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Study on Reliability Improvement of Voltage Transformers by Increasing Voltage Factor
Tae‑Sik Kong,Hee‑Dong Kim,Hung‑Sok Park,Soo‑Hoh Lee,Soon‑Yong Kim,Pil‑Bum Joung,Jin‑Yeub Park 대한전기학회 2020 Journal of Electrical Engineering & Technology Vol.15 No.3
Voltage transformers (VTs) must be highly reliable as they are essential components of the electric power industry. VT failures can cause a signifcant impact for important facilities such as nuclear power plants. In fact, VTs which passed the international standard, were damaged and sometimes resulted in the shutdown of the nuclear power plants. In order to improve the reliability, VTs with various iron core was studied. The electromagnetic feld simulation, a saturation characteristics test, and an overvoltage breakdown test were conducted. The result shows that the magnetic fux density signifcantly afects the reliability of VTs. To increase the reliability of VTs, it is required to reduce the magnetic fux density by increasing the knee-point and voltage factor. Owing to limited installation space, increasing the size of the iron core is difcult. Instead, VT by decreasing the thickness of the conductor and increasing the number of turns, it was possible to reduce the magnetic fux density without the size change. Therefore, improved VTs were obtained by decreasing the thickness of the conductor and increasing the number of turns, and the improved reliability was verifed through a comparison test with existing VTs. The fabricated VTs shows a signifcantly higher saturation voltage and breakdown time than existing VTs. Thus, by proposed VTs can contribute the stable operation of the nuclear power plant and improve the manufacturer’s quality.
최태식,공형윤,최원호 울산대학교 2001 공학연구논문집 Vol.32 No.1
다양한 멀티미디어 통신이 발달함에 따라 채널부호화를 사용하여 오류를 정정하는 기술이 발달되어 왔다. 본 논문에서는 압축영상의 전송에서 LDPC 부호화를 이용하여 영상통신채널에서의 오류를 복원하고, 영상을 재구성할 수 있는 영상통신시스템을 제안한다. 제안된 영상통신시스템은 패리티검사행렬을 사용하여 가장 많은 오류를 발생하는 열과 가장적은 오류를 발생하는 열을 교환하는 방식을 사용하였고, 가우시안 노이즈를 가지는 통신채널의 신호 대 잡음비는 0dB에서 4dB의 범위로 설정하였다. 패리티 검사 행렬이 작은 경우 제시한 교환 방식을 사용하였을 때 사용하지 않은 경우보다 BER 성능이 우수함을 확인하였으며, 영상을 재구성한 경우에도 PSNR 성능이 우수함을 확인할 수 있었다. As a various multimedia communication has been developed, the error correction technique using the coding method was improved. In this paper, an image communication system using the LDPC decoding method for restoring the error and reconstructing the image in the image compression transmission is proposed. The proposed system has a parity check matrix that can alternate the least occurring error column with the most occurring error column. The signal to noise ratio of a communication channel with the gaussian noise was determined the range between 0dB 4dB. When a parity check matrix was a small size, the system's BER efficiency with the parity check alternating method was better than the parity check without it. Also in reconstructing image, the proposed system's PSNR efficiency was superior to system without alternating method.
3-차원 블록인터리버기법의 터보코드를 이용한 영상통신시스템설계
최태식,공형윤,최원호 울산대학교 2001 공학연구논문집 Vol.32 No.1
본 논문에서는 3-차원 블록인터리버기법의 터보코드를 사용하여 무선 통신 환경 하에서 효과적으로 전송할 수 있는 영상 통신 시스템을 제안한다. 웨이브릿 변환과 벡터양자화를 영상의 압축알고리즘에 사용하였으며, 무선통신시스템의 코딩방식 중 하나인 터보코드를 사용하여 압축영상데이터의 통신에 사용하였다. 터보코드의 성능은 데이터율, 부호기의 구속장의 길이, 복호 방식, 순환복호의 횟수, 인터리버의 종류 및 블록크기에 의존되어 진다. 같은 비트 크기에서의 2차원 블록인터리버보다 비트간의 거리를 크게 하는 3차원 인터리빙알고리즘을 적용한 시스템이 영상통신에서 높은 성능을 얻었다. 컴퓨터 시뮬레이션을 이용하여 3차원 블록인터리버의 성능을 압축된 영상과 가우시안 잡음 채널 환경 하에서 비교분석 하였다. In this paper, an image communication system that can effectively work in wireless communication environment is proposed. The wavelet transform and the vector quantization are used to the compress images. The turbo code that is one of the coding methods in wireless communication is used for the compressed image data communication. The efficiency of turbo code depends on the data rate, the constraint length, the decoding algorithm, the number of decoding iteration, the type of interleavers and the block size. The system with 3-D interleaving algorithm whose bit distance is longer than the 2-D block interleaver in the same size had the higher performance in image transmission. To verify the performance of the proposed method, computer simulation was performed in Gaussian noise model.
절연파괴 사례분석을 통한 진공함침 방식 발전기 고정자권선의 절연특성 연구
공태식(Tae-Sik Kong) 대한전기학회 2010 전기학회논문지 P Vol.59 No.3
According to increase of combined cycle power generation, the manufacturing market of gas turbine generator has become more competitive, so there is high pressure on the manufacturer to reduce generator price. Global VPI(vacuum pressure impregnation) method is effective to save the production cost and time for manufacturing stator windings, but it has an abrasion problem by vibration between stator windings and slots. This paper presents the insulation breakdown case, which is for VPI type generator during high voltage insulation tests, and also shows the cause analysis, repair works as well as reliability test. the purpose of this paper is to understand the insulation properties of VPI type generator and to know prevention of insulation weakness.
고압전동기 고정자권선 오염에 의한 고전압 절연진단 시험 중 연면방전 사례
공태식(Tae-Sik Kong),김희동(Hee-Dong Kim),이영준(Young-Jun Lee) 대한전기학회 2009 대한전기학회 학술대회 논문집 Vol.2009 No.10
This paper is purpose to understand the surface discharge properties of the contaminated high voltage motor stator windings. we carried out the insulation diagnostic tests for the contaminated 6.6㎸ motor in power plant. During the high voltage test, the flash-over occurred at 6.1㎸. We couldn't make sure if the ground -wall insulation was broken or it was just a surface discharge between an end-winding and the stator core. So we washed-out the stator windings with steam and dried in 110℃ during the 48 hours. and we carried out the insulation diagnostic tests and dielectric strength again. the insulation diagnostic tests are consist of the megger, the polarization index, the AC current test, the dissipation factor test and the partial discharge test. we analyzed the test results of the flash-over before and after.