Search

Effective quench detection technologies are extremely important for protecting high temperature superconducting (HTS) applications. In recent years, an optical fiber encapsulated HTS tape (OF-tape) is proposed for quench detection by using distributed temperature sensing (DTS) technology. In this paper, an HTS coil (OF-coil) wound with a 39 m long OF-tape was prepared and energized by an AC overcurrent of 700 A to verify the feasibility of temperature observation during quench events. Furthermore, anti-stokes intensity was also measured to understand dependence of temporal resolutions on response times of coil quenches. The main results show that temperature variations of the OF-coil can be correctly measured after quench and the maximum temperature is shown at the middle turn of the OF-coil. Particularly, for the method of detecting anti-stokes intensity, quench response time of temporal resolution (TR.) with 30 ms is about 500 ms faster than that with 300 ms. However, when the TR. is 30 ms, more noise signal is observed. Accordingly, a trade-off should be considered between response time and noise signal for efficient quench detection. [ABSTRACT FROM AUTHOR]

Because of a much higher power density than a conventional underground cable, several high-temperature superconductor cables with different voltages and designs have been developed worldwide and demonstrated in a power grid. The 100-m 22.9-kV/50-MVA BSCCO cable system developed for long-term demonstration has been tested during phase I of three years, after being installed at Gochang Test Yard in Korea first: initial cooling, engineering properties, and its reliability. In this paper, we particularly focused on its dielectric and transport current characteristics investigated under high voltage up to 30 kV or large current, experimentally and theoretically. The results show that the dielectric parameters such as permittivity and loss tangent are similar to a conventional oil filled cable. However, the impedance is one fifth of a concentric neutral cross-linked polyethylene insulated cable with a similar conductor size. In addition, separate estimation of ac loss in the conductor and shield, which has not been clear yet, is also established: the shield's loss is evaluated directly from the shield lead, but the conductor's loss indirectly through the virtual-voltage lead. Then this conductor's loss at the rated current may raise its temperature to a coolant by a few degrees. The lumped circuit model shows that the three-phase shield suggested in our cable system can sufficiently cancel magnetic field generated from any variation of a power load in an actual grid. Finally, the theoretical models based on a home-written code and a commercial package are in good agreement with their corresponding experimental results. [ABSTRACT FROM AUTHOR]

The superconducting linear synchronous motor is one of the main applications of the high-temperature superconducting (HTS) magnet made out of coated conductors. The high operation current density and temperature of HTS magnet can lower the requirement of the cryocooler system. Moreover, if the superconducting rotor magnet is designed to work in persistent-current mode, the heat load of the magnet system can be further reduced because there is no joule heat and heat leakage on the current leads. However, in real working conditions, the rotor magnet is exposed to an alternatingmagnetic field (AMF) caused by the vibration and harmonic magnetic field from the stator magnet. This AMF may accelerate the decay process of the magnetic field in rotor magnet. In this paper, the magnetic field decay property of the HTS coil in AMF is experimentally discussed. In order to eliminate the impact caused by the joint resistance, a kind of joint-less stack coil that can operate in real persistent-current mode is fabricated and tested in an AMF generated by an electromagnet. The tests were conducted with different AMF amplitudes and frequencies, as well as different initial magnetic field in HTS coil. [ABSTRACT FROM AUTHOR]

Because of the small square dimension, a solderedstacked-square (3S) high-temperature superconducting (HTS) wire with 1 mm width is considered as a candidate for cabling large current conductors through twist process. For studying the twist structure, in this work, we prepared several twisted 3S wire samples fabricated from the same piece of the 3S wire with 10 m length. For the 3S wire, the uniformity of critical current was evaluated. As well, we investigated basic electrical and mechanical characteristics for the twisted 3S wire. The main results show that the critical current distribution for the 3S wire is relatively uniform at the average value of 90 A; the allowable minimum twist pitch of the twisted 3S wire is about 60 mm; the critical current of the twisted 3S wire shows isotropy characteristics; through the test for frequency dependence of self-field loss, we can know the eddy-current loss in the twisted 3S wire can be ignored, and the measured losses are identical to the calculated one fromthe thin strip equation; the minimum bending diameter and allowable tensile force for the twisted 3S wire are approximately 80 mm and 400 N, respectively. [ABSTRACT FROM AUTHOR]

This paper reports the feasibility of the impregnation of no-insulation (NI) high-temperature superconducting (HTS) coils using solder. NI coils are widely studied and used in many situations. To utilize an HTS coil under high mechanical loads such as field coils for rotating machines, the HTS tapes must be stabilized mechanically. Epoxy impregnation is a common method to protect the HTS field from mechanical disturbances caused by the magnetic field and rotational vibration of the rotor to enhance the mechanical stability. However, traditional epoxy resins are electrical insulating materials which might cause the turn-to-turn contact resistance of NI coils to increase. Therefore, we proposed a new kind of impregnation method using the electrically conductive material, solder. Two coils were fabricated and tested for comparison. One is the NI coil without impregnation and the other is the NI coil impregnated with solder. The charge-discharge and sudden-discharge tests were performed in liquid nitrogen at 77 K. The experimental results were studied with equivalent circuit analyses. The results of this paper could provide useful data for the application of solder impregnated NI HTS coils. [ABSTRACT FROM AUTHOR]

This paper proposes a novel accuracy improvement technique for the double-layer charge (DLC) formulation in shielding problems. Although the DLC formulation has advantages over the direct methods from the viewpoint of computational cost, the calculation accuracy can be worse because of cancellation errors. In order to improve the accuracy, we apply a new technique based on the difference field concept. Numerical results, which verify the effectiveness of the proposed method, are presented. [ABSTRACT FROM AUTHOR]

Multi-wire conductors consisting of YBCO wires with magnetic substrate are usually applied in the high temperature superconductor (HTS) applications. In these applications, ac loss is a critical factor to determine the capacity of a refrigerator. And the ac losses of YBCO-NiW wires will be affected by the magnetic substrate. In this work, the self-field loss of the YBCO wire with the magnetic substrate is firstly measured, and compared with the numerical data. Moreover, the ac losses of a multi-wire YBCO-NiW conductor consisting of three wires are investigated for three transport modes. The main results show that the measured self-field loss of the wire is identical with the numerical ones. Accordingly, the reliability of the experimental and numerical methods is verified. Also, the ac losses of the conductor are in good agreement with the numerically calculated losses. As for the multi-wire conductor's total losses, the change of the direction of current in wires will not have an apparent influence on the total ac losses. [ABSTRACT FROM PUBLISHER]

In order to electrically investigate the AC losses of the conductor and the shield in an actual HTS cable with shield, we attached two voltage-leads to the conductor and shield of a short cable which is the same as the Korea Electric Power Corporation (KEPCO) HTS cable under the field test, and examined it. The result shows that the polarities of the loss voltages measured from both voltage-leads are opposite. The ratio (1.6) between the losses for different transport periods measured from the conductor-lead is quite large. It is considered from these results that the conductor loss is the sum of the losses measured from the conductor-lead and shield-lead. And this conductor loss corresponds well with the numerical result too. Moreover, the total loss of the short cable measured from the proposed electrical method at 77 K was compared with that of the KEPCO cable by calorimetry at 66.6 K through our numerical model. The difference between the measured losses and numerical ones is almost the same. This means that the shield loss is measured from the shield-lead, and the conductor loss from both voltage-leads. [ABSTRACT FROM AUTHOR]

The Bi-2212 monofilar bulk element was selected as a candidate in developing a 24 kV/630 A class superconducting fault current limiting (SFCL) system. This study investigated the Bi-2212 monofilar element both experimentally and theoretically regarding the DC voltage-current characteristics, AC loss characteristics, inductance, current limiting characteristics and local temperature distribution. It was found that the critical current of the Bi-2212 monofilar element increased 3.3 times as the operation temperature decreased from 77 K to 65 K. Although the arrangement of the Bi-2212 conductor was a coil shape, the measured AC loss was at a level similar to what is calculated from the Norris equation at both the temperatures 77 K and 65 K. The temperatures measured at each section during a fault were in good agreement with the results of the numerical analysis. Moreover, the results showed that the monofilar element was not yet sufficiently homogeneous to be used at its full rated voltage. [ABSTRACT FROM AUTHOR]

In order to meet the needs of economical and stable power supply and high current density cable with compact size, several countries carry out researches on High Temperature Superconducting (HTS) cables. Korea Electric Power Corporation (KEPCO) established the HTS cable test center and installed 22.9 kV, 1250 A, 50 MVA, 100 m class HTS cable system to investigate the performances and application possibility in real power grids. The HTS cable system went through seven cool down and warm-up cycles and also many kinds of performance tests. for 3 years. Rated voltage-current tests, over voltage tests, and measurements of heat loss and AC loss with various currents have been examined. Moreover, DC critical current tests were performed for checking conductor degradation before warming up or after cooling down. Through the performance tests of the HTS cable system, the overall efficiency and loss factors are estimated and compared with conventional power cables in this paper. We conclude the present status of HTS cable system and application possibility in the real power grid. [ABSTRACT FROM AUTHOR]

The high-temperature superconductor (HTS) with large current capacity has been developed for power applications such as power transmission cables and fault current limiters. Especially, in these power applications, AC loss is very important in an economic point of view but this issue has not been completely elucidated due to its many complexities. In this work, two HTS conductors with very different critical current densities, which consist of several Bi-2223 tapes placed on a cylindrical former, were fabricated in an attempt to arrive at a clear understanding of their AC loss characteristics. AC loss characteristics for such two cylindrical multi-tape conductors have been experimentally investigated. Moreover, the influence of current transport mode on the AC loss of the Bi-2223 tape in the conductors was investigated. DC voltage-current characteristics of the Bi-2223 tapes were also measured for discussions on the measured AC losses. The results show that for the conductor with high critical current density, the measured AC loss strongly depends on the transport mode as in the conductor with low critical current density. However, the transport mode dependence of the conductor with high critical current density becomes weaker and weaker as transport current increases. In the simultaneous mode, the measured AC loss of the conductor with low critical current density is in good agreement with the calculated loss from the monoblock model. However, the measured loss of the conductor with high critical current density does not coincide with both the numerically calculated loss and loss calculated from the monoblock mode. [ABSTRACT FROM AUTHOR]

Carbon nanotubes (CNT) exhibit distinctively different properties from their bulk counterparts due to their remarkable electrical, mechanical, optical, and chemical properties. Some of the most advance synthesis, properties, and various application of CNTs are discussed. [ABSTRACT FROM PUBLISHER]

A cylindrical high temperature superconductor (HTS) is often used in power applications such as power transmission cables and matrix fault current limiters. In commercialization of these apparatuses, AC loss is a critical factor but not elucidated completely because of complexities in its measurement, e.g. non-uniform current distribution and phase difference between currents flowing in an individual HTS tape. We have prepared two cylindrical conductors composed of a Bi-2223 tape with different critical current density and one hollow conductor made of Bi-2212 bulk material. In this paper, the AC loss characteristics of the conductors have been experimentally investigated and numerically analysed. The results show that the measured losses for all the conductors are not dependent on both arrangements and contact positions of a voltage lead. This implies that most of loss flux is only in the conductors. The loss for the Bi-2223 conductor with high critical current density is in good agreement with the numerically calculated one based on the polygon model, whereas the loss measured for the Bi-2223 conductor with low critical current density coincides with the calculated loss from the monoblock model. [ABSTRACT FROM AUTHOR]

This work is development of HTS motor at DOOSAN heavy industry and Korea Electrotechnology Research Institute in Korea, and is sponsored by DAPAS program which is supported by Korean government. The final aim of the project is realization of HTS motor in the field of industry such as large driving pumps, fans and compressors for utility and industrial environments. In the first phase (2001–2004), 100 hp HTS motor was developed in order to implement the preliminary technology for the large applicable HTS motor. All of the performance characteristics are well met to the designed ones. In second phase (2004–2007), 1 MW HTS motor is developed for the purpose to fully represent the design and manufacturing issues for the larger capacity machine. The machine is 2 pole and 3600 rpm, and all of the components are completely manufactured. This machine is now under assembly. This paper summarizes the status of 1 MW HTS motor development, such as design, construction, and experimental test results. [ABSTRACT FROM AUTHOR]

A Bi-2223 tape has been developed for power applications such as a fault current limiter, a power cable and a superconducting magnetic energy storage system (SMES). In such applications, the Bi-2223 tape carries time varying transport current and in addition experiences time varying external magnetic field. It is well known that the external magnetic field not only causes magnetization loss in the Bi-2223 tape, but also drastically increases transport loss due to a so-called şdynamic resistanceç. We developed an evaluation setup, which can measure transport loss in an external AC magnetic field. Using this equipment, we measured the dynamic resistances for various amplitudes and frequencies of external AC magnetic field perpendicular to the face in the tape. Simultaneously we investigated the effect of external AC field on transport loss with different experimental conditions. This paper describes test results and discussions on correlation between the dynamic resistance and the transport loss for various technical Bi-2223 tapes. [ABSTRACT FROM AUTHOR]

A transient numerical simulation was conducted to have variation of temperature on an element of resistive SFCL (Superconducting Fault Current Limiter) under quench condition. It is very important engineering information for an optimum design of cryogenic system for cooling of a resistive SFCL element. A bifilar coil for resistive SFCL for 10 MVA system was incorporated as a model in this numerical study. From the result, it was found that the averaged temperature on the shunt and Bi-2212 element at 500 kW, 100 ms was 711.1 K and 198.4 K respectively. The temperature variation with the change of the hot-spot size and time is also obtained. The maximum temperature was continuously increased in all cases until the hot-spot stops at 100 ms and it was going down after then. Such as, the details of temperature distribution on the SFCL element obtained from this numerical study and it should be very valuable information on the decision of the cooling capacity of cryogenic system. [ABSTRACT FROM AUTHOR]

The purpose of this study is to develop a superconducting magnet energy storage system (SMES), which protects sensitive loads on the power system, when an interruption or voltage sag occurs. Industries have many sensitive machines, and keeping the power in a good condition is very important for nonmilitary machines also. Korea Electrotechnology Research Institute (KERI) has developed a 3 MJ/750 kVA SMES system to improve power quality in sensitive electric loads. It consists of an IGBT based power converter, NbTi mixed matrix Rutherford cable superconducting magnet, and a cryostat with HTS current leads. The operating current of the 3 MJ SMES magnet was 1000 A. The SMES system is tested under short time power interrupt to verify the feasibility of the SMES system as a 750 kVA power converter. [ABSTRACT FROM AUTHOR]

AC loss is an important issue to design high temperature superconductor power cables, which consist of a number of Bi-2223 tapes wound on a former. In the cables, the tapes have intrinsically different critical currents, and they are electrically connected to each other and current leads. This makes loss measurements considerably complex, especially for short samples. In this work, we have prepared a multi-tape conductor composed of Bi-2223 tapes. The ac losses of the conductor have experimentally investigated. The loss tests indicate that the effect of critical currents of each tape on AC loss measurement in the multi-tape conductor is negligible only if currents in the tapes flow uniformly. Moreover, the measured loss of the conductor is in good agreement with the stun of the transport loss in each tape. However, in the case of nonuniform current distribution, the measured AC loss considerably depends on the current distribution parameter γ, and the positioning of a voltage lead. Thus it should be very careful to measure the AC losses in the short power cable samples. [ABSTRACT FROM AUTHOR]

A 3-phase, 100 hp, 4 pole, 1800 rpm superconducting synchronous motor built and tested in Korea Electrotechnology Research Institute(KERI). This machine consists of HTS rotor and air-core stator. The HIS field windings are composed of the double-pancake coils wound with AMSC's stainless steel-reinforced Bi-2223 tape conductor. These were assembled on the support structure and fixed by a bandage of glass-fiber composite. The cooling system is based on the heat transfer mechanism of the thermosyphon by using GM cryocooler as cooling source. The cold head is in contact with the condenser of a Ne-filled thermosyphon. The rotor assembly was tested independently at the stationary state and combined with stator. The open circuit, no-load, and short circuit characteristic were obtained. Also, load tests in motor mode driven by inverter and generator mode connected to resister load bank were conducted. This paper will present design, construction, and experimental test results of the 100 hp HTS machine. [ABSTRACT FROM AUTHOR]

A Bi-2223 tape has been developed for low-field power applications such as power cables or transformers working at liquid nitrogen temperature. For such applications it is required to understand fault current characteristics of the technical high temperature (Tc) superconductor. In this paper, we prepared two types of the samples with similar insulation structures to power cables and transformers: the straight sample and the pancake sample. Then we examined the normal transition characteristics for a sinusoidal steady current and the fault current characteristics for a sinusoidal pulse current. It is found that temperatures slightly higher than critical one of the technical high T superconductor make normal transition easily. However over-critical currents can't make it normal state completely up to ∼ 5Ic if the superconductor's temperature remains bath one. The fault current tests show that the temperatures and resistances measured in both the insulated straight sample and the pancake sample with conductor insulation are similar to each other, while the pancake sample with layer insulation is significantly different from the two samples above. This means that from damage point of view under the grid's fault conditions, the pancake sample with layer insulation has better characteristic in comparison with conductor insulation. [ABSTRACT FROM AUTHOR]

The ac loss is an important issue in the design of high-To superconducting power devices such as transformers and cables. In these devices many Bi-2223 tapes are closely stacked together and exposed to alternating magnetic fields that can have different orientations with respect to a tape. In such arrangement the magnetization loss is influenced by the screening current induced in adjacent tapes and thus different from that in a single tape. This stacking effect was experimentally investigated by measuring the magnetization loss in a stack, which consists of a number of tapes. First the magnetization loss in the single tape was measured in order to confirm the reliability of the loss data measured in the stack. The results for the single tape coincide well with the loss characteristics described in other previous works. For the stack in parallel and longitudinal magnetic fields the measured loss is independent of both the number of tapes and stacking type. The longitudinal magnetization loss is well explained rather by the slab model for decoupled filaments. For the tall stack in perpendicular field the measured loss at low fields is greatly decreased, compared to the loss of the single tape. However the loss at high fields is unaffected. These loss behaviors in the tall stack are well described by the slab model for full coupling. [ABSTRACT FROM AUTHOR]

To develop a stable and compact small-sized superconducting magnetic energy storage (SMES) coil, which provides electric power with high quality to sensitive electric loads, we fabricated a SMES coil and tested it. Because such a large-sized superconducting coil quenches far away from its critical current, the recovery current is frequently used as a stability criterion in the coil fabrication. Therefore, we first investigated the recovery current characteristics of the large current conductor, which was used in our SMES coil fabrication. The test results indicate that the recovery currents measured in the conductor are nearly identical to those based on the single wire. This implies that the recovery current is affected by the conductor's cooling condition rather than its size and current capacity. In the SMES coil test the first quench occurred at 1250 A, which is equivalent to the stored energy of about 2 MJ. It corresponds to the quench current density of about 130 A/mm². This value is much higher in comparison with that reported in the other work. In addition, the first quench current of the coil agrees well with the measured recovery current of the conductor having similar cooling condition with it. This means that to determine the recovery current of a conductor is, first of all, important in the design and fabrication of a large-sized superconducting coil. [ABSTRACT FROM AUTHOR]

A superconducting solenoid with large inner diameter has much lower current capacity than expected from short wire sample tests, and a solenoid of multi-strand cable has worse results. It is known that this degradation is observed when the inner diameter of the solenoid is bigger than a certain value (30 cm usually). However the reason is not clarified yet and some people called this just the "size effect." To obtain some clues to understand the size effect and to develop big solenoids with higher operating current, we prepared and tested two sample solenoids made of Rutherford type cables with and without soldering. Quench currents and AC losses of the two solenoid coils are measured and compared. The test results show that the soldering on the Rutherford cable improves the current capacity, but makes the AC loss much higher. [ABSTRACT FROM AUTHOR]

Examines factors affecting the stability of superconducting magnetic energy storage device. Energy storage capacity; Recovery current density; Cooling conditions; Size of conductors.

Discusses the design, fabrication and testing of a model coil for a superconducting magnetic energy storage system. Features of the coil; Critical current; Quench currents; Winding tensions of the coil.

Discusses the effect of the neighboring tape's alternating currents (AC) on transport current loss of a Bi-2223 superconducting tape. Development of Bi-2223 for low-field power applications at liquid nitrogen temperature; Transport losses for different AC levels and arrangements of neighboring tapes; Dynamic resistance loss; Normalization of peak transport current.

Describes the development of a small-sized superconducting magnetic energy storage (SMES) coil with the storage capacity of three megajoules. Initial step in the fabrication of the coil; Stability of the conductor against localized disturbances; Quench current characteristics for different charge rates.

We present the results of a systematic change of magnetic-domain structure of epitaxial Mans film on GaAs(001) in a temperature range of 17.5 °C-45 °C by magnetic-force microscopy (FM). As temperature decreases, the small localized domains are formed and gradually collapse to the stripe domains. Finally, at 17.5 ° C the whole film turns to be a nearly single magnetic domain including only a small fraction of the non ferromagnetic β-Mans phase, as directly confirmed in the FM experiment. [ABSTRACT FROM AUTHOR]

We have observed the magnetic domain evolution under an external magnetic field in an epitaxial MnAs film on GaAs(001) by magnetic force microscopy. Owing to the strain involved, the ferromagnetic α-MnAs and the paramagnetic β-MnAs phases coexist as self-aligned stripes at room temperature. It was found that a complex magnetic domain structure appeared in the ferromagnetic α-phase region at the demagnetized state (H = 0 Oe). As the magnetic field increased, the magnetic domain structure was gradually changed, and reached a completely saturated state at H = 600 Oe. Especially, at H 300 Oe, the observed magnetic domain wall distribution is well matched with the topographical shape. [ABSTRACT FROM AUTHOR]

Mobility was extracted from top-contact pentacene organic field effect transistors with minimal assumptions. Low-frequency capacitance-voltage (C-V) measurements were used to calculate the sheet charge density of the channel, and current-voltage measurements with low drain-to-source voltage were used to extract mobility. The separation of charge and mobility with the use of C-V measurements illustrates that the mobility increases with gate voltage, differing significantly from mobility dependence on gate voltage in crystal silicon MOSFETs. The physical meaning of this mobility and the possible mechanism for the increase in mobility as a function of gate bias are discussed. [ABSTRACT FROM AUTHOR]

Presents information on a study which calculated the saturation magnetostriction from measured second-harmonics during a hysteresis loop in silicon steel. Details on harmonic profiles; Methodology of the study; Results and discussion.