• KEPCO Journal on Electric Power and Energy
• /
• 제2권2호
• /
• pp.307-310
• /
• 2016

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.

• 한국수소및신에너지학회논문집
• /
• 제32권5호
• /
• pp.365-373
• /
• 2021

In this study, evaporation of LN2 non-spreading pool on concrete plate was dealt with experimentally. The thermophysical properties of concrete, which is a composite material, were obtained by minimizing the difference between the numerical analysis results obtained from the assumed properties and the results from experiments. The thermal energy required for evaporation of the liquid pool is supplied from the concrete plate and the wall of the container. As a result of the measurement, the thermal energy flowing in from the wall was negligible compared to the one supplied from the concrete plate. It was found that the measured evaporation rate of the liquid pool by the heat energy supplied through the concrete plate agrees well with the PTC model except for the initial section of the experiment. The validity of the semi-infinite assumption and the one-dimensional assumption, which are the main conditions of the PTC model, was also verified through experiments. The evaporation rate model in the non-spreading pool discussed in this study can provide a basic frame for the one in the spreading pool, which is a meaningful result considering that the spreading pool is very realistic compared to the non-spreading pool.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2004년도 추계학술대회 논문집 Vol.17
• /
• pp.331-336
• /
• 2004

Due to the outstanding insulating characteristics, Laminated Polypropylene paper (LPP) and Kraft paper have been used as ac power insulation for conventional cable. Recently, both of LPP and Kraft has been studied as main insulation fur high temperature superconducting (HTS) cable. Ifowever, studies on the use of LPP/Kraft paper for HTS cables are thinly scattered. In this paper, the comparison among LPP, Kraft and LPP/Kraft Samples impregnated with liquid nitrogen $(LN_2)$ on dielectric insulation characteristics was investigated. It was found from the experimental data that the breakdown strength becomes lower in the order LPP, Lpp/Kraft and Kraft but the lifetime indices n becomes lower in the order Kraft, LPP/Kraft, LPP. Moreover, partial discharge inception and dielectric loss tangent become lower in the order Kraft, LPP, LPP/Kraft.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 1998년도 하계학술대회 논문집 E
• /
• pp.1699-1701
• /
• 1998

This paper was studied on the surface discharge characteristics on the solid insulators in the Liquid Nitrogen($LN_2$) at atmospheric pressure. Liquid Nitrogen has been widely used as a tooling and insulating materials for superconducting and cryogenic cable. Considering the effect of bubbles, we observed tracking Phenomena on the surface of solid insulators and investigated surface breakdown characteristics of several solid insulators.

• Structural Engineering and Mechanics
• /
• 제68권5호
• /
• pp.519-526
• /
• 2018

In this article, experimental training of the commercial available shape memory alloy fibre (SMA) fibre under the combined thermomechanical loading is reported. SMA has the ability to sense a small change in temperature (${\geq}10^{\circ}C$) and activated under the external loading and results in shape change. The thermomechanical characteristics of SMA at different temperature and mechanical loading are obtained through an own lab-scale experimental setup. The analysis is conducted for two types of the medium using the liquid nitrogen (cold cycle) and the hot water (heat cycle). The experimental data indicate that SMA act as a normal wire for Martensite phase and activated behavior i.e., regain the original shape during the Austenite phase only. To improve the confidence of such kind of behavior has been verified by inspecting the composition of the wire. The study reveals interesting conclusion i.e., while SMA deviates from the equiatomic structure or consist of foreign materials (carbon and oxygen) except nickel and titanium may affect the phase transformation temperature which shifted the activation phase temperature. Also, the grain structure distortion of SMA wire has been examined via the scanning electron microscope after the thermomechanical cycle loading and discussed in details.

• 전기학회논문지
• /
• 제61권10호
• /
• pp.1471-1476
• /
• 2012

A study on the dielectric characteristics of the Glass Fiber Reinforced Plastic (GFRP) is important for designing a reliable high voltage superconducting machines such as transmission superconducting fault current limiters, superconducting cables, and superconducting transformers. In this paper, dielectric experiments of the GFRP under lightning impulse voltage are conducted in liquid nitrogen($LN_2$) according to various experimental conditions such as the thicknesses of the GFRP, the diameters of electrode systems and the pressures. The dielectric characteristics of the GFRP are analyzed by using a Finite Elements Method(FEM) according to various field utilization factors. It has been reported that the electrical insulation design of the GFRP would be conducted by considering the mean electric field intensity($E_{mean}$) distributed inside the GFRP. In this study, it is found that the dielectric performance of the GFRP could be explained by not only $E_{mean}$ but also the maximum electric field intensity ($E_{max}$). Finally, the empirical formulae of the GFRP to estimate an electrical breakdown voltage at sparkover under the lightning impulse condition are deduced. It is expected that the presented experimental results in this paper are helpful to design electrically reliable high voltage superconducting machines using the GFRP as an insulation material.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2002년도 하계학술대회 논문집
• /
• pp.494-498
• /
• 2002

HTS transformer experimentally. High temperature superconductors can only be applied against an engineering specification that has to be determined for each particular application form the design requirements for economic viability and for operation margins in service. High temperature superconducting(HTS) power apparatus are very promising candidates for application. Especially, these advantages make superconducting transformers very promising candidates for application in electrical power engineering and locomotives. In order to realize the HTS transformer, it is necessary to establish the high voltage insulation technique in cryogenic temperature. So far, insulation research of Pancake type HTS transformer is lacking nothing but insulation research of . solenoid type transformer consisted. Therefore, the composite insulation of double pancake coil type transformer are described and ac breakdown voltage characteristics of liquid nitrogen(LN$_2$) under HTS pancake coil electrode made by Bi-2223/Ag are studied. Breakdown in LN$_2$ is dominated electrode shape and distance. The relation between surface flashover voltage is considered for FRP. This research presented basis information of electrical insulation design for double pancake coil type HTS transformer.

• Transactions on Electrical and Electronic Materials
• /
• 제6권6호
• /
• pp.294-300
• /
• 2005

According to the trend for electric power equipment of high capacity and reduction of its size, the needs for the new high performance electric equipments become more and more important. On of the possible solution is high temperature superconducting (HTS) power application. Following the successful development of practical HTS wires, there have been renewed activities in developing superconducting power equipment. HTS equipments have to be operated in a coolant such as liquid nitrogen ($LN_2$) or cooled by conduction-cooling method such as using Gifford-McMahon (G-M) cryocooler to maintain the temperature below critical level. In this paper, the dielectric strength of some insulating materials, such as unfilled epoxy, filled epoxy, and polyimide in $LN_2$ was analyzed. Epoxy is a good insulating material but fragile at cryogenic temperature. The filled epoxy composite not only compensates for this fragile property but enhances its dielectric strength.

• 한국전기전자재료학회논문지
• /
• 제26권7호
• /
• pp.545-549
• /
• 2013

To realize the high-Tc superconducting (HTS) DC cable system, it is important to study not only high current capacity and low loss of conductor but also optimum electrical insulation at cryogenic temperature. A model HTS DC cable system consists of a HTS conductor, semi-conductor, cooling system and insulating materials. Polypropylene laminated paper (PPLP) has been widely adopted as insulating material for HTS machines. However, the fundamental insulation characteristics of PPLP for the development of HTS DC cable have not been revealed satisfactorily until now. In this paper, we will discuss mainly on the breakdown characteristics of 3 sheets PPLP in liquid nitrogen ($LN_2$). The characteristics of the diameter, location of butt-gap, distance between butt-gap length, pressure effect, polarity effect under DC and impulse voltage were studied. Also, the DC polarity reversal breakdown voltage of mini-model cable was measured in $LN_2$ under 0.4 MPa.

• 한국추진공학회지
• /
• 제20권6호
• /
• pp.91-100
• /
• 2016

액체로켓엔진에 적용되는 원심형 터보펌프의 효율특성을 실험적으로 고찰하였다. 펌프 단품에 대한 시험결과를 토대로 터보펌프 조립체의 성능을 예측하면서 시험매질에 따른 펌프의 효율특성에 대한 변화를 분석하였다. 펌프에 적용된 작동유체로 단품시험을 위해서는 상온 청수와 액체질소, 터보펌프 조립체 시험에서는 케로신(Jet A-1)과 액체산소(LOX)가 적용되었다. 설계점과 탈설계점 영역을 포함하는 전반적인 작동조건에 대하여 펌프의 효율특성을 파악하였고, 단품시험으로부터 실매질 환경에서 보정된 펌프효율을 구할 수 있었다.