From Gutta Percha to XLPE

Insulation for Seawater in 1840s

The first undersea telegraph cable was installed in 1849, but failed after only a few weeks. The key technical advance that made this endeavour possible was the use of an insulating material called, gutta percha—also used in golf balls. The cable was “redeployed” and saw the first transatlantic telegraph sent via cable in 1858. A second cable was completed in 1866. Those first baby steps of an industry 150 to 160 years ago began the history of insulated cables used in undersea applications. The first undersea telephone cable was built in 1921 linking Florida to Cuba; this cable was insulated with a blend of gutta percha and rubber. Subsequent materials advancements allowed this cable’s replacement in 1950 with a cable using polyethylene (PE) and butyl rubber insulation. The first transoceanic telephone cable was built in 1956.

 

The first subsea power cable was installed in 1811 in Germany and insulated with natural rubber. Over the years, various other approaches towards cable protection were: Use of extruded lead as a water barrier; and the introduction of oil-filled insulation in 1952. Commercial deployment of the first undersea HVDC power cable wasn’t until 1954 when ABB installed a 98 km, 20 MW, 100 kV cable to connect Gotland with the Swedish mainland. The cable was upgraded several times over the following decades to deliver more power. A key advancement nine years later—the advent of crosslinked polyethylene (XLPE) developed by a GE Research Laboratory in New York further improved power cable’s reliability—from ten to fifteen years to as many as thirty years. The cable’s ability to cope with higher operating temperatures also was increased to keep pace with modern society’s ever increasing energy consumption.

 

Higher Power for Undersea Cables

In January of this year, Con Edison activated a 345 kV, undersea cable in New York harbour to deliver 512 MW of power to the New York area wholesale market. The cable runs 10.4 km from a new gas-fired generating facility in Bayonne, NJ, to Brooklyn, NY. ABB, which supplied the cable, said it was the world’s first cross-linked polyethylene (XLPE) insulated 345 kV AC cable, and it was extruded in a single continuous length without factory joints.

 

Longer Spans for Power Cables

Energy projects, including offshore wind farms and platforms for oil and gas production are requiring longer power cables. In 2006/7 a 580 km subsea power cable between Norway and theNetherlands was installed, making it the longest subsea power cable. This cable operates at 450 kV DC and has a ca pacity of 700 MW. At that time, it was said the 123 kV, 75 MW XLPE cable was the longest, most powerful cable to be ordered for an offshore oil and gas application. The cable contains a fibre optic distributed temperature sensor and communication functions.

 

Slide 1 provides a timeline of significant developments relating to the development of undersea power cables, while Slide 2 depicts several subsea power cable designs.

 

Subsea power cables are akin to high voltage transmission lines, thus these undersea designs mean cables are either: high voltage (HV), which CRU defines as 60 kV to 230 kV and extra high voltage (EHV), which we define as greater than 230 kV. Subsea power cables are generally installed as single core cables and so for AC links typically three cables are used and for DC two cables, so a 100 km AC link would use 300 km of cable and a 100 km DC link would use 200 km of cable.

 

Cable costs in any undersea deployment are typically a line item as part of the whole project, and since these are almost always turnkey projects, won in a competitive bid, total project cost is used to describe both the power cable itself and the optical unit deployed within it for supervisory control and data acquisition (SCADA) purposes, plus accessories and installation.

Power Cables: Primary Building Block in Economic Development

Undersea power cables are necessary for a number of reasons. The rationale for investment originally was: 1) they delivered bulk power to island communities or to inaccessible locations, and 2) they provided a means to arbitrage energy usage between countries where high power generation capacity and relatively lower domestic demand could be sold to neighbouring countries that require additional power to meet peak demand.

 

For example the link between the UK and France has allowed power to be sent from the UK to France when France experienced peak power demand and then power could be sent in the opposite direction during the UK peak, with the time difference between the two countries and cultural differences resulting in peak power being at different times.

 

These two drivers remain relevant, but a number of new factors have served to give this market a big boost. The new drivers can be grouped into four areas.

  1. Deregulation of the power sector has opened up the market to much greater trading of power between countries, coupled with the targets for renewable energy generation. With the growing internationalization of power companies, this trend has been enhanced. Both of these trends will increase requirements for higher transmission capacity between countries; often the only way to achieve this is by using a submarine cable. Thus a large number of new links have been planned with the majority of HVDC cables installed in the last several years having been in Northern Europe linking Scandinavian countries with power company grids in Germany, Poland and the Baltic countries; other projects connect UK to France and the Netherlands.
  2. Development of offshore wind farms, along with other potential offshore renewable energy generation such as wave power. By definition you need to get the power from an offshore wind farm to shore and the only practical method for this is by using a submarine power cable. Power is generally transmitted from the individual turbines to a central point using submarine MV cables, where the power is aggregated using an HV cable, which transmits power to a shoredbased substation.

  3. Increased difficulty in obtaining authorisation for new transmission lines on shore due to environmental considerations or community outcry against transmission towers built in their locale. One option is to run a length of submarine cable along the coast of a country rather than over land. This option works for links close to the coast, but it is a viable alternative and is receiving serious consideration. Just recently Prysmian has won a contract to supply a subsea power cable down the west coast of the UK, an option that has been chosen over a land based transmission line.

  4. Growth in offshore oil exploration and extraction. In the past rigs had their own power generation facilities, but an alternative is to supply power to a rig using a submarine cable. This means the rigs can be smaller and a more efficient source of power generation can be used. This is not a big part of the market but it is another area that is growing.