• 한국전기전자재료학회논문지
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• 제36권3호
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• pp.280-285
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• 2023

A breakdown voltage and breakdown electric field of the transformer insulating oil of liquid dielectric were studied in uniform electric field and non-uniform electric field and the transformer insulating oil was observed by the process reached breakdown. Insulation performance evaluation of the liquid dielectric was evaluated at the electrode spacing of 2.5 mm under the conditions of domestic and international standards (KS C IEC 60156), so a comparative review was conducted at the electrode spacing of 2.5 mm. When the electrode spacing is 2.5 mm, the average breakdown voltage is 38.5 kV for sphere-sphere electrodes, 26.6 kV for plate-plate electrodes, 22.9 kV for needle-needle electrodes, and 24.3 kV for sphere-needle electrodes. 23.7 kV for the sphere-plate electrode, and 20.7 kV for the needle-plate electrode. From these results, it can be seen that the average value of the breakdown voltage at the electrode spacing of 2.5 mm, in ascending order, is sphere-sphere, plate-plate, sphere-needle, sphere-plate, needle-needle and needle-plate. It was found that the breakdown voltage of the unequal field was lower than that of the equal field.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2001년도 춘계학술대회 논문집
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• pp.1080-1084
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• 2001

In manufacturing a micro die with half spherical cavity by MEDM, it is necessary to prepare an electrode with the same shape. This paper suggests a simple method to manufacture a half spherical electrode based on tool wear. The tool wears more rapidly at the edge of a cylindrical electrode. In order to make a half spherical micro electrode, cylindrical electrode was fed into the workpiece by the distance of its radius. The d/R(depth/Radius) value varied with respect to capacitance and electrode diameter. The smaller the size of electrode was, the closer the electrode tip geometry approached to a half sphere.

• 한국화재소방학회논문지
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• 제10권1호
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• pp.3-9
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• 1996

Electrostatic charge is generated in large scale or high speed processes dealing with materials with large resistance, or under complicated condition. Fire and explosion often occur due to electrostatic charge accumulated in flammable gases, vapor, liquids and powder. It is usually very difficult to verify the cause of accidents as well as the prevention. In this study, it is shown that the needle electrode needs the electrode gap from 1.8mm to 3.8mm, sphere electrode and plate electrodes need the electrode gap of 1.9mmfor the minimum ignition energy. The sphere electrode and the plate electrode requires 12.8mJ and 3.2mJ of minimum ignition energy respectively with the electrode gap of 1.1mm. The ignition voltage rises to very large value as the ground resistance increases.

• 조명전기설비학회논문지
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• 제19권1호
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• pp.44-51
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• 2005

본 연구에서는 구-구갭을 수평 배치하였을 때, 연소화염에 의한 교류 및 직류 플래시오버전압 특성을 조사하였다. 화염에 의한 플래시오버 극성을 조사하기 위해 전압 및 전류파형을 측정하였으며, 플래시오버가 발생되기 전에 쿨롱력에 의한 화염의 형상 변화를 관찰하였다. 또한 플래시오버 전압의 저하 요인으로서 상대공기밀도의 저하 및 연소화염의 열전리 영향에 대해 고찰하였다. 실험 결과, 구-구갭에서 접지측 전극과 갭길이의 비를 k라고 할 때, 화염위치 k:0(접지측), k=0.5(중앙부) 및 k=1.0(전원측)인 경우 화염에 의한 교류 섬락전압의 평균값은 화염이 없을 때에 비해 각각 79.9, 82.9 및 $87.5[\%]$ 저하되었으며, 또한 화염의 높이 h=0, h=5 및 h=9[cm]일 때 교류 플래시오버 전압의 평균값은 화염이 없는 경우를 기준으로 하였을 때 각각 85.0, 40.8 및 $28.2[\%]$ 저하되었다. 소규모 연소화염에서의 열전리 영향은 크지 않는 것으로 나타났다.

• 한국전기전자재료학회논문지
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• 제28권6호
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• pp.396-399
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• 2015

We analyzed the correlation between breakdown voltage(BDV) of liquid nitrogen(LN2) and factors. The chosen factors affecting the breakdown are the diameter of electrode, gap length, temperature of LN2, and pressure of LN2. The BDV of LN2 was increased with increasing the diameter, the gap length and the pressure. And The BDV of LN2 was increased with decreasing the temperature. However, correlation coefficient was different from each other depending on the situation. The BDV exhibited a very high correlation coefficient of 0.92227 to dependence on the diameter. And a very high correlation coefficient of 0.94980 to dependence on the pressure under sphere(D 7.5 mm)-plane electrode. When the pressure is applied, sphere-plane electrode is the correlation coefficient was higher than that of the needle-plane electrode. It shows the dependence of a temperature coefficient of -0.758290 ~ -0.39946 under needle-plane electrode.

• 한국전기전자재료학회논문지
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• 제36권4호
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• pp.408-412
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• 2023

In this paper, in order to analyze high electrical insulation and cooling performance using mineral oil, the liquid insulating oil was changed in electrode shape and distance between electrodes to compare and analyze electrical characteristics according to equal electric field, quasi-equivalent electric field, and unequal electric field. As a result, the breakdown voltages were 36,875 V and 36,875 V in the form of sphere-sphere and plate-plate electrodes with equal electric fields. The breakdown voltage was 31,475 V in the sphere-plate electrode type, which is a quasi-equilibrium field, and the breakdown voltage was 28,592 V, 27,050 V, and 22,750 V in the needle-needle, sphere-needle, and needle-plate electrode types, which are unequal fields. Through this, it is possible to know the difference in breakdown voltage according to the type of electric field. The more equal the field, the higher the breakdown voltage, and the more unequal field, the lower the breakdown voltage. The difference in insulation breakdown voltage could be seen depending on the type of electric field, the insulation breakdown voltage was higher for the more equal electric field, and the insulation breakdown voltage was lower for the more unequal electric field. Also, it was confirmed that the closer the distance between the electrodes, the higher the insulation breakdown voltage, the higher the insulation breakdown current, and the insulation breakdown voltage and the insulation breakdown current were proportional.

• 한국초전도ㆍ저온공학회논문지
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• 제17권3호
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• pp.33-36
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• 2015

A liquid nitrogen ($LN_2$) is usually used to be a coolant and insulant for a HTS coil system. HTS wires for a superconducting apparatus may be surrounded by gaseous nitrogen ($GN_2$) due to film boiling generated by a quench or voids occurred by electrical breakdown. The increased maximum electric field intensity at $GN_2$ may result in the degradation of dielectric strength of a HTS coil system. In this paper, a study on the dielectric characteristics of a composite insulation system composed of $LN_2$ and $GN_2$ is performed. A sphere-to-plane electrode system made with stainless steel is used to perform the experiments under AC and lightning impulse voltage condition. A sphere electrode is surrounded by $GN_2$ and a plane electrode is immersed into $LN_2$ to conduct dielectric experiments with a composite insulation system. The dielectric experiments are performed according to the level of $LN_2$ from the plane electrode to a sphere electrode. It is found that the dielectric characteristics of a composite insulation system are dependent on the level of $LN_2$ and the field utilization factor of an electrode system.

• 전기화학회지
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• 제17권2호
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• pp.124-129
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• 2014

본 논문에서는 리튬/공기 이차전지의 공기전극에 사용될 수 있는 카본미소구체/$Fe_3O_4$ 나노복합체의 합성과 전기화학적 특성에 대해 보고하고 있다. 산화물 촉매 중 하나인 $Fe_3O_4$의 부족한 전도성을 보완하기 위해 카본미소구체와 복합화를 시도하였고 그 결과 카본미소구체 표면에 수 nm 크기의 $Fe_3O_4$를 균일하게 분산시켜 복합화 할 수 있었다. 이와 같이 미세하게 분산된 산화물 촉매와 카본과의 결합은 촉매의 비표면적을 넓히고 카본과 촉매와의 접촉면을 넓혀 전도성을 높임으로서 높은 촉매 활성을 기대할 수 있다. 카본미소구체/$Fe_3O_4$ 나노복합체를 이용하여 만든 전극은 카본미소구체를 사용한 전극에 비해 낮은 과전압과 상대적으로 안정한 사이클 특성을 관찰할 수 있었다.

• 한국조명전기설비학회:학술대회논문집
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• 한국조명전기설비학회 2007년도 추계학술대회 논문집
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• pp.259-262
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• 2007

In this paper approves AC high voltage by experimental GIS(Gas Insulated Switchgear) chamber and AC 300[kV] power source to study breakdown characteristics by pressure(P) change and change of electrode distance(d) at AC high voltage of Imitation Air(I-Air, $N_2$ : $O_2$ = 79(%) : 21[%]) to alternate $SF_6$ and achieved research. Gave P change of I-Air to study I-Air's breakdown characteristics using uniform(Sphere-Sphere electrode) and non-uniform fields(Needle-Plane electrode) and studied relations breakdown voltage($V_B$) by each P different d.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2005년도 춘계학술대회 논문집
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• pp.407-412
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• 2005

For micro electrochemical machining (ECM), tool electrodes with various sizes and shapes are necessary. In this paper, tool electrodes were fabricated by micro electrical discharge machining (EDM). Electrode material is tungsten carbide which has high rigidity and good conductivity for micro electrochemical machining. Disk-type and sphere-type electrodes were fabricated to prevent taper shape of side walls or to produce spherical features. Various 3D micro structures were fabricated by electrochemical milling with developed electrodes.