A high-temperature superconducting transformer will improve the quality of power transmission and reduce the risk of fire in the power system.
Arseny Semenov, a young scientist and a post-graduate of Industrial Power Supply Systems Department, Faculty of Power Engineering, NSTU NETI won a grant of 450 thousand rubles from the Novosibirsk city administration for the development of a high-temperature superconducting transformer with a current-limiting function.
The transformer operation process is structured as follows: when a short circuit occurs in the electrical network, a current flows through the superconductor above the critical value forcing the superconductor to shift from the superconducting state and acquire active resistance thus reducing the short-circuit current. The advantage of this development is that this process occurs instantly, since the resistance increases not because of the current-limiting device operation, but because of the superconductor nature.
"When an emergency occurs in an external element of the network, for example, a short circuit, a normal transformer passes this current through itself. Short-circuit currents can cause damage to equipment and disconnect electrical network elements. To reduce the negative consequences, the electrical network needs current-limiting devices. Our transformer is able to limit the current without using such devices, " says Arseny Semenov.
In his project, Arseny uses a high-temperature superconductor (HTS) winding instead of the traditional copper winding (the material is 2nd generation ReBCO HTS wire). This material is able to conduct current without active resistance. To do this, it must be cooled to a temperature of -196 °C by placing it in liquid nitrogen. The state of superconductivity occurs only when it is cooled, not at the room temperature. The difference between high-temperature and low-temperature superconductors is that the latter need deeper cooling.
"We buy liquid nitrogen at the factory, bring it in a special container and regularly add it into the transformer housing. One pack (~16 l) is enough for a day or two of experiments. The new transformer will have a bigger volume, so we will use two packs at a time. There are plants that produce liquid nitrogen on site, but they are very expensive, this option is not suitable for us. Now, at the prototype stage, the need for liquid nitrogen complicates the process. When high power industrial transformers will be produced and installed at the electrical grid substations, then it will be justified to buy a plant for the production of liquid nitrogen at the substation, " says Arseny Semenov.
Liquid nitrogen is also an electrically insulating non-flammable medium, replacing traditional transformer oil, thereby eliminating the problem of fire hazard. Unlike transformer oil, liquid nitrogen does not emit explosive gases.
Superconductors allow the transformer to implement the function of limiting short-circuit currents, which is usually performed by the current-limiting devices in the network. Changing the mass and volume of the winding, the development can be suited for use in autonomous power systems on water transport and in traditional electric grids. "You can pass more current through a superconductor than through copper, so you do not need thick copper wires, but rather a thin HTS wire whose thickness is less than a millimeter," comments Arseny Semyonov.
"Superconducting transformers have been known for a long time, but have not yet become widespread. Until recently, superconductors were very expensive, but now the technology of their production is improving, and the price is falling. This makes the superconducting transformer a mass phenomenon. The superconductive transformer solves the main problem of high short-circuit currents. This is not just a problem of individual transformers, it is a problem of electric grid in general. Widespread use of such transformers will make the grids more reliable, " says Arseny Semenov.
A team of developers designed and manufactured a low power single-phase prototype. The experiments with it were partly carried out immediately after production, the remaining experiments will be carried out after the self-isolation period. Now the project team is modeling and designing a high-power three-phase prototype; its production and experimental research is the next stage of the project.
Arseny Semyonov won a grant of 450 thousand rubles for "Development and production of energy-efficient and fire-safe electrical equipment based on high-temperature conductors with a current-limiting function" within the competition of the Department of Industry, Innovation and Entrepreneurship of the Novosibirsk city administration.
"There have been attempts to build such a transformer in Russia, but there are no publications about putting it into commercial or even experimental operation. But there is a similar development, a current-limiting device created using a similar technology. It has been tested and put into commercial operation in the Moscow electric grid which allows us to conclude that our development has a potential, " comments Arseny Semenov.
The project's team also includes Ivan Martynov, Dmitry Ivanov (Master's degree students at the Faculty of Power Engineering, majoring at "Electric and Power Engineering") and Sergey Shein (a student of Aircraft Faculty majoring at "Technical Physics"). The work is supervised by Vadim Manusov, Doctor of Technical Sciences, Professor at the Industrial Power Supply Systems Department, NSTU NETI.
Power transformers are the elements of electrical grids, they are used to increase or decrease the voltage class in the electricity transmission. The main parts of a power transformer are the windings, magnetic core, cooling system and auxiliary systems.