Installation of Submarine Power Cables

Introduction

The Technical Brochure (TB) focusses on the main installation aspects concerning the installation (laying, protection in and on the seabed and pulling to shore or onto an offshore asset) of submarine power cables. The technical brochure does not go into details about installation of accessories at offshore assets, electrical testing etc.

If cables and installations are optimally designed and installed, submarine cable systems should provide long periods with little or no maintenance – especially for cables with extruded insulation. If not optimally designed and installed, submarine cable systems can be a costly asset to operate, repair or even replace, especially when considering lost revenue due to forced outages. CIGRE TB 815 and TB 398 considers service experience of HV underground and submarine cable systems. From the information provided within, it is obvious that well protected cables have a significantly lower risk of of outages due to external damage. This underlines the importance of well-executed installation activities particularly considering the natural and anthropogenic threats that the installed cable will be subjected to over its lifetime.

The brochure is written as a guide for people who are interested in various types of submarine cable installation activities. Examples include, but are not limited to, the following:

• Interconnectors between countries or regions
• Export and inter array cables for connecting to offshore renewable assets
• Cables with power from shore to offshore oil and gas production platforms
• Cable installation in harbours
• Cable installation across rivers or other types of applications.

The power cables considered would typically be in the range of 30 kV to 550 kV for both AC and DC applications with various insulation types. However, the aspects covered within the TB would also be relevant for lower voltages as well as higher Voltages, as a reminder of the most important factors to be considered.

The aspects of submarine cable installation typically extend from the sea to onshore transition joint bays or manholes where they transition into an underground cable system. However, for some cases where the termination points are close to shore, submarine cables could be installed directly to the onshore termination points / switchgear etc, without transition joints.

Managing submarine cable projects and the installation thereof, may need to be handled differently from country to country. However, the principles pertaining to various disciplines and various fields of activity described in the TB, will be relevant for reference. Aspects closely related to submarine cable installation are also covered. Examples are interactions with government authorities and stakeholders for permitting/consenting purposes, insight into engineering practices and management of complex submarine cable installation projects. Aspects concerned with the operation, maintenance and decommissioning are discussed in the brochure. Submarine cable manufacturing is not included.

The activities described in the TB are intended to apply on a general level and not dictate how each individual submarine cable installation project is to be approached.

Consents and permitting

For submarine cable projects, obtaining the necessary permits and consents to construct and operate the cable system is essential but can often be a complex task. Generally, consents from affected / interested parties need to be discussed and agreed between the affected stakeholders.

It should be noted that some permitting authorities are not well versed on the technicalities of a cable installation and might object to proposals. These proposals which from a knowledgeable technical point of view, would normally be considered as being reasonable. It is important to understand the concerns of the permitting authorities and engage and discuss these concerns and furthermore propose acceptable solutions.