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

Abstract

Abstract:The thermal stability of superconducting YBCO coated conductors subject to over-currents are analysed. We have studied the effect of DC and AC over-current pulses in Cu-stabilized and non-stabilized coated conductors by measuring the electric field and temperature profiles of these conductors immersed in liquid nitrogen. Current pulses of short duration of about 90 ms and long duration of a few seconds were applied to the samples. Three different cooling regimes of the liquid nitrogen: convection, nucleate boiling and film boiling were observed, and their influence in the recovery time of superconductivity in the coated conductors after the over-current pulses has been analysed. We have studied the recovery behaviour under two different conditions, in which the current was set to zero and to the operating current after the current pulses.These experiments simulated the conditions during an over-current situation in different electric power applications with special attention given to the behaviour of these coated conductors acting as in fault current limiters.2

Composite Heat Sink Material for Superconducting Tape in Fault Current Limiter Applications

“…In this state, the tape resistance is governed by resistance of adjacent metallic layers-substrate and protection layer [3]. Low magnitude of limited current is advantageous; therefore, metallic layers should be as thin as possible to keep overall electrical resistance of the composite tape high [4]. During the limitation event, the SCFCL experiences electric current and voltage simultaneously and thus a large amount of heat is generated.…”

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.…”

Losses in Coated Conductors Under Nonsinusoidal Currents and Magnetic Fields

“…Let us estimate the parameter c h which is the same in the expressions for the total losses in both cases and depends on frequency of the main harmonic and characteristics of the normal-metal strip (resestivity, thickness, and width) only. For a coated conductor without protective silver layer and stabilizer [5] the parameter c h is evaluated as (10 6 s -1 )/f , for a conductor with the silver layer with thickness of ~2 k [9] c h (8 10 4 s -1 )/f, for a well stabilized coated conductor with cooper stabilizer thickness of 100 k [10] the parameter c h is evaluated as (1.6 10 3 s -1 )/f . The estimations were done for the coated conductor with the width of 1 cm, the resistivity of a hastelloy-C substrate was taken 1.24 10 -6 & m and resistivity of silver and cooper -2 10 -9 & m at 77 K. One can see that the losses in a superconductor dominate in the two first conductor types till high frequencies of the order of 1 MHz.…”