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강신동,김주희,최준표,김재호 한국안전학회 2017 한국안전학회지 Vol.32 No.6
According to the National Fire Data System (NFDS), more than 5,000 vehicle fires have occurred every year for the last 10 years. Vehicle fires are primarily caused by mechanical (breaking system and engine), electrical (wiring and battery), and chemical (oil and fuel gas leakage) problems. The electrical factor has increased with the installation of driver convenience equipment. For example, today, the black box is widely used to provide video data recording of motor vehicle accidents. The black box consists of a front camera, rear camera, and wires. The black box wires are directly connected to the junction box or fuse box from the start battery that operates to provide normal on power supplying for engine stop. It is extremely dangerous when the wires short circuit due to insulation aging, mechanical and electrical stress, etc. In this study, the black box wiring fire risk have been analyzed and investigated when the steady state and abnormal operations, and under the following conditions: wiring arrangements with a high temperature condition, insulation aging, poor contact, and short circuits. The results showed that black box wiring short circuits had a higher fire risk than the other fire hazard elements. To prevent fire hazards caused by black box wiring, the black boxes must be installed by qualified service personnel. Do not modify the wiring, remove the fuse and secure the wiring using cable ties or insulation tape.
강신동,박예진,김시현,김재호 한국안전학회 2023 한국안전학회지 Vol.38 No.4
This study presents the characteristics of short circuits (SCs) caused by excessive currents in high-voltage cables used in electric vehicles and emphasizes the need to calculate the cross-sectional areas of these cables according to the SC current. Three direct current power supplies were connected in parallel to test the SC characteristics caused by excessive currents, and a timer and a magnetic contactor were used to deliver the conduction time and SC current. A circular infrared-radiation heater was used to test the temperature-dependent SC characteristics, a thermocouple was used to measure the temperature, and a shunt resistor was used to measure the current. As the SC current increased, the fusing time of the cable decreased. Additionally, a high-voltage cable (with an area of 16 mm2) used in electric vehicles fused when a current (approximately equal to 55 times the allowable current) flowed for 0.2 s (operating time of the protective device). When the SC current is 10 kA, the cable may fuse during the operating time of the protective device, thus creating a fire hazard. In electric vehicles, the size of the SC current increases in proportion to the capacity of the battery. Thus, the cross-sectional areas of the cables used should be calculated accordingly, and cable operations should be properly coordinated with the surrounding protective devices.
가속 열화 시험에 따른 저압용 차단기의 물리적 특성에 관한 연구
강신동,김재호 한국안전학회 2022 한국안전학회지 Vol.37 No.6
This study analyzed the characteristics of insulation resistance and operating time based on an accelerated degradation test of a low-voltage circuit breaker. The experimental sample used a molded case circuit breaker (MCCB) and an earth leakage circuit breaker (ELCB). After measuring the insulation resistance of the circuit breakers, the leakage current was affected by an external rather than an internal structure. Furthermore, the insulation resistance of the circuit breakers with accelerated degradation was measured using a Megger insulation tester. In the accelerated degradation test, aging times of five, ten, 15, and 20 years were applied according to a temperature derived using the Arrhenius equation. Circuit breakers with an equivalent life of ten, 15, and 20 years had increased insulation resistance compared to those with less degradation time. In particular, the circuit breaker with an equivalent life of ten years had the highest insulation resistance. Component analysis of the circuit breaker manufactured through an accelerated degradation test confirmed that the timing of the increase in insulation resistance and the time of additive loss were the same. Finally, after analyzing the operating time of the circuit breakers with degradation, it was confirmed that the MCCB did not change, but the ELCB breaker failed.
강신동(Sin-Dong Kang),김재호(Jae-Ho Kim) 한국조명·전기설비학회 2019 조명·전기설비학회논문지 Vol.33 No.10
In this study, the thermal and flame propagation characteristics of cable in perforated cable tray used in a low voltage indoor distribution line were analyzed according to the arrangement of the cable using Light PVC sheathed circular cord(VCTF) cable. A thermocouple was attached to the inside and outside of the cable to measure the temperature. The cables were arranged in vertical and horizontal directions and, layered in triangular and rectangular shapes. As compared to the temperature inside a single cable, the temperatures increased when numerous cable were arranged in a horizontal direction and layered in triangular and rectangular shapes. The temperature inside the cables reached a peak of 305 ℃ when the current was twice the allowable current. At allowable current, the temperature increased to 62℃ when the cables were layered in a rectangular shape. This was close to the maximum permissible temperature for VCTF cable(i.e., 70 ℃). The insulation resistance of the VCTF cable declined dramatically in accordance with increases in temperature, which not only raised the risk of short circuit and ground faults but also accelerated the cable deterioration. The flame propagated at a velocity of 2.7 ㎝/sec in the vertical direction and 0.95 ㎝/sec in the horizontal direction at twice the allowable current. The faster propagation velocity in the vertical direction was due to the characteristics of flame and plume, which moved in an upward direction due to a buoyancy effect.