Cable route planning

 „Unlike on a typical road or rail project, on a project to create a new HVDC transmission connection – which may be hundreds of kilometres long – we cannot benefit from a continuous construction site where everything can be done simultaneously. Instead, the construction process is repeatedly interrupted by crossings such as roads, railway lines, rivers and other utilities. Each of these crossing points requires its own logistical solution using existing transport routes. This doesn't necessarily increase the design scope, but it does present fundamentally different planning challenges. Logistics for cable installation are particularly challenging: The cable drums, with an average cable length of approximately 1.2 km, have a total transport weight of over 150 tonnes and are up to 36 metres long. To ensure everything runs smoothly, each of these must be delivered safely and on schedule to the part of the site where it is needed. This requires real teamwork.“ 
Andreas Völkel, Linear Infrastructure Division

The technical preparations and the specialised planning and design work are the crucial foundation for ensuring that the new infrastructure will reliably transport energy as expected.

Route planning and combining
One goal of route planning is to allow for new infrastructure to share existing infrastructure or utility corridors, such as power lines or gas pipelines, to minimise new land use and environmental impacts. But numerous other considerations apply, including various guidelines and restrictions:

• Roads: For new linear infrastructure running parallel to federal highways and other major roads, a minimum distance must be maintained to the existing infrastructure.
• Railway lines: The requirements of Deutsche Bahn AG (German Rail) regarding minimum distance to railway lines must be observed – parallel alignments are avoided.
• Crossings of major roads and railway lines: These are generally constructed using methods that avoid impacts on the existing infrastructure. For railway lines, railway-approved methods such as pipe jacking are used, and for highways and other major roads, horizontal directional drilling (HDD) is typically employed – while open-cut construction is predominantly used for secondary roads and paths.

Dealing with existing lines

• Water pipes: Minimum distances are prescribed in order to prevent, for example, the growth of Legionella bacteria due to heating
• Other power lines: Minimum distances must be observed in order to prevent thermal or electromagnetic interference between the new and existing lines

Fragmented construction process
Unlike road construction projects, in which first the bridges are built and then the continuous roadway, the construction of HVDC transmission lines is fragmented. All conflict areas – e.g. bodies of water, transport infrastructure, valuable biotopes, planted avenues, archaeological monuments, etc. – must be traversed using trenchless construction methods if they cannot be bypassed and if unacceptable impacts cannot be otherwise avoided. This affects:

• Logistics: Section-specific execution method (open/closed), increased relocation of equipment and transport of materials
• Scheduling: More necessity for working in parallel
• Coordination: Numerous interfaces with authorities and residents

Logistical challenges

• Cable transport vehicle: Total vehicle length of 36.10 m (axles: 4+4+6), total loaded weight of up to 150 t
• Transport: Vehicle dimensions for normal travel: Clearance height 4.50 m, width 4.20 m, therefore classified as oversized and heavy transport (GST) to be carried out at night and with an appropriate escort.
• Cable lengths: Maximum transportable length is approximately 2 km. Therefore, depending on the overall length, splicing is generally required, necessitating additional space and logistics planning.
• Access: Some route sections can only be accessed via secondary or temporary roads. This requires precise planning of the access routes, taking into account the vehicle's dimensions and capabilities – especially in relation to width, height, curve dimensions and maximum permissible gradients.