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Passenger Exposure to Magnetic Fields in Electric Vehicles

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  • Passenger Exposure to Magnetic Fields in Electric Vehicles

    All of the radiation emitted by an electric vehicle is nonionizing and the relationship between nonionizing EMR and human health has been studied for decades. The magnetic fields in EVs could become an issue from the point of view of human health due to a combination of three factors: average and peak current levels, short distances between field generators and the passengers, and lengthy exposures.

    The traction drive of an electric car is an electrical system of considerable power, ranging from 40 to 120 kW. Even higher power levels are found in high‐end models. These power levels are usually achieved with high currents rather than voltages. This means that these traction drives could generate magnetic fields of considerable strength when compared to other conventional sources.

    In electric vehicles, passengers sit very close to an electric system of significant power, usually for a considerable amount of time. IEEE C95.6 defines exposure levels to protect against adverse effects in humans from exposure to electric and magnetic fields at frequencies from 0 to 3 kHz.

    The rear seats were the most exposed and the highest magnetic field values were found at the rear left side. Design recommendations to minimize magnetic field exposure in EVs include power devices should be oriented so that the magnetic field suffered by the passengers is minimized. DC wires must be taped together; similarly, the three‐phase AC wires must be taped together, preferably in a triangular disposition so the magnetic field generated by each cable in the interior of the vehicle will be cancelled. Batteries carry currents up to hundreds of amperes and it is difficult for the magnetic field generated by all of them as a whole to be cancelled out. The higher the voltages, the lower the currents and the magnetic field, but the electric field could become higher.

    A magnetic shield can be placed around the main devices responsible for the magnetic field in the interior of the car. A ferromagnetic alloy of high magnetic permeability, such as Mu‐metal or similar, could be used. If switching frequencies grow above 100 kHz (by using SiC power devices, for instance), Faraday shielding could become necessary. This consists of radio frequency shields made of copper, such as those found in microwave ovens.

    In 2015, two journal papers were published with measurement results from a wide variety of hybrid and electric cars. The vehicle that showed highest values reached 18% of safe levels. Unsurprisingly, the researchers found that magnetic field exposure was higher in EVs than in ICE‐based vehicles.

    An additional point: it is highly advisable to remain outside of the vehicle, and at some distance from it, while fast charge is in process. As battery technology improves, higher recharge rates are achieved, which obviously imply higher currents, and hence stronger magnetic fields.

    Magnetic Field Strength (T = Tesla) for common environmental sources

    .001mT 500kV transmission power line .008mT
    .01mT Earth gravitational field .060mT
    .1mT EV .2mT
    1mT Home appliances - range of .002mT - 5 mT

    WHO recommended maximum exposure limits are .2mT maximum