원전 저압케이블 열화도 평가를 위한 초음파 음속계측에 관한 연구

김경조,강석철,구철수,김진호,박재석,주금종,박치승 한국비파괴검사학회 2004 한국비파괴검사학회지 Vol.24 No.4

원자력발전소에는 여러 종류의 케이블이 전력공급, 감시 및 제어신호의 전달을 위해 열악한 환경하에서 이용되고 있다. 발전소의 안전한 운전을 위해서 이 케이블이 어느 정도 열화 되었는지 확인할 필요가 있다. 특히, 원자력발전소의 수명 연장과 더불어 저압 케이블을 장기간 사용함에 따라서 저압케이블의 열화를 평가하기 위한 방법이 필요하게 되었다. 저압케이블의 열화를 측정하는 파라미터로는 주변 온도, 절연재질의 경도, 파단시 연신률(EAB, Elongation At Breaking Point)등이 있다. 그러나, 온도나 경도를 계측하는 검사는 정량적인 판단기준의 설정이 곤란하고 진단의 정밀도가 낮으며, 부분적으로 샘플링하는 방법은 샘플링되는 케이블에 연결된 부하를 정전시켜야 하고 장소와 시간적인 제약이 있으며, 전기적 측정법은 노화 초기부터 중기까지의 열화정도를 확인하기 어렵다. 본 연구에서는 재료의 열화에 따라서 초음파의 음속이 변화한다는 이론적인 배경 [1,2]를 바탕으로 저압 케이블 재료의 열화에 따른 초음파의 음속을 측정하였다. 이를 위해, 원자력발전소에서 사용되는 저압케이블을 가속 열화시켰으며, 저압케이블의 피복재에서 초음파의 음속을 측정할 수 있는 장비를 개발하여, 초음파의 음속측정 후 인장시험을 통해 파단시 연신률을 측정하였다. 파단시 연신률이 증가함에 따라서 음속이 선형적으로 감소 하였으며, 초음파의 음속은 열화의 정량적 평가 파라미터로서의 사용 가능성을 확인할 수 있었다. Several kinds of low voltage cables have been used in nuclear power plants for the supply of electric power, supervision, and the propagation of control signals. These low voltage cables must be inspected for safe and stable operation of nuclear power plants. In particular, the degradation diagnosis to estimate the integrity of low voltage cables have recently been emphasized according to the long use of nuclear power plants. In order to evaluate their degradation, the surrounding temperature or hardness is not useful because of the absence of quantitative criteria; the inspection of a sample requires turning off of the power plant power; and, the electrical inspection method is not sufficiently sensitive from the initial through the middle stage of degradation. In this research, based on the theory that the ultrasonic velocity changes with relation to the degradation of the material, we measured the ultrasonic velocity as low voltage cables were degraded. To this end, an ultrasonic degradation diagnosis device was developed and used to measure the ultrasonic velocity with the clothing on the cable, and it was confirmed that the ultrasonic velocity changes according to the degradation of low voltage cables. The low voltage cables used in nuclear power plants were degraded at an accelerated rate, and EAB was measure in a tensile test conducted after the measurement of ultrasonic velocity. With the increasing degradation degree, the ultrasonic velocity decreased, whose potential as a useful parameter for the quantitative degradation evaluation was thus confirmed.

전압강하를 고려한 저압간선의 설계 알고리즘

고영곤,최홍규,조계술 한국조명전기설비학회 2002 조명·전기설비학회논문지 Vol.16 No.3

저압간선의 굵기는 계통의 전압강하, 간선의 포설조건별 온도 보정계수를 적용한 허용 전류 및 간션의 임피 던스 값에 따라 결정된다. 따라서, 간선의 허용전류 값올 결정하기 위하여 간선의 포셜조건에 따른 적정 보정계 수가 적용되어야 하며, 저압간선의 정확한 임피던스 값을 분석하기 위하여 간선의 종류, 간선의 규격, 포셜조건 에 따른 온도, 표피효과 및 근접 효과 둥이 고려되어야 한다. 본 연구는 저압계통의 전압강하를 고려한 간선의 굵기 산정에 대한 체계적인 설계 흐름도를 제시 하였으며, 일반적인 계산 방식에 비하여 오차가 적은 계수로서 저압간선 굵기 선정 설계 실무에 적용할 수 있는 계산 방식을 연구하였다. A size of low-voltage conductor cables is determined by the voltage drop of a system the cable impedance and the cable ampacity based on temperature correction factor in accordance with the condition of cable installation. Therefore, the proper temperation correction factor according to the condition of cable installation should be applied to determining the cable ampacity and also the skin effect and proximity effect, along with the kind and size of conductor and the condition of cable installation, should be properly considered to analyze the proper value of resistance and the reactance of the conductors. This paper addresses the systematic design flow for determining the size of low voltage level con여ctor cables in calculating the voltage drop of a power system and proposes a new improved the calculating formula what error should be minimized in comparison with the general formula and which can be applied in design work for determining the size of conductor cables.

과부하 전류로 인한 케이블 소손방지를 위한 저압 배선의 설계방법

연기용,김동규,이현명,김재언 대한전기학회 2020 전기학회논문지 Vol.69 No.8

The Korea Electro-Technical Code (KEC) was enacted in March 2018 to meet international standards and develop the country's power industry, and will be implemented in January 2021. In KEC, the protection coordination between the cable and protection devices was to be in accordance with KS C IEC 60364. In this paper, I propose the design of protection coordination between cable and protection devices applying KS C IEC 60364 to draw out the problems of the design method based on the Technical Regulation in Electricity Business Act. In addition, the application method of demand factor for economical low-voltage wiring design was proposed. For the verification of the proposed design method, the design of low-voltage wiring in a certain apartment complex was modeled, and the analysis applied with the Technical Regulation in Electricity Business Act and KS C IEC 60364 was performed. Finally, it is expected that this paper is utilized as a reference for designing economical and reasonable low-voltage wiring.

Condition Assessment of Low Voltage Photovoltaic DC Cables under Thermal Stress Using Non-Destructive Electrical Techniques

Ehtasham Mustafa,Ramy S. A. Afi a,Zoltán Ádám Tamus 한국전기전자재료학회 2020 Transactions on Electrical and Electronic Material Vol.21 No.5

The output power of the photovoltaic system is heavily dependent on the low voltage (LV) DC cables which are exposed to multiple stresses such as climatic, mechanical, electrical, and thermal stress, hence makes them more exposed to aging as compared to other components in the system. Accordingly, it is essential to monitor the state and know the real cause of the insulation degradation of the cable. The physio-chemical changes inside the insulation during service is attributed to the thermal stress, which the cable has to endure constantly. Traditionally, destructive test techniques have been adopted to study the aging phenomenon in the cable insulation, making them unsuitable for on-line condition monitoring. This research work has been aimed to study the degradation in LV photovoltaic DC cables under thermal stress by measuring the dielectric properties; complex permittivity, tanδ with the change in frequency and decay and return voltage slopes using extended voltage response method. The non-destructive diagnostic methods used are based on the phenomenon of polarization and conduction in the insulation material. The noteworthy change in the values of the imaginary part of permittivity, tanδ at low frequencies, and the overall decrease in the values of return voltage slope showed the change in the structure of the polymer matrix under the stress which was related to the cross-linking based chemical reactions. The results show that the techniques can be adopted for the on-line condition monitoring of the cable for the PV system and the dielectric parameters can be used to study the chemical and physical changes happening inside the material eff ectively.

저압범위 확대에 따른 태양광발전시스템 직류배선 설계방법

현동근,김동규,이현명,김재언 대한전기학회 2020 전기학회논문지 Vol.69 No.7

The Korea Electro-technical Code (KEC) established in 2018 extended the DC low-voltage range under 750 V to 1,500 V. Accordingly, it is expected that there will be some changes in the domestic photovoltaic industry. In Korea, most of PV generation systems have been operated under 750 V for cost and regulatory reasons. If KEC is implemented from 2021, PV generation system is expected to improve power generation efficiency by constructing under 1,500 V. However, in order to apply the new low- voltage range in PV generation system, it seems to be prepared more concretely. Especially, KEC currently deals with regulations for low-voltage cables and PV generation system, but the impact on PV generation system and existing cables by applying the expansion of DC 1,500 V is not considered. And the rated voltage 1 kV cable currently used is not appropriate to PV generation system expected to be constructed under 1,500 V from 2021. In addition, due to the characteristics of PV generation system, it is necessary to regulate the use of cable for PV generation system rather than using general cables at 1,500 V. Therefore, this paper proposes a revision plan of KEC applied in 2021 and a design method to prepare DC wiring for PV generation system applicable to DC 1,500 V.

탄소섬유를 이용한 600V 이하 저압 케이블의 전자파 차폐특성

김영석,김택희,김종민,송길목,김지연,김원석,곽동순,Kim, Young-Seok,Kim, Taek-Hee,Kim, Chong-Min,Shong, Kil-Mok,Kim, Ji-Yeon,Kim, Won-Seok,Kwag, Dong-Soon 대한전기학회 2017 전기학회논문지 Vol.66 No.1

This study used general carbon fibers(CF), which can be utilized for a low voltage cable screen, as well as metal-coated carbon fibers(MCF) to make cables and analyzed the properties of electromagnetic effectiveness. Both braid CF and MCF cables with 3,000 strands, 16 spindles, and braid density of 90% or over were adopted. The tape-type MCF specimens were spread into a tape(width: 15mm) using a hot melt to make a cable. The shield effectiveness was measured up to the 1GHz range in accordance with IEC 62153-4-6; braid shielded cables featured a superior shielding effect at 63dB than tape-type shielded cables. That was because the tape-type shielded cable has relatively more gaps and holes between carbon fibers than the braid type, resulting in a more inflow or emission of electromagnetic waves. In the case of braid cables, the characteristics of their electromagnetic waves were enhanced, with higher spindles and higher conductivity of carbon fibers. The shield effectiveness of the MCF shielded cable, however, was lower than that of tin-coated one.

탄소섬유를 이용한 600V 이하 저압 케이블의 전자파 차폐특성

김영석(Young-Seok Kim),김택희(Taek-Hee Kim),김종민(Chong-Min Kim),송길목(Kil-Mok Shong),김지연(Ji-Yeon Kim),김원석(Won-Seok Kim),곽동순(Dong-Soon Kwag) 대한전기학회 2017 전기학회논문지 Vol.66 No.2

This study used general carbon fibers(CF), which can be utilized for a low voltage cable screen, as well as metal-coated carbon fibers(MCF) to make cables and analyzed the properties of electromagnetic effectiveness. Both braid CF and MCF cables with 3,000 strands, 16 spindles, and braid density of 90% or over were adopted. The tape-type MCF specimens were spread into a tape(width: 15mm) using a hot melt to make a cable. The shield effectiveness was measured up to the 1GHz range in accordance with IEC 62153-4-6; braid shielded cables featured a superior shielding effect at 63dB than tape-type shielded cables. That was because the tape-type shielded cable has relatively more gaps and holes between carbon fibers than the braid type, resulting in a more inflow or emission of electromagnetic waves. In the case of braid cables, the characteristics of their electromagnetic waves were enhanced, with higher spindles and higher conductivity of carbon fibers. The shield effectiveness of the MCF shielded cable, however, was lower than that of tin-coated one.

Lifetime Assessment Method using Multiple-Stress Acceleration Aging for Flexible Cable of Portable Electric Machines

Jeongtae Kim,Ji-Sub Yoon,Sang-Won Choi 대한전기학회 2016 Journal of Electrical Engineering & Technology Vol.11 No.5

In this study, in order to analyze the lifetime for flexible cables used in portable electric machines, artificial accelerating aging was carried out for VCT(Vinyl Cab-Tire) cables in consideration of thermal, mechanical and electrical multiple-stresses. Accelerated aging factors were calculated with aging temperatures based on the Arrhenius relationship. Through Weibull statistical analysis in the AC breakdown voltages for aged cables after low-temperature mechanical tests, it was analyzed that AC breakdown voltages were proportional to the elongation rates and 19kV of the scale parameter in Weibull analysis was suggested as limit value of lifetime. Using this criterion, it was deduced that the lifetimes with thermal and mechanical multiple-stresses for 70℃, 50℃ and 40℃ continuous operation were calculated to be 3.3 years, 9.9 years and 15.7 years respectively. Based on these analysis procedure, it is possible to suggest the lifetime assessment technique with multiple-stresses for low voltage cables.

Lifetime Assessment Method using Multiple-Stress Acceleration Aging for Flexible Cable of Portable Electric Machines

Kim, Jeongtae,Yoon, Ji-Sub,Choi, Sang-Won The Korean Institute of Electrical Engineers 2016 Journal of Electrical Engineering & Technology Vol.11 No.5

<P>In this study, in order to analyze the lifetime for flexible cables used in portable electric machines, artificial accelerating aging was carried out for VCT(Vinyl Cab-Tire) cables in consideration of thermal, mechanical and electrical multiple-stresses. Accelerated aging factors were calculated with aging temperatures based on the Arrhenius relationship. Through Weibull statistical analysis in the AC breakdown voltages for aged cables after low-temperature mechanical tests, it was analyzed that AC breakdown voltages were proportional to the elongation rates and 19kV of the scale parameter in Weibull analysis was suggested as limit value of lifetime. Using this criterion, it was deduced that the lifetimes with thermal and mechanical multiple-stresses for 70 degrees C, 50 degrees C and 40 degrees C continuous operation were calculated to be 3.3 years, 9.9 years and 15.7 years respectively. Based on these analysis procedure, it is possible to suggest the lifetime assessment technique with multiple stresses for low voltage cables.</P>

Al 비율에 실리콘 고무의 정전기 대전 특성

이성일,Lee, Sung-Ill 한국전기전자재료학회 2014 전기전자재료학회논문지 Vol.27 No.8

In this study, using the silicone rubber sample of $4cm{\times}4cm{\times}0.1cm$ for low voltage cable, the electrostatic electrification properties of three samples that the conductive Al of 0%, 25%, and 50% is attached to the surface of sample was measured. The following conclusion was obtained through this experiment. 1) In case of the sample which has the Al area of 50%, the higher the humidity to 90% in the temperature of $10^{\circ}C$, the electrostatic electrification voltage was reduced about 0.25 kV to 0.02 kV, and it confirmed that the electrostatic electrification voltage was in constant about 0.02 kV in the temperature over $20^{\circ}C$. 2) Increasing the Al area of samples of 0%, 25%, and 50% in temperature of $10^{\circ}C$, it confirmed that the electrostatic electrification voltage was reduced by about 2.67 kV, 2.02 k, 0.21 kV. 3) This study shows that the conductor, followed by temperature and humidity affects the electrostatic electrification voltage.