• Proceedings of the KSR Conference
• /
• 2005.11a
• /
• pp.705-711
• /
• 2005

In DC traction substation with 12-pulse diode rectifiers, the DC line voltage tends to rise above noload voltage because it can't absorb the regenerative power caused by electric brakes of train. To solve this problem, an IGBT regenerative inverter should be installed and recycles the surplus regenerative power by delivering it. to the supply grid. In this paper, the DC traction substation equipped with a IGBT regenerative inverter is studied using computer simulation. Matlab/simulink is used to simulate the operation of regenerative inverter which injects the regenerative power into the supply grid and stabilizes the DC line voltage. It is confirmed that the high quality regenerative power is delivered to the supply grid thorough computer simulation.

• Proceedings of the KSR Conference
• /
• 2000.05a
• /
• pp.86-92
• /
• 2000

Recently, the Korea National Railways (KNR) is undertaking a program of electrification of the existing railway routes. In order to implement the ongoing plan, KNR authorized a preliminary engineering study of its electrical systems. This effort included a comprehensive analysis of new grounding networks. The new grounding system runs in parallel with the rails and is connected to all metal structures such as rails, overhead protection wires and substation grounding grids etc., creating an equipotential ground network. This paper presents a study on coupling levels that can disturb signaling and telecommunications in adoption of the new grounding network The simulation for the study is carried out using Matlab software, Several different scenarios are analyzed, including the load condition and a few fault conditions with different fault locations. The induced potentials on the communication cables are computed. The effect of the buried ground wires is also analyzed by comparing the results with and without the presence of the ground wires, The results presented in the paper can be used as a reference for estimating coupling levels in similar rail systems.

• Journal of the Korean Chemical Society
• /
• v.40 no.4
• /
• pp.249-253
• /
• 1996

The synthesis of new 5-benzyl-4-cyanomethyl-2-methylpyrimidine derivatives (5) containing chloro, methoxy, ethoxy, phenoxy and anilino groups at 6-position on the pyrimidine ring were prepared from 5-benzyl-4-chloro-2-methylpyrimidine derivatives (3) and tert-butylcyanoacetate. The derivatives of 5-benzyl-4-chloro-2-methylpyrimidine (3) containing chloro, methoxy, ethoxy, isopropoxy, phenoxy and anilino groups at 6-position on the pyrimidine ring were prepared from 5-benzyl-4,6-dichloro-2-methylpyrimidine (2).

• Proceedings of the KOR-BRONCHOESO Conference
• /
• 1996.04a
• /
• pp.85-85
• /
• 1996

경부기도의 종양은 편평상피암과 함께 이비인후과의에게 있어서 호흡곤란 환자의 감별진단을 위해 매우 중요한 임상적 의미를 갖는다. 종양은 암종에 의한 사망률의 0.1%이하를 차지하는 드문 질환이며 선양낭성암종은 기도의 원발성 종양중 두 번째로 많은 질환이다. 갑상선종양의 기도의 직접적인 침범이 흔히 발견되는 상태이며, 그다음으로 편평상피암, 선양낭성암종이 기도의 원발성 종양으로 흔한 질환이다. 갑상선의 악성종양이 기도의 벽이나 내강을 침입하는 것과 마찬가지로, 기도의 원발성 악성종양도 흔히 갑상선을 침범하여 갑상선의 종괴처럼 발현할 수 있다. 본 연구는 이와 같이 갑상선의 악성종양과 유사한 임상경과를 보이는 기도의 선양낭성암종의 향후 감별진단을 위해 4명의 조직학적으로 증명된 갑상선을 침범하는 기도의 선양낭성암종환자의 임상기록과 전산화 단층촬영소견을 후향적으로 관찰하였다. 전산화 단층촬영에서 이들은 기도에 넓은 기저부를 가지고 갑상선을 밀고있는 균일한 음영의 일반적으로 부드러운 경계를 가지는 종괴로 보였으며, 횡단면과 두정면에서 모두 기도 벽의 비후소견을 보였다. 이러한 소견은 기도의 원발성 선양낭성암종의 감별에 도움이 될 것으로 생각된다.

• Journal of the Korean Society for Railway
• /
• v.7 no.4
• /
• pp.307-311
• /
• 2004

Arresters are the best protective device on electrical power systems against transient overvoltages generated by lightning and/or switching operation. Nonetheless, arresters are deteriorated by absorption of moisture in the environments of its use, repetition in the protective operation to overvoltages, and some defects at manufacturing. It is therefore important to estimate the electrical characteristic changes of ZnO blocks. In this paper, an accelerated ageing test by a standard lightning impulse current was carried out to extract parameters needed for arrester diagnosis, and leakage current components were measured. Total energy applied to the ZnO blocks at each time is about 1,050[J] in 8/20[${\mu}\textrm{s}$] impulse current. From the experimental results, we proposed electrical parameters and leakage current level to diagnose arrester soundness.

• Proceedings of the KSR Conference
• /
• 2002.10a
• /
• pp.553-558
• /
• 2002

The harmonics in railway high voltage system is due to common use of 3 phase incoming bus and doing the power converter for traction system on the electric car(or electric locomotive). This paper, we analyze the harmonics mechanism and characteristics of railway high voltage system, also we analyze the problem according to the actual measurement about influence of harmonicsontherailwayhighvoltagesystem. And we proved the countermeasure device(passive filter or L-C filter) of harmonics applies in the field. The test result, we have know that the filter is not fit. Consequently, The countermeasure of harmonics for the railway high voltage system be able to resolve by another filter.

• Transactions of the Korean Society of Automotive Engineers
• /
• v.13 no.6
• /
• pp.63-69
• /
• 2005

For the case that center crack is surrounded by four small cracks which are symmetrically distributed around center crack, the same values of normalized stress intensity factor of center crack according to the position of the tip of small cracks are located on the smooth curve. And the stress intensity factor according to any position of small cracks can be sufficiently obtained from this curve. The plastic zones between distributed cracks are also investigated by changing the positions of nearly small cracks. The occurrence of plastic zone due to the interaction between center crack and small cracks are analyzed by finite element method. The mechanical behavior at the vicinity of crack tips is investigated by plastic areas. The changes of plastic zones according to positions of distributed cracks are drawn schematically. The safety of materials is also analyzed.

• Journal of the Korean Ceramic Society
• /
• v.27 no.5
• /
• pp.625-630
• /
• 1990

Cordierite powders were prepared from Si(OC2H5)4, Al(OC3H7i)3 and Mg(OC2H5)2 by the sol-gel method. Two different methods were applied for producing fine and homogeneous powders. One is that Si(OC2H5)4 with a lowr rate of hydrolysis was partially hydrolyzed and then Al(OC3H7i)3 and Mg(OC2H5)2 were mixed and reacted. The other is based on the simultaneous hydrolysis of these metal alkoxides using i-C4H9OH which retards the rate of hydrolysis of Al(OC3H7i)3 and Mg(OC2H5)2. It was confirmed that ifne and homogeneous powders were obtained from both methods. Also these powders were calcined at four different temperatures during two hours. X-ray diffraction patterns show only ${\mu}$-cordierite phase at 1000$^{\circ}C$, ${\mu}$-cordierite and ${\alpha}$-cordierite phases at 1100-1200$^{\circ}C$ and ${\alpha}$-cordierite phase at 1300$^{\circ}C$ respectively.

• Journal of the Korean Ceramic Society
• /
• v.27 no.6
• /
• pp.777-782
• /
• 1990

The sintering behavior of cordierite powders synthesized using a sol-gel method of metal alkoxides Si(OC2H5)4, Al(OC3H71)3 and Mg(OC2H5)2 was investigated. Densification of the powder compacts fabricated using the precursor powders calcined at 900$^{\circ}C$ for 2hrs was improved over the sintering temperature range of 800 to 980$^{\circ}C$. The powder compacts, fabricated using the calcined precursor powders and sintered at 1300$^{\circ}C$ for 2hrs, showed relative density of 97-98%, 3-point bending strength of 120-140Mpa, KIC of 2.4-3.7 Mpam1/2, and thermal expansion coefficient of 1.48-1.66${\times}$10-6/$^{\circ}C$.

• Proceedings of the KIEE Conference
• /
• summer
• /
• pp.1361-1363
• /
• 2004

전기철도에서는 한 전철변전소에서 급전이 용이하지 못할 경우 인근변전소에서 연장급전을 수행한다. 특히 AT(Auto Transformer)와 BT(Booster Transformer)급전시스템이 인접한 경우 연장급전운영을 하기 위한 방안 및 전기적인 요소를 급전계통모의를 통하여 검토하여 그 급전가능성을 제시한다.