New Guidance on Offshore Wind Farm Cable Burial

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New guidance has been published by the Carbon Trust’s Offshore Wind Accelerator (OWA) to give the offshore wind industry a unified, systematic approach to the risk management of cable burial.

The Cable Burial Risk Assessment (CBRA) Guidance offers a standardised, repeatable and qualitative method to improve risk management of subsea cables for offshore wind farms, improve conservative estimates of residual risk, and ultimately reduce the installation and insurance costs for subsea cables, Carbon Trust reported.

Cables are the root cause of the most frequent and largest insurance claims against offshore wind developments. According to industry figures shared by GCube, specialist offshore underwriter, over 80 per cent of construction projects have resulted in a cable related incident. Over half of these claims are solely down to incorrect installation and load out of cables. Between 2007 and 2014, the cumulative costs to insurers was £75 million with over 60 incidents alone resulting in pay outs of between £0.5 million and £13.5 million per claim.

The CBRA Guidance provides a risk based assessment and enables the burial Depth of Lowering specification to be optimised. In addition, it provides a means to assess the residual risk to the cable after burial operations are complete to a specified depth.

Dimitris Kostopoulos, Electrical Systems and Cable Installation Project Manager, OWA, the Carbon Trust, commented: “The CBRA Guidance will give the industry a new mind-set rather than simply being a Depth of Loweringcalculation method. The Guidance details a pioneering method to evaluate the real external threat to cables based on actual site conditions available for all stakeholders. For the first time CBRA enable the cable protection level to be assessed once the installation operation is performed through the evaluation of the residual risk, as well as over time, by periodically updating the site survey data.”

Truels Kjaer, Chef Risk Engineer, Codan Insurance added: “Codan Insurance has been involved in nearly every offshore project in Europe. Based on this experience we are very aware of the importance of a well-defined and in detail specified cable route. Here the burial depth is essential. Not just a general depth but a depth depending on soil conditions and general activity in the area. Therefore the CBRA Guidance will to my opinion really give value in planning and executing offshore cable installation.”

Claus Fridtjof Christensen Lead Principal Specialist, DONG Energy Wind Power commented: “Risk based assessment is widely used in several industries as this approach has larger flexibility and can handle the continuous development and changes that are particularly relevant in the wind industry, whereas a prescriptive method that although applicable for the situation it has been developed for, would most likely not be able to handle modifications or changes in the industry. The Guidance for cable burial risk assessment methodology is therefore highly appreciated. Furthermore, as the guidance refers to a lot of background information and has been developed together with – and reviewed by the industry, the suggested values and related uncertainties are aligned with the industry. The CBRA Guidance therefore gives a good common methodology for the industry and will also ensure that risk assessments can be compared.”

Leon Eliassen Notkevich, Head of Electrical Systems, Statkraft Wind Offshore commented: “The CBRA Guidance provides the industry with a long sought after methodology for striking the right balance between the need to protect cables from external threats and at the same time minimise cost and risk of damage during installation. Furthermore, the guidance introduces a common glossary, a useful discussion of the main contributors to cable damage and a comprehensible approach for targeting a reasonable depth of lowering along the cable route. Finally, the guidance provides a means of determining the residual risk of cable damage for the as laid asset. This is extremely useful for underpinning system availability calculations and engaging in dialogues with stakeholders such as financiers, OFTOs and insurance companies.”

The first generation of offshore wind farms have seen significant cost overruns and delays. A review of the insurance claims indicates that issues with cabling have been disproportionate to their capital cost and are the root cause of the most frequent and largest claims. Minimising the specified depth of lowering and therefore, reducing cable handling and maximising the number of tools capable of trenching the cables is considered one method of reducing these problems.

To date, the absence of a suitable method of assessing risk management in cable burial has led to a proliferation of approaches developed individually by developers. The Burial Protection Index (BPI), which was originally developed for fibre optic communication cables in the 1990’s has been widely applied to the first generation offshore wind farms. However the BPI has limitations and as a result is no longer widely used. The purpose of the CBRA Guidance is to present a new Cable Burial Risk Assessment method which advances the BPI method.

In addition to the impact on project financing, increased understanding of the risks will help to open up assets market as it introduces more options for suitable solutions, Carbon Trust concluded.

 

 

 

 

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