• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2004년도 추계학술대회 논문집 Vol.17
• /
• pp.636-639
• /
• 2004

This paper presents the fabrication and performance evaluation of zinc oxide varistors for the arresters used for station system. ZnO varistors were fabricated with typical ceramic production methods and the structural and electrical characteristics were investigated. All varistors exhibited high density, which were in the range of $5.41{\sim}5.49g/cm^3$. In the electrical properties the reference voltage increased in the range of $4.410{\sim}5.250kV$ with increasing their thickness and the residual voltage exhibited the same trends as the reference voltage. In the long duration current impulse withstand test, E-2 and F-1 samples failed in the two and four shots, respectively, but E-1 and F-2 samples survived 18 shots during the test. Before and after this test, the variation ratio of residual voltage of E-1 and F-2 samples were -0.34% and 0.05%, respectively, which were in the acceptance range of 5%. According to the results of tests, it is thought that if the fabrication process such as insulating coating, sintering condition, and soldering method is improved, these ZnO varistors would be possible to apply to the station class arresters in the new future.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2003년도 하계학술대회 논문집 Vol.4 No.2
• /
• pp.1106-1110
• /
• 2003

The electrical characteristics of $A{\sim}C's$ ZnO varistors fabricated according to variable sintering condition, which sintering temperature is $l130^{\circ}C$ and speeds of pusher are A: 2mm/min, B: 4mm/min, C: 6 mm/min, respectively, were investigated. The varistor voltage of $A{\sim}C's$ ZnO varistors sintered at $1130^{\circ}C$ increased in order A < B $A{\sim}C's$ ZnO varistors exhibited below 2mA at rated voltage. Lightning impulse residual voltage of A's ZnO varistor suited standard characteristics, which is 3.85kV at 2.5kA, 4.4kV at 5kA and 5.16kV at 10kA. After multi lightning impulse residual voltage test of A's ZnO varistor exhibited good discharge characteristics which ZnO varistor reveals no evidence of puncture, flashover, cracking in visual examination. After high current impulse test of A's ZnO varistor exhibited good discharge characteristics, which variation rate of residual voltage is 0.4% before and after test, and revealed no evidence.

• 한국강구조학회 논문집
• /
• 제10권2호통권35호
• /
• pp.303-315
• /
• 1998

크레인 주행거더에 발생된 피로균열에 대한 보수방법으로 stop-hole(5mm 또는 9mm), stop-hole에 고력볼트 체결, 용접. 첨판과 고력볼트에 의한 4가지 보수방법을 적용하였다. 이중에서 stop-hole로 보수를 한 경우와 용접보수를 한 경우에는 재균열이 발생하였다. 그러나 stop-hole에 고력볼트를 체결한 경우 및 첨판과 고력볼트로 보수한 경우에는 재균열이 발생하지 않았다. 보수전과 보수후 피로강도를 비교해보면 stop-hole 또는 stop-hole과 고력볼트로 보수를 한 경우에는 모두 보수전과 동등한 피로강도를 얻었다. 용접보수를 할 경우에는 정확한 시공이 시행되면 보수전과 동등한 피로강도를 기대할 수 있지만. 시공이 잘못되면 피로강도가 현저하게 저하될 수 있음을 알 수 있었다. 피로균열이 발생된 위치에 첨판과 소요볼트를 시공할 수 있는 조건이라면 첨판과 고력볼트로 보수하는 것이 가장 확실한 보수법임을 알 수 있었다.

• 한국전기전자재료학회논문지
• /
• 제15권2호
• /
• pp.190-197
• /
• 2002

In this thesis, ZnO varistors with various formulation, such as A∼E, were fabricated according to ceramic fabrication method. The microstructure, electrical properties, and surge characteristics of ZnO varistors were investigated according to ZnO varistors with various formulation. In the microstructure, A∼E\`s ZnO varistor ceramics sintered at 1130$\^{C}$ was consisted of ZnO grain(ZnO), spinel phase (Zn$\_$2.33/Sb$\_$0.67/O$\_$4/), Bi-rich phase(Bi$_2$O$_3$) and intergranuler phase, wholly. Lightning impulse residual voltage of A, B, C and E\`s ZnO varistors suited standard characteristics, below 12kV at current of 5kA. On the contrary, D\`s ZnO varistor exhibited high residual voltage as high reference voltage. In the accelerated aging test, leakage current and watt loss of B, C and D\`s ZnO varistors increases abruptly with stress time under the first a.c. stress(115$\^{C}$/3.213kV/300h). Consequently, C varistor exhibited a thermal run away. On the contrary, leakage current and watt loss of A and C\`s ZnO varistors which show low initial leakage current exhibited constant characteristics. After high current impulse test, A\`s ZnO varistor has broken the side of varistor but impulse current flowed. On the contrary, E\`s ZnO Varistor exhibited good discharge characteristics which the appearance of varistor was not wrong such as puncture, flashover, creaking and other significant damage. After long duration impulse current test, E\`s ZnO varistor exhibited good discharge characteristics which the appearance of varistor was not wrong such as puncture, flashover, creaking and other significant damage. After high current impulse test and long duration impulse current test, E\`s ZnO varistor exhibited very good characteristics which variation rate of residual voltage is 1.4% before and after test.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2002년도 추계학술대회 논문집 Vol.15
• /
• pp.552-556
• /
• 2002

The microstructure and electrical characteristics of A~C's ZnO varistors fabricated according to variable sintering condition, which sintering temperature is $1130^{\circ}C$ and speeds of pusher are A: 2mm/min, B: 4mm/min, C: 6mm/min, respectively, were investigated. In the microstructure, A~C's ZnO varist-ors fabricated variable sintering condition was consisted of ZnO grain(ZnO), spinel phase$(Zn_{2.33}Sb_{0.67}O_4)$ Bi-rich $phase(Bi_{2}O_{3})$, wholly. Varistor voltage of A~C's ZnO varistors sintered at $1130^{\circ}C$ increased in order A < B < C's ZnO varistors. C's ZnO varistor exhibited good characteristics that nonlinear exponent is 31.70. Leakage current of A~C's ZnO varistors exhibited below 2mA at rated voltage. Lightning impulse residual voltage of A's ZnO varistor suited standard characteristics, which is 3.85kV at 2.5kA, 4.4kV at 5kA and 5.16kV at 10kA. After multi lightning impulse residual voltage test of A's ZnO varistor exhibited good discharge characteristics which ZnO varistor reveals no evidence of puncture, flashover, cracking in visual examination. After high current impulse test of A's ZnO varistor exhibited good discharge characteristics, which variation rate of residual voltage is 0.4% before and after test, and revealed no evidence.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2005년도 춘계학술대회 논문집
• /
• pp.46-49
• /
• 2005

This paper presents the electrical characteristics of metal oxide varistors for lightning surge arresters. ZnO varistors were fabricated with typical ceramic production methods and two types of varistors were also prepared to be compared. The nominal discharge current and line discharge class of those varistors are $10kA(8/20{\mu}s)$ and class 3, respectively. The diameter of varistors manufactured and prepared were in the range of 61.6~65.0mm and the thickness of those were in the range of 27~42.52mm. The reference and residual voltage were tested and reference and residual voltage per 1mm and the ratio of reference and residual voltage were calculated. The reference voltage per 1mm of varistors manufactured was about 175V/mm but that of A's and B's varistors was nearly 200V/mm. The residual voltage exhibited the same trends as the reference voltage, so the reference and residual voltage per 1mm of domestic varistors should be increased. According to the results of tests, it is thought that if the reference and residual voltage per 1mm were increased to 200V/mm and 330V/mm, domestic ZnO varistors would be possible to apply to the station class arresters in the near future.

• 조명전기설비학회논문지
• /
• 제21권2호
• /
• pp.46-53
• /
• 2007

현재 급속한 발전을 거듭하고 있는 이동통신 및 무선 멀티미디어 관련 서비스(W-CDMA, DMB, WiBro 등)의 확장은 이들 시스템을 구현하기 위한 수많은 기지국과 안테나 및 다수의 신호전송선로를 필요로 한다. 기지국 또는 중계시설의 안테나는 신호전송선로를 통하여 고가의 통신 네트워크 장비들과 결합되어 있으므로 주요 통신기기 시스템은 안테나를 통해 유입하는 직격뢰 및 유도뢰에 의한 순간적인 과전압의 위험에 항시 노출되어 있다. 현재 통신용 보호기로 사용되고 있는 가스방전튜브(GDT) 또는 협대역 스터브형 어레스터는 고속 광대역의 통신설비에 대한 뇌서지 보호수단으로서는 한계점이 드러나고 있다. 따라서 본 연구에서는 안테나를 통해 입사하는 뇌서지를 효과적으로 저감시켜주는 서지어레스터의 성능향상을 위해 세라믹 필터를 적용하였으며, 잔류전압 저감에 효과적임을 성능실험을 통해 입증하였다.

• 한국안전학회지
• /
• 제35권6호
• /
• pp.78-84
• /
• 2020

The F&EI technique is one of the risk assessments with many advantages. It can save time and effort compared to quantitative risk assessment (QRA). By using the evaluation result of this technique, it is possible to check the effectiveness of the investment cost. In addition, a relative risk ranking can be created and used to establish the facility management cycle and to prioritize investment. However, evaluating the target process can be evaluated more than the actual risk since the LCCF, a loss prevention measure, is too limited. In addition, calculating premiums via this method can result in excessive premiums, making it difficult to evaluate the risk precisely. Therefore, new safety guard was added to the LCCF of the F&EI risk assessment with reference to HAZOP and LOPA techniques. Newly added LCCFs are Deflagration arrester, Check valve, SIS, and Vacuum beaker, etc. As a case study, F&EI risk assessment was performed on Acetone storage tank of a API (Active pharmaceutical ingredient) plant to compare actual MPPD. The estimated loss amount was 592,558$ for the existing technique and 563,571$ for the improved technique, which was reduced by about 5% compared to the previous one.This proved that a more precise evaluation is possible and that the efforts for safety at the workplace are reflected in the evaluation results.

• 한국항행학회논문지
• /
• 제27권2호
• /
• pp.203-208
• /
• 2023

본 연구에서는 정전류 회로와 전압 강하법을 이용한 접촉 저항 측정 회로의 정밀도를 개선하는 방법을 제안하고, MQTT 브로커 서버를 통해 접촉 저항 측정 시스템의 측정값을 모니터링할 수 있는 대시보드를 구현한다. 접촉 저항 측정 시스템은 저항값을 측정하고 무선통신을 이용해 MQTT 브로커 서버로 측정값을 전달하고, 대시보드는 Node-RED와 Node-RED-Dashboard을 이용하여 최대 4개의 접촉저항 측정 시스템의 저항값을 받아 이를 사용자 화면에 출력하여 보여준다. 사용자는 하나의 대시보드를 이용해 복수의 측정 데이터를 관리할 수 있고, MQTT 브로커 서버를 통해 다른 장치와 쉽게 인터페이스 가능하게 한다. 실제 데이터 측정을 통해 정밀도 상대표준편차가 평균적으로 40.37%, 그리고 최대 64.73% 각각 감소하여 정밀도의 개선 효과가 있다.

• 한국화재소방학회논문지
• /
• 제34권2호
• /
• pp.86-93
• /
• 2020

본 연구는 옥외저장탱크에서 발생한 화재·폭발사고의 근본적인 사례분석을 통해 저장탱크의 안전을 유지할 목적으로 수행되었다. 이 사고는 저장탱크 야드에 사업장 외에서 날아온 풍등이 저장탱크 주변 잔디에 떨어지며 발생한 잔재 화재가 서서히 확산되어 탱크 내부의 유증기와 만나 폭발·화재로 이어진 사고였다. 사고의 원인을 밝혀내기 위하여 CCTV영상분석을 통한 대기확산 조건 도출, 전산유체역학을 이용한 풍향 분석, 플러팅 루프가 최저 위치일 때의 탱크 내부 유증기 발생량, 최고 위치일 때의 탱크 내부 유증기 거동을 통하여 저장탱크의 폭발이 일어난 원인을 밝혀내어 저장탱크의 레벨을 내부부상형 지붕 이하로 유지했을 경우 위험물이 충전되면서 그 공간에 있던 유증기가 내부 부상지붕위에 정체될 가능성이 있으므로 저장탱크의 Low liquid level이 폰튠 서포트 밑에 위치하지 않도록 운전절차를 개선하고, 오픈 벤트에는 화염방지기를 설치하여 화염이 저장탱크로 유입하지 못하도록 하는 대책을 제시하고자 한다.