Magnetic Fields Encountered in Electric Transport: Rail Systems, Trolleybus and Cars Natalia Ptitsyna
Antonio Ponzetto
Department of Magnetic Measurements SPbFIZMIRAN, Russian Academy of Science, Sankt Petersburg, Russia
[email protected]
Department of Internal Medicine Turin University Turin, Italy
[email protected]
Abstract— The recent tendency to move from conventional combustion-based mobility to electric mobility poses many questions, some of which are connected to electromagnetic compatibility. In view of this it became necessary to measure and evaluate magnetic field inside electric mobility systems. We present here results of our study of magnetic fields on different electrified transport systems (electric trains, metro, trams and trolleybus) and compare them with scanty information on magnetic fields onboard electric/hybrid cars.
current flow through the circuits, and compare these results with known information on MF in electric/hybrid cars.
Keywords-electric mobility; magnetic fields; multifrequency spectra
I.
INTRODUCTION
Electrification of road transport is currently deserving first priority in EU. Public expectations to move towards electric mobility are driven by multiple reasons and concerns including: detrimental effects of fossil fuel-based road transport on world climate, air quality, environment, energy security and public health, as well as cost and scarcity of raw materials. While all vehicles are subjected to externally produced electromagnetic fields (EMF), including geomagnetic field, electric transportation systems generate additional significant magnetic fields because of their design features. Several electric vehicle manufacturers are currently facing various problems that require the recall of particular models, where the electronic driving controls are affected by both low and high frequency internal electromagnetic fields. On the other hand, a concern of media and public is the possible impact on the health of the vehicle occupants of the non-ionizing radiation they are bathed in, generated by the internal electrical currents or by high frequencies.
Figure 1. ULF magnetic field (X, Y, Z components) in a car (with motors) of a DC electric motor unit (EMU) train. Dashed area: acceleration phase; black area: power substation; square: oncoming train; circle and ellipse: braking phase.
II.
MAGNETIC FIELD VARIATIONS ONBOARD TRAIN, TRAM, AND TROLLEYBUS
In view of this, it is important to develop information about the electromagnetic radiation which is associated with existing electrically powered transportation systems and with those systems presently at the stage of early deployment, or prototypes and systems still under development.
Relatively little scientific investigation of transportation system EMF has been carried out to date [1, 2]. We have studied various urban and interurban transport technologies: DC and AC powered railway systems, metro, train, trolleybus and tram. Measurements were done in 0.03-50 Hz frequency range for DC technologies and in 0.03-200 Hz frequency range for AC railway. Results were partly published in [3-5].
Thus, it became necessary to evaluate magnetic field (MF) inside electric vehicles. However, since electric automobile is new emerging technology, it is not possible to find comprehensive set of related measurement data. We present here results of magnetic surveys taken in various electric transport systems, where magnetic fields are generated by the
Figures 1 and 2 show “moving pictures” of the measured MF in three orthogonal components registered onboard in DC and AC railways. The coordinate system of magnetometer was: X - horizontal component, directed along rails to the direction of motion; Y- horizontal component, perpendicular to the train axis; Z - vertical component, directed downward.
This work was supported by the European 7th Framework Program (project N 265772)
The three sensors were arrayed on a staff at 12.5 cm intervals. Most part of measurements were taken in driver’s cabs; in this case the staff was placed in a position near the head of the sitting engine driver. A number of measurements were done in other train coaches and in platforms. This allowed relating different magnetic field peculiarities to operational regime of trains and to electromagnetic environment. It is clearly seen that magnetic fields are increasing during acceleration, braking, passing substations and incoming trains.
Figure 3. Magnetic field measured onboard a DC-powered locomotive under different train’s speed. Analysis of measured MF variations allowed defining sources of onboard variations and classifying them as follows: static geomagnetic field; distortion of static magnetic field due to the iron/steel mass of electric train; varying magnetic field from catenary and rails current; varying magnetic field from different current systems onboard electric transport system;
Figure 2. Magnetic field measured onboard Swiss AC (16.67 Hz) electric locomotive in a 20-min interval (lower plot) and in a 20-sec interval (upper plot). A: acceleration, L: low speed, O: zero current.
varying magnetic field arising when passing different nearby stationary and moving ferromagnetic objects (oncoming trains, railway switches, bridges, etc.). In this case geometry of fields (relative position) is important. varying magnetic fields from different kind of groundbased man-made current sources;
Figure 3 demonstrates magnetic field variations onboard the same electric locomotive under different train speed regimes from 45 till 120 km/hour. We see that frequency and amplitudes of magnetic variations are proportional to train speed: higher frequencies and amplitudes were observed under higher speeds.
varying magnetic field caused by variable induced current generated by train movement (change in direction, accelerations, braking, etc) in the static geomagnetic field.
Similar measurements and analysis was done onboard other transport technologies. It shows that MF on all studied electric transport (DC and AC powered railways, metro, train, trolleybus and tram) present complex-and variable structure.
To analyze observed frequency patterns and their changes in time we calculated dynamic power spectral density (DPSD) of magnetic field data registered in all studied transport technologies. The spectral-temporal representation was
varying geomagnetic field;
obtained by Fourier transforms of successively cut-out parts of the analyzed data. In Figure 4 it is shown an example of the dynamic spectral analysis of magnetic fields in a DC-powered locomotive. We remind that -20 dB in comparison with 0 dB means a decrease in amplitude by 10 times, -40 dB - by 100 times, etc. For normalization the amplitude spectrum values were converted to decibels values. A “colorscale” is shown. The top panels of Figure 4 show the 3-component magnetic field variations measured on a DC powered locomotive during 10-min interval. The dynamic amplitude spectrum for frequencies 0.1-50 Hz in the same time interval is plotted at the bottom frames of Figure 4.
of the dominant frequency. The greatest changes in the DC level in DC trains were observed in locomotives in the horizontal Y component perpendicular to rails (or catenary contact wire) during acceleration phase or passing substations. The most probable DC levels in DC trains were in the range of 40 µT. Peak-to-peak values reached 150 µT in electric locomotives, and were somewhat less in electric motor units EMU. In trolleybus maximum levels were found near driver’s head where they reached up to 325 µT. In trams the highest field levels of 500–1000 µT were found in passenger’s coach. Significant quasi-static field variations were observed in St. Petersburg metro. Peak-to peak values were 425 µT in motorman’s coach, and 50-325 µT on platforms. In trolleybus maximum MF values were 300 µT. In AC-powered trains changes in DC level were 5-10 µT. III.
MAGNETIC FIELDS IN ELECTRIFIED CARS
Till now magnetic fields in electrified individual transport (HEV and EV) have not been studied thoroughly. There are very few published information on measurement and evaluation of magnetic fields generated by hybrid, and especially by fully electric cars [6-9]. In Figure 5 we show MF variations in a hybrid car [6] shows the magnetic field variations in dependence on operational regimes. In this research MF strength was found in the range of 0-3.5 μT. It was observed that the maximum magnetic field strength above 1 μT was radiated at 12 Hz.
Figure 4. Time variations (top panels) and dynamic amplitude spectra of MF in a DC–powered locomotive (engineer’s cab). The top panels of Figure 4 show the 3-component magnetic field variations measured on a DC powered locomotive during 10-min interval. The dynamic amplitude spectrum for frequencies 0.1-50 Hz in the same time interval is plotted at the bottom frames of Figure 4. The spectrum shows the presence of magnetic field bursts in wide frequency range (0.1-50 Hz) in all three components. The spectra show variations in all studied frequency range. More than 90% of the MF energy is concentrated in frequencies < 15 Hz. A presence of MF bursts in wide frequency range (0.1-50 Hz) may be observed, as manifested by vertical strips of different colors. These bursts of increased amplitudes correspond to the changes in speed regimes. A number of constant frequencies (5 Hz, 12 Hz, 32 Hz) are also observed as horizontal lines.
Figure 5. Hybrid car: magnetic fields in the left rear seat (floor level). Measurement results [6-7] show that the highest field is generated during regenerative braking and maximum acceleration. According to measurements done in Switzerland by the Biel Technical University [9] the strength of the magnetic fields changes constantly as the car travels along, and is greatly dependent on the way the car is advancing or braking; the magnetic fields were between 0.1 and 3 µT.
Very similar dynamic structure comprising the same kind of bursts in wide frequency range have been also observed in dynamic spectra of magnetic field in other electric technologies (not shown here): EMU, metro, tram and trolleybus.
In [8] authors determined the low-frequency MF (5-2000 Hz) in all four seats of seven stationary cars with their engine and air conditioning running. A maximum magnetic field of 14 µT was measured at the left rear seat.
The 16.67 Hz component of fields measured onboard Swiss trains (AC supply at 16.67 Hz) is obviously the dominant frequency. Out of the dominant 16.67 Hz frequency, there are small peaks at higher frequency ranges that can be harmonics
In [6, 7] it was found that hybrid cars generate a mixture of magnetic fields at frequencies of 5 to 500 Hz (see Figure 6 taken from [6]), as it was established in our research for MF onboard public electric transport.
V.
CONCLUSION
We can conclude that main characteristic features of electric car magnetic fields are similar to other electric transport fields. Transport magnetic fields are different from 50 (60) Hz power lines fields, which are predominantly sinusoidal. Transport magnetic fields are multifrequency fields that are highly variable with time. Magnetic field patterns are characterized by extremely complex combination of static and time-varying components up to a few hundred hertz. This is due to two reasons: (1) the onboard magnetic fields originate from multiple onboard sources and Figure 6. Amplitude-frequency dependence of low frequency magnetic fields in a hybrid car. Fields ≤ 5 Hz were not measured.
IV.
COMPARISON OF MF ON DIFFERENT ELECTRIC TRANSPORT TECHNOLOGIES
Onboard electric vehicle systems we measure a superposition of all magnetic fields produced by multiple sources. The superposition of variations with different amplitudes and frequencies determines complex magnetic field patterns. These patterns are highly variable with time due to changes in route conditions and nearby magnetic environment. Due to this, transport magnetic fields exhibit complex frequency patterns, including quasi-static variations and pulses, providing complex combination of static and time-varying components. Measurements performed in different electrified transport technologies show that most part of MF energy is distributed in the lowest frequency range (quasi-static and ULF: 0.001-10 Hz). Below we compare maximum levels of magnetic field intensities in this frequency range found in our survey with those found in electric cars and buses [1, 8]: Tram
500 μT
Metro
450 μT
Trolleybus
350 μT
Electric train
120 μT
Electric cars and light tracks
104 μT
Electric Shuttle Bus
80 μT
Electrified (hybrid) cars
14 μT
(2) frequency content and intensity are continuously changing in accordance with transport operational regimes (acceleration, braking, turning etc). For members of the general public, the range of magnetic field exposures (in terms of intensity) in electric cars is comparable in magnitude to exposures from other electric transport technologies. Since high variability and intermittency is the generic feature of magnetic fields onboard all electric transport technologies, including hybrid/electric cars, it would be important to take it into account in future electromagnetic field surveys in electric cars in regard to human exposure assessment. REFERENCES [1]
[2]
[3]
[4]
[5]
[6]
[7]
Thus, magnetic field amplitudes found (till now) in hybrid/ electric cars are of the same order of magnitudes or less than fields found in other electric transport technologies. However this information needs verification on the base of more extensive EMF measurements in electric cars.
[8]
F. M. Dietrich, and W. L Jacobs, “Survey and assessment of electric and magnetic field (EMF) public exposure in the transportation environment”. US Department of Transportation, Federal Railroad Administration, Report No. PB99-130908,1999. A. M. Muc, “Electromagnetic fields associated with transportation systems, radiation health and safety consulting”, Contract Report 4500016448, Air Health Effects Division, Healthy Environments and Consumer Safety Branch Health, Canada, 2002. p. 52. N. G. Ptitsyna, G. Villoresi, Y. A. Kopytenko, M. I. Tyasto, E. A. Kopytenko, N. Iucci, P. M. Voronov, and D. M. Zaizev, “Magnetic field monitoring on DC electrified transport in Russia”. In Electricity and Magnetism in Biology and Medicine, ed. F. Bersani. Plenum Publ. Corporation, New York, 1999, pp. 773-776. N. G. Ptitsyna, Y. A. Kopytenko, G. Villoresi, D. H. Pfluger, V. Ismaguilov, N. Iucci, E. A. Kopytenko, D. B. Zaitzev, P. M. Voronov, and M. I. Tyasto, “Waveform magnetic field survey in Russian DC- and Swiss AC-powered trains: a basis for biologically relevant exposure assessment”. Bioelectromagnetics. Vol. 24, pp. 546-556, 2003. N. G. Ptitsyna, G. Villoresi and Yu. A. Kopytenko, “Magnetic fields from railway: environmental aspects”. In Railway Transportation: Policies, Technology and Perspectives, ed. F. Columbus, New York, Novapublishers. 2019, pp 87-141. M. N. Halgamuge, C. D. Abeyrathne and P. Mendis, “Measurement and analysis of electromagnetic fields from trams, trains and hybrid cars”, Radiation Protection Dosimetry, vol. 141, No 3, pp. 255-268, 2010. S. H. Berisha, G. G. Karady, R. Ahmad, R. Hobbs, and D. Karner. “Magnetic field generated from different electric vehicles”, Electric Transportation Application, DOI: 10.4271/951934, 1995. K. Vedholm, and J. K. Hamnerius, 1997. "Personal exposure resulting from low level low frequency electromagnetic fields in automobiles," Abstract F-9, Second World Congress for Electricity and Magnetism in Medicine and Biology, June 8-13, Bologna, Italy, 1997.
[9]
Federal office of Public Health, “Cars, hybrid cars”, [http://www.bag.admin.ch/themen/strahlung/00053/00673/02377/index. html?lang=en]
