- Keywords: Technical
Relevant for ship owners and managers, yards, suppliers, design offices and flag states.
Traditionally, power cables for marine use have been made with copper. Copper is an ideal electrical conductor, but the price of copper has been rising sharply over the last decades, adding costs to the maritime industry. Today, the price of aluminium is roughly one third of the copper price. At the same time, electric propulsion, batteries and hybrid solutions are becoming more widespread in shipping. This is increasing the demand for more economical power cables.
Properties and benefits
Aluminium’s lower conductivity means that a thicker cable is required, but this is compensated for by an overall lower weight. For example, a typical offshore support vessel may have 60 tonnes of large copper cables installed. If these were replaced with aluminium, the weight would be reduced to less than 30 tonnes. Even with the price of special high-quality terminations factored in, the overall estimated saving from switching to aluminium from copper may be more than 50 per cent.
Lighter cables also result in easier installation for the ship builder, further savings on cable trays, less strain on workers and reduced transport costs. Finally, a vessel with aluminium rather than copper cables is lighter and more fuel efficient – resulting in lower operational costs over the vessel’s lifetime.
On a fast ferry where several tonnes of copper weight could be replaced with increased cargo capacity, this would generate added revenue on every trip. Or, alternatively, the weight savings would result in reduced fuel consumption, reduced cost and lower emissions.
Testing and possible issues
The use of aluminium cables has been tested for the past three years in a pilot installation onboard the Olympic Subsea owned and managed, Olympic Artemis, a multipurpose offshore support vessel. The cables have been used to supply power to one of the vessel’s thrusters.
Recently, DNV GL experts, together with representatives from the cable manufacturer, checked the aluminium cables on board Olympic Artemis with a thermographic camera. The survey confirmed perfect connections after more than 11,000 operating hours at sea.
Aluminium has some special properties which can create potential risk for bad electrical contact: Aluminium oxide on the surface must be penetrated to make good contact. Aluminium is soft, and so-called cold flow may cause material to loosen under pressure. Both these issues have been considered and tested in the approved terminations. Furthermore, aluminium cables are intended for fixed installations only – aluminium cables are not designed for moving applications.
Until recently, DNV GL rules did not accept the use of aluminium cables on board vessels. The IEC (International Electrotechnical Commission) has not yet implemented aluminium conductors in their standards for marine cables, but are following the development.
Cables installed on ships are exposed to vibration. A salty atmosphere increases risk of corrosion. Together with our industry partners, DNV GL has carried out thorough environmental, electric and mechanical testing, including vibration and salt mist tests. This, combined with the three-year successful pilot installation on board Olympic Artemis, makes DNV GL confident that aluminium cables provide an “equivalent safety level” compared with conventional copper cables when type approved equipment is used and installed according to the instructions.
The costs for power cables can be reduced by replacing expensive copper conductors with aluminium. DNV GL recommends the consideration of aluminium cables on vessels where large power cables are needed. For installations in ships where weight is important, aluminium cables are indeed interesting due to reduced operational costs. From an HSE perspective, lighter cables mean less strain on workers installing the cables and jobs can be done faster.
- DNV GL rules for classification: Part 4: Systems and components, Chapter 8: Electrical Installations
- DNV GL offshore standards, Electrical installations, D-201
- DNV GL class programme, Terminal lugs for LV power cables with aluminum conductors, DNVGL CP-0409
- DNV GL class programme, Electric cables, DNVGL CP-0399
- DNV GL press release from 15 June 2018: “DNV GL issues first type approval for aluminium cables onboard ships
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