Daisy-chain – two inter-array cables are required per wind turbine, which connect wind turbines together in sequence. The wind turbines located at either end of the grouping are connected to a single subsea junction box via the second inter-array cable exiting each of the two wind turbines. Once reaching the subsea junction box, a single static inter-array cable exits, to connect into the OSP.
Fishbone – each wind turbine is connected to a single subsea junction box via one inter-array cable. Lengths of static inter-array cable connect the subsea junction boxes together in sequence and then a single static inter-array cable exits the final subsea junction box in the sequence to connect into the OSP.
Star – several wind turbines are connected to a single subsea junction box via one inter-array cable per wind turbine. A single static inter-array cable exits the subsea junction box, to connect into the OSP.
Fishbone and star hybrid – several wind turbines are connected to a single subsea junction box via one inter-array cable per wind turbine. Lengths of static inter-array cable then connect multiple subsea junction boxes together in sequence. A single static inter-array cable exits the final subsea junction box in the sequence to connect into the OSP.

A diagram of a network

Description automatically generated

The maximum design envelope for inter-array cables, presented in Table 4.18 Open ▸ , takes into account these potential configurations and, therefore, allows flexibility in design should any of these configurations be employed alongside the subsea junction boxes.
The maximum design envelope for the subsea junction boxes is presented in Table 4.19 Open ▸ . At this stage, the design of the subsea junction boxes is conceptual, therefore, some parameters included are estimated; this is indicated in Table 4.19 Open ▸ as appropriate. In addition, the parameters presented in Table 4.19 Open ▸ take into account the junction boxes associated with the various inter-array cable configurations, therefore, the parameters represent a conservative estimate which is considered to be the maximum design scenario. The parameters included within the maximum design envelope for the subsea junction boxes account for ongoing development of this technology and allows flexibility in the future.

Interconnector cables connect OSPs to one another and provide redundancy should there be any failures within the electrical transmission system. It is expected that these cables will be a combination of HVAC and HVDC. The maximum design envelope is presented in Table 4.20 Open ▸
Up to 236 km of interconnector cables will be installed within the Array. It is anticipated that cables will be protected via burial methods and will be buried at a minimum target depth of 0.4 m (subject to CBRA). External cable protection will be used in areas where minimum target burial depth cannot be achieved. Site preparation activities may also be required to provide relatively flat seabed surface for installation of cables and enable burial of interconnector cables to target depths.

Where minimum target cable burial dept h cannot be achieved, external cable protection methods will be employed to restrict movement and prevent exposure over the lifetime of the Array. This will protect cables from activities such as fishing, anchor placement or dropped objects, and limit effect of heat and/or electromagnetic fields. External cable protection systems include concrete mattresses, rock placement, cast iron shells or polyurethane/polyethylene sleeving. The final solution(s) chosen at final design stage (post-consent) will be dependent upon seabed conditions and any potential interactions with human activities which may occur within the Array. Table 4.21 Open ▸ presents the maximum design envelope for external cable protection for inter-array cables and interconnector cables.

Concrete mattresses comprising high strength concrete blocks and Ultraviolet (UV) stabilised polypropylene rope may be used as a means of external cable protection for inter-array and interconnector cables and at cable crossings. The standard size of units is 6 m x 3 m x 0.3 m with standard density, however, size, density, and shape of units may be modified (within the parameters presented in Table 4.21 Open ▸ ) for example, by tapering edges of units for use in high current environments, or using denser concrete, so that they are engineered for and bespoke to the locality in which they are installed.
69. Concrete mattresses are installed above the cables using a Dynamic Positioning (DP1) vessel and free swimming installation frame. The mattresses are lowered to the seabed and the installation frame is released in a controlled manner once in the correct position to deploy the mattress on the seabed. This installation process is repeated for each mattress along the length of cable that requires external protection. Dependant on expected scour, mattresses may be gradually layered in a stepped formation on top of each other.

Rock placement may also be utilised as a form of external cable protection for inter-array and interconnector cables and at cable crossings. Rock is placed on top of cables either by creating a berm or using rock bags ( Figure 4.15 Open ▸ ).
Installation of rock placement in the form of berm creation will utilise a vessel with equipment such as a ‘fall pipe’ so that rock can be placed close to the seabed. Rock may be placed to a maximum height of 3 m and 20 m width (see Table 4.21 Open ▸ ). The berm created via rock placement will be designed to provide protection from anchor strike and anchor dragging, and to reduce risk of snagging by towed fishing gear as far as practicable in line with best practice guidance. Depending on expected scour, the cross-section of the berm may vary, and the length of the berm will be dependent on the length of the cable which requires protection.
Alternatively, pre-filled rock bags may be used which will be placed above the inter-array and interconnector cables or cable crossings using installation beams. Rock bags consist of various sized rocks contained within a rope or wire net which are lowered to the seabed and deployed on to the seabed once in the correct position. Rock bags have typical dimensions of 0.7 m in height and 3 m diameter; the number of rock bags which may be required will be dependent on the length of cable which requires protection.

Up to 12 inter-array cable crossings and up to 12 interconnector cable crossings may be installed across the Array. Cable crossings may comprise several different methods as demonstrated in Table 4.22 Open ▸ , and additional cable protection will be installed at cable crossings. Table 4.22 Open ▸ presents the maximum design envelope for cable crossings, and accounts for additional protection required.

Tables ▼