The Shielding effect and surface temperature properties of low-voltage cable with MCF screen layer

Transcription

1 Volume 118 No , ISSN: (printed version); ISSN: (on-line version) url: ijpam.eu The Shielding effect and surface temperature properties of low-voltage cable with MCF screen layer Yong-Seok Kim* 1, Dong-Ju Chae 2, Taek-Hee Kim 3, Chong-Min Kim 4, Kil-MokS hong 5, Ji-Yeon Kim 6, Won-Seok Kim 7, Dong-Soon Kwag 8 1,2,3,4,5 Electrical Safety Research Institute, Korea Electrical Safety Corporation, Wanju,55365,Korea 6,7 Korea Institute of Carbon Convergence Technology, Jeonju, 54853, Korea 8 Department of Fire Safety, Kyungil University, Gyeongsan,38428, Korea athens9@kesco.or.kr 1, chaedju@kesco.or.kr 2, taki@kesco.or.kr 3, cmkim@kesco.or.kr 4, natasder@kesco.or.kr 5, genie5462@gmail.com 6, kimws1210@kctech.re.kr 7, dskwag@kiu.ac.kr 8 Corresponding author* Phone: February 4, 2018 Abstract Background/Objectives: Electric cables used in a restricted space such as automobiles and ships require electromagnetic shielding,light weight as well as thermal stability

2 Methods/Statistical analysis: This study was investigated a low-voltage cable with metal-coated carbon fiber(mcf) screen layer and analyzed the properties of electromagnetic effectiveness and surface temperature. Epoxy sizing for cable braiding was found to be most effective.we manufactured a low-voltage cable and MCF used 8 and 16 spindles based on 3,000 strands and density of 90.2%. Findings:It was found that when the current suitable for the conductor cross-sectional area is used, the temperature change of the cable surface is not greatly affected. However, after applying the 2 times the allowable current for 10 minutes, the temperature of the PVC sheath increased greatly from 60.2 C to C, which is close to the melting point of PVC of C. The surface of the PVC sheath was observed to be swollen due to a severe thermal change, but no change in the MCF of the screen layer was observed. The MCF cable braided with 8 spindles and 16 spindles has a value of about 56 db and 63 db from the frequency of 100 KHz to 3 MHz, the shielding effect is better as the number of spindles in the braid increases because the number of holes between braids decreases. Improvements/Applications: A MCF was used as a substitute for conventional metal screen layer for light weight of a low-voltage cable. Although it is lower than the shielding rate of metal screen layer, shielding ratio could be improved. Key Words: Electromagnetic shielding, Low-voltage cable, Shielding effect, MCF, Braiding, Screen layer 1 Introduction In general, since carbon is lighter than metal, and has excellent elasticity and strength, it is widely used in sports, aerospace, automobile and civil engineering fields. In Korea, the so-called Carbon law is being implemented to promote the carbon industry 1. In addition, research is being conducted on the application of the cable field, by using the advantages of high electrical conductivity and tensile strength 2,3.Low-voltage cables consist of conductors using copper and aluminum, polymer insulators, metals having the role of shielding, and sheaths. Low-voltage cables function as exter

3 nal noise shielding, as well as powering equipment units depending on the environment. Cablesare used in information communication, electric and electronic industry, and electronic device in which cable is used is largely exposed to electromagnetic wave in industrial field. The failure or malfunction of equipment causes not only performance deterioration of equipment itself but also social unrest. Electric cables used in a restricted space such as automobiles(am/fm radio frequencies) and ships require electromagnetic shielding,light weight as well as flexibility 4. In particular, the automobile companies are demanding cables with a shielding effect of more than 40dB from the frequency of 510 KHz to 3 MHz.Screen is required for electromagnetic shielding of cables 5,6 to that end, designsusing tape, thin film,braiding and other high-permeability metal or conductive materials are used. Among them, braided shielding has been reported to be effective in the audible and radio frequency (RF) ranges(3 KHz to 300 GHz) 7. For light weight and flexibility of cables, replacing conventional metal with MCF 8 for screen layers of cables has continuously been studied as well. MCF has high conductivity and can be freely used since the ISO standard 9 defines the screen material of the cables used in road vehicles shall be conductive. As part of an effort to develop 600V low-voltage cablesin this study, a braided cable was manufactured using MCF which can be used as a screen layer; then, the shielding effectand the thermal characteristics after supplying current were examined. 2 Manufacture of MCF braided cable The density of the carbon fiber (CF) under consideration as the material of the screen layer for lighter weight is 1.76 g/cm 3, which is lower than 8.92 g/cm 3 of copper and the resistance, is about 10-5Ω.cm. Because of the nature of the fibers, the screen layer is made in a braided form, in which case a fluff is generated due to friction of the braid. Since carbon fibers have low flexibility and are brittle fibers, sizing treatment is required to impart flexibility. In addition, it also has the purpose of preventing static electricity and the damage of the fiber due to friction. The MCF is a carbon fiber coated with copper or nickel and plating has also an important aspect in addition to the sizing treatment. Table 1 shows the characteristics

4 of the sizing treatment to reduce the fluff caused by friction during braid manufacturing of the screen layer. Epoxy, urethane (PU-1, PU-2) and silicone (PDMS-1, PDMS-2) were used for the sizing treatment. In Table 1, the epoxy and urethane sizing treatments were found to be effective in focusing, flexibility and fluff reduction. However, in the acid stability at the time of plating, epoxy was stable, but urethane was coagulated and settled, and epoxy sizing for cable braiding was found to be most effective.figure 1 shows photograph of braided MCF. Table 1. Fluff characteristics according to sizing treatment Fig. 1.Braiding of MCF Table 2 shows the specification of the MCF braided cable. In cables, the cross-sectional area of the conductor was 3mm 2, and cross-linked polyethylene (XLPE) was used for the insulator, and polyvinyl chloride (PVC) was used for the sheath. For cable manufacturing, twisting was progressed with the number of strands (119/φ 0.18mm) by going through drawing process and gathering process to finely increase the size of the copper to the desired size. The conductors were covered with an insulator (XLPE) in an extrusion process, and braided MCFs were used thereon. MCF used 8, 16 spindles based on 3,000(3K) strands. The braid width was 1.9 mm and the pitch was 35.5 mm, and the braid density was manufactured as 90.2 % based on the IEC standard (90% or more). Table 2. Parameters of MCF braided cable

5 3 Experimental Methods In this experiment, a cable was installed on a device based on IEC standard 10 and the shielding effect was measured as shown in figure 2. The length of the cable is 0.7 m, and it is made to well observe the reduction of the shielding effect in the band after the cut-off frequency in the cable. After connecting the feed wire and the measuring wire to the instrument probe for the sample, connect a resistor to both ends. Connect the ground of the feed line and the measurement line and measure it up to the frequency of 1GHz. The shielding performance was measured using a network analyzer capable of measuring up to 3 GHz. Fig. 2.Schematic of shielding effect measurement of MCF braided cable Figure 3 shows the experimental equipment for measuring the temperature change of the MCF braided cable according to the current variation. First, the jig configuration for fixing the cable was selected as 1 m. A copper conductor was used at both end connecting parts. A cable was fixed to both ends of the jig, and a current was applied using a DC current source (220 V/210 A, USA). The voltage was set to 50 V, and the allowable current of the conductor and the current of 2 times were applied to the MCF braided cable, and the application time was set to 10 minutes. In addition, direct current was applied to the MCF braid used as the screen to measure the temperature change, and the temperature was measured by using a thermal imaging camera at a distance of 50 cm

6 Fig. 3.Schematic of temperature measurement of MCF braided cable due to current variation 4 Results and Discussion Figure 4 is a thermal image showing the temperature change after applying the current for 10 minutes in the allowable current (41.3A) range of the MCF braided cable with a conductor cross-sectional area of 3 mm 2 After applying a current for 10 minutes, the temperature of the PVC sheath increased from 24.7 C to 46.5 C, but no significant change in the surface was observed. Fig. 4.IR image of MCF braided cable due to allowable current Figure 5 is a thermal image showing the temperature change after a current of 2 times the allowable current of a MCF braided cable is applied for 10 minutes. After applying the electric current for 10 minutes, the temperature of the PVC sheath increased greatly from 60.2 C to C, which is close to the melting point of PVC of C. In particular, the surface of the PVC sheath

7 was observed to be swollen due to a severe thermal change, but no change in the MCF of the screen layer was observed. This is because the thermal property of the MCF is higher than the melting point of the PVC sheath.as described above, it was found that when the current suitable for the conductor cross-sectional area is used, the temperature change of the cable is not greatly affected. However, depending on the use environment of the cable, the screen layer is used in connection with the earth terminal. In this case, a minute leakage current flows or a current due to a short circuit or an earth fault is greatly increased. Therefore, it is necessary to examine the state change by applying a direct current to the MCF which is the screen layer. Fig. 5.IR image of MCF braided cable due to 2 times allowable current Figure 6 shows the temperature change when a current of about 1/10 of the allowable current is applied to the screen layerof the MCF braided cable. In the figure, the temperature rise of the MCF braided cable PVC sheath did not occur significantly. In other words, when a minute leakage current flows to the earth side, the influence of the cable was not greatly affected

8 Fig. 6.IR image of MCF screen layer on cable due to current variation(current=4a) Figure 7 shows the temperature change of the screen layerof the MCF braiding cable when a current of about 1/5 of the allowable current of the conductor flows. When the current of about 8A of the allowable current of the conductor flowed into the screen layer, the temperature of the PVC surface showed a similar shape as shown in Figure 3. Although the current is significantly lower than the allowable current, it can be seen that when the current flows directly to the screen layer, the temperature of the conductor surface increases greatly. Fig. 7.IR image of MCF screen layer on cable due to current variation(current=8a) Figure 8 shows the temperature change when a current of about 1/2 of the allowable current of the conductor is flowed to the screen layer of the MCF braiding cable. When about 21A current of the conductor was flowed to the screen layer, the temperature of the PVC surface of the cable increased sharply and the phenomenon of exceeding the melting point of PVC occurred. In other words, when an earth fault or a short circuit occurs in the screen layer, and high current flows, we can see that the risk of fire is high

9 Fig. 8.IR image of MCF screen layer on cable due to current variation(current=20a) Figure 9 shows the results of the shielding effectof MCF braided cable according to braiding spindles. It can be seen that the tendency of the shielding effectof both samples has a similar shape. We can know that the MCF cable braided with 8 spindles and 16 spindles has a value of about 56 db and 63 dbfrom the frequency of 100 KHz to 3 MHz, and the shielding effect is stable. However, as can be seen from the figure, the shielding effect is better as the number of spindles in the braid increases because the number of holes between braids decreases and so it is less influenced by electromagnetic waves. Fig. 9.Shielding effect of MCF braided cable due to braiding spindles Figure 10 is the result of comparing the shielding effect of metal shielded cables and MCF braided cables. As can be seen in the figure, metal shielded cables showed better shielding effect than MCF braided cables. In the initial 10 KHz, a difference of about 3 db occurs, but the value difference of about 20 db is shown at 1 MHz interval. In case of the metal shielded cable, the shielding effect was judged to be high because the resistance value was smaller than that of the MCF braided cable, and the conductivity was excellent. Although the shielding effect is lower than that of metal shielded cables, it has been confirmed that the shielding effect can be improved by improving the conductivity through metal coating and braiding spindles in case of the MCF braided cable

10 Insert figure 10 Fig. 10.Comparison of Shielding effect of MCF and metal screen cable In this paper, a MCF was used as a substitute for conventional metal screen layer for light weight of a low-voltage cable. Although it is lower than the shielding rate of metal screen layer, shielding ratio could be improved by metal coating. When the cable is used within the allowable current range, the abnormality of the MCF braided cable does not appear much, but when the short circuit or the earth fault occurs, it can be seen that the temperature of the cable PVC surface increases and the fire is highly likely to occur due to that. 5 Conclusion To develop low-voltage cables, we studied the electromagnetic waveeffectiveness and thermal properties of braided cable using MCF which can be used as a screen layer. A sizing treatment was used to reduce the fluff of the MCF braided cable, and an epoxy resin was most suitable. MCF used 8 and 16 spindles based on 3,000 strands. The braid width was 1.9 mm and the pitch was 35.5 mm, and the braid density was manufactured as 90.2 %. When the current suitable for the conductor cross-sectional area is used, the temperature change of the cable is not greatly affected. However, after applying the 2 times the allowable current for 10 minutes, the temperature of the PVC sheath increased greatly from 60.2 C to

11 128.1 C, which is close to the melting point of PVC of C. The surface of the PVC sheath was observed to be swollen due to a severe thermal change, but no change in the MCF of the screen layer was observed. MCF cable braided with 8 spindles and 16 spindles has a value of about 56 db and 63 db from the frequency of 100 KHz to 3 MHz, and the shielding effect is stable. However, as can be seen from the figure, the shielding effect is better as the number of spindles in the braid increases because the number of holes between braids decreases and so it is less influenced by electromagnetic waves.although the shielding effect is lower than that of metal shielded cables, it has been confirmed that the shielding effect can be improved by improving the conductivity through metal coating and braiding spindles in case of the MCF braided cable. Acknowledgment This work was supported by Civil-Military Technology Cooperation Program (15-CM-MA-14). References [1] MOTIE Notice , Carbon material convergence/integration technology development and infrastructure development act on support to an enforcement ordinance, [2] Yue Liu, Bernd Zwingmann and Mike Schlaich, Carbon Fibers Reinforced Polymer for cable Structures, Polymers, 2015, 6, pp [3] Xu Xuehong, et al, Improvement of the Compressive Strength of Carbon Fiber/Epoxy Composites via Microwave Curing, Journal of Materials Science & Technology, 2015, Vol. 32, No. 3, pp [4] Kim, Jae shin, Song, Gui Sub, Na, Seung Hyun, Lee, Dong Hui, Review on the Shielding Effectiveness of Cable Harness, Korea Association of Defense Industry Studies,2008, Vol. 15, No. 1, pp

12 [5] IEEE Power and Energy Society, IEEE Guide on Shielding Practice for Low Voltage Cables, IEEE Std 1143, pp. 1-79, [6] Zi Ping Wu et al, Electromagnetic interference shielding effectiveness of composite carbon nanotube macro-film at a high frequency range of 40 GHz to 60 GHz, AIP ADVANCES 5, 2015, pp , [7] Shinn-ShyoungTzeng, Fa-Yen Chang, EMI shield effectiveness of metqal-coated carbon fiber-reinforced ABS composite, Materials Science and Engineering:A, 2001, Vol. 302, Issue 2, pp [8] M.S. Ahmad, A.M. Zihilif, E. Martuscelli, G. Ragosta, E. Scafora, The electrical conductivity of polypropylene and nickel-coated carbon fiber composite, Polymer Composites, Vol. 12, Issue 1, pp , [9] ISO 14572(2006), Road vehiclesround, screened and unscreened 60V and 600V multi-core sheathed cablestest methods and requirements for basic and high-performance cables. [10] IEC (2006), Electromagnetic compatibility (EMC)Surface transfer impedance - Line injection method

13 1571

14 1572