Heat waves, strong winds, torrential rains, in short, intense environmental events, which affect certain cities more frequently and, in addition, locations most affected by climate change, lack protected urban infrastructure installations of wires and cables to avoid the risk of falls energy, general damage and electrical shocks that can be fatal. As most of the risks in large cities are in overhead cables, taking power cables underground is an important measure.
In more detail below, we can say that overhead electrical cable structures have considerable disadvantages.
Overhead wires are much more sensitive to failure during storms than underground cables. The loss of electrical energy causes major economic disruptions. The cost of maintaining and repairing damaged lines is often borne by utility company customers.
Overhead wires have sparked many of the disastrous fires that have devastated large areas, which have been reported in the press in recent years, causing loss of life and property. This is because sparks from OHL (overhead lines) are routinely identified as the cause of fires in dry areas.
When extreme weather events occur, first responders must deal with downed and exposed high-voltage power lines, a major hazard associated with the adversity of power loss, while trying to deal with medical emergencies. Removing these threats makes it easier for emergency teams to save lives.
The risk of contact by passers-by with downed wires in cities can cause exposure to intense electrical discharges with a risk of death.
But you would be wrong to imagine that the search for a better solution to the problems arising from overhead electrical wires is recent. Long ago, many countries made investments in urban infrastructure using underground cables and, to this day, enjoy significant benefits. The pioneering experience in the news took place 134 years ago, in 1890, with the first successful installation carried out by Vincent de Ferranti, using his famous 10,000 volt concentric cable, in the United Kingdom.
Underground utilization is the most comprehensive and effective solution to reducing the impact of utility wires. The practice is common in the Netherlands, Switzerland, Germany and England, which, in addition to the natural beauty they offer, took care and precaution to guarantee a “clean” and safe scenic view, with their wires and cables far from sight. and protected against adverse weather conditions, installed underground.
But underground cabling efforts are not limited to the aforementioned countries. In Australia, for example, the Infrastructure Project entitled “Powering Sydney's Future” carried out through densely populated suburban areas, started from the observation that the electricity transmission networks that were built in the 1960s and 1970s and some underground cables, were approaching the end of their useful lives. As Sydney's population grew, demand for electricity increased and replacing aging infrastructure would ensure future supply for residents and businesses in Sydney and surrounding suburbs. Thus, in 2022, Australian energy company Transgrid completed the main construction works of the Powering Sydney's Future project.
Although higher voltage lines tend to be tied to overhead cables, this does not mean that higher voltage cables are unfeasible underground in large cities.
Aerial cables are installed much more easily compared to underground cables. It also has the benefit of open natural ventilation, which prevents cables from overheating. However, this does not mean that higher voltage cables are unfeasible underground in large cities (in areas of high energy consumption), which can coexist with the predominant lower voltage cables. Despite the closed underground environment, the tunnels can be cooled, improving the temperature conditions of the cables.
In London, beneath its busy streets, there are miles of 8-foot-wide concrete tunnels lined with power distribution cables that can reach extremely high temperatures. To cool the tunnels, vertical shafts spaced every kilometer or two supply fresh air and eject hot air into the open air.
UNDERGROUND CABLING STRUCTURE IN LONDON
Researchers at London South Bank University (LSBU) , in 2019, developed a study with the aim of using this waste heat. A typical 1.8km stretch of tunnel between ventilation shafts produces 400 kilowatts of heat, enough to heat 100 homes or a small commercial office. This was discovered by researchers in a preliminary analysis carried out with the city's electricity grid operator, UK Power Networks.
A project started in 2018 to provide underground cabling for London is underway. Scheduled to be completed and fully operational in 2027, London Power Tunnels Two is underway to build 32km of tunnels and two substations in north London – claimed to be the first major investment in the capital's electricity transmission system in over of half a century.
Three meters in diameter, the tunnels have a lifespan of more than 100 years – although the high-voltage cables they carry will need to be replaced more regularly to meet future demand and facilitate the growth of entire systems across the city.
This issue of changing high voltage cables, according to Lesur (2021), the current generation of underground systems requires less maintenance, and renovation is only necessary every 40 or 50 years, which is the specified useful life of a transmission line and cables are generally buried to a depth of 3 ft/0.9144 m for distribution networks, and 4 ft/1.2192 m or 5 ft/1.524 m for transmission networks.
In terms of safety, there is no disturbance to the ground surface when a short circuit occurs or a very high amount of energy is released, because the ground contains the fault, states Lesur (2021), who also argues that the ground also protects against damage caused by third parties, as long as proper authorization procedures are followed before excavation, especially in urban areas.
According to Lesur (2021), underground systems require very little maintenance, as the insulation is made of extruded plastic ¹ (a passive component). There is no fluid under pressure or potential leakage. Overhead lines, on the other hand, need monitoring and maintenance to avoid corrosion (frequent painting of metal supports) and require maintenance against weather risks (lightning strikes, storms, ice, sticky snow).
Studies also show that losses dissipated due to heating by the Joule effect ² are smaller for underground cables due to the use of pure copper and aluminum, while aluminum and steel alloys are necessary for the mechanical strength of bare overhead conductors, according to Lesur (2021).
It is worth mentioning that not only countries most affected by natural events should have the initiative to build infrastructure of underground wires and cables, but also cities that have used, to exhaustion, wire structures and overhead cables, suspended from poles. This reality has generated a series of adverse situations, such as tangled and fallen wires, due to accumulation on poles, risks of power outages and exposure to intense electrical discharges, which can affect passers- by with the risk of death.
ACCUMULATION OF DISORDERED OVERHEAD WIRES, FALLEN AND CROSSING THE ROAD PHOTO: © high-techsociety.com
By placing cabling underground, most of the harsh weather conditions that traditional transmission infrastructures are exposed to can be avoided. This largely refers to precipitation and windstorms, which can cause damage to overhead power lines directly or indirectly through falling trees, resulting in power outages.
Underground cabling can alleviate the need for additional and more frequent investment in transmission infrastructure maintenance and repairs. Expected benefits include a more secure energy supply with fewer instances of weather-related power outages, while realizing long-term cost savings due to reduced maintenance and repairs, ensuring predictability for diverse business segments.
Underground cable lines have many advantages and benefits over overhead lines and are gaining momentum for safety, reliability and cost-effectiveness.
It is observed that underground cabling has higher costs for construction and implementation of physical structures, costs for purchasing inputs, civil works, installations, but in the long term its savings and safety advantages are unquestionable. On the other hand, despite the initial advantage of airlines, of much lower construction and implementation costs for physical structures, they concentrate higher costs related to operation and maintenance. This is because they operate with a certain instability, directly associated with climatic conditions, causing unpredictable interruptions in the energy supply and may result in various costs to be borne by individuals, companies in general and industries, both to cover necessary maintenance costs arising from the adversity. of time, as well as to support losses resulting from loss of food that requires conservation in refrigerators and freezers, as well as losses resulting from interruptions in production activities.
One way to guarantee the economic viability of these projects, with greater viability for large cities, is the union between service providers and governments, not only in sharing the costs involved, which are highly high, but also in the temporal integration of projects. The construction of an underground structure represents a valuable opportunity for modernizing structures, not only for public and private companies that provide public energy services, but also for water service providers, with their pipes and for telephone and internet service providers. , via optical cables.
Grades:
¹ The extruded plastic profile is manufactured using an extruder machine that melts granulated plastics, normally from recycling processes. In this machine, the plastic is melted through a cylinder that is heated by electrical resistance.
² The Joule Effect is the transformation of electrical energy into thermal energy when electric current passes through a conductor.
Sources:
THE UTILITY WEEK EVENT. Digging 32km of 'Power Tunnels' beneath London . Available at < https://utilityweek.co.uk/digging-32km-of-power-tunnels-beneath-london/ > Accessed on March 23, 2024.
CLIMATE ADAPT. Replacing overhead lines with underground cables in Finland . Available at < https://climate-adapt.eea.europa.eu/en/metadata/case-studies/replacing-overhead-lines-with-underground-cables-in-finland > Accessed on March 21, 2024.
LESUR, Frédéric. Power Grid International. Why underground cables are a better long-term choice for utilities . Available at < https://www.power-grid.com/td/why-underground-cables-are-a-better-long-term-choice-for-utilities/#gref > Accessed on March 21, 2024.
MACPHEE, Brian. Quora. Available at < https://www.quora.com/Why-are-the-UK-power-lines-underground > Accessed on March 22, 2024.
PATEL, Prachi. IEEE Spectrum . London's Hidden Cable Tunnels Could Warm Thousands of Homes . Available at < https://spectrum.ieee.org/londons-hidden-cable-tunnels-could-warm-thousands-of-homes > Accessed on March 23, 2024.
SCENIC AMERICA . Undergrounding Utility Infrastructure: Burying Utilities for Safety, Resiliency, and Scenic Beauty . Available at < https://www.scenic.org/why-scenic-conservation/energy-infrastructure-and-equity/undergrounding-utility-infrastructure/ > Accessed on March 21, 2024.
TRASGRID . Powering Sydney's Future . Available at <https://www.transgrid.com.au/projects-innovation/powering-sydney-s-future > Accessed on March 21, 2024.