Energy Technology [E-BOOK]

Underground High Voltage Cables: Wiring Europe for the Future

Underground High Voltage Cables: Wiring Europe for the Future

In many of Europe's largest cities and in areas where construction of overhead transmission lines creates difficulties, high and extra-high voltage underground electricity cable systems rated 220kV and above have become part of the backbone of modern day power transmission infrastructure. Although cables have been in use for over half a century, today's underground high voltage cables are leveraging state-of-the-art technology and advanced design to expand their reach and are increasingly becoming an efficient and reliable alternative to overhead lines. Underground high voltage cables are powering a changing world.

This eBook presents the main benefits of underground high voltage cables:

If you are a cable specialist and are interested in learning more details about underground high voltage cables, choose from the topics below:

  • Environmental: Information about EMFs, land issues, recyclability, installation impacts, and sensitivity benefits.
  • Regulation: Details on basic mechanisms, regulatory drivers, and incentives.
  • Case Studies: Presentation of reliability showcases, unstopping bottlenecks, overcoming obstacles, and strategies for success.
  • System Reliability: Information about overload capacity, failure issues, technical changes, and warranties and testing.
  • Life Cycle: Details about transmission losses, planning delays, and replacement cycles.

Versatile and Unique

Underground cables have unique properties for transmitting power - they are out of sight, often require only a narrow band of land to install, emit no electric field and can be engineered to emit no magnetic fields, have better power loss characteristics and can absorb emergency power loads. As a result, underground cables assist the transmission of power across:

  • Densely populated urban areas;
  • Areas where land is unavailable or planning consent is difficult;
  • Rivers and other natural obstacles;
  • Land with outstanding natural or environmental heritage;
  • Areas of significant or prestigious infrastructural development; and
  • Land whose value must be maintained for future urban expansion and rural development.

Cost Effective Solution

In the past, the higher cost of underground cables was a significant deterrent to their use. However, with lower cost production methods, improved technologies and increased reliability, the cost differential between underground cables and overhead power lines is narrowing. This means that power project developers are more frequently turning to underground cables as an economic and technically effective alternative when physical obstructions or public opinion hinder the development of networks. Opportunity costs from lengthy planning delays are reduced and the expense and complexity of public legal cases are minimized.

Apart from the reduced visual impacts, underground cables also offer lower maintenance costs than overhead lines. They are also less susceptible to weather-related issues such as storm damage, interruptions, costs of storm damage surveys and precautionary storm shutdowns. In addition, underground cables contain high quantities of copper, the most conductive engineering metal, resulting in 30 percent lower power losses than overhead lines at high circuit loads and improved system efficiency.

Advanced Features Offer Savings and Reliability

Today's cable manufacturers are able to provide innovative and customized solutions for the modern state-of-the-art power transmission industry. Underground high and extra-high voltage cables are equipped with new design features, such as real-time monitoring, which make them an effective and reliable alternative to overhead lines.

Enhanced Technology

Cables for burial on land using extruded insulation technology are taking the place of traditional oil-filled cables because of significant advantages that include:

  • Easier installation and jointing;
  • Better environmental compatibility and friendliness in service;
  • Reduced installation costs; and
  • Reduced or practically zero maintenance.

Increased Reliability

Today's cable systems, using cross-linked polyethylene (XLPE) as the primary insulation material, have been performance tested to ensure reliability. New cables based on this technology have been running for over 20 years with an excellent reliability record.

Reduced Transmission Losses

Underground extra-high voltage cables generally have more efficient copper conductors and operate at lower temperatures than overhead lines. These properties combine to transmit energy to end users as efficiently as possible, which is especially important for remote renewable and low carbon generators. Reducing these power transmission losses makes a valuable contribution to lowering greenhouse gas emissions.

Advanced Installation Techniques

With new burial and jointing techniques, underground cable projects that once took years to complete can now take only months to install. Through the use of directional drilling and "trenchless" burial techniques, cable manufacturers are applying leading edge design know-how to dramatically reduce installation times. In some installations, where it is not possible to trench or duct the cables, underground tunnels have been built to carry the cables. In some cases, significant cost savings have been made by placing cables in existing tunnel systems.

Improved Monitoring

To reduce outage time, power system operators can monitor underground cables through built-in temperature sensors. The sensors allow the cable to safely accept enormous emergency power overloads when other parts of the network are down. This means that the overall system becomes more robust and supply is maintained. In the rare event of a cable fault, generally caused by external disturbance, advanced monitoring of temperature and integrity in real time will allow faults to be located and repairs to be carried out in a much shorter timeframe than in the past.

Powering a Changing World

Power markets across Europe are being challenged by four often conflicting drivers:

  1. Requirements to carry more power generated from remote renewable and nuclear sources of energy;
  2. Requirements to increase the interconnection capacity between countries;
  3. Requirements to increase system security while replacing ageing transmission assets; and
  4. Increased planning delays for new overhead transmission infrastructure due to heightened public interest in environmental matters.

Transmission companies and cable manufacturers are searching for new ways to manage the response to these drivers.

By targeting problem locations for overhead transmission projects at the planning stage and by proposing underground cable solutions, developers can:

  • Gain support from stakeholders who would otherwise oppose transmission projects;
  • Reduce or eliminate planning delays so projects are completed on reliable timescales to satisfy investors, customers and regulators;
  • Leverage the improved lifecycle cost of underground cables to control costs on the overall project; and
  • Demonstrate to investors that business risk from emerging environmental and corporate social responsibility drivers is being managed effectively.
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