Underground Power Transmission Technology Compared

This is a summary of technology documentation describing the Pro’s and Con’s of Underground Power Transmission Technologies. Understanding this will enable informed decisions to be made regarding when it may be appropriate to consider underground power deployments instead of the traditional overhead ones.

Keep in mind that many of these studies & documents are over ten years old and do not factor into their analyses any recent developments in cable technology, deployment techniques, monitoring technologies, nor consideration of any comparative performance analytics in the interim.

Another consideration when reviewing material, is that much of the information supplied originates from power companies whose primary goal in any project is to reduce cost, so there is always a possibility that some of the information offered may be subject to unintended bias towards a particular technology, for that reason. 

An important distinction to note is that where any article refers to the need for three electricity conductor cables and discusses their inherent associated issues, they are describing the inferior and short range HVAC power transmission technology, not the preferred long distance HVDC system.

Types of Power Transmission Lines

The Western Victoria Transmission Network Project proposes to commission both the 220kV and 500kV towers. 

Technology Articles Describing the HVAC and HVDC Systems

National Grid UK Technical Paper

The purpose of this document is to provide information about the technical merits and challenges associated with undergrounding high voltage electricity lines, compared with installing overhead lines.

Overall, there are a number of issues that make the undergrounding option more technically challenging and expensive.

However, despite the costs and technical challenges, there are circumstances in which underground cables are a more preferable option than overhead cables.

This document explains the cost and potential impact on the environment of cable installations. It explains the cable types available and the various installation methods, as well as the separate components that make up an underground installation

Underground Electric Transmission Lines Paper by the Public Service Commission of Wisconsin

This is a 2011 overview of information about underground electric transmission lines.

Underground cables have different technical requirements than overhead lines and have different environmental impacts.

Due to their different physical, environmental, and construction needs, underground transmission generally costs more and may be more complicated to construct than overhead lines.

Issues discussed in this paper include:

 Types of Underground Electric Transmission Cables

 Ancillary Facilities

 Construction and Operation Considerations

 Costs

 Repairs

All low and medium voltage electrical power (<50 kV) in the Netherlands is now supplied underground.

In Germany, 73% of the medium voltage cables are underground and 87% of low voltage cables are underground. The high percentage of underground cables contributes to the very high grid reliability (SAIDI < 20). 

In comparison, the SAIDI value (minutes without electricity per year) in the Netherlands is about 30, and in the UK it is about 70.

The picture on the left shows a former pylon transformer south of Markgröningen, Germany. Today, the pylon carries only a switch, which is fed by two underground cables.