Quench nucleation obtained by local reduction ofI_cin coated conductors

Abstract

Abstract. The normal zone propagation velocity in coated conductors is very small compare to YBCO on sapphire. For fault current limiter, it is more difficult to use them and obtain predictable behaviors under electrical faults. In the present work, we have measured the normal zone propagation on short coated conductors samples submitted to current pulses of variable length and amplitude (from 10-500 ms and ≈0.9-2.0 I c respectively). The normal zone nucleation is obtained using a magnetic tip to reduce locally the critical current density of the tape. This reproducible technique allows to choose and modify the initial nucleation site position as well as to perform multiple experiments on the same sample without making any physical defect on the conductor. The normal zone propagation measurements as well as the characteristic shape of the resulting I-V curves obtained from various current pulse waveforms are presented here. From the experiments, it is shown that field-induced defects allow to increase the normal zone propagation velocity as well as to reduce the initial delay before quenches in coated conductors. In addition, sub-cooled measurements have shown that an increase of the heat diffusivity obtained by lowering the coolant temperature improve the quench propagation.

High normal zone propagation velocity in second generation high-temperature superconductor coated conductors with a current flow diverter architecture

“…A cylindrical NdFeB magnet (diameter 3 mm) was used to initiate the quench at the desired location. The strong magnetic field generated by the magnet is sufficient to locally reduce I c and simulate a defect in the HTS layer, as in [8,14]. A series of equally spaced voltage probes were used to record the voltage over time at various locations along the tape (the distance between two successive probes being ≈2.5 mm).…”

“…Destructive hot spots in 2G HTS CCs result from a combination of low NZPV [7,8] and the presence of defects in the microstructure that reduce the local I c [9,10]. Since defects cannot be completely eliminated, it seems that unless one increases significantly the thickness of the metallic sheath (often called the 'stabilizer') [11] the only way to reduce the severity of hot spots is to increase the NZPV.…”

Engineering of second generation HTS coated conductor architecture to enhance the normal zone propagation velocity in various operating conditions

“…One important aspect to consider when designing superconducting devices is the protection of the device when a quench occurs. Quench dynamics of 2G HTS CCs has been investigated by several groups over the years, both experimentally [1][2][3][4][5][6] and by numerical simulations [7][8][9][10][11]. A crucial issue that needs to be resolved is the low normal zone propagation velocity (NZPV) in those (RE)BaCuO-based tapes in comparison to low-temperature superconducting wires.…”

Stability of DC transport in HTS conductor with local critical current reduction

“…Then, the weak spot temperature, T ws , can be considered uniform in the whole volume of the conductor within ∆x ws . Such simplification, essential for the development of an analytical model, differs from the formulation used in numerical modeling where the composite structure has been implemented [27,41,73,80,91,92]. The local rise of temperature triggers a heat flow towards the ambient, while the latter is assumed to keep the baseline temperature T 0 all the time.…”

“…Experimental testing of conductor stability by applying a local heat pulse became a standard methodology for lowtemperature superconductor wires and magnets [6][7][8][9][10][11][12][13], and has been transferred to the study of conductors based on hightemperature superconductor (HTS) materials too [13][14][15][16][17][18][19][20][21][22][23][24][25]. In some investigations of HTS tapes and coils, the quench was induced by other means like short overcurrent pulse [26], by applying a magnetic tip [27], or by laser irradiation [28].…”