Electromagnetic Radiation from Cable Harnesses on board Addis Ababa LRT
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Date
2016-03
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Addis Ababa University
Abstract
Electromagnetic Compatibility (EMC) is becoming the main concern of many industries. One aspect of EMC is limited Electromagnetic (EM) radiation from the source. In order for a given device, equipment or system not to cause Electromagnetic Interference (EMI), its radiation level must not exceed some regulatory limits accepted worldwide. This thesis researches electromagnetic radiation from cable harnesses on board Light Rail Transit (LRT) trams. Main target of the research is to compute high-frequency (HF) and low-frequency (LF) Electromagnetic Field (EMF) inside and outside the LRT tramcar and assess them against known standard limits. HF and LF fields have different nature in generating interference to a system. As a result, separate consideration of these fields was important.
Radiation level mainly depends on physical and electrical parameters of a given structure. To adhere to this basic principle, the study was conducted by collecting data about electrical value and geometrical positioning of cables on board Addis Ababa (AA) LRT trams. After collecting all relevant data, equivalent three-dimensional (3D) model was developed for electromagnetic simulation with the help of software. CST Studio Suite is mainly used for numerical computation of electric and magnetic fields in both LF and HF ranges.
The results obtained from software simulations were compared with standard regulatory limits. The limits are taken from International Commission on Non-Ionizing Radiation Protection (ICNIRP) for static magnetic fields, and Institute of Electrical and Electronics Engineers (IEEE) for static electric fields. IEEE sets 5 kV/m as exposure limit for general public and 20 kV/m for controlled environment. The ICNIRP limits on static magnetic fields have many varieties depending on the exposure characteristic (ceiling value, continuous exposure, and medical device). For Radio Frequency Interference (RFI), regulatory limits of Federal Communications Commission (FCC) are adopted.
Field distributions inside and near the tramcar vary spatially. In this thesis, more focus was given to internal floor of the tramcar and outside levels of the track. On smaller portion of the floor, near the cab side, static magnetic field distribution exceeding the limit for medical devices (0.5 mT) was observed; it reached 12 mT. However, the place with such phenomenon was very limited, and the other exposure characteristics (ceiling value and continuous exposure) were never exceeded around the floor. Static electric field distribution around the floor of the tramcar was far below the corresponding regulatory limit, too. 5 kV/m was taken as assessment limit, and all field values were below it. Coming to RF EM radiation, the limits varied over subrange of the frequencies. EM simulation of a structural model was conducted, and the radiation levels were below the limits in both vertical and horizontal polarization.
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Keywords
Electromagnetic Compatibility, Electromagnetic Interference, Radio Frequency Interferences, Radiated Emission, differential-mode current, common-mode current