For a superhydrophobic coating, its limited durability has been a persistent issue that prevents its widespread usage in outdoor applications. Here, we propose a scalable, self-recoverable CeO2/PDMS hybrid coating that harnesses synergetic benefits from hydrocarbon adsorption of rare earth oxides and hydrocarbon supply by a hydrocarbon-based polymer. It is demonstrated that this hybrid coating substantially outperforms other super -hydrophobic surfaces in self-recovery of superhydrophobicity and weather resistance. The synergetic effect expedites the recovery of superhydrophobicity via a facilitated hydrocarbon adsorption: e.g., the self-recovery time of our coating was over 30 times less than that with CeO2 nanoparticle-based coating after plasma treatment. Furthermore, our coating showed excellent weather resistance by (1) sustaining superhydrophobicity over 1 year without any deterioration in the outdoor environment and (2) surviving accelerated weathering tests. Finally, our coating was successfully applied to the outdoor electrical insulators, while exhibiting excellent self-recovery performance of superhydrophobicity even after exposure to 600 V of electrical stress in presence of conductive water droplets. We believe that our coating provides robust superhydrophobicity via a rapid self-recovery performance and can be applied to any type of substrates with complex geometry by a one-step spraying process, both of which would be crucial to the application of the superhydrophobic coating in a wide range of energy and environmental applications.

When a 22.9 kV, 50 MVA HTS (high temperature superconducting) power cable was applied to a real power system and the system was being operated as part of the Icheon project, a current redistribution problem occurred in the shield layer. To clarify the reasons for this, the authors analyzed the characteristics of the current distribution and induced current ratio with a phase angle in the HTS power cable considering an asymmetrical three-phase current that flowed into the conducting layer and the impedance variation of the shield layer according to a grounding method using the PSCAD/EMTDC (power system computer aided design/elector magnetic transients DC) analysis program and vector calculation. It was found that the increases in the asymmetrical current flowing through the conducting layer of the HTS power cable and in the impedance of the shield layer affected the magnitude and phase of the induced current. In addition, depending on the grounding method used, a problem in which the zero current generated by the asymmetry affects the induced current and flows through the cryostat was found. The results obtained through the simulation analysis will provide valuable information for the installation and operation of HTS power cable systems in actual utilities.

In this work, we manufactured icephobic coating materials, consisting of aluminum pigment-added room temperature vulcanized silicone rubber, by varying the particle size and type of the aluminum pigment. From the measurements of contact angle and surface energy, the coating with higher surface roughness revealed superior water repellency. However, icephobic performance was inversely proportional to surface roughness and hardness. The continuous allowable current application test showed that the silicone rubber (SR) coating exhibited the highest heat dissipation capacity due to its higher emissivity close to similar to 1. Furthermore, the SR coating revealed the remarkable durability for the icephobicity in the long-term period, as evidenced from the accelerated degradation test and cyclic icing/de-icing test. The developed coating material broadens industrial applicability as the icephobic coatings in transmission line. Moreover, it is expected that the superior heat dissipation capability of the SR coating would enhance the power efficiency in summer.

In this work, we fabricated hydrophobic anti-freezing materials using room temperature vulcanized (RTV) silicone rubber and hydrophobic fumed silica, and investigated the chemical and corrosion properties of the coated materials with varying amounts of hydrophobic fumed silica. As the amount of the hydrophobic fumed silica increased, the surface texture became rough and the water repellency increased. With the addition of 30 wt% hydrophobic fumed silica, the coated materials exhibited superhydrophobic characteristics, indicating superior anti-icing performance by prohibiting nucleation of ice. On the other hand, hydrophobic material showed better de-icing performance than the superhy-drophobic one due to a relatively smaller surface roughness As compared with AA 6061 aluminum alloy, both developed hydrophobic and superhydrophobic coated materials improved corrosion resistance, and the degradation of the surface morphology, wettability and de-icing properties was not significant after the salt spray test. The developed coated materials enhanced industrial applicability as anti-freezing materials used in transmission line.

In this paper, new time-frequency-based anomaly detection methodology is proposed for the condition monitoring of high-temperature superconducting (HTS) cable systems. The time-frequency-based anomaly detection methodology includes two indices, which are obtained via cross Wigner-Ville distribution and scattering parameter. For the validation of the proposed methodology, the methodology is applied to an ac 22.9-kV/50-MVA HTS cable system connected to the real power grid network. Furthermore, the changes in dielectric properties of the HTS cable system during the cooling process and the current imbalance failure are monitored. The proposed anomaly detection indices are shown to be able to detect the heat and the current imbalance caused by the malfunction of the joint box. For the application of the two validated indices, new anomaly detection procedure for HTS cable systems is also presented.

Supercapacitor, especially electrical double-layer capacitance(EDLC), have many advantage that can operate at very high charge and discharge rates and have lifetimes of over a million cycles [1]. Furthermore, supercapacitor can complement batteries to reduce the size of batteries using with frequency regulation. Their utilization in a system can potentially eliminate the need for frequent replacement as required by batteries, hence, saving the resources invested in the upkeep of the whole system in the long run of power grid. However, supercapacitor are still far from being able to replace batteries and struggle in meeting the demand for a high energy density [2]. Since electrode material is the main key to improve the energy density, today, graphene considered as an attractive material because graphene has excellent conductivity, stability, and high surface area [3]. However, many aspects of the electrochemical behaviour of electrode still need to be examined closely in order to apply for electrode for commercial use, and there is another issue that graphene production methods are easy to aggregate or stack and lead to reduce surface area. In this reason, it is very difficult to maintain an outstanding graphene property for electrode production in case of large scale area for mass production. In this study, in order to practical application, we compared various electrode properties of activated carbon and activated graphene. To demonstrate the electrochemical performance of the activated carbon and graphene electrode, we manufactured a series of supercapacitor on CR2032 coin cells. The samples were punched into round

The operational cost for maintaining the superconductivity of high-temperature superconducting (HTS) cables needs to be reduced for feasible operation. It depends on factors such as AC loss and heat transfer from the outside. Effective operation requires design optimization and suitable operational conditions. Generally, it is known that critical currents increase and AC losses decrease as the operational temperature of liquid nitrogen ($LN_2$) is lowered. However, the cryo-cooler consumes more power to lower the temperature. To determine the effective operational temperature of the HTS cable while considering the critical current and AC loss, critical currents of the HTS cable conductor were measured under various temperature conditions using sub-cooled $LN_2$ by Stirling cryo-cooler. Next, AC losses were measured under the same conditions and their variations were analyzed. We used the results to select suitable operating conditions while considering the cryo-cooler's power consumption. We then recommended the effective operating temperature for the HTS cable system installed in an actual power grid in KEPCO's 154/22.9 kV transformer substation.

For the practical application of a YBCO superconductor bulk, the superconductor bulk magnet with high magnetic field on a large area surface should be fabricated. To make this, YBCO single crystal bulks with fine $Y_2BaCuO_5$(Y211) particles have been prepared by the top-seed melt growth(TSMG) method with $YBa_2Cu_3O_x$, $Y_2O_3$, and $CeO_2$ mixing precursor. By using $Y_2O_3$ instead of $Y_2BaCuO_5$ as precursor, the manufacturing process became simpler and more economical. The microstructures, trapped field and critical current density of the various conditioned YBCO bulks have been observed, analyzed and measured. The different characteristic values of the several samples have been analyzed from the viewpoint of their microstructures. We have developed a $8{\times}12cm$ size superconductor bulk magnet, up to 3 T class, by using the 4 T class-high field superconducting magnetizer and confirmed the applicability of the transmission level circuit breakers by measuring the strength and speed of the superconductor bulk magnet actuator.

This paper proposes an application of superconducting flywheel energy storages (SFESs) to compensate the power fluctuation of the large scale wind farm. Based on the global interest against global warming, the power capacity of the renewable generation, especially wind generation, has been increased steeply. However, since wind generations depend on the natural wind speed completely, the power output cannot be controlled. The power fluctuation caused by the non-controllable output characteristic may create voltage problem for local system and frequency problem for whole power system. To solve those problems, the hybrid application of the large-capacity battery energy storage system (BESS) and the high-speed superconducting flywheel energy storage system (SFES) are considered in Heangwon wind farm in Cheju Island in Korea. Through the case studies based on the site-measured output data, the optimal power and energy capacity of the BESSs and SFES are figured out.

The recent increase in power demand has been pressuring industries to continuously extend or expand power sources and transmission and transformer systems. On the other hand, the equivalent impedance of power systems is decreasing. Accordingly, the fault current magnitude in power systems is increasing. Because of such developments, and the rising need to counter this trend, current-limiting technology has been getting much attention as it can efficiently limit the short-circuit faults and improve power system reliability. For this purpose, studies are being carried out on the superconducting fault current limiter (SFCL). In particular, studies on SFCL where normal-conducting devices are combined, instead of the resistor-type SFCL that depends only on the superconductor, are being continued. The development of the element that is suitable for the superconducting fault current limiter combined with the normal-conducting device is also underway. In this study, YBCO thin-film wires that have and do not have a stainless steel stabilizer layer, which is recently studied as the superconducting current-limiting element, were used as superconducting elements of the flux-lock and transformer-shape SFCL consisting of normal-conducting core and coil. The effect of the difference between the resistance values of the two elements on the current-limiting performance of the flux-lock and trans former-shape current limiter was evaluated. For this purpose, the resistance values trend of the two superconducting elements was examined. The initial operational characteristics were compared in terms of quenching time (I ini , I Imi , and T r ) and stability (V max ).

In this paper, we assessed the characteristics of the rotational energy loss by drag force according to a size change of the new amorphous stator core used on PMSM/G. The accurate method for measuring rotational energy was presented through the spin down test using superconductor flywheel energy storage system (SFES). The mathematical model for core loss of amorphous was constructed using the radial and tangential components of magnetic flux density through the experimental data analysis for the cores of PMSM/G. Rotational losses in the cores of PMSM/G were more influenced by radial component than by tangential component of magnetic flux density. Experimental results and proposed mathematical model of core loss using radial component and tangential component of magnetic flux density were in good agreement. Also it was confirmed that use of the new amorphous stator core on PMSM/G core could considerably improve the energy storage efficiency of the SFES.

The analysis of the steady and transient states is very important for the application of the superconducting wire to electric devices. Through many studies, the detailed evaluation technology for BSCCO wire, referred to as “the first-generation superconducting wire,” has been established to some extent. Meanwhile, the detailed analysis of the steady and transient states of YBCO thin-film wire, the second-generation wire that is increasingly being applied to more electric devices, is insufficient. Accordingly, in this study, the quench behavior at a below-critical temperature was evaluated, especially in the flux flow state, using two types of commercial YBCO thin-film wires, to determine the electric devices to which the wire can be applied, and to define its operating conditions. For this, YBCO thin-film wires with copper and stainless-steel stabilizer layers, which were manufactured considering the specific resistance and conductivity of the stabilizer layer, were prepared. The critical currents of the two wires were 85 A and 70 A, respectively, but their critical temperatures were identical at 90 K. The resistance values of both wires increased over time, within the range above the critical temperature, but they were different within the range below the critical temperature, according to the stabilizer layer. This can be an index that clearly represents the conducting and current-limiting characteristics of YBCO thin-film wire. Therefore, in this study, the two wires' current division characteristics were examined within the temperature range of 77 K (at which the liquid nitrogen starts to boil) to 90 K (the critical temperature) to determine which of the two wires was the conduction wire and which was the current-limiting wire. In addition, the conduction region was defined based on the trend of increase resistance below and above the critical temperature.

In this paper, an actuator model of the thrust magnetic bearing for the flywheel energy storage is derived using magnetic circuit theory. And we compared this result with finite element magnetic field analysis result. Based on the actuator model, we made a simulation model of the thrust magnetic bearing system. We showed the closed loop transfer function and sensitivity function of the thrust magnetic bearing system using both the simulation model and the experiment. The experimental result at rotation velocity 18,000rpm of thrust magnetic bearing system is included.

The ongoing Superconducting Fault Current Limiter(SFCL) development mainly has focused on the application of commercializaton and power system through combining with normal-conducting device, moving away from current-limiting method, which is solely dependant on the existing superconductor. Compared to the structural development above, on the other hand, the research on applying superconducting current-limiting element to SFCL, the heart of SFCL, still has a lot left to do, apart form traditional resistive type SFCL. In this study, we looked into the current limiting characteristic of SFCL using core and coil. YBCO coated conductor with stainless steel stabilizer layer was verified by the excellent of current-limiting element of the resistive type SFCL that has a high Jc and index as well as being superior in mechanical property. Also, we study temperature characteristics and resistance characteristics, max voltage, response time and current-limiting ability that can be an indicator as current-limiting element while applying to superconducting current-limiting element caused by variation of winding direction, winding ratio of SFCL using core and coil.

This study estimated experimentally the loss distribution caused by magnetic friction in magnetic parts of a superconductor flywheel energy storage system (SFES) to obtain information for the design of high efficiency SFES. Through the spin down experiment using the manufactured vertical shaft type SEES with a journal type superconductor magnetic bearing (SMB), the coefficients of friction by the SMB, the stator core of permanent magnet synchronous motor/generator (PMSM/G), and the leakage flux of the metal parts were calculated. The coefficients of friction by the stator core of PMSM/G in case of using Si-steel and an amorphous core were calculated. The energy loss by magnetic friction in the stator core of PMSM/G was much larger than that in the other parts. The level of friction loss could be reduced dramatically using an amorphous core. Energy loss by the leakage magnetic field was small. On the other hand, the energy loss could be increased under other conditions according to the type of metal nearby the leakage magnetic fields. In manufactured SFES, the rotational loss by the amorphous core was approximately 2 times the loss of the superconductor and leakage. Moreover, the rotational loss by the Si-steel core is approximately 3 similar to 3.5 times the loss of superconductor and leakage.

- In this paper , the relative stability of magnetic bearing system for the flywheel energy storage is evaluated using both simulation and experimental analysis. We make the simulation model for the magnetic bearing flywheel system using the rigid body shaft model. According to international standard ISO 14839-3, We experimentally analyzed the relative stability of magnetic bearing system . Additionally using both the simulation model and experimental tests , Phase margin and Gain margin is acquired through Nyquist plot.Key Words : Flywheel, Relative stability, Magnetic levitation† 교신저자, 정회원 : 한전 전력연구원 선임연구원E-mail : bcpark@kepri.re.kr*비 회 원 : 한전 전력연구원 선임연구원** 비 회 원 : 한전 전력연구원 책임연구원․공박***정 회 원 : 한전 전력연구원 연구원․공박§ 정 회 원 : 한전 전력연구원 책임연구원․공박§§ 비 회 원 : 한전 전력연구원 연구원 접수일자 : 2010년 6월 24일 최종완료 : 2010년 7월 28일 1. 서 론 플라이휠의 에너지 저장용량은 회전속도의 제곱에 비례하기 때문에 에너지 저장밀도를 향상시키기 위해서는 회전속도를 높이는 것이 필요하며, 이때 회전축을 지지해주는 베어링의 성능은 최대회전속도의 향상에 직접적인 관계를 가지고 있다. 비접촉식 자기부상베어링은 회전속도가 볼베어링에 비해 높으며, 수명이 길고 진공환경에서 적용하기에 적절한 장점을 가지고 있어 터보진공펌프, 공작기계, 터보압축기, 플라이휠 에너지 저장 장치 등에 상업화가 이루어졌거나 적용 연구가 진행되고 있다.[4][5][6][7]자기부상베어링은 feedback 제어가 없으면 기본적으로 불안정한 특성을 가지므로 제어기, 증폭기, 전자석 구동기, 위치센서로 구성되어 있는 것이 일반적이다. 이때 제어기는 자기베어링시스템의 불안정한 pole을 안정한 영역으로 이동시키는 역할을 한다. 본 논문에서 자기베어링에 사용한 제어기는 PD제어기로써, 적절한 P 게인, D 게인을 tunning 함으로써 자기베어링이 안정영역에서 동작하도록 제어기를 설계하였다. 본 논문에서 실험에 사용한 플라이휠 에너지 저장장치의 사진은 그림 1 의 5kWh급 플라이휠 에너지 저장장치 시스템이다. 이 시스템에서 실험하고 있는 회전축은 두 가지이며 첫 번째는 회전에너지를 주로 저장하는 부위가 회전축의 복합재 부위로써, 정격속도(18,000rpm)에서 사용가능한 저장 에너지가 5kWh인 회전축 이며, 두 번째는 고속회전 및 전동/발전기 검증용으로 사용하는 스틸로터형(steel rotor) 회전축으로써 회전에너지를 주로 저장하는 부위가 STS304로 제작된 형태이며, 본 논문에서는 스틸로터형 회전축에 대해 시뮬레이션 및 실험을 하였다. 그림 1 5kWh급 플라이휠 에너지 저장장치Fig. 1 5kWh flywheel energy storage그림 2는 본 논문에서 사용한 플라이휠 에너지저장장치의 주요구성품들의 개략도를 보여준다. 본 플라이휠 에너지저장장치는 스틸로터 휠, 전동/발전기, 자기베어링, 회전축으로 구성되어 있다. 회전축은 비자성체이며 가공성이 양호한 STS304를 사용하였다. 전동/발전기는 slotless형 동기 영구자석 전동/발전기로써 정격출력 10kW, 정격속도 22,000rpm, 최대토크는 4.53 Nm의 성능을 가진다. 본 전동/발전기는 회전손실을 최소화 하기위해 slotless형으로 설계/제작 하였다.

The yttrium-barium-copper-oxide (YBCO) coated conductor, which supplement the fault of the existing superconducting current-limit materials YBCO thin film, bismuth-strontium-calcium-copper-oxide(BSCCO) wire and bulk, has been improved its mechanical weakness and has high index; hence, after quench YBCO coated conductor could limit the fault current effectively because of fast resistance occurrence speed. Furthermore, it has wide applicable area as an current limit material because it shows different resistance occurrence tendency by the thickness and kind of stabilization material sputtered on the superconducting layer. Therefore, many researchers are carrying out the study of application of YBCO coated conductor to superconducting fault current limiter (SFCL) for making high quality current limit element, based on resistance type. On the other hand, the study for other type except resistance type has been rarely conducted for the application of YBCO coated conductor to SFCL as an current limit element. Consequently, in this study, YBCO coated conductor with different stabilization layer Cu and Stainless steel, is applied to SFCL using iron core and coil, and examine the many index points as an current limit element, such as current limit characteristic, the tendency of resistance occurrence, response time, the temperature trend for stability.

The most important thing in developing a superconducting fault current limiter (SFCL) is to find the maximum operating condition for each current-limiting element to increase its SFCL capacity. The maximum operating condition can be defined using Vmax, Tr, Imax and Iq, which are detected after the quenching of the SFCL. In this study, YBCO coated conductor whose characteristics were proved as the superconducting fault current limiting element was used to test the operating characteristics of the unit current limiting element and to find the maximum operating condition using Vmax, Tr, Imax and Iq, which are detected after the quenching against the fault current according to the fault angle. YBCO coated conductors used in the test are one wire with stainless-steel stabilizing layer and one wire with no stabilizing layer. Critical current value is 70 Arms and the critical temperature is 90 K. The YBCO coated conductor with non stabilizing layer had a critical current of 80 Arms and a critical temperature of 90 K. Therefore, the two YBCO coated conductors in this study had different critical currents and an identical critical current of 90 K.