• 한국지열·수열에너지학회논문집
• /
• 제16권3호
• /
• pp.8-16
• /
• 2020

This paper presents the heating performance analysis results of a ground-source heat pump (GSHP) system using hybrid ground heat exchanger (HGHE). In this paper, the HGHE refers to the ground heat exchanger (GHE) using both a surface water heat exchanger (SWHE) and a vertical GHE. In order to evaluate the system performance, we installed monitoring sensors for measuring temperatures and power consumption, and then measured operation data with 4 different load burdened ratios of the HGHE. During the entire measurement period, the average heating capacity of the heat pump was 37.3 kW. In addition, the compressor of the heat pump consumed 9.4 kW of power, while the circulating pump of the HGHE used 6.7 kW of power. Therefore, the average heating coefficient of performance (COP) for the heat pump unit was 4.0, while the system including the circulating pump was 2.7. Finally, the parallel use of SWHE and VGHE was beneficial to the system performance; however, further researches are needed to optimize the design data for various load ratios of the HGHE.

• 전자공학회논문지C
• /
• 제35C권2호
• /
• pp.36-47
• /
• 1998

Low power circuit techniques have been developed to realize the highest possible performance of embedded SRAM at 1V power supply with$0.5\mu\textrm{m}$ single threshold CMOS technology in which the unbalance between NMOS and PMOS threshold voltages is utilized to optimize the low power CMOS IC design. To achieve the best trade-off between the transistor drivability and the subthreshold current increase, the ground potential of memory array is raised to suppressthe subthreshold current. The problems of lower cellstability and bit-line dealy increase due to the enhanced array ground potential are evaluated to be controlled within the allowable range by careful circuit design. 160MHz, 128kb embedded SRAM with 3.4ns access time is demonstrated with the power consumption of 14.8mW in active $21.4{mu}W$ in standby mode at 1V power supply.

• 한국철도학회:학술대회논문집
• /
• 한국철도학회 2006년도 추계학술대회 특별세미나 특별세션
• /
• pp.209-218
• /
• 2006

This paper presents the comparison and analysis of the power supply system of a Maglev train and conventional electric railway. Even though all Maglev trains have batteries on their vehicles, electric power supply from the ground side is necessary for levitation, propulsion, on-board electrical equipment, battery recharging, and so on. At low speeds up to $100{\sim}150(km/h)$, the Maglev train, generally, uses a mechanical contact, a current collector as same as conventional electric railway. However, at high speeds, the Maglev train can no longer obtain power from the ground side by using a mechanical contact. Therefore, high speed Maglev trains use their own way to deliver the power to the vehicle from the ground. In this paper, the power supply systems of the german, japanese, and korean low- and high-speed Maglev trains have been reviewed.

• 한국마린엔지니어링학회:학술대회논문집
• /
• 한국마린엔지니어링학회 2005년도 전기학술대회논문집
• /
• pp.412-416
• /
• 2005

In this paper we propose low-impedance and miniaturized a wilkinson power divider on MMIC passive component which was fabricated by a novel microstrip line structure employing periodically perforated ground metal (PPGM). The novel microstrip line structure showed much lower impedance and shorter guided-wavelength than conventional one. Using the novel microstrip line with periodically perforated ground metal, a miniaturized 17 ${\Omega}$ power divider was fabricated. The line width of the power divider was 20 ${\mu}m$, and the size of it was 0.110 $mm^2$, which is 21 % of conventional one. The power divider exhibited good RF performances from 10 to 20 GHz.

• Nuclear Engineering and Technology
• /
• 제48권1호
• /
• pp.211-217
• /
• 2016

Most nuclear power plants now utilize solid grounded low voltage systems. For safety and reliability reasons, the low voltage (LV) high resistance grounding (HRG) system is also increasingly used in the pulp and paper, petroleum and chemical, and semiconductor industries. Fault detection is easiest and fastest with a solidly grounded system. However, a solidly grounded system has many limitations such as severe fault damage, poor reliability on essential circuits, and electrical noise caused by the high magnitude of ground fault currents. This paper will briefly address the strengths and weaknesses of LV grounding systems. An example of a low voltage HRG system in the LV system of a nuclear power plant will be presented. The HRG system is highly recommended for LV systems of nuclear power plants if sufficient considerations are provided to prevent nuisance tripping of ground fault relays and to avoid the deterioration of system reliability.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 2003년도 하계학술대회 논문집 D
• /
• pp.2666-2668
• /
• 2003

The most widely employed grounding apparatus in distribution systems is a driven rod. But this method has some difficulties to get a specified ground resistivity in cities or islands. Recently, the new ground apparatus are proposed. This paper describes the research which relates with the system to evaluate the performance of novel grounding apparatus.

• 대한전기학회논문지:전기물성ㆍ응용부문C
• /
• 제51권8호
• /
• pp.347-353
• /
• 2002

This paper presents an accurate method for measuring the ground resistance in powered grounding system. Most of substations and electric power equipments are interconnected to an extensive grounding network of overhead ground wires, neutral conductors of transmission lines, cable shields, and etc. The parasitic effects due to circulating ground currents and ground potential rise make a significant error in measuring the ground resistance. The test current transition method was proposed to reduce the effects of stray ground currents, ground potential rise and harmonic components in measurements of the ground resistance for powered grounding systems. The instrumental error of the test current transition method is decreased as the ratio of the test current signal to noise(S/N) increases. It was found from the test results that the proposed measuring method of the ground resistance is more accurate than the conventional fall-of-potential method or low-pass filter method, and the measuring error was less than 3[%]when S/N is 10.

• International Journal of Railway
• /
• 제7권3호
• /
• pp.71-79
• /
• 2014

Subway systems have been a proved method of public transport and are widely used in major cities around the world. However, the time and cost it takes to construct such systems are very high, as it requires underground tunnels. Cities in various countries have implemented monorail systems as public railway transport as it can be more economical and quicker compared to subway systems in terms of construction. In addition, it provides more convenience towards the public as it is not affected to traffic, and also provides an aerial view of the city. However, the overall construction cost for monorail systems is still significantly high, and as a possible solution to further reduce the overall cost, implementation of ground-level stations and wireless power transfer technology has been proposed in this paper. A concept application layout of ground-level stations and wireless power transfer systems has been discussed, using the Daegu monorail Line 3 system as a simulation base. The expected cost for monorail systems implementing ground-level stations and/or wireless power transfer technology has been estimated based on literature survey, and was compared with the current construction cost of Daegu monorail system. Based on comparison, it has shown that implementation of ground-level stations are the most economical, and can be easily implemented for either starting or expanding the monorail line. Implementation of wireless power transfer technology is also economical, but is more feasible when starting a new monorail line as it requires components which will alter the configuration of the train and infrastructure.

• 한국지진공학회논문집
• /
• 제25권5호
• /
• pp.223-232
• /
• 2021

The spatial variation characteristics of seismic motions at the nuclear power plant's site and structures were analyzed using earthquake records obtained at the Fukushima nuclear power plant during the Great East Japan Earthquake. The ground responses amplified as they approached the soil surface from the lower rock surface, and the amplification occurred intensively at about 50 m near the ground. Due to the soil layer's nonlinear characteristics caused by the strong seismic motion, the ground's natural frequency derived from the response spectrum ratio appeared to be smaller than that calculated from the shear wave velocity profile. The spatial variation of the peak ground acceleration at the ground surface of the power plant site showed a significant difference of about 0.6 g at the maximum. As a result of comparing the response spectrums at the basement of the structure with the design response spectrum, there was a large variability by each power plant unit. The difference was more significant in the Fukushima Daiichi site record, which showed larger peak ground acceleration at the surface. The earthquake motions input to the basement of the structure amplified according to the structure's height. The natural frequency obtained from the recorded results was lower than that indicated in the previous research. Also, the floor response spectrum change according to the location at the same height was investigated. The vertical response on the foundation surface showed a significant difference in spectral acceleration depending on the location. The amplified response in the structure showed a different variability depending on the type of structure and the target frequency.

• 한국철도학회:학술대회논문집
• /
• 한국철도학회 2005년도 추계학술대회 논문집
• /
• pp.736-741
• /
• 2005

This paper presents electric characteristics analysis and safe configuration for extension power supply between existent 6.6kV ungrounded distribution system and establishment and improvement 22.9kV direct grounding distribution system. For this, we model 6.6kV ungrounded and 22.9kV direct grounding distribution system of urban underground, ground region. and rural electrical, unelectrical region using PSCAD/EMTDC and analyze voltage drop, charging current, ground and short fault through simulation. To analyze electric characteristics of extension power supply, we simulate extension power supply of overhead line of 6.6kV ungrounded system and underground line of 22.9kV direct grounding system of rural electrical region and propose operation condition for safe extension power supply through result of analysis. Characteristics of voltage drop, charging current, ground and short fault appear almost similarly with electrical characteristic of direct power supply. However, because unbalance of phases may cause relay's malfunction of ungrounded system and ground fault current of direct grounding system may demage facilities of ungrounded system, we propose safe system configuration such as impedance grounding system of neutral point.