Experimental Study on Quench Detection and Protection Conditions of Copper-Stabilized Coated Conductors Using Short Samples
TL;DR: In this paper, the conditions for successful quench detection and protection of magnet wound with REBa2Cu3Oy (RE-123) coated conductors were clarified using short samples.
Abstract: In order to clarify the conditions for successful quench detection and protection of magnets wound with REBa2Cu3Oy (RE-123) coated conductors, experiments using short samples of copper-stabilized coated conductors were performed. A short sample of coated conductor was conduction-cooled to 30 K, a magnetic field was applied (µ0 H up to 2 T), a current was supplied, and subsequently quench was initiated using a small heater. When a normal voltage (over a preset threshold) was detected, the supplied current would be decreased exponentially. This procedure simulated the conventional quench detection (detecting voltage) and protection (using a dump resistor; current decaying exponentially with a time constant = coil inductance/resistance of dump resistor) for superconducting magnets. We examined how the critical current, time constant of current decrease, and voltage threshold for quench detection affected the hot-spot temperature. By comparing the critical currents and n values of a sample before and after quench, we identified the maximum current at which the sample exhibited no degradation (not-degrading current). The effect of transverse thermal diffusion and longitudinal thermal conduction was evaluated using one-dimensional/zero-dimensional quench simulation. The conditions for successful quench detection and protection were evaluated using not-degrading currents as well as the current at which the maximum hot-spot temperature reached 300 K.
Citations
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TL;DR: In this paper , the authors simulate the thermal runaway initiation of a short monofilament/multifilament REBa2Cu3Oy (RE-123) conductor with a short sample by pressing using a drill bit or bending.
Abstract: We experimentally studied the thermal runawayinitiating at a low critical current (Ic) part. This low Ic part is determined by the combination of two reasons in a real coil: (a) the unavoidable defects caused by the manufacturing process, which reduce local critical currents (and might not be uniform across the width of a coated conductor) and (b) the magnetic field distribution along the coated conductor. To simulate the thermal runaway using a short monofilament/multifilament REBa2Cu3Oy (RE-123) coated conductor, we artificially created a local defect (low Ic part) in a short sample by pressing using a drill bit (creating a defect close to one edge of a coated conductor) or bending (creating a uniform defect across the width of a coated conductor). The sample of the coated conductor was conduction-cooled to 30 K, and a magnetic field was applied (μ0H up to 2 T) perpendicular to the wide face of the conductor to control its critical current. Transverse voltages in a multifilament coated conductor were measured to obtain the transverse currents among the filaments through the copper layer. Thermal runaway currents (operating currents above which thermal runaway initiates) of the monofilament sample and those of the multifilament sample with additional Joule loss due to the transverse currents were determined and compared to study the effect of the transverse currents on the initiation of thermal runaway in the multifilament coated conductor. Experiments on the protection against thermal runaway were conducted. When a normal voltage (over a preset threshold) was detected, the supplied current would be decreased exponentially. The thresholds for protecting monofilament and multifilament coated conductors from degradation after thermal runaway were compared.
8 citations
01 Jan 2012
TL;DR: In this article, the hot spot temperature of a superconducting coated conductor with copper stabilizer during quench protection sequence is calculated by a numerical analysis for quenches by both of the origins mentioned above.
Abstract: Generally, high-temperature superconducting coated conductors (CC) are hard to be quenched by local and transient disturbances during normal operation because of the high temperature margin and high heat capacity of the conductor. However, the CCs still have possibilities of unexpected quenches originated by the appearance of local defects due to repeated mechanical stresses, and by temperature rise of the long part of the CCs due to malfunction of the cryogenic system, for example. In this work, the hot spot temperature of a CC with copper stabilizer during quench protection sequence is calculated by a numerical analysis for quenches by both of the origins mentioned above. The practical amount of the stabilizer is discussed not to over-protect but for a coil system to surely survive from sever damages caused by quenches considering quench origins.
6 citations
TL;DR: In this paper, a superconducting magnet was tested on the beam line of the heavy ion medial accelerator in Chiba (HIMAC) to examine its stability, which might have been affected by shielding currents in the coated conductors.
Abstract: A cryocooler-cooled high-temperature superconducting magnet was constructed, and it was tested on the beam line of the heavy ion medial accelerator in Chiba (HIMAC). The magnet consists of a pair of four-stacked racetrack coils wound with RE-123 coated conductor that are plated with 41- μ m copper for protection. The magnet has a room temperature beam duct, at which 2.4 T of magnetic field is generated, whereas the maximum magnetic field to which coated conductors are exposed is approximately 4 T. The magnetic field in the beam duct was measured and calculated to examine its stability, which might have been affected by shielding currents in the coated conductors. On the beam line of the HIMAC, at first, the beam guiding by the magnet was demonstrated. The measured beam-guiding characteristics were compared with the beam tracking calculations. Next, a carbon ion beam was injected intentionally into the RE-123 coils of the magnet to simulate the incidents of uncontrolled beam injection into accelerator magnets. Prior to this test, the possible heat deposition to the coil by the beam injection was calculated, and the feasibility of quench protection using a dump resistor was studied through quench experiments using short pieces of the RE-123 coated conductors.
3 citations
TL;DR: In this paper, the quench properties of REBa2Cu3Oy (RE-123) coated conductors with various plated-copper thicknesses (20 and 40 μm) were investigated.
Abstract: We experimentally studied the quench properties of REBa2Cu3Oy (RE-123) coated conductors with various plated-copper thicknesses (20 and 40 μm). A short sample of coated conductors was conduction-cooled to 45 K, a magnetic field (μ0H, up to 2 T) was applied perpendicular to its wide face to control the critical current, an operating current was supplied, and subsequently quench was initiated using a small heater. Normal zone propagation velocities (NZPVs) were measured at various operating currents, and the NZPVs of coated conductors with various copper thicknesses were compared with each other. To understand the impact of the copper stabilizer on quench protection, hot-spot temperatures were measured during the processes that simulate quench detection using voltage taps and protection using dump resistor. The maximum hot-spot temperatures were plotted against the operating current as well as the overall current density, and the impact of the thickness of the copper stabilizer on hot-spot temperature was examined. The impact of the initial temperature on hot-spot temperature was also studied.
3 citations
Cites methods from "Experimental Study on Quench Detect..."
...In this study, hot-spot temperature during the quench process was calculated from v5-6 based on the current sharing model and the temperature dependence of the resistivity of plated copper, which was introduced in a previous study [7]....
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TL;DR: In this paper , a numerical analysis model to simulate the thermal runaway in copper-plated multifilament coated conductors was developed, and the effect of current sharing on the initiation of thermal runaway was determined.
Abstract: We have developed a numerical analysis model to simulate the thermal runaway in copper-plated multifilament coated conductors. We combined a circuit model to calculate current distribution in filaments and copper and a two-dimensional heat conduction model to calculate temperature distribution. The thermal runaway simulations of multifilament coated conductor with local defects were performed, and compared with the experimental results to validate the developed model. According to the simulation results, the effect of current sharing on the initiation of thermal runaway was determined.
References
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TL;DR: The new NI winding offers HTS coils enhanced performance in three key parameters: overall current density; thermal stability; and mechanical integrity.
Abstract: This paper reports a study of HTS pancake coils without turn-to-turn insulation. Three no-insulation (NI) pancake coils were wound: each single and double pancake coil of Bi2223 conductor and one single pancake of ReBCO conductor. An equivalent electrical circuit for modeling NI coils was verified by two sets of test: 1) charge-discharge; and 2) sudden discharge. Also, an overcurrent test in which a current exceeding a coil's critical current by 2.3 times was performed, and analysed, to demonstrate that in terms of stability NI HTS coils outperform their counterparts. The new NI winding offers HTS coils enhanced performance in three key parameters: overall current density; thermal stability; and mechanical integrity.
526 citations
"Experimental Study on Quench Detect..." refers background in this paper
...winding is a practical solution to this problem [4]–[6]; however, it is not always applicable to certain types of magnets, such as...
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TL;DR: In this paper, the effects of localized heat pulses in powder-in-tube conductors and Ni-alloy substrated YBa 2 Cu 3 O x coated conductor tapes cooled by N 2 gas were studied.
103 citations
"Experimental Study on Quench Detect..." refers background in this paper
...I T HAS been reported that the quench protection of magnets fabricated using REBa2Cu3Oy (RE-123)-coated conductor is more difficult than that of low-temperature superconductor magnets [1], because the normal zone propagation velocity of RE-123 coils is significantly slower [2], [3]....
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TL;DR: In this article, Rayleigh-backscattering interrogated optical fibers (RIOF) was used to detect hot-spot quenches in high temperature superconducting materials, and the results show that RIOF quench detection is intrinsically faster than voltage taps and thermocouples.
Abstract: High temperature superconducting materials are the only option for the generation of magnetic fields exceeding 25 T and for magnets operating over a broad range of temperature and magnetic field for power applications. One remaining obstacle for the implementation of high temperature superconductors magnets into systems, however, is the inability to rapidly detect a quench. In this letter we present a novel quench detection technique that has been investigated experimentally. Optical fibers are co-wound into two small Bi2Sr2Ca2Cu3O10+x superconducting coils and interrogated by Rayleigh-backscattering. Two different configurations are used, one with the fiber atop the conductor and the other with the fiber located as turn-to-turn insulation. Each coil is also instrumented with voltage taps (VTs) and thermocouples for comparison during heater-induced quenches. The results show that Rayleigh-backscattering interrogated optical fibers (RIOF) have significant advantages over traditional techniques, including very high spatial resolution and the ability to detect a hot-spot well before the peak local temperature exceeds the current sharing temperature. Thus, RIOF quench detection is intrinsically faster than VTs, and this intrinsic advantage is greater as the coil size and/or current margin increases.
96 citations
"Experimental Study on Quench Detect..." refers methods in this paper
...For example, a novel quench detection method using Rayleigh-backscattering interrogated optical fibers [8], [9] and another novel method measuring nonuniform currents caused by normal transitions [10] have been proposed....
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TL;DR: In this article, the quench behavior of conduction-cooled Y Ba2Cu3O7?? (YBCO) coated conductor pancake coils is reported, and two coils, one stabilized with copper and one with brass, are wound with 25m of conductor and instrumented with a heater and a large number of voltage taps and thermocouples.
Abstract: The quench behavior of conduction-cooled Y Ba2Cu3O7?? (YBCO) coated conductor pancake coils is reported. Two coils, one stabilized with copper and one with brass, are wound with 25?m of conductor and instrumented with a heater and a large number of voltage taps and thermocouples. The critical current, minimum quench energy (MQE) and two-dimensional normal zone propagation velocity (NZPV) are measured as a function of I/Ic, where I is the transport current and Ic is the critical current. Although the non-uniform temperature and self-field distributions within the coils result in a non-uniform Ic, the heater is able to induce quenches with energies above the MQE and both longitudinal and transverse propagation velocities are measured. In both coils, the longitudinal NZPV (10?40?mm?s ? 1) is about one order of magnitude larger than the transverse NZPV (1?2?mm?s ? 1). Moreover, a comparison between the Cu-stabilized coil and a short, straight Cu-stabilized sample shows that the one-dimensional longitudinal propagation in the short sample is significantly faster than the longitudinal propagation in the coil. This is due to transverse heat conduction (transverse propagation) which reduces the temperature gradients in the coil but also slows down the longitudinal propagation. Thus, designing a quench detection system based upon data from one-dimensional experiments may result in an unintended level of risk.
76 citations
TL;DR: In this paper, self-field quench behaviors of YBa2Cu3O7−δ coated conductors with different stabilizers are studied, and measurements of the minimum quench energy (MQE) and normal zone propagation velocity (NZPV) are taken at various temperatures (30−75 K), and transport currents (30% Ic to 90% Ic) at a typical pressure of 10 −5 Pa.
Abstract: Self-field quench behaviours of YBa2Cu3O7−δ coated conductors with different stabilizers are studied. Samples include one with Cu on both sides (Cu‐Cu), one with stainless steel on both sides (SS‐SS), and one with Cu on one side and stainless steel on the other (Cu‐SS). The measurements of the minimum quench energy (MQE) and normal zone propagation velocity (NZPV) are taken at various temperatures (30‐75 K), and transport currents (30% Ic to 90% Ic) at a typical pressure of 10 −5 Pa. Of the three samples, the Cu‐Cu sample has the highest MQE while the SS‐SS one has the lowest MQE at the same temperature and percentage of Ic ;t he NZPV in the SS‐SS sample is found to be the highest while those of the Cu‐Cu and Cu‐SS samples are similar. The normal zone voltage and the hot-spot temperature are also compared. Both the classic adiabatic quench propagation model and the interface resistance model are used to explain the NZPV and MQE differences between the samples. The implications for conductor design and quench detection and protection are discussed. (Some figures in this article are in colour only in the electronic version)
50 citations
"Experimental Study on Quench Detect..." refers background in this paper
...Many experimental studies have been performed to investigate the quench characteristics of RE-123 coated conductors, such as normal zone propagation velocity and hot-spot temperature [11]–[14]....
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