CABLE PROTECTION FEATURE
SUBSEA CABLE PROTECTION A KEY CONSIDERATION
Protection of the subsea cables from external damage is a key consideration for offshore wind farms. Fully operational cables are essential both for export of electricity from the wind farm, and for control of the turbines (using the fibre optic communication cores included within the power cable) from onshore.
CABLE DAMAGE CAUSES Causes of cable damage range from dropped object impact, being snagged by fishing or anchor gear and dragged, causing either the cable to exceed its maximum allowed tension or be bent tighter than the allowable minimum bend radius, or abrasion or fatigue damage due to unprotected cable movement.
CABLE BURIAL – NOT ALWAYS AN OPTION Cables can often be protected by burial into the seabed, however this is not always possible, for instance close to
TUBULAR PRODUCTS Tubular products that are fitted around the cable during the cable laying operation have the advantages of instant protection, certainty that the protection is around/ over the cable, and obviate the need for a second operation.
Tubular products are available in polyurethane and ductile iron. Polyurethane products have tended to derive from the subsea oil and gas market, where the waters are typically deeper and stiller than in the renewable energy market.
A disadvantage of polyurethane in shallower water application such as most offshore wind farms, and certainly any tidal energy site, is that it is a very light material underwater, and consequently adds little or no stabilising weight whilst still adding drag to the cable through the increased diameter. The consequence is that the overall stability of the cable (expressed as ‘weight
many years (known as ‘split pipe’ or ‘articulated pipe’), and the use of iron split pipes for this application dates right back to 1924 when Siemens took out their first patent for the product.
In more recent years, the development of ductile iron since the 1960s, under the slogan of ‘more strength for less expense’, has transformed many industries, particularly the automotive and related industries. Ductile iron provides more strength, impact resistance (e.g. use in construction plant bucket teeth), fatigue life (e.g. use for engine crankshafts) and abrasion and wear resistance (e.g. use in plough shares).
BLUE OCEAN PROJECTS LTD (BOP) DESIGN Blue Ocean Projects entered the ductile iron cable protection market in 2009, and
developed a new range of ductile iron cable protectors, aimed primarily at the renewables market, to fill a gap in the market.
turbine foundations, in shallow water and at landfalls, boulder fields or areas of rocky seabed.
Alternative protection methods to burial include rock placement, gabion bags, concrete mattresses and tubular products fitted around the cable, all of which have their place in the market, sometimes in combination.
84
www.windenergynetwork.co.uk
to diameter ratio’) is reduced, leading to higher risk of cable movement. In contrast ductile iron tubular products have the opposite characteristic, and will increase, rather than reduce, the overall seabed stability of the cable.
DUCTILE IRON TUBULAR PRODUCTS Ductile iron tubular products have been around for subsea cable protection for
A key consideration was a design for quick and secure assembly on board deck of the cable ship, rather than using a design based primarily on diver installation.
The new design provides greater articulation angle at each joint than conventional ‘split pipe’, facilitating use over sheaves, chutes and quadrants. It also provides an all bolted assembly with identical top and bottom castings and use of large fasteners with built in nut recesses for simplicity, speed and reliability of assembly.
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100