A Study on the Accelerated Degradation Test of VCTF Cable According to the Calculation Method of Activation Energy

Kang Sin-Dong,Kim Jae-Ho 대한전기학회 2022 Journal of Electrical Engineering & Technology Vol.17 No.5

This study analyzed the characteristics of insulation resistance according to activation energy, which is an important index in accelerated degradation testing for the lifetime assessment of cables. The experimental sample used an indoor low-voltage VCTF cable, and the activation energy was calculated using analysis (TGA) and the rate factor. The TGA method measured the mass loss rate of the cable insulator at heating rates of 1 K, 2 K, 5 K, and 10 K and calculated the activation energy of 1 eV. The method using the rate constant analyzed the temperature–time degradation properties of the cable insulation, calculating activation energy of 0.89 eV. Therefore, the accelerated degradation time of the cable was derived from the calculated activation energy, and the degradation test of the cable was performed using a forced convection oven. Furthermore, the insulation resistance of cables with accelerated degradation was measured using a Megger insulation tester. For cables with an equivalent life of less than 20 years, insulation resistance decreased as the equivalent life increased. However, when the activation energy was 0.89 eV, cables with an equivalent life of 30 years had increased insulation resistance compared with those with less degradation time. Accordingly, surface analysis and plasticizer content analysis of the cables manufactured through an accelerated degradation test confi rmed that the timing of the increase in insulation resistance and the time of loss of plasticizers were the same. This study, it is confi rmed that the insulation resistance of cables was aff ected by temperature and plasticizer content. Thus, plasticizer content analysis should be considered during the accelerated degradation testing of cables.

원자력발전소용 안전등급 케이블의 경년열화에 따른 연소 및 연기특성 분석

이석희(Seok-Hui Lee),김민호(Min-Ho Kim),이상규(Sangkyu Lee),이주은(Ju-Eun Lee),이민철(Min-Chul Lee) 한국화재소방학회 2021 한국화재소방학회논문지 Vol.35 No.1

본 연구에서는 원자력 발전소에서 사용되는 안전등급 케이블을 대상으로 경년열화에 따른 연소 및 연기특성을콘 칼로리미터 시험을 통해 분석하였다. 열발생률의 1st peak 구간인 초기 특성의 경우, 비열화 케이블이 열화 케이블에 비해 20-50 kW/㎡ 높게 측정되었으나, 2nd peak인 중/후기에는 열화에 따른 난연성능의 저하에 기인하여 비열화케이블에 비해 열화 케이블들이 높게 측정되었다. 또한, Char 층이 불안정하게 형성됨에 따라 char 층의 유지시간이비열화 케이블에 비해 열화 케이블들이 약 200 s 단축됨을 확인하였다. 총발열량은 열화 케이블이 비열화 케이블에비해 약 1.4배 높게 측정되었다. 연기특성의 경우, 연기발생률은 열발생률과, 총 연기발생량은 총발열량과 비슷한 양상을 띄며, 총 연기발생량은 열화 케이블이 비열화 케이블보다 높게 측정되었다. 연기인자는 열화 기간이 증가함에따라 증가하는 경향성을 보였으며, 4년 이상 열화된 케이블들은 비열화 케이블에 비해 약 1.76-2.0배 정도 차이가 났다. 따라서 경년열화가 진행된 케이블일수록 열 및 연기방출의 위험성이 증가하였다. In this study, combustion and smoke characteristics according to the aging of class 1E cables in nuclear power plants wereanalyzed through a cone calorimeter test. In the case of combustion characteristics, during the early period, which was thefirst peak of the heat release rate, the peak value of the non-aged cable was higher by approximately 20-50 kW/㎡ than thatof aged cables. However, in the mid-late periods, which was the second peak, the value of the aged cables were higher thanthe non-aged cable due to the decrease in flame retardant performance with aging deterioration. In addition, the duration ofthe char layer of the aged cables was shortened by 200 s than that of the non-aged cables due to the unstable formation ofchar layer. The total heat release measured was approximately 1.4 times higher in the aged cables than in the non-aged cables. In the case of smoke characteristics, the smoke production rate and total smoke release show a similar trend with the heatrelease rate and total heat release. The total smoke release of the aged cables was measured to be higher than that of thenon-aged cables. The tendency of the smoke factor increased with aging deterioration, and the values of the smoke factor inthe aged cables beyond 4 years were approximately 1.76-2.0 times different from those in the non-aged cables. Consequently,the smoke risk increased with aging deterioration. Therefore, the risk of heat and smoke release increased as aging progressed.

사장교 케이블의 장력 추정을 위한 인공신경망 모델 개발

김기중(Ki-Jung Kim),박유신(Yoo-Sin Park),박성우(Sung-Woo Park) 한국산학기술학회 2020 한국산학기술학회논문지 Vol.21 No.3

본 연구에서는 사장교의 케이블 가속도계로부터 확보한 방대한 계측데이터의 활용을 확대하고자 인공지능 기반의 케이블 장력 추정 모델을 개발하였다. 케이블 장력 추정 모델은 진동법에 따른 장력 추정 과정에서 고유진동수를 판정할 수 있는 알고리즘을 핵심으로 하며 학습데이터 구성에 적합하고 판정 결과에 대한 성능이 확보될 수 있도록 입력층, 은닉층, 출력층으로 구성되는 인공신경망(Artificial Neural Network)을 적용하였다. 인공신경망의 학습데이터는 케이블 가속도 계측데이터를 진동수로 변환 후 구성하였으며 고유진동수를 중심으로 일정한 패턴을 갖는 특성을 활용하여 기계학습을 진행하였다. 학습데이터 구성 시 다수 패턴의 고유진동수를 대표할 수 있도록 다양한 크기의 진폭을 갖는 진동수를 사용하고 일정 수준으로 진동수를 누적하여 사용할 경우 고유진동수에 대한 판정 성능이 개선됨을 확인하였다. 장력 추정 모델의 성능을 판단하기 위해 계측분석 기술자에 의해 추정한 장력의 관리기준과 비교하였다. 케이블 가속도계로부터 확보한 139개의 진동수를 입력값으로 사용하여 검증을 수행한 결과 실제 정답과 유사하게 고유진동수를 판정하였고 고유진동수에 의해 케이블의 장력을 추정한 결과는 96.4%의 수준으로 관리기준에 부합하는 결과를 보여주고 있다. An artificial intelligence-based cable tension estimation model was developed to expand the utilization of data obtained from cable accelerometers of cable-stayed bridges. The model was based on an algorithm for selecting the natural frequency in the tension estimation process based on the vibration method and an applied artificial neural network (ANN). The training data of the ANN was composed after converting the cable acceleration data into the frequency, and machine learning was carried out using the characteristics with a pattern on the natural frequency. When developing the training data, the frequencies with various amplitudes can be used to represent the frequencies of multiple shapes to improve the selection performance for natural frequencies. The performance of the model was estimated by comparing it with the control criteria of the tension estimated by an expert. As a result of the verification using 139 frequencies obtained from the cable accelerometer as the input, the natural frequency was determined to be similar to the real criteria and the estimated tension of the cable by the natural frequency was 96.4% of the criteria.

변위 비교를 통한 케이블지지교량의 긴급 지진 안전성 평가 방법의 고찰

박성우,이승한 한국구조물진단유지관리공학회 2018 한국구조물진단유지관리공학회 논문집 Vol.22 No.6

이 연구에서는 사장교 및 현수교에 부착된 지진가속도계측기를 활용하여 교량의 안전성을 긴급하게 평가할 수 있는 기법을 제안한다. 실측된 지진가속도계측기의 상시 응답을 이용하여 구조해석 모델의 고유주파수와 비교를 통해 최대한 유사한 동적특성을 갖도록 모델링을 개선한다. 설계지진에 대한 지진해석을 수행하여 지진가속도계측기 설치 위치별 최대 변위를 도출하며, 도출된 변위는 사전에 관리기준치로서 시스템에 기 입력된다. 지진발생 시 실시간으로 측정된 가속도 시간이력을 필터링 후 2중적분을 통해 변위시간이력으로 변환한 뒤 최대 변위를 추출한다. 최종적으로 시스템에 기 입력된 관리기준치와 추출된 변위와의 비교를 통해 안전성을 평가한다. 경주지진 시 기록된 데이터를 활용한 12개 특수교량의 긴급 안전성평가 수행을 통해 제안된 방법의 적용성을 확인한다. This study presents the emergency assessment method about seismic safety of cable-supported bridges using seismic acceleration sensors installed on the primary structural elements of them. The structural models of bridges are updated iteratively to make their dynamic characteristics to be similar to those of real bridges based on the comparison of their natural frequencies with those of real bridges estimated from acceleration data measured at ordinary times by the seismic acceleration sensor. The displacement at the location of each seismic acceleration sensor is derived by seismic analysis using design earthquake, and the peak value of them is determined as the disaster management criteria in advance. The displacement time history is calculated by the double integration of the acceleration time history which is recorded at each seismic acceleration sensor and filtered by high cut(low pass) and low cut(high pass) filters. Finally, the seismic safety is evaluated by the comparison of the peak value in calculated displacement time history with the disaster management criteria determined in advance. The applicability of proposed methodology is verified by performing the seismic safety assessment of 12 cable-supported bridges using the acceleration data recorded during Gyeongju earthquake.

Dynamic deflection monitoring method for long-span cable-stayed bridge based on bi-directional long short-term memory neural network

Wen-Yu He,Yi-Fan Li,Wei-Xin Ren,Gang Liu,Hai-Peng Sun 국제구조공학회 2023 Smart Structures and Systems, An International Jou Vol.32 No.5

Dynamic deflection is important for evaluating the performance of a long-span cable-stayed bridge, and its continuous measurement is still cumbersome. This study proposes a dynamic deflection monitoring method for cable-stayed bridge based on Bi-directional Long Short-term Memory (BiLSTM) neural network taking advantages of the characteristics of spatial variation of cable acceleration response (CAR) and main girder deflection response (MGDR). Firstly, the relationship between the spatial and temporal variation of the CAR and the MGDR is described based on the geometric deformation of the bridge. Then a data-driven relational model based on BiLSTM neural network is established using CAR and MGDR data, and it is further used to monitor the MGDR via measuring the CAR. Finally, numerical simulations and field test are conducted to verify the proposed method. The root mean squared error (RMSE) of the numerical simulations are less than 4 while the RMSE of the field test is 1.5782, which indicate that it provides a cost-effective and convenient method for real-time deflection monitoring of cable-stayed bridges.

경주 지진에 대한 국내 공용 중 케이블지지교량의 지진응답특성: 사례 연구

박성우,이승한,최가희 한국구조물진단유지관리공학회 2018 한국구조물진단유지관리공학회 논문집 Vol.22 No.5

이 연구는 2016년 발생한 경주 지진의 규모 4.5이상의 3개 지진, 즉, 전진(규모 5.1), 본진(규모 5.8), 여진(규모 4.5)에 대한 국내 공용 중 케이블교량의 지진응답 특성을 제시한다. 교량 주위의 자유장과 교량 내 지정된 위치에 설치된 지진가속도계측기에서 측정된 지진가속도응답기록을 이용하여 케이블교량의 각 구조부재별 지진응답을 분석한다. 측정 가속도 시간이력의 푸리에 변환을 이용한 주파수 영역 해석을 통하여 교량의 동적 거동 특성을 분석한다. 주탑 상부에서의 최대가속도를 자유장 위치에서의 최대가속도로 표준화하여 주탑 상부에서의 가속도 증폭에 대하여 분석한다. 분석 결과를 통해 지진 재난에 대응하기 위한 케이블지지교량의 지진가속도계측기 위치별 관리 기준치 개발의 필요성에 대해 논의한다. This study presents the seismic response characteristics of domestic cable-supported bridges due to 3 earthquakes with magnitudes of 5.1, 5.8, and 4.5 in Richter scale, which occurred around Gyeongju region in 2016. The seismic acceleration response signals, recorded by the seismic acceleration sensors at the free field near bridge and designated positions on bridge, are utilized to characterize the seismic responses of structural elements of cable-supported bridges. The dynamic behaviors of bridges are presented through Fourier transform of acceleration time history. Using the peak accelerations normalized by those at the free fields, amplification effects on the tops of the pylons are analyzed comparatively bridge by bridge. Using aforementioned analyses, the necessity of development on the creteria of alert levels is discussed for the earthquake disaster response of cable-supported bridges.

사장교 주 거더 중앙에 설치된 지진가속도계 측정 가속도 시간이력을 이용한 변위 응답의 재구성: 포항 지진 사례 연구

이승한 한국복합신소재구조학회 2019 복합신소재구조학회논문집 Vol.10 No.1

A method of calculating dynamic displacement from measured acceleration, which is simpler to use than other displacement calculation methods, was introduced by Lee et al.(2010) and Hong et al.(2010). The target frequency is one of the important parameters that the user must decide when using the displacement reconstruction technique and it requires experience in frequency domain analysis to determine the target frequency. This paper presents a method for determining the target frequency of the displacement reconstruction technique limited to a cable-stayed bridge under earthquake loading. When a cable-stayed bridge is excited by an earthquake, the target frequency is determined as the lowest frequency among the natural frequencies of the effective mode. Here, the effective mode means a mode having a mode shape that significantly affects the degree of freedom of acceleration. In order to verify the validity of the proposed frequency determination method, we analyzed the acceleration and displacement time histories measured at the center of the main span of the three actual bridges measured at the time of the Pohang earthquake. Also, the proposed method was applied to the pylon top acceleration of an actual bridge measured at the time of the Pohang earthquake. 가속도로부터 변위를 계산 방법 중 상대적으로 사용이 간단한 변위재구성기법이 Lee et al.(2010)과 Hong et al.(2010)에의해 제안되었다. 목표주파수는 변위재구성기법을 사용할 때 사용자가 결정해야 할 중요한 변수 중 하나로 이것을 결정하기 위해선 주파수영역 분석에 대한 경험이 필요하다. 이 논문은 지진하중을 받는 사장교에 한정된 변위재구성기법의 목표주파수 결정방법을 제시한다. 사장교가 지진에 의해 가진될 경우 목표주파수는 유효한 모드의 고유주파수 중 가장 낮은 주파수로 결정된다. 여기서 유효한 모드라 함은 가속도의 자유도에 유의미한 영향을 주는 모드형상을 가진 모드를 의미한다. 제안된 목표주파수 결정방법의 타당성을 검증하기 위해 포항지진 발생 당시 측정된 3개 실 교량의 주경간 중앙에서 측정된 가속도와 변위 시간이력을분석했다. 또한 제안된 방법을 포항지진 발생 당시 측정된 실교량의 주탑 상단 가속도에 적용해 계산된 변위를 분석했다.

전단형 MR 감쇠기를 이용한 사장교 구조물의 진동제어

허광희 ( Heo Gwanghee ),전준용 ( Jeon Joonryong ),김충길 ( Kim Chunggil ),정기수 ( Jung Kisoo ),오주원 ( Oh Juwon ) 한국구조물진단유지관리공학회 2008 한국구조물진단유지관리공학회 학술발표대회 논문집 Vol.12 No.2

The ultimate purpose of this research on the whole is to develop a vibration control method effectively applied for cable-stayed bridges which is structurally flexible, and to evaluate its effectiveness. As a primary step on the way to the ultimate goal, this paper describes our experiment on vibration control which was performed through the on-off control method of shear mode MR damper. The response values (displacement and acceleration) acquired from this experiment are contrasted with those of un-control method, and thus we evaluate the performance capacity of each different control method. For the experiment, we used a model bridge structure which was a reduced one of Seohae Grand Bridge one two hundredth in size, and also installed two shear mode MR dampers with electromagnetic yoke in the center of middle span. Also installing both displacement meters and accelerometers on each one fourth, two fourth, and three fourth position of the middle span, we estimated displacement and acceleration under each different control method. In order to measure the excitation of the structure, we use a shaker on the center of left span which would be able to perceive the El centro earthquake wave. The performance index we used were peak absolute displacement and peak absolute acceleration, by which the effect of controlling is evaluated. Finally, this paper concludes that the on-off control method using the MR damper turns out to be functionally superior to the un-control one, and thus the method is effective for the vibration control of cable-stayed bridges. It also proves that the results of the experiment performed in this research can be utilized as objective performance index in evaluating the effectiveness of the semi-active control which applies a variety of control algorithms.

전선 케이블의 전자선 조사에서 몬테칼로 코드를 이용한 선량 계산

노영창,표성환,강원구,정승태,김유리,김진규,박종석,강창무 (사)한국방사선산업학회 2020 방사선산업학회지 Vol.14 No.3

The reason for crosslinking the insulation polymer in wire and cable by radiation isto improve their performance at elevated temperature, the chemical resistance, toughness, andabrasion resistance to slow crack growth. Radiation process quality depends not only on the doselevel but also on homogeneity of the dose distribution in especially circular objects like cableswhich have different density in core and insulation part, respectively. It is important to optimizecrosslinking processes to reduce the operation cost while sustaining adequate quality of the finalproduct. The computer simulation method becomes a very effective tool for optimization processproviding necessary information in short time and reducing cost in comparison with conventionalapproach based on experimental dosimetry. The availability of several Monte Carlo codes forelectron and photon transport and the advances in the performances of computing systems,make possible to tackle quantitative dosimetry tasks by numerical simulation. With increasedcomputing speed and decreasing hardware cost, it is expected that Monte Carlo based electrondose calculation algorithms will soon become available for routine electron beam dosimetry. Thecomputer simulation of the dose distributions in electric cables was performed for various processparameters, namely level of electron beam energy, irradiation positions, and density of insulatorof cable.

XLPE 절연체의 등가 및 가변온도 가속열화실험을 통한 기계적 특성 비교 분석

김태준,황재상,정성훈,김태영,Taejoon, Kim,Jae-Sang, Hwang,Sung Hoon, Jung,Tae Young, Kim 한국전력공사 2022 KEPCO Journal on electric power and energy Vol.8 No.2

Recently, as the number of years of operation has increased for more than 30 years, interest in evaluating the remaining life of major power facilities such as transformers and ultra-high voltage cables is increasing. In particular, the risk of failure is increasing because the underground transmission XLPE cable has been built since 1980 and has been operating in excess of 30 years of design life or close proximity. Therefore, it is necessary to develop an algorithm to evaluate the residual life of the XLPE cable considering the load to determine the risk of failure. Since load data is large amount of data, it is necessary to make the variable load information equivalent to the time unit first in order to calculate the remaining life of the system quickly. In overseas literature, transformers are reported to be standardized for variable load equivalent conversion formulas, but they have not been reported for ultra-high voltage cables. Therefore, in this paper, whether the equivalent conversion formula of a transformer can be applied to XLPE cables was reviewed through accelerated degradation tests under equivalent and variable temperature conditions, and considerations were studied when evaluating the remaining operating life of XLPE cables based on the experimental results.