ANALYSIS OF TIME-VARYING LOW-FREQUENCY MAGNETIC-FIELD EMITTED FROM THE SHIP'S INVERTER-FED INDUCTION MOTOR

This paper focuses on the analysis of low-frequency magnetic-field emissions (MFEs) in ship's environment, in reference to admissible levels for exposures to time-varying electromagnetic field (EMF), proposed by International Commission on Non-Ionizing Radiation Protection (ICNIRP). It concerns the special case of simultaneous exposure to multiple frequency fields, when a summation formula (from ICNIRP guidelines) has been applied. Due to a time-varying behavior of the sinusoidal components of the magnetic flux density (MFD), the time-frequency analysis based on the short-time Fourier transform (STFT) was performed. The level of the magnetic field intensity was evaluated, in reference to the standard for occupational environments, which takes into account the people's protection against the excessive emission of the low-frequency magnetic field. The selected results of the off-line analysis of the recorded magnetic flux density near by the ship's inverter-fed induction motor are presented.