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김광화,한민철,한천구 청주대학교 산업과학연구소 2004 産業科學硏究 Vol.21 No.2
In this paper, tests are carried out using the concrete incorporating shrinkage reducing admixture(SRA) to reduce drying shrinkage. According to test results, for fresh concrete properties, increase of SRA content leads to reduce the fluidity and air content sharply. For setting time, use of SRA cause concrete to accelerate setting time. For compressive strength, FA10 concrete(incorporating 10% of fly ash) shows remarkable drop in compressive strength compared to that of plain concrete, meanwhile, slight decrease of compressive strength of BS 20 concrete(incorporating 20% of blast furnace slag) is found with the increase of SRA content. For drying shrinkage, concrete shows decline tendency in drying shrinkage with increase of SRA content. In the scope of this paper, the use of SRA 10% has optimum effects on the concrete properties such as reducing drying shrinkage reasonably as well as enhancing mechanical properties except fluidity.
GIS에서 주파수 특성을 갖는 이중 대역법에 의한 UHF 부분방전 측정기술
김광화,이상화,선종호,강동식 대한전기학회 2006 전기학회논문지C Vol.55 No.3(C)
- This Paper describes a dual bands PD measurement method which has two different bandwidths. The one bandwidth is 0.5 - 2 ㎓ and the other is 1 - 2 ㎓. This method is used for GIS diagnosis. In the experiment, it shows that the ratios between two PD quantities in dual bands depend on the defect types and gas pressures. The variations of ratios in different pressures are more sensitive than ones in defect types. And These ratios increase with increasing SF6 gas pressures. As these ratios give us additive information of PD we can analyze the defect type as well as risk assessment for the GIS reliably. Therefore the above result shows that these ratios are one of parameters for diagnosing GIS.
유입 변압기에서 폴디드 다이폴형 센서의 부분방전 펄스 검출 특성
김광화,이상화,선종호,강동식,김재철 대한전기학회 2006 전기학회논문지C Vol.55 No.10C
- This paper describes that the distribution of electromagnetic field occurred by PD(Partial Discharge) pulse was calculated with simulation program and characteristics of calibration and PD pulses measured with folded dipole types sensors were analyzed. As the distribution of electromagnetic field in simulation was very random the wide band measuring methods were good. Therefore three folded dipole antenna types sensors which had different their widths were designed and made. The signal according to direction and distance between sensor and pulse source in these sensor was measured and the spectrum of surface PD were acquired in the experiment of model transformer. In this result the characteristics of sensor which had middle width was better than others and the main spectrum of PD signals in surface discharge were existed in around 220㎒, 320㎒ and from 450㎒ to 750㎒.
안정화제를 사용한 회수수의 고형분량 및 방치시간에 따른 시멘트 모르터의 특성
金光華,김기정,이문환,이세현,한천구 대한건축학회 2003 대한건축학회 학술발표대회 논문집 - 계획계/구조계 Vol.23 No.2(구조계)
This study is intended to investigate the fundamental properties of cement mortar with solid content and leaving time of recycled water that stabilizing agent is added. According to the results, fluidity and air content does not make a big difference with variation of solid content. As the leaving time of recycled water is long, fluidity and air content increases. Setting time is shortened due to fine particle with an increase of solid content and leaving time. Compressive strength and flexural strength increase with an increase of solid content, and they increase at the leaving time of 1 day, but decrease after 2days. Length change by drying shrinkage is smaller than that of plain concrete, and is almost same with variation of solid content. And it is reduced at the leaving time of 1 day, but increases after that. Therefore, it analyzed that the effect of stabilizing agent is best under condition of adding ratio of 0.15%, solid content of 3% and leaving time of 1day, and it also works upto solid content of 5% and leaving time of 2days.