• 한국초전도ㆍ저온공학회논문지
• /
• 제14권3호
• /
• pp.38-42
• /
• 2012

Fixtures such as bushings in terminations of high temperature superconducting(HTS) power cable systems are subjected to high voltages, which have to transition from ambient to cryogenic temperatures. As such it is imperative to ensure the integrity of the dielectrics under all operating conditions, including thermal aspects brought about by the passage of current. Gaseous helium(GHe) at high pressure is regarded as a potential coolant for superconducting cables. The dielectric aspects of cryogenic helium gas are both complex and demanding. In this experimental study we looked at the interface between a smooth epoxy surface and high pressure helium gas in a homogeneous electric field. The alternating current(AC) flashover voltages of epoxy samples are presented. The results have been analyzed by using Weibull statistics. In addition to the behavior of the epoxy in gaseous helium as a function of pressure and temperature we also present data of the characteristics of the epoxy in mineral oil and in liquid nitrogen($LN_2$). The breakdown characteristics of a uniform field gap in gaseous helium as a function of pressure and temperature under AC, direct current(DC) and lightning impulse voltages are also given. Electric field calculations have been made for one of the experimental geometries in an attempt to explain some of the anomalies in the experimental results.

• 한국안전학회지
• /
• 제23권6호
• /
• pp.95-99
• /
• 2008

Halon was known as a cause of the ozone layer destruction. In 1987, it was designated as one of the ozone-layer-destroying materials in the Montreal Protocol. Therefore substitutes of Halon agent has been developed including inert gas extinguish system, which is one of the most widely used fire extinguishing system. This study intended to increase the efficiency of inert gas extinguishing agent by using inert gas additives. As IG-541 shows high extinguishing power, the experiment was performed to measure the effects of gaseous additives to it. Cup-burner fire extinguishing apparatus was used with n-Heptane fuel. Among many of pure inert gaseous agents, Helium showed the most excellent extinguishing power. When Helium was added to IG-541, fire extinguishing power was increased and the concentration of oxygen in chimney also risen. By adding Helium to IG-541, the effectiveness of inert gas fire extinguishing system is able to be increased.

• 한국초전도ㆍ저온공학회논문지
• /
• 제21권3호
• /
• pp.47-50
• /
• 2019

The paper gives the results of the experiments with a model two-section REBCO solenoid cooled by either gaseous helium (GHe) or sub-cooled/solid nitrogen (SN2) in (50-77) K temperature range. The major cooling source was a single-stage cryocooler Sumitomo CH-110 with the cooling power of 175 W and 130 W at 77 K and 50 K respectively. The coil itself was not directly conduction cooled. We compare the time taken by both coolants to obtain the temperature of the magnet of about 50 K and the homogeneity of the temperature distribution within the cryostat. Test results for the coil operation in solid nitrogen together with the comparison of its critical properties in SN2 and GHe are also presented.

• 한국추진공학회:학술대회논문집
• /
• 한국추진공학회 2009년도 제33회 추계학술대회논문집
• /
• pp.293-297
• /
• 2009

극저온 가압제를 사용하는 가압시스템에서 가압제의 공급을 차단하기 위하여 많이 사용되고 있는 밸브로는 공압구동밸브나 솔레노이드밸브, 파이로밸브 등이 있다. 공압구동밸브와 솔레노이드밸브는 파이로밸브에 비하여 구조가 복잡하고 무게가 무거운 단점이 있어, 본 연구에서는 극저온 및 고압에 적용이 가능하고 구조가 비교적 간단하고 무게가 가벼운 극저온 헬륨가스용 파이로밸브를 개발하여 내압 및 기밀시험과 진동시험, 극저온 공급시험을 수행하였다.

• 한국초전도ㆍ저온공학회논문지
• /
• 제25권4호
• /
• pp.65-69
• /
• 2023

Hydrogen is an eco-friendly energy source and is being actively researched in various fields around the world, including mobility and aerospace. In order to effectively utilize hydrogen energy, it should be used in a liquid state with high energy storage density, but when hydrogen is stored in a liquid state, BOG (boil-off gas) is generated due to the temperature difference with the atmosphere. This should be re-condensed when considering storage efficiency and economy. In particular, large-capacity liquid hydrogen storage tank is required a gaseous helium circulation cooling system that cools by circulating cryogenic refrigerant due to the increase in heat intrusion from external air as the heat transfer area increases and the wide distribution of the gas layer inside the tank. In order to effectively apply the system, thermo-hydraulic analysis through process analysis is required. In this study, the condenser design and system characteristics of a gaseous helium circulation cooling system for BOG recondensation of a liquefied hydrogen storage tank were compared.

• 한국추진공학회:학술대회논문집
• /
• 한국추진공학회 2009년도 제33회 추계학술대회논문집
• /
• pp.363-367
• /
• 2009

산화제로 액체산소를 사용하고 산화제 탱크 내부에 가압제 용기가 설치된 액체추진기관의 가압시스템에서는 가압제 용기에서 극저온으로 토출되는 가압제가 가스발생기 후단의 열교환기를 통과하여 극저온에서 고온으로 온도가 상승되어 추진제 탱크의 얼리지로 공급된다. 이러한 가압시스템을 개발하기 위해서는 열교환기를 모사할 수 있는 가열장치를 적용하여 인증시험을 수행하여야 한다. 본 연구에서는 가압시스템 개발시험에 적용할 수 있는 극저온 헬륨가스 가열장치를 개발하였고 이에 대한 가열시험을 수행하였다.

• 한국추진공학회지
• /
• 제15권1호
• /
• pp.63-68
• /
• 2011

산화제로 액체산소를 사용하고 산화제 탱크 내부에 가압제 용기가 설치된 액체추진기관의 가압시스템에서는 가압제 용기에서 극저온으로 토출되는 가압제가 가스발생기 후단의 열교환기를 통과하여 극저온에서 고온으로 온도가 상승되어 추진제 탱크의 얼리지로 공급된다. 이러한 가압시스템을 개발하기 위해서는 열교환기를 모사할 수 있는 가열장치를 적용하여 인증시험을 수행하여야 한다. 본 연구에서는 가압시스템 개발시험에 적용할 수 있는 극저온 헬륨가스 가열장치를 개발하였고 이에 대한 가열시험을 수행하였다.

• 한국초전도ㆍ저온공학회논문지
• /
• 제9권3호
• /
• pp.72-82
• /
• 2007

This paper relates to reducing the temperature of a cryogenic liquid by contacting it with gas bubbles, which can be characterized by diffusion-driven evaporative cooling, The characteristic of diffusion-driven evaporative cooling is thoroughly examined by theoretical. analytical and experimental methods specifically for the case of helium injection into liquid oxygen. The results reveal that if the gaseous oxygen partial pressure in helium bubbles is lower than the liquid oxygen vapor pressure, cooling occurs autonomously due to diffusion mass transfer. The method of lowering the injected helium temperature turns out to be very effective for cooling purpose.

• 한국초전도ㆍ저온공학회논문지
• /
• 제14권1호
• /
• pp.25-29
• /
• 2012

The novel type of cable under consideration is cooled by gaseous Helium at elevated pressure. Helium is known for having poor electric breakdown strength; therefore the dielectric capabilities of this type of cable must be tested under conditions similar to the envisaged operation. In order to study the dielectric performance we have designed and built a novel high pressure cryostat rated at 2.17 MPa which has been used for testing model cables of lengths of up to 1 m. The cryostat is an open system where the gas is not re-circulated. This allows maintaining a high purity of the gas. The target temperature range is between 40 K and 70 K. This substantially increases the critical current density of the HTS compared to 77 K, which is the typical temperature of cables cooled by liquid nitrogen. The cryostat presented allows for adjusting the temperature and keeping it constant for the time necessary to run a complete dielectric characterization test. We give a detailed description of the cryostat. Measurements of partial discharge inception voltages as well as the temperature distribution along the model cables as a function of time are presented.

• 한국초전도ㆍ저온공학회논문지
• /
• 제13권1호
• /
• pp.27-30
• /
• 2011

A sub-cooled liquid nitrogen cooling system is known as a most promising method to develop large scale superconducting apparatuses such as superconducting fault current limiters and superconducting cables [1]. Gaseous helium (GHe), gaseous nitrogen ($GN_2$) and sulfur hexafluoride ($SF_6$) are commonly used for designing an high voltage applied superconducting device as an injection gaseous medium [2, 3]. In this paper, the analysis on the dielectric characteristics of GHe, $GN_2$ and $SF_6$ are conducted by designing and manufacturing sphere-to-plane electrode systems. The AC withstand voltage experiments on the various gaseous insulation media are carried out and the results are analyzed by using finite element method (FEM) considering field utilization factors (${\xi}$). It is found that the electric field intensity at sparkover ($E_{MAX}$) of insulation media exponentially decreases according to ${\xi}$ increases. Also, the empirical expressions of the functional relations between $E_{MAX}$ and ${\xi}$ of insulation media are deduced by dielectric experiments and computational analyses. It is expected that the electrical insulation design of applied superconducting devices could be performed by using the deduced empirical formulae without dielectric experiments.