Przewody nadprzewodnikowe drugiej generacji z jakich wykonuje się uzwojenia transformatorów nadprzewodnikowych wykazują dużą podatność na uszkodzenia termiczne. Określenie gęstości prądu w poszczególnych warstwach przewodu HTS 2G pozwala stwierdzić czy uzwojenia transformatora HTS ulegną termicznemu uszkodzeniu w trakcie różnych stanów jego pracy. Przedstawiono i omówiono schemat zastępczy taśmy HTS 2G pozwalający policzyć gęstość prądu w poszczególnych jej warstwach zarówno w stanie nadprzewodzenia jak i rezystywnym warstwy nadprzewodnika.
Słowa kluczowe: nadprzewodnictwo, taśma nadprzewodnikowa, rozpływ prądów, transformator.
Abstract. Second generation superconducting wires from which the windings of superconductor transformers are made are highly susceptible to thermal damage. Determining the density of current in individual layers of the 2G HTS wire allows to find out whether the windings of the HTS transformer will be thermally damaged during various operating conditions. The study presents and discusses a substitute diagram of the 2G HTS tape, allowing to calculate the current density in its individual layers both in the superconducting and resistive state of the superconductor layer.
Keywords: superconductivity, superconductor tape, current flow, transformer.
Despite good failure statistics, transformers are one of the weak points of the transmission system. That is why a lot of attention is paid to ensuring protection of transformers, which minimises the risk of emergency situations. The basic operational problem of superconducting transformers (HTS) is the necessity of uninterrupted maintenance of superconducting windings at cryogenic temperature and not allowing losses of the superconducting state in them. The condition in which the HTS windings come out of superconductivity should be treated as an emergency condition of the HTS transformer's operation, which makes switching it on difficult and threatens interrupting the continuity of the windings as a result of their thermal damage. The substitute diagram of the HTS transformer does not deviate substantially from the conventional transformer scheme (Figure 1). Fig. 1. Substitute diagram of the HTS transformer Resistances R1HTS and R2HTS, representing power losses in the windings, are non-linear in the function of changes in current intensity, changes in the strength of external magnetic field and temperature changes. The non-linearity of R1HTS and R2HTS resistance is determined by the properties of superconducting winding wires. Second-generation high-temperature cables (2G HTS), currently used on windings of superconductor transformers, are made in the form of tapes with a layer structure (Fig. 2) . They are relatively thin wires, compared to copper winding wires, and the superconductor alone constitutes only 5% of the entire cable's volume. The SCS4050 cable with a critical current of 87 A has a thickness of 0.1 mm and a width of 4 mm. The thickness of the superconductor layer is 1 m in it. The remaining volume consists of metallic layers. The SCS12050 cable with a critical current of 333 A differs only in its width, which in this case is 12 mm. Fig. 2. Structure of the 2G HTS cable from SuperPower Inc. [1 [...]
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