Superconducting cable project aims to boost urban electricity grid
A UK project is using high temperature superconducting cables to increase the capacity of the electricity grid in urban areas.
The need for this has been highlighted by restriction on building homes and factories in three areas of London as a result of limited electricity supply. The restrictions on new homes in Ealing, Hillingdon and Hounslow could last as long as three years before the grid is updated.
The SCADENT (SuperConductor Applications for Dense Energy Transmission) project runs from next month to the end of 2022 to develop superconducting cables with lower losses. Led by National Grid Electricity Transmission, the project includes cable maker Nexans France as well as the Universities of Strathclyde and Manchester and consultancy Fazer-Nash.
Compared to conventional alternatives, superconducting cables have three to ten times higher power density, meaning they deliver higher capacity at lower voltage levels and via a lower number of routes. This will allow faster network capacity increase, delivering time, cost, and carbon savings. HTS technology can also deliver reduced energy losses and environmental benefits
The also goes beyond existing applications of HTS in Europe by going to higher voltages and running longer cable lengths.
Superconducting cables
Three types of superconductors are commercially available for AC or DC power cables:
- Bi2Sr2Ca2Cu3O10 (BSCCO) with a critical temperature of – 160 °C
- YBa2Cu3O7 (YBCO) with a critical temperature of – 180 °C
- MgB2 with a critical temperature of – 235 °C
There are two main types of superconducting power cables according to the type of dielectric used. The ‘warm dielectric design’ is based on a conductor, cooled by the flow of liquid nitrogen surrounded by a cryogenic envelope using two concentric flexible stainless steel tubes with vacuum and superinsulation in between; the outer dielectric insulation, the cable screen and the outer cable sheath are at room temperature.
In the ‘cold dielectric’ design, the liquid nitrogen is used as a part of the dielectric system. Although more ambitious to manufacture, the cold configuration has the advantage of containing the electromagnetic field inside the superconducting screen, which significantly reduces the cable inductance.
Cooling
Another project by the National Grid is looking at cooling schemes for cables, which will be needed for the HTS cables.
Cable installed within tunnels are often a thermally limiting section of circuits due to the relatively poor heat transfer through the air surrounding the cables. When reinforcement is required, this can require the construction of costly additional tunnels .
The Cable Alternative Cooling Technologies for Underground Systems (CACTUS) project runs to 2024 and will investigate alternative cooling methods to enhance cable ratings in tunnels through bespoke finite element analysis simulations and targeted experiments. The first stage of the project will investigate the use of established technologies, such as chilling inlet air, which are nevertheless novel for cable tunnel applications. Subsequently more exotic techniques, such as liquid nitrogen cooling systems, will be considered.
The funding from SCADENT comes from Ofgem’s Strategic Innovation Fund (SIF) and is one of 18 projects given the go ahead this week.
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