - Test methods and requirements ISO 9001 Quality management systems - Requirements ISO 13628-5 Petroleum and natural gas industries - Desi gn and operation of subsea production systems - Part 5: Subsea umbilicals ISO 14688-1 Geotechnical investigation and testing - Identification and classification of soil - Part 1: Identification and description ISO 14688-2 Geotechnical investigation and testing - Identification and classification of soil - Part 2: Principles for a classification ISO 19901-6 Petroleum and natural gas industries ñ Specific requirements for offshore structures ó Marine Operations ITU-T G Test methods applicable to optical fibre submarine cable systems
Standard, DNVGL-ST-0359 ñ Edition June 2016 Page 8
1.2 Guidelines ....................................................................................
1.2 Terminology and definitions.............................................................
Table 1-3 Overview on referenced guidelines
Document no. Title API RP 2A Recommended Practice for Planning, Designing and Constructing Fixed Offshore Platforms ñ Working Stress Design API RP 2RD Dynamic Risers for Floating Production Systems CIGR... Technical Brochure 177 Accessories for HV cables with extruded insulation CIGR... Technical Brochure 279 Maintenance for HV cables and accessories CIGR... Technical Brochure 398 Third-party damage to underground and submarine cables CIGR... Technical Brochure 415 Test procedures for HV transition joints for rated voltages 30 kV (Um = 36 kV) up to 500 kV (Um = 550 kV) CIGR... Technical Brochure 476 Cable accessory workmanship on extruded high voltage cables CIGR... Technical Brochure 490 Recommendations for testing of long AC submarine cables with extruded insulation for system voltage above 30 (36) to 500 (550) kV CIGR... Technical Brochure 496 Recommendations for testing DC extruded cable systems for power transmission at a rated voltage up to 500 kV CIGR... Technical Brochure 560 Guideline to maintaining the integrity of XLPE cable accessories CIGR... Technical Brochure 610 Offshore generation cable connections CIGR... Electra 189 Recommendations for tests of power tr ansmission DC cables for a rated voltage up to 800 kV DNV-OS-H102 Marine Operations, Design and Fabrication DNV-OS-H205 Lifting Operations (VMO Standard Part 2-5) DNV-OS-H206 Loadout, transport and installation of subsea objects (VMO Standard - Part 2-6) DNV-OS-J103 Design of Floating Wind Turbine Structures DNV-RP-F401 Electrical Power Cables in Subsea Applications DNVGL-RP-0360 Subsea power cables in shallow water GL-IV-2 GL Rules and Guidelines - IV Industrial Services - Part 2 - Guideline for the Certification of Offshore Wind Turbines, Edition 2012 ICPC Recommendation 3 Criteria to be applied to proposed crossings between submarine telecommunications cables and pipelines/power cables ICPC Recommendation 9 Minimum technical requirements for a desktop study (also known as cable route study) ICPC Recommendation 11 Standardization of electronic formatting of route position lists IMCA M 190 Guidance for Developing and Conducting Annual DP Trials Programmes for DP Vessels IMO MSC/Circ Guidelines for vessels with dynamic positioning systems
Table 1-4 Definitions of verbal forms
Term Definition shall verbal form used to indicate requirements strictly to be followed in order to conform to the document 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 document
Standard, DNVGL-ST-0359 ñ Edition June 2016 Page 10
cable engine collective term for machinery used to move cables. Includes, for instance, the following:
ó linear cable engine, with wheel pairs: Pairs of motor-driven wheels gripping a cable for pay- out or recovery. Holding force depends on the number of wheel pairs, the squeeze force acting on the cable and the friction between wheels and cable surface ó linear cable engine (tensioner), with tracks: Arrangement of e. two or four belts / tracks gripping a cable for pay-out or recovery. Holding force depends on track length, pad shape, the squeeze force acting on the cable and the friction between pads and cable surface. Also referred to as tensioner or caterpillar ó drum cable engine (capstan): A drum-shaped device for pay-out or recovery of a cable, used especially when large holding power is required. Fitted with a fleeting mechanism to control the position of the cable on the drum. Commonly used in conjunction with a draw off / hold back cable engine ó draw-off / hold-back (DOHB) cable engine: Linear cable engine used in conjunction with drum cable engines ó transporter: Small cable engine with typically one or two wheel pairs for moving cable cable protection any means protecting a cable from external mechanical forces cable protection system
collective term for protective tubular elements which can be fitted onto a cable for mechanical protection to ensure that the cable can operate for its service life cable route path of a cable, landfall and offshore, planned or installed cable route study process of reviewing available information and identifying a safe, technically and economically viable cable route cable system a subsea power cable system may consist of cable(s), termination(s) and joint(s) Above definition applies specifically for testing of power cables. In a wider definition the cable system may also include components like hang-off, cable protection measures and optical fibres cable tension axial force on a cable. Inter-dependent with cable bending catenary a curve assumed by a cable suspended between two points, (e. vessel and seabed) chinese fingers sometimes also referred to as cable grip Wire mesh stocking often made from galvanized wire rope or stainless steel wire rope, specifically designed for pulling cable, strain relief or cable support chute a curved channel for passing a cable from a higher to a lower level, e. overboard a vessel, which does not compromise the mechanical parameters of the cable coiling simultaneous twisting and bending of a cable, one full twist per turn. If the design of the cable allows and the manufacturer confirms that a cable can be coiled, it is often referred to as coilable. Otherwise, it is referred to as non-coilable conductor part of a cable core designed for transmissi on of electric current, typically made of copper or aluminium core an assembly consisting of a conductor and its own electrical insulation corridor width of the area along a cable route, specified e. for cable route consenting, surveying purposes or post-construction exclusion zones departure angle cable, cable protection system or abandonment & recovery (A&R) line position with respect to the guide surface or last roller, (see Figure 4-1). dependability collective, non-quantitative term describing availability performance which is determined by reliability performance, maintainability performance and maintenance support performance see IEC 60300- depth of burial a measure describing the lowering of a cable into the ground / seabed. Specific terms as follows apply, (see Figure 1-3):
ó depth of trench - vertical distance between bottom of trench and undisturbed (mean) seabed level ó depth of lowering - vertical distance between top of cable and undisturbed (mean) seabed level ó depth (height) of cover - vertical distance between top of cable and average level of the backfill above top of the cable
Where depth of burial has not been defined specifically for a project, it should, as a default, be understood as depth of lowering defined above.
Table 1-5 Definition of terms (Continued)
Term Definition
Standard, DNVGL-ST-0359 ñ Edition June 2016 Page 11
Figure 1-3 Depth of burial design basis a set of conditions and regulatory requir ements which are taken into account when designing a facility or a product design criteria the criteria applied for verification of systems, equipment, structures, etc. design life the service life of a component or system multiplied by an appropriate factor which is equal to or greater than 1 DP acceptance test specific trials programme for dynamically positioned vessels covering key elements of a fault tolerant system including performance, protection and detection, meeting the requirements of the IMO equipment classes 1, 2 or 3 and/or those of the classification society Typically carried out annually to demonstrate acceptance criteria are met and supplemented by shorter field arrival trials, see IMCA M 190 dynamic positioning (DP)
a method of automatically controlling a vesselís position and heading within certain predefined tolerances by means of active thrust. IMO MSC/Circ distinguishes equipment classes 1, 2 and 3 Manual position control and automatic heading control is sometimes referred to as DP earthing system or process of equalising the electrical potential of conductive parts with the potential of the Earth emergency an unplanned situation where there is a high risk of (further) extensive damages and/or personnel injuries/casualties export cable subsea power cable connecting an offshore electricity generation project (e. an offshore wind farm) to a point to which power is delivered fixed offshore unit non-buoyant construction (e. offshore wind turbine, offshore substation) that is founded in the seabed (e. monopile, piled jacket structure) or on the seabed (e. gravity based structure), see e. IEC 61400-3, GL-IV-2 or DNV-OS-J free span unsupported section of a cable between two intermediate support points generating unit generating units are defined as single current generating installations like single wind turbines, tidal turbines etc. converting renewable energy sources like e. wind speed into electrical energy geological study collection and analysis of information about the geological history of the general area of development ground investigation a methodological approach to assess the properties of the ground (soil, rock), commonly including geological studies, geophysical surveys and geotechnical investigations Also referred to as soil investigation hang-off a system used in offshore units to suspend a cable end through clamping For wind farm applications armor steel wires of a subsea cable are often restrained in a steel flange welded to the interface structure. high voltage (HV) see voltage I-tube an open-ended, I-shaped section of a tube or pipe attached internally or externally to a fixed offshore unit for guiding and protection of a cable or cable assembly
Table 1-5 Definition of terms (Continued)
Term Definition
Standard, DNVGL-ST-0359 ñ Edition June 2016 Page 13
minimum bending radius (MBR)
the smallest radius that a cable may be bent to, at a specific tensile load and for a specific time MBR can be assumed to mean the internal bending radius (except if specified by the manufacturer at the cableís centre line). Conditions for which MBR applies should be stated, e. during storage or installation. Sometimes distinguished into static and dynamic minimum bending radii near shore zone of the shore where waves are transformed through interaction with the seabed offshore zone beyond the near shore area offshore unit facility (fixed to the seabed) to which a cable is connected, e. offshore substation or offshore wind turbine on-bottom stability ability of a subsea power cable to remain in position under lateral displacement forces due to the action of hydrodynamic loads out of service (cable) part of a decommissioned cable system left in situ ploughing towing a plough across the seabed to (a) bury a cable or (b) open a trench pre-lay grapnel run dragging of a grapnel over the seabed prior to cable installation in order to clear debris (e. wires or ropes) which is lying on the seabed or buried in the very top layer of the soil pulling stocking / pulling grip
gripping device holding onto the outer surface (serving, sheath) of the cable, comprised of interwoven wires or rope and a built-in anchorage arrangement Also referred to as chinese finger reef ridge of rock, sand or coral that rises to or near the surface of the sea Natural reefs are results of abiotic processes like deposition of sand or biotic processes dominated by corals, calcareous algae, and shellfish. Artificial reefs are the result of anthropogenic activities reliability the probability that a component or system will perform its required function without failure under stated conditions of operation and maintenance and during a specified time interval remotely operated vehicle (ROV)
a crewless, fully submersible vehicle with three-dimensional manoeuvrability that is powered by and controlled from a vessel through an umbilical The ROV typically features a range of sensors and manipulative devices to perform a variety of tasks risk the qualitative or quantitative probability of an accidental or unplanned event occurring, considered in conjunction with its potential consequences In quantitative terms, risk is the probability of a failure mode occurring multiplied by its quantified consequence. route clearance removal of identified objects on or near a cable route, such as out-of-service cables, unexploded ordnance or boulders which may affect cable installation route position list (RPL)
list with coordinates, water depths, etc., typically in accordance with ICPC Recommendation 11
routine test test(s) made after manufacture on every produced component (length of cable, accessory) to demonstrate that the requirements are met sample test test(s) made after manufacture, at a specified frequency, on samples of completed components (length of cable, accessory) to verify that the specifications are met sand wave large-scale depositional feature of the seabed, formed by the movement of sediments due to (tidal) current or wave action Movement of sediments is divisible into:
ó rippled rigdes (small-scale bed forms with asymmetrical languid forms (produced by tidal currents) or straight crested symmetrical or asymmetrical forms (produced by waves) and ó mega rippled ridges (intermediate-scale bed forms, formed by waves) ó sand waves
Typically, ripples have heights of less than 0 m and wavelengths of less than 0 m; mega ripples have heights of up to 1 m and wavelengths of up to 30 m; sand waves have heights exceeding 1 m and wavelengths from 30 m to 500 m scour erosion of the seabed caused by shear forces due to currents and waves, resulting in relocation of sediments Due to up-speed effects, deep holes can form around fixed structures. scour protection protection against erosion of the seabed at fixed offshore structures or installed cables
Table 1-5 Definition of terms (Continued)
Term Definition
Standard, DNVGL-ST-0359 ñ Edition June 2016 Page 14
sealing technical measure to render air-tightness or water- tightness Sealing may apply, for instance, to cable end caps (preventing humidity ingress) or subsea power cable entry into an offshore unit (limiting or preventing water exchange). Due to less than perfect mating surfaces, the effectiveness of a seal depends on factors like adhesion or compression. Specifications like watertight or airtight should be qualified, e. by a maximum fluid / gas exchange rate over a specified period of time. sediment particulate material broken down by weathering and erosion processes and subsequently transported Classified by grain size or composition. sediment transport movement of sedimentary material by wind, current, wave, ice or gravity action service life the planned time period from initial installation or use until permanent decommissioning of a component or system during which the component or system shall be capable of meeting the functional requirements serving outer covering of cable, over the armour layer Typically made either as a continuous tubular polyethylene sheath or of helical polypropylene roving. sidewall pressure (SWP)
not a pressure, but a force exerted per unit length of cable when pulled around a bend (e. of storage device or in a tube). SWP = pulling force / bend radius, measured in kN/m Sidewall pressure increases with increased pulling load and smaller bend radius. Also referred to as sidewall bearing pressure. tensile strength ability of a cable to withstand tensile loads termination connection between cable and equipment or panels, including for instance:
ó mechanical termination - fixing of cable armouring, e. by hang-off ó electrical cable termination - device fitted to the end of a cable core ensuring electrical connection and maintaining the insulation ó optical fibre termination - connection of optical fibres to connectors and patch panels touch-down point point where, during installation, the cable first touches the seabed trefoil arrangement of three single cores of 3-phase AC systems in a triangular formation trenching opening of a trench for simultaneous or post-lay of a cable type test test(s) made on components (cable, accessory) to verify their properties prior to supplying them on a general commercial basis unexploded ordnance (UXO)
explosive ordnance that has or has not been primed, fused or otherwise prepared for use and which has been fired, dropped, launched, projected or placed in such a manner as to constitute a hazard to personnel or material and remains unexploded either through malfunction, design or for any other reason vessel barge, ship, tug, mobile offshore unit, crane vessel or other ship-shaped unit involved in a marine operation voltage electromotive force or potential difference expressed in volts:
ó low voltage (LV), < 1 kV ó high voltage (HV), in general ≥ 1 kV, here e. 33, 132, 150 or 220 kV AC water depth still water level to seabed distance In fluid mud, a nautical depth is defined as the vertical distance between the water surface and the level where seabed characteristics reach a limit beyond which contact of a vesselís keel causes damage or unacceptable effects on controllability. The distinction between shallow and deep water is context-specific. In this recommended practice, very shallow generally means up to 20 m water depth, shallow up to 50 m, deeper more than 50 m and deep more than 100 m.
Table 1-5 Definition of terms (Continued)
Term Definition
Standard, DNVGL-ST-0359 ñ Edition June 2016 Page 16
SECTION 2 PROJECT LIFE CYCLE
2 General.................................................................................................
2.1 Objective
This section defines the requirements for the overall design and project implementation philosophy that
shall be applied by stakeholders in all phases of subsea power cable system certification projects from
concept development through in-service up to decommissioning.
2.1 Application
This section applies to all subsea power cable systems which are planned to be designed, manufactured and
installed in accordance with this standard. The integrity of subsea power cable systems shall be ensured
through all phases.
The life cycle of a subsea power cable system shall be split into the following phases:
2.1 Dependability and risk based design
Safety, environmental performance and functionality of the overall cable system can be ensured by
application of dependability and risk based design methodologies. The overall cable system shall be
designed based on failure consequences and their prob ability to demonstrate that project objectives will be
met.
Guidance note: For guidance on third party damage to underground and subsea cables, see CIGR... Technical Brochure 398.
---e-n-d---of---g-u-i-d-a-n-c-e---n-o-t-e---
2 Preliminary design ..............................................................................
2.2 Approach
Conditions of soil and site, but also impacts on the cable assumed to come in later project stages have to
be considered early in the development process. Relevant information on operational and environmental
conditions, applied standards or necessary calculation techniques shall be defined and outlined in a design
basis document, which constitutes the groundwork for the conceptual cable design.
2.2.1 Functional requirements
Functional requirements shall be defined by the purchaser / wind farm developer by detailing the
performance expectations / characteristics. The cable system shall have:
ó ability to meet health, safety and environmental objectives of the project
ó capability to transmit power (and, if applicable, information) during the design life with the required
dependability
ó capability to operate under the stated envelope of environmental conditions during the design life
Phase I: Preliminary design [2] defines the site conditions, applied guidelines and standards (norm
hierarchy) and conceptual design.
Phase II: Detailed design [2] addresses the final design ready for manufacturing. It is the result of an iterative process that initially starts with the design basis and ends with the final design.
Phase III: Manufacturing and testing Sec covers the surveillance of manufacturing processes and quality assurance.
Phase IV: Load-out, transport and installation Sec covers requirements of surveillance of load out,
transport, installation and corresponding procedures.
Phase V: Commissioning Sec involves all follow-up verification and testing after installation
Phase VI: In-service Sec outlines necessary operational activities like regular inspection, repair works and condition monitoring.
Phase VII: Decommissioning Sec addresses cable recovery at the end of lifetime.
Standard, DNVGL-ST-0359 ñ Edition June 2016 Page 17
ó capability to withstand specified design loads and load combinations (mechanical and electrical)
ó capability of being stored, installed, recovered, repaired and reinstated.
2.2.1 Design basis
A design basis shall be established, detailing all boundary conditions of the cable project, which, together
with the functional specifications, enables a designer to pursue the design activities. Subjects covered in a
design basis may include the following:
ó system overview
ó terms of reference
ó applicable standards and codes
ó project specific requirements/client specifications
ó site conditions
ó technical interfaces
ó manufacturing and storage aspects
ó load-out, transportation and installation aspects
ó operation and maintenance aspects
ó decommissioning aspects.
The proposed solution shall be assessed whether it meets the design criteria or not. A range of scenarios
shall be considered for the various components of a cable system, covering normal operation, but also
emergency situations/loads in both temporary and permanent conditions. Industry recognized calculation
tools, or proprietary tools documented to provide valid results, shall be used for design and installation
analyses of the subsea cable system.
2.2 System analysis...........................................................................
Loads acting on parts of a cable system can be classifi ed as functional, environmental or accidental. A load
combination (i. a set of loads acting simultaneously), rather than single loads, frequently governs the
design. The cable system shall withstand the most onerous combination of loads that can be predicted to
occur simultaneously.
2.2 Conceptual design........................................................................
2.2.3 General approach
An overall design philosophy including general principles shall be established for the cable project.
A project safety and hazard review shall be initiated (see DNVGL-RP-360 Sec [2]) and shall be based
on a consistent risk management framework.
Potential failure modes, their causes and consequences shall be described in the design documentation
during the conceptual design stage in order to define corresponding mitigation measures along the cable
route, if required.
2.2.3 Project layout
Cable design is highly depending on the conditions of the renewable energy project being developed.
Important assumptions and applicable parameters shall be clearly described, including at least:
ó overall number of turbines
ó type and rating of turbine
ó location of the individual turbines
ó location of offshore substation or onshore grid connection.
ó step-up voltage
ó choice of the cable type(s)
ó choice of cable route(s)
ó feasibility of cable installation and burial.
Standard, DNVGL-ST-0359 ñ Edition June 2016 Page 19
ó determination of cable losses and thermal behaviour [2.3.3]
ó basic cable route engineering [2.3.3] and protection studies [2.3], yielding e. cable lengths, burial
methods and burial depths
ó sea bottom stability, if applicable
ó if applicable, design of crossings
ó design of interface with fixed offshore units [2.3]
ó if applicable, design of interface with the land-based power system [2.3].
2.3 Subsea power cables
2.3.3 Electrical specifications
Voltage, frequency, short-circuit ratings and the current-carrying capacity (or the conductor cross-section)
shall be specified as determined during electrical network studies in the course of conceptual design phase.
Power core conductor design shall comply with IEC 60228 and cross-sectional areas for conductors defined
herein. Other conductor profiles shall be agreed in each individual case.
Power core design shall comply with relevant IEC standards, like e. IEC 60502 and IEC 60840.
2.3.3 Thermal specifications
Current losses from conductors and metallic covers as well as dielectric losses in the insulation are
transferred through the cable surface to the environment, e. soil, water or air. In steady state conditions,
the temperature difference between conductor (limited by the maximum temperature of the insulating
material) and ambient depends on the total loss per metre cable and the total thermal resistance.
The current-carrying capacity of the cable is largely determined by the thermal properties of its
surroundings. A list of cases shall be established and results of an assessment shall be documented. This
includes, but is not limited to cable in J- or I-tube, cable buried in the seabed, cable inside conduit or at
landfall.
Ambient temperatures, solar radiation or proximity to other cables and pipelines shall be considered, when
analysing the current-carrying capacity of cables.
2.3.3 Mechanical specifications
The mechanical properties of the cable are strongly in fluenced by its armour and shall allow all required
handling during the manufacturing, storage, load-out, transport, installation, operation phases as well as,
if required, repair and decommissioning phases of the project.
Design documentation shall include information about:
ó diameter, dry mass and submerged weight
ó minimum bending stiffness, axial stiffness and torsional stiffness
ó maximum allowable tension (straight pull), maximum allowable tension at bend radii specified by the
client/cable manufacturer, e. corresponding to the radius of the installation chute, J-tube bend or similar
ó minimum allowable bending radius at combined tension and bending, at a tension representative of the
touchdown region and any other relevant load case for transport and installation operations
ó maximum allowable sidewall pressure at maximum installation tension (relevant for installation over
chute) and maximum tension around J-tube bend, if applicable
ó maximum allowable twist
ó maximum allowable duration of a stand-by condition, alternatively maximum fatigue damage over the
cross-section, for specified load combinations (i. tension and curvature) provided by the installation contractor
ó for coilable designs, minimum coiling diameter, coiling direction and maximum allowable number of
coiling cycles
ó temperature dependency of properties, where relevant.
Subsea power cables shall be qualified by testing using appropriate mechanical loading which represents
Standard, DNVGL-ST-0359 ñ Edition June 2016 Page 20
worst handling conditions, if not proven earlier with similar cable design. Testing shall be in accordance with
CIGR... Technical Brochure 623, see [3].
Cable integrity when subjected to applicable crush / squeeze loads (e. from stacking, use of cable engine, chinese fingers) and impact from falling objects (e. rock placement) shall also be verified by significant
testing.
2.3.3 Testing specifications
Non-electrical and electrical tests for the cables including the applicable standards shall be specified for
verification of design implementation and quality assurance.
2.3.3 Power cable accessories
Subsea power cable accessories may include, but not be limited to, the following:
ó joints
ó termination kits
ó cable end caps
ó hang-off modules
ó pulling head / chinese fingers.
Joints and terminations shall be designed and tested in accordance with applicable IEC standards (e. IEC
60502 or IEC 60840) and, if not addressed sufficiently therein, CIGR... guidelines, see [3].
The joints and terminations shall have the same electrical strength as the cable itself.
The design of the termination kit shall be compatible with the selected power cable design, voltage
requirements and switchgear design with regard to selected standards, operational requirements, dimensions and materials.
Hang-off or armour terminations of subsea cables shall be designed in accordance with relevant design codes such as DNV-OS-H102 applying the maximum operational and installation loads respectively.
Chinese fingers shall be designed according to recogn ized lifting standards, e. ISO 19901-6 or DNV-OS-
H205 considering applicable safety factors. Standard DNV-OS-H206 shall be applied for corresponding
qualification and testing.
2.3.3 Optical fibres
Subsea power cables may contain a number of optical fibres. The design documentation for the integrated
fibre optic cables shall at least include following information:
ó fibre type (single-mode or multi-mode) and operational wavelength
ó number of fibres, including spare fibres
ó dimensions and optical properties of single fibres, e. attenuation, bending loss
ó construction details
ó earthing of metallic parts of fibre optic package
ó marking of individual fibres, i. colour coding scheme
ó testing standard.
It shall be possible to connect the optical fibres of different cables using a standard splicing tool.
Guidance note: A general expectation for subsea power cables is that continuous lengths of optical fibres are used which do not require splicing in the power cable factory. ---e-n-d---of---g-u-i-d-a-n-c-e---n-o-t-e---
Splices, connectors and splice/connection boxes shall be available for the optical fibres and suitable for the
intended application (e. offshore).
2.3.3 Cables for application in dynamic environment
For subsea power cables connected to floating structures, like e. floating wind turbines or wave energy
conversion units, aspects shall be considered in addition to [2.3.3] for design and mechanical strength in order to reach expected lifetimes. A life-time (fatigue) analysis under consideration of environmental
conditions shall be performed.
Dnvgl st 0359 subsea power cables for wind power plants
Course: BS Electrical Engineering (Math 17)
University: University of the Philippines System
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