Electromagnetic Interference between Power/ Telecommunication Lines

Transcription

1 Electromagnetic Interference between Power/ Telecommunication Lines and Railway Systems 1 Eugene Rhee, 2 Changjae Kim 1, First Author Dept. of Computer System Engineering, Sangmyung University, Korea, eugenerhee@smu.ac.kr *2,Corresponding Author Dept. of Civil Engineering, Sangmyung University, Korea, cjkim@smu.ac.kr Abstract This paper presents the electromagnetic interference effects from the railway systems to electric power supplier systems and telecommunication lines. As the railway system emits the electromagnetic radiation mainly from 30 MHz to 1 GHz frequency bands, the interfering noise can be induced to the nearby power lines or telecommunication lines in the frequency band of same frequency spectrum or higher. This paper modeled and analyzed the radiated electromagnetic emission levels from the railway system to validate the electromagnetic interference from the railway system. As the first step, the electromagnetic coupling between the railway system and overhead power lines crossing the railways were modeled and analyzed. And then, the electromagnetic coupling between the railway system and telecommunication lines in the tunnel were modeled and analyzed. In the analysis result, it was shown that the radiated electromagnetic interference level from the railway system is so considerably low that the induced noise level from the railway systems to the electricity supplier and telecommunication systems would be an insignificant level. Keywords: Electromagnetic Compatibility, Electromagnetic Interference, Radiated Emission 1. Introduction Today s equipment designers need to do more than just make their systems operate under ideal conditions in the laboratory. Besides that obvious task, they must also make sure the equipment will actually work in the real world, with other equipment nearby. This means that the equipment should not be affected by external noise sources, and should not itself be a source of noise to the environment. This is the basic concept of electromagnetic compatibility [1]. This paper gives the list of the applicable integrated electromagnetic compatibility tests to be performed on the railway system to provide the compliance proof of identified electromagnetic compatibility system issues in the railway systems operating environment. The integrated tests are complementary tests to the factory tests performed in a testing laboratory. This study was started to evaluate and analyze any possible electromagnetic interferences from operating trains to the outside radio frequency services. The widespread use of electronic circuits for communications, computations, automations, and other purposes makes it necessary for diverse circuits to operate in close proximity [2-13]. All too often these circuits affect each other adversely. Electromagnetic interference has become a major problem for circuit designers, as well as system designers in the railway system company. By verifying all the possible victims, railway system engineers can be sure whether their railway system affects the electromagnetic environment of the sensitive equipment or utilities of external entities. The completion of this study would contribute to understand and take countermeasure actions against to the complaints from the radio frequency device users or/and organizations. This study includes investigations and analysis on the influence of the unwanted signals generated by the railway system on the sensitive equipment or utilities of external entities which exist along the track line and on the influence of the nearby high power equipment or devices on the railway system. This analysis is performed above ground between power/ telecommunication lines and the railway system, and the analysis is performed from 30 MHz to 1 GHz (HF/VHF/UHF/SHF). Electromagnetic emission level modeling is referenced as introduced in the European Norm (EN) international standard which is used as a basic technical standard throughout the train related research [14-19]. Especially, EN international standard describes nominal electromagnetic emission levels with respect to the frequencies [16]. The terrestrial coverage is between power/ International Journal of Digital Content Technology and its Applications(JDCTA) Volume 7, Number 10, June 2013 doi : /jdcta.vol7.issue

2 telecommunication lines and the railway system. Digital map information with global positioning system (GPS) was used and logged in digital data format [4]. Digital images were also taken at each possible victim location and corresponding image files in jpg were logged. As mentioned above, the frequency for the analysis started from 30 MHz to 1 GHz, and the most concerned possible victims are power/ telecommunication lines. 2. Electromagnetic emission level model As the train is in operation, it inherently emits electromagnetic energy to the outside of its boundary. The sources could be driving motors, pantographs, electronic devices, train control systems, etc. The exact emitted electromagnetic levels from a train should be measured at the site while a train is in operation, however, estimated of these values are described in the EN international standards [14-16]. These levels are as shown in Figure 1 [16]. There are two figures in the EN international standard which represents limits for stationary and slow moving test [13]. For the analysis, the limits for slow moving test were chosen for the worst case analysis. The limits for stationary test are 10 db lower than slow moving test from 30 MHz to 1 GHz. Among A, B, and C limits in the above Figure 1, limit A was chosen for the analysis. It is based on the statements described on EN , which is 25 kv a.c [16]. The emission values in the Figure 1 is specified with peak detection mode, whereas interfering electromagnetic noise level is generally specified with quasi-peak mode which is at least 20 db below the peak values [15]. Therefore, the values from 80 dbμv/m at 30 MHz to 55 dbμv/m at 1 GHz was chosen through the analysis. It is showed as Limit D in red color, which means Limit A 25 kv a.c. in quasi-peak value. As shown in Figure 1, the E field levels are from frequency of 30 MHz to 1 GHz. For the electromagnetic wave analysis, it is reasonable to start from 30 MHz where radio waves are practically implemented. And the levels beyond 1 GHz is not shown in the original EN document, however it would be technically reasonable to extend its level linearly from the previous level [14-16]. Figure 1. Emission limits in frequency range 9 khz to 1 GHz 164

3 In general, it is very well known technical fact that electromagnetic levels decrease as the distance increases from the electromagnetic source. There exist two regions, near field and far field regions. And also there exist transition region near the distance of λ/2π from the electromagnetic source. In the near field region where magnetic field predominates, H field component of electromagnetic decreases proportional to 1/r 3 whereas E field component of electromagnetic decrease proportional to 1/r 2 as the distance increase up to transition region. However, in the far field region, both E and H field decrease proportional to 1/r as the distance increase. Throughout this study, it would be reasonable to assume that only far field region is considered for the analysis because all of the possible victims are located in the far field region. 3. Railway system model Most of the electromagnetic specifications are defined by received power density P [W/m 2 ] or E field intensity in [Volts/m or dbvolts/m] [20][21]. Between these two different units, there can be conversion equation as follows. P dbm 20log E 20 log f 75.06, (1) where E is in [Volts/m] and f is frequency in [Hz]. Assuming lossless transmission lines, these can be also converted to [dbμv] at the input port of measurement equipment, such as a spectrum analyzer. dbv dbm log( impedance) (2) The following two tables are comparisons between different units. Table 1 is the same received power density at different frequencies, and Table 2 is the same received field intensities at different frequencies. The train must pass the qualification test for accelerating up to 110 km/h and electrical braking. Three train operating modes specified for the train are as follows: a) Measurement at a speed greater than 100 km/h (to ensure that the dynamics of current collection are involved in the noise level) and at the maximum power which can be delivered at that speed. This may then not allow the maximum power to be delivered. This means that the train shall reach 100 km/h at 50 m before the test site to allow an acceleration with the maximum power available at this speed when the train passes by the test site. b) At the maximum rated power for a selected speed (particularly if the lower frequencies are of concern). This means that the train shall reach 50 km/h at 50 m before the test site to allow an acceleration with the maximum rated power when the train passes by the test site. c) At an electrical brake power of at least 80 % of the maximum rated brake power. This means that the train shall brake from 70 km/h at 50 m before the test site to allow a braking with 80% of the maximum rated brake power. Table 1. Received same power density at different frequencies Frequency Received power Equivalent E field intensity Voltage across 50 Ω 40 MHz -143 dbm -6 dbμv/m 0.5 μv 157 MHz -143 dbm 6 dbμv/m 0.5 μv 455 MHz -143 dbm 15 dbμv/m 0.5 μv 165

4 Table 2. Received same E field intensities at different frequencies Frequency Received power Equivalent E field intensity Voltage across 50 Ω 160 MHz dbm 3 dbμv/m 0.75 μv 450 MHz dbm 3 dbμv/m 0.27 μv 930 MHz dbm 3 dbμv/m 0.13 μv 4. Measurement set up The distance of the measuring antenna from the centerline of the track is 10 m. In the case of the log-periodic (and bilog) antenna, the 10 m distance is measured to the mechanical center of the logcomb as shown in Figure 2. Loop antenna (H-field between 9 khz and 30 MHz) Plotter 1.5 m Spectrum Analyzer 10 m Biconic antenna (E-field between 30 MHz and 300 MHz) Plotter 3 m Spectrum Analyzer Top of rail level Log-periodic antenna (E-field between 300 MHz and 1 GHz) = = Plotter 3 m Spectrum Analyzer Top of rail level Figure 2. Test set-up for electromagnetic radiation measurement 166

5 If the 10 m distance can not be fulfilled at the chosen test location, all measurements at D meters from the track center shall be converted using the following conversion equation: E 10 E D D 20. n.log10 ( ) 10, (3) when n is picked up in the following Table 3 [18]. Table 3. n at each frequency band Frequency range [MHz] n Crossing overhead power lines In this paper, two overhead power lines (154 kv, 345 kv) crossing the railways were considered and they are shown in broken orange lines as shown in Figure Telecommunication lines Figure 3. Overhead power lines near the railway system Audio frequency (AF) cable and radiating coaxial (RCX) cable in the railway tunnel in Figure 4 are considered in this paper. The frequency components of induced voltage due to power current fundamental and its harmonics is far apart compared to the operating frequency of digital communication subsystems of the railway system and outer telecommunication lines, therefore it can be assessed that there is no risk of frequency interference. As all railway system cables are shielded and the frequency component of them is far from telecommunication lines, in particular concerning the analogue telephone lines, there will be no significant coupling. 167

6 Figure 4. Telecommunication lines in the railway tunnel 7. Electromagnetic interference measurement and analysis It has to be considered that low level of interference noise may affect the systems when the communication channel is operational under minimum S/N conditions, on the contrary even high level of interference noise may not affect the systems when the communication channel is operational under very strong S/N conditions. There are also 820 MHz frequency band for digital telecommunications relay service (TRS) systems used among police and formally used by the District Attorneys networks, and unexposed 380 MHz band used for a special forces. It is investigated that their repeater stations are along the road side specially existing highways. Figure 5 and 6 are the ambient noise measured all along the track. All the measurement method and procedure were done according to the CISPR 16-1 international standard [20]. The ambient noise level at the analysis site is recorded in the peak value and it is about 35 dbμv/m as shown in Figure 5 and 6. The electromagnetic noise level from the train is dbμv/m. Compared to the ambient noise level, the electromagnetic noise levels from the railway system are very weak. So there will be little chance of interference by the railway system at the analysis site. Figure 5. Ambient noise level at MHz band 168

7 8. Conclusion Figure 6. Ambient noise level at MHz band Power or telecommunication lines, which are located near the railway systems, were considered to have a little chance to be interfered by the train. However, most of the victims have little chance to function improperly by the train. In this analysis, some victims located close to the railway can be interfered by the unintended electromagnetic environment generated by the train. But, as the interfered time is generally short to make the victims function improperly, the victims can be considered to operate in acceptable conditions. 9. Acknowledgement This research was supported by a 2013 Research Grant from Sangmyung University. 10. References [1] Henry W. Ott, Noise Reduction Techniques in Electronic Systems, 2nd ed.,john Wiley & Sons, Canada, [2] Seung-Joon Lee, Dong-Hwan Shin, Yong-Hwa Kim, Jae-Jo Lee, Ki-Hwan Eom, Analysis and Modeling of Noise on 22.9-kV Underground Power Distribution Cable for Broadband Power Line Communication, International Journal of Control and Automation, SERSC, vol. 3, no. 3, pp.1-12, [3] Jae-Hoon Lee, Myung-Soo Lee, Sang-Hoon Lee, Se-Ghok Oh, Bo-Hyun Kim, Sung-Ho Nam, Joong-Soon Jang, Development of Computerized Facility Maintenance Management System Based on Reliability Centered Maintenance and Automated Data Gathering, International Journal of Control and Automation, SERSC, vol. 6, no. 1, pp.1-12, [4] Ahmed Mudheher Hasan, Khairulmizam Samsudin, Abdul Rahman Ramli, GPS/INS Integration Based on Dynamic ANFIS Network, International Journal of Control and Automation, SERSC, vol. 6, no. 3, pp.1-22, [5] Sagarika Pal, Niladri S. Tripathy, Remote Position Control System of Stepper Motor Using DTMF Technology, International Journal of Control and Automation, SERSC, vol. 4, no. 2, pp.35-42, [6] Wook Hyun, Mi-Young Huh, Seung-Hei Kim, Shin-Gak Kang, Considerations on Audience Measurement Procedures for Digital Signage Service, International Journal of Control and Automation, SERSC, vol. 5, no. 2, pp ,

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