Exposure to Magnetic Field Harmonics in the Vicinity of Indoor Distribution Substations

Abstract

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%.

Public Magnetic Field Exposure Based on Internal Current Density for Electric Low Voltage Systems

“…12. There seems to be a slight negative correlation between the cumulative magnetic field normalized to 50 Hz (coefficient K) and the relative load current in agreement with earlier observations (Keikko et al 2006b). The same negative correlation exists between B THD and the relative load current.…”

“…According to ICNIRP, the maximum cumulative magnetic field, K, normalized to the 50 Hz magnetic field component, B 1 , can be obtained as the maximum value of the sum of magnetic field harmonic components, B f , over frequencies, f (ICNIRP 1998(ICNIRP , 2003Jokela 2000;Keikko 2003;Keikko et al 2000Keikko et al , 2006aKeikko et al , 2006b. The maximum cumulative magnetic field, K, can be presented in a general form as a function of time, t, for long-term measurements as follows:…”

“…Basics for the calculation procedure of eqns (1) and (2) have been presented by several authors (ICNIRP 2003;Jokela 2000;Keikko 2003). It has been recently used to evaluate the magnetic field exposure ratio in an indoor MV/LV distribution substation environment (Keikko et al 2006b) and has been used in the measurements of this paper. However, one should note that a discrete summation of eqn (1) is quite adequate for power engineering applications.…”

“…2) corresponds to the floor of the space above the substation. From a public exposure point of view, these measurements are very reliable (Keikko et al 2006a(Keikko et al , 2006b and the results can be classified as significant. With other structures it was not possible to use symmetry and the sensor was located in the ceiling of the substation.…”

“…In recent years, the research has concentrated on evaluating exposure to magnetic fields. An early measurement system developed at TUT was based on commercial magnetic field meters and power quality analyzers (Keikko et al 2006b). …”