Review of Cabling Techniques and Environmental Effects Applicable

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Review of Cabling Techniques and Environmental Effects Applicable to the Offshore Wind Farm Industry – Technical Report Table 3.2: Typical Cable Characteristics for 33kV cables Details 33kV Cable Type 22 95 mm² 240 mm² 400 mm² 630 mm² 800 mm² Overall Diameter (mm) 89 104 127 143 153 Weight (kg/m) 12.2 18.6 38 49 59 MVA (approx) 18 29 36 44 48 3.4 Telecoms Cables This section outlines the types of cables which are commonly used by the subsea telecommunications industry to install their networks on a worldwide basis. It is normal practice for the subsea telecommunications industry to conduct a Burial Assessment Survey in advance of the design of the cable type along the full route of the cable (see Section 3.10). The Burial Assessment Survey will be used to assess the level of armouring required for a section of the cable length together with the proposed depth of burial. Many of these cable systems can be in excess of thousands of kilometres in length, therefore, the design of armouring for the cable can have a significant influence on the overall cost of the cable. There is also a relationship between the design of outer protective armouring and the proposed depth of burial to protect the cable in its in-service condition. Hence, the results of the Burial Assessment Survey are used to identify what level of burial can be achieved along the cable route. This assessment will take into account the burial system to be employed on the project together with the design armouring for the cable. Section 3.10 of this report reviews Burial Assessment Surveys in more detail. Table 3.3 gives typical armoured cable characteristics for a number of subsea telecommunication cables. The characteristics of these cables are set out in detail in the following sub-sections. Table 3.3: Typical Characteristic for Subsea Telecommunication Cables Characteristic Unit Lightweight Armour (AL) Single Armour (A) Double Armour (AA) Lightweight cable diameter mm 21.5 21.5 21.5 First lay steel wire diameter mm 4.0 4.9 4.9 Number of steel armour wires in the lay 19 16 16 Pitch of armour wire mm 530 539 539 Second lay mild steel wire diameter mm - - 7.0 Number of steel wires in the lay (left hand) - - 18 Pitch mm - - 610 Outside diameter mm 36.7 38.5 57.7 Weight in air kg/m 3.0 3.5 9.7 Weight in water kg/m 1.9 2.9 7.0
3.4.1 LIGHTWEIGHT CABLE Cable types and installation techniques Lightweight cable, as its name suggests, is cable which does not have any form of outer protective armouring. This type of cable is typically used in very deep water (usually in excess of 1000m) where the cable risk assessment has identified that the cable is highly unlikely to be subject to any form of hostile seabed intervention (e.g. anchoring or trawling). 3.4.2 ‘SHARK BITE’ CABLE Shark Bite cable was initially developed by AT&T in the USA when they discovered that the electromagnetic field emanating from the power feed system in their subsea telecommunication cables was agitating the local shark population. The sharks would then attempt to bite any surface laid sections of cable. To protect the cable, a new design, which provided a light single armour around the cable adequate to repel any potential shark attack, was derived. The cable also had additional screening installed in the cross sectional make-up in an attempt to reduce the amount of electro magnetic field propagation. 3.4.3 LIGHTWEIGHT ARMOURED CABLE Lightweight armoured cable is a lighter version of single armoured cable where the steel armour wires would typically be 4mm in diameter, as opposed to the 4.9mm diameter steel wires which are used in the conventional armoured cable (Figure 3.2). A typical application of lightweight armour would be for a deep sea section of cable which was going to be laid over a rocky seabed area and where the risk of abrasion damage to a lightweight type cable was considered to be high. 3.4.4 SINGLE ARMOURED CABLE Single armoured cable is a cable type which is typically used in conjunction with cable burial as a means of providing overall protection for the installed cable (Figure 3.3). This type of cable would be employed in areas where the risk from hostile seabed intervention such as fishing had been identified. This may occur in water depths anywhere between 50m to 1000m. 3.4.5 DOUBLE ARMOURED CABLE Double armoured cable would typically consist of an inner armoured layer (similar to the single armoured cable type) with steel wires of 4.9mm in diameter, which would then be overlaid with a second layer of armouring with steel wires of 7mm in diameter (Figure 3.4). Double armoured cable is significantly heavier and more inflexible than the single armoured cable which makes it more difficult and expensive to produce and install. Double armoured cable would typically be employed where there is a perceived high risk that the cable may 23
Page 1: REVIEW OF CABLING TECHNIQUES AND EN
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Page 9 and 10: Abbreviations AIS Automatic Identif
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4 Physical change 4.1 Introduction
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6 Good practice measures This secti
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7 Gaps in understanding Research fo
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References Introduction Sinden, G.
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Appendix A: Standards and codes of
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Printed in UK on recycled paper. De
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