With increased urbanisation and infrastructure replacement, the benefits of undergrounding are starting to outweigh the costs. NRG Expert takes a look at some of the advantages and disadvantages to this process and answers the question, ‘will it continue?’
Electrical energy worldwide is mainly transmitted with High Voltage Alternating Current (HVAC), overhead line technology. 96% of the onshore Transmission network in Europe is overhead HVAC line and the remaining consists of underground cable. Underground cables are mainly used over short distances, in areas where overhead lines are inappropriate or impossible to use and for specific technical applications. Underground cabling is becoming increasingly attractive for use, mainly for environmental and aesthetic reasons. Undergrounding is not a new trend, as underground cables have been used for low and medium voltage lines in urban areas for a long time. In countries such as the Netherlands (high population density/easily penetrable surface) it can even be cost neutral to cable underground for cables up to 150kV. Several countries use underground LV distribution cables in almost their entire network, with a target of 100%, such as the Netherlands, Singapore and Denmark. Use in HV applications is still limited owing to their high cost and the cost of maintenance and repair in case of an outage. The Dutch TSO,TenneT, has estimated that underground lines can take anywhere from 48 to 480 hours to repair should an outage occur, versus 8 to 48 hours for an overhead line.
Underground cabling can cost as much as twenty times as much as single circuit overhead lines but usually is in the ratio of 5 to 10 times as much. Various developments in the manufacturing of cables and their accessories, coupled with more efficient installation methods, have led to significantly reduced construction costs for underground cables in the last few years. However, underground cables remain very much more expensive than the equivalent overhead lines with the same transmission capacity. This is less the case in lower voltages but in higher voltages the cost of cables is still many times higher than the equivalent for overhead lines.
Despite the costs and technical limitations, the desire for undergrounding is ever increasing. Where possible, undergrounding is being planned in new developments and in dense urban areas, it is often the only feasible way to supply electricity. As urban density increases together with our need for energy, there will be a continual push and growth in the underground cables market and the market will continue to see increased growth.