Due to possible health effects of electric and magnetic fields, the International Commission on Non-Ionizing Radiation Protection (ICNIRP) published in 1998 guidelines in which upper limits for public and occupational exposure were established. The guidelines are widely referenced by the EU directive of 2004. Thus, in Europe we have passed the time for discussion about the possible biological effects of magnetic fields and the duration of exposure to be allowed. Furthermore, in 2003, ICNIRP expanded their guidelines by taking into account the harmonic components of the magnetic field with phase angles. This statement has not been referenced widely. The aim of this study was to investigate magnetic fields, especially the harmonic components, in electric distribution (20/0.4 kV) substations from the public and occupational exposure point of view. The main finding is that the harmonic content of the magnetic field can dominate the exposure. The harmonic contents analyzed following the original ICNIRP guidelines varied between 49 and 74%. When taking into account the magnetic field phase angles, the harmonic content was only between 16 and 62%. By taking into account only the amplitudes of the harmonic components, ignoring their phase angles, the content of harmonic components is overestimated, on the average, by 30%.
Requirements and expectations associated with power quality have been become increasingly important in our modern society. The quality of power distribution includes both power quality and quality of customer services. At the same time with the developments in distribution automation and the electricity market, many practices at electricity distribution companies are changing, and new possibilities and challenges are emerging.
A measurement concept utilizing a new magnetic field exposure metering system has been developed for indoor substations where voltage is transformed from a medium voltage of 10 or 20 kV to a low voltage of 400 V. The new metering system follows the guidelines published by the International Commission on Non-Ionizing Radiation Protection. It can be used to measure magnetic field values, total harmonic distortion of the magnetic field, magnetic field exposure ratios for public and workers, load current values, and total harmonic distortion of the load current. This paper demonstrates how exposure to non-sinusoidal magnetic fields and magnetic flux density exposure values can be compared directly with limit values for internal current densities in a human body. Further, we present how the magnetic field and magnetic field exposure behaves in the vicinity of magnetic field sources within the indoor substation and in the neighborhood. Measured magnetic fields around the substation components have been used to develop a measurement concept by which long-term measurements in the substations were performed. Long-term measurements revealed interesting and partly unexpected dependencies between the measured quantities, which have been further analyzed. The principle of this paper is to substitute a demanding exposure measurement with measurements of the basic quantities like the 50 Hz fundamental magnetic field component, which can be estimated based on the load currents for certain classes of substation lay-out.
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