Current limitation properties of YBa₂Cu₃O₇  /Au thin films: application to transformer connection

Abstract

In view of the development of superconducting fault current limiters, the properties of switching and recovering of YBa 2 Cu 3 O 7−δ /Au (YBCO/Au) thin films are studied at 77 K and 50 Hz for overcurrents. The bilayers present an abrupt transition to a high dissipative state leading to a current limitation at a maximum value of about 2.5 times the critical current I c , and allow the development of electric fields of 3 kV m −1 without any damage. After the overcurrent regime, the recovery of the superconducting state under the rated current I n is studied as a function of overcurrent parameters. These results show clearly the strong potential of YBCO/Au thin films which can recover their superconducting state under nominal mode. This last point is crucial for transformer connection, as experimentally shown in this paper.

Simulation of the initial response of a highTcsuperconducting film submitted to a voltage source

“…Therefore in nearly homogeneous systems the maximum current density only depends on intrinsic properties of the superconductor, regardless of the particular design of the device. In experiments performed at 77 K, values ranging from 5 to 10 MA cm −2 are found [5,6,3,4]. Note that the speed of this switching process is only limited by the induction L and can be quasi-instantaneous when the inhomogeneity is small.…”

“…The similarities appear during the first microseconds, where a fast transition occurs, turning part of the sample into the normal state. In this microsecond timescale, the current density peaks very rapidly up to a value 2-3 times larger than the critical current j c (the traditional name for the current density initiating a non-zero dissipation) [5,6,[2][3][4]. We call this peak current j max .…”

“…All these systems use the ability of the superconductor to rapidly switch from a superconductive or, more precisely, low dissipative state into a highly resistive state, when a certain current is exceeded. With the object of realizing a resistive SFCL, one direction of research, which is now intensively explored, is to use a high T c thin film as the limiting element [1][2][3][4].…”

Experimental and numerical analysis of quench propagation on MgB2tapes and pancake coils

“…Most thermal stability studies simulate the behaviour of superconducting systems during a quench fault (transition from the superconducting to the normal state), either by applying local heat pulses [1][2][3][4][5][6] or over-currents [7][8][9][10][11] and analyse the temperature and electric field profiles along the conductor wire and the system. These experiments allow the determination of the parameters that characterise the local appearance of a quench and its propagation to the overall conductor as: Minimum Quench Energy, MQE; normal zone propagation velocity or quench velocity, v p ; temperature profile around the disturbance, which gives the Minimum Propagation Zone, MPZ; quench current; etc.…”

Thermal stability analysis of YBCO-coated conductors subject to over-currents

“…Thermal stability of a superconducting material is generally studied by applying over-currents [1,[3][4][5] or heat pulses [6,7] to the conductor and analysing the electric field and temperature profiles along the conductor. These experiments simulate the behaviour of the superconducting conductor during a fault in different applications and allows the determination of parameters such as the minimum quench energy, quench propagation velocity, quench current, etc.…”