In this blog post, we’ll explore the principles and advantages of superconducting cables, their current status of commercialization, and their potential in future power systems.
The figure “3.58%” refers to South Korea’s power reserve rate at the time this article was written. At that time, television and newspapers urged the public to conserve energy, and South Korean citizens and businesses made efforts to reduce their electricity consumption. It was a moment when the entire nation acutely felt the importance of electricity. As such, electricity demand continues to rise, and the challenge of expanding transmission infrastructure to ensure a stable power supply persists. However, increasing transmission capacity in urban areas is no easy task. It is difficult to lay additional underground transmission lines, and overhead transmission not only detracts from the city’s aesthetic appeal but also results in power losses during transmission. As an alternative to solve these problems, superconducting cables—often referred to as “dream transmission lines”—are gaining attention.
Before understanding superconducting cables, it is necessary to first examine the phenomenon of superconductivity. Superconductivity refers to the phenomenon in which electrical resistance disappears below a certain temperature, allowing current to flow without loss. Materials that exhibit this phenomenon are called superconductors, and among them, those that remain superconducting even at temperatures around -196°C—the temperature of liquid nitrogen—are known as high-temperature superconductors. Since superconductivity occurs only in cryogenic environments, it is not something we encounter easily in daily life; however, thanks to its characteristic of having electrical resistance that is virtually zero, it is utilized in various fields such as medical devices, power generators, and research equipment.
Superconducting cables are also manufactured using these properties of superconductors. Looking at their structure, a copper core and the superconducting material wrapped around it serve to conduct electricity, and liquid nitrogen is enclosed within a vacuum-insulated structure along with the wire to maintain the superconducting state. Thanks to this structure, the superconducting state can be maintained even during power transmission, offering several advantages over conventional power transmission cables.
One key advantage is that they can transmit more power using wires that are much thinner than conventional ones. For example, while the 765-kV ultra-high-voltage transmission cables under construction at the time had a diameter of over 40 cm, superconducting cables can achieve a much higher transmission capacity with a diameter of only about 15 cm. The second advantage is a significant reduction in power loss. In particular, superconducting direct-current (DC) cables have virtually no power loss, and even alternating-current (AC) cables experience much less loss than conventional cables. Another advantage is the ability to transmit large amounts of power at lower voltages than conventional systems.
So, what principles underlie these advantages? The answer can be understood through Ohm’s law, which applies to conventional power transmission lines. According to Ohm’s law, voltage and current have a fixed relationship; when applied alongside the power equation, this explains the losses that occur during power transmission. Conventional power lines have resistance, so as current flows, power loss occurs, and the magnitude of this loss is proportional to the square of the current and the resistance. Therefore, in conventional power transmission systems, methods such as increasing voltage to reduce current or increasing the cross-sectional area of the wire to lower resistance are used to minimize losses. However, since superconducting cables have virtually zero resistance, power losses are extremely small, eliminating the need to use high voltages or thicker wires as in conventional systems.
These characteristics offer various benefits to society as a whole. From an economic perspective, they reduce power losses during transmission and enable the transmission of large amounts of power at lower voltages, which helps reduce the need for substation equipment. Furthermore, the smaller diameter of the cables offers the potential to reduce material usage and installation costs. From a social perspective, they can help reduce conflicts related to the construction of ultra-high-voltage transmission lines, and since superconducting cables effectively shield magnetic fields, they also help mitigate electromagnetic interference issues. Environmentally, they have the potential to reduce the number of transmission towers and substations, and by minimizing power loss, they can contribute to lowering carbon dioxide emissions generated during power generation. It is also regarded as an eco-friendly technology because it can reduce the use of certain shielding materials found in conventional cables.
As such, superconducting cables—which are expected to provide significant benefits to society as a whole—are currently the subject of active research and demonstration projects in many countries around the world. However, challenges remain to be addressed, such as the maintenance of liquid nitrogen cooling systems, installation costs, and the price of superconducting materials. Nevertheless, countries such as Germany, the United States, Japan, and South Korea are continuing to pursue the demonstration and commercialization of superconducting cables, and in some regions, they are already being applied and operated in actual power grids. Superconducting cables are no longer merely a technology of the future but are establishing themselves as one of the core technologies for next-generation power grids. If related technologies continue to advance and economic viability is achieved, power transmission systems are expected to evolve in a direction that is far more efficient and environmentally friendly than they are today.
