Heejoon Lee

Comparison of AC losses of HTS pancake winding with single tape and multi-stacked tape

AC losses generated in the HTS winding differ from that of the short sample because each turn of winding is magnetically affected by adjacent turns. In this paper, we calculated the AC loss of HTS pancake windings. Numerical calculation was carried out to figure out the magnetic field in the windings. During the AC loss calculation of both windings, AC losses were obtained by using the short sample AC losses data. According to the results of calculation, loss calculation by using the short sample data of multi-stacked tape was more approached to winding loss than that by using the single tape data. To prove the effectiveness of the calculations, AC losses of windings was measured and compared. Finally the single phase HTS transformer with multi-stacked tape was constructed and tested.

Magnetization Loss and Shield Effect in Multi-Stacked Tapes With Various Stacking Configurations

AC loss is one of the major topics in large AC power applications using high temperature superconductor such as power transformers, transmission cables and fault current limiters because it is closely related to operation efficiency. Multi-stacked tape conductors should be used to transport the large current in those power applications. A research of various arrangements of HTS tapes for multi-stacked tapes has been performed to increase the capacity of transport current in HTS power applications. In this paper, we studied magnetization loss and shield effect from several different arrangements of BSCCO tapes such as Face-to-Face type, regular matrix type (mtimes2) and irregular matrix type. The results show that the magnetization loss of the Face-to-Face arrangement was lower than those of the other matrix types for the same stacking numbers. We think that the result was due to the shield effect by demagnetization of adjacent HTS tapes which were located as face to face

Current Estimation of an HTS BSCCO Magnet Having Multiple Power Sources Based on the Field Dependent

Due to the anisotropy of a tape-shaped HTS wire, the method to determine the operating current of an HTS magnet needs to be different from that of a LTS magnet. This paper presented estimation of the critical current of pancake windings excited by multiple power sources. Critical currents were determined by using field dependent E-J relation. A new method to define the magnetic field of the HTS wire has been proposed in this paper. Calculated critical currents of pancake windings were compared with measured ones of the HTS BSCCO magnet consisting of 10 pancake windings. Effects of multiple power excitation on the increment of the central magnetic field has been also described. Test results showed the estimated critical currents of pancake windings agreed well with that of measured ones and the central magnetic field was increased at multiple power excitation by 28.4% comparing with that of single power excitation.

E{\hbox{–}}J

HTS pancake windings have been commonly used for the insert coil of high field magnets. All pancake windings have been connected in series and excited by a single power source. In that case, currents of the whole pancake windings were limited by the minimum current of the top and the bottom pancake windings where maximum perpendicular magnetic field was applied. This paper proposed the multiple power excitation of the HTS magnet which consists of pancake windings. It was able to increase the magnetic field of the magnet by conducting critical currents to all pancake windings. Results of calculation by using a model BSCCO magnet shows that proposed method was able to generate higher magnetic field comparing with the conventional single power excitation.

Relation

In a high temperature superconducting magnet consisting of pancake windings, the perpendicular magnetic field considerably reduces the value of the critical current of the outer pancake windings due to anisotropy. An air gap was inserted between each pancake winding in this paper to reduce the decrement of the critical current in each pancake winding. In a low temperature superconducting magnet, the central magnetic field decreases when there is an air gap between the pancake windings. On the other hand, the central magnetic field of a HTS magnet increases when an air gap is provided. The properties of the HTS insert/outsert magnet having an air gap between the pancake windings are examined in this paper. YBCO wire and BSCCO wire were used in the insert and the outsert magnets, respectively. An E - J relation and the evolution strategy were adopted to calculate the optimum critical currents of both magnets. The calculation results showed that there was an optimum air gap which maximized the central magnetic field. The optimum air gap was dependent on the specifications of the HTS magnet.

Design Method of a High Field HTS Magnet Consisting of Pancake Windings Having Different Current in Each Pancake Winding

In the HTS magnet consisting of pancake windings, all pancake windings have been connected in series and excited by a single power source. Most of the pancake windings cannot conduct their critical current values at single power excitation. Current of each winding can be controlled separately to its critical current at multiple power excitation. This paper presents the excitation of an HTS YBCO magnet consisting of pancake windings by multiple power sources. To estimate the critical currents of the pancake windings more precisely, the magnetic field variation in the HTS wire was considered. Properties of multiple power excitation were measured by using the HTS YBCO magnet consisting of 8 pancake windings. Test results showed calculated currents agreed very well with measured ones and central magnetic field increased by multiple power excitation.

The Optimal Air Gap Between the Pancake Windings in a HTS Magnet Consisting of Insert and Outsert Magnet

In a High Temperature Superconducting (HTS) magnet consisting of pancake windings, HTS tape with the same width has been used for all pancake windings. If a wider HTS tape is used for the outer pancake windings, the critical current of the HTS magnet can be increased. This paper shows the properties of BSCCO magnets in which the outer pancake windings are wound with a wider HTS tape. In order to examine the effects of a wider HTS tape, a HTS magnet with an inner radius of 20 mm and a height of 202.4 mm was used. The number of turns of each pancake winding was 150, and the number of pancake windings was 46. The critical current of the pancake winding was determined by using E-J relation. Results of calculation show that the critical current was higher in the HTS magnet with a wider HTS tape at the outer pancake windings than in the HTS magnet with the same width of HTS tape for all pancake windings.

Increment of the Central Magnetic Field of an YBCO Magnet by Using Multiple Power Sources

In large actuators for water gate control of hydraulic dams, precise position measurement of the actuator cylinder is very important. An inductance type sensor can be used to measure the position of the actuator cylinder. This paper presents the effects of the slot shape on the properties of the inductance type sensor consisting of a permanent magnet and pick-up coils. The inductance type sensor is able to measure the position of actuator travelling over 10 m with 0.5 mm resolution. Result of the calculation is able to provide the data for choosing the appropriate shape of the slots to produce the proper magnitude of flux linkage and to minimize the mechanical stress imposed on the cylinder.

Characteristics of Magnets Depending on the Width of High Temperature Superconducting Tapes Applied to the Outer Pancake Windings

A load line method has been used to calculate the critical current of superconducting magnets. However, in high-temperature superconducting tapes that have a rectangular cross section, as the critical currents vary depending on the direction of an external magnetic field, the load line method cannot be used to precisely calculate the critical currents of the HTS magnets because it cannot fully consider the magnetic anisotropy of the HTS tape. In nested HTS magnets that have multiple layers, calculating the critical current considering the magnetic anisotropy is very time consuming. This paper presents an efficient calculation method to calculate the critical current of nested HTS magnets. The secant method and the fixed-point iteration method are used to reduce the calculation time. The critical currents of two nested HTS magnets are calculated: a double magnet consisting of a YBCO inner coil and a BSCCO outer coil and a triple magnet consisting of a YBCO inner coil, a YBCO middle coil, and a BSCCO outer coil. The calculation results demonstrate that it is possible to very effectively calculate the critical current of nested HTS magnets by using a combination of the secant method and the fixed-point iteration method.

Properties of an inductance type sensor for position control of a long stroke actuator

태양광 모듈 효율의 증가를 위해 렌즈나 반사판 등을 이용한 집광 시스템 개발이 활발하게 진행되고 있으며, 집광장치는 일반적으로 렌즈를 사용하거나 고집속비의 광학장치를 이용하여 태양광 추적형으로 설계하여 고집속화를 추구하고 있다. 그러나 집속비에 비례하여 열로 소산되는 에너지 밀도가 증가하므로, 고집속에 따른 태양전지 온도상승에 의한 태양전지 효율 저하를 방지하기 위해 집광장치의 냉각에 유의해야 한다. 본 논문에서는 이러한 여러 가지 제약 조건을 피하여, 저가격의 반사형 광학장치를 이용한 경제적인 저집광형 태양광 모듈 시스템을 연구 개발하였다. 일반모듈에 저집광장치를 사용하여 태양광 모듈의 발전효율을 증대 시키면서 집광으로 인해 발생하는 열을 냉각장치를 통해 방출하였다. 제안된 저집광형 냉각장치(MCS, Micro Cooling System)의 특징은 모세관력에 의한 자연 순환 방식으로서 외부 동력원이 불필요하며, 유체 상변환시의 잠열을 이용함으로써 고성능 냉각 구현이 가능하다. 117W 태양광 모듈에 반사판을 설치하고 냉각장치가 있는 모듈과 냉각장치가 없는 모듈을 비교 하였다. 냉각장치를 설치한 모듈에서의 발전량이 28% 증가하였다. 【To increase the efficiency of a solar module, the development of solar concentrator using a lens or reflection plate is being proceeded actively and the concentrator pursues the a concentration using a lens or an optical device of a concentration rate and designing as a solar tracking system. On the other hand, as the energy density being dissipated as a heat according to the concentration rate increases, the cares should be taken to cool the solar concentrator to prevent the lowering of efficiency of solar cell by the increasing temperature of the solar cell. This study, researched and developed an economical concentrator module system using a low priced reflection optical device. A concentrator was used as a general module to increase the generation efficiency of the solar module and heat generated was emitted by the concentration through the cooling system. To increase the efficiency of the solar concentrator, the cooling system was designed and manufactured. The features of the micro cooling system (MCS) are a natural circulation method by the capillary force, which does not require external power. By using the potential heat in the case of changing the fluid, it is available to realize high performance cooling. The 117W solar modules installed on the reflective plate and the cooling device in the cooling module and the module unit was not compared. The cooling device was installed in the module resulted in a 28% increase in power output.】