Tommi Keikko

Exposure to magnetic field harmonics in the vicinity of indoor distribution substations

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%.

Electric fields in 400 kV transmission lines

The 400 kV transmission line electric field was measured, and these results were compared to the guidelines. Transmission lines were measured in surroundings of Tampere, Helsinki and Paimio for 25 spans with 38 measurements. In the study, the measured electric field values did exceed the 5 kV/m guideline for general public exposure by ICNIRP in 10 measured spans. The aim of this study was to compare measured 400 kV transmission line electric fields to the guidelines.

Public magnetic field exposure based on internal current density for electric low voltage systems.

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.

Effect of power frequency harmonics on magnetic field measurements.

Abstract This paper presents a study of the effect of harmonic frequencies on magnetic field measurements. We introduced magnetic field meters in a known magnetic field of different frequencies: power frequency (50 Hz) as well as 3rd (150 Hz) and 5th (250 Hz) harmonic frequencies. Two magnetic field levels (0.25 A and 2.5 A) were used. A Helmholtz coil was applied to generate an exact magnetic field. The difference between the measurement results at harmonic frequencies and at power frequency was analyzed using the t-test for matched pairs. The test results show significant differences (P≤0.01) for 13 out of 28 tests carried out, which is probably due to a curved frequency response near the power frequency. It is, therefore, essential to consider harmonic frequencies in magnetic field measurements in practice.

Power frequency electric and magnetic fields at a 110/20 kV substation

The aim of this paper is to study electric and magnetic fields at a 110/20 kV substation. The fields were measured on the switchyard of the substation. Magnetic field measurements were carried out at two heights along two straight lines and on a quadrangular area. The currents in the conductors were also recorded during the measurements. The highest magnetic field was 18.6 /spl mu/T at the height of 1.0 m and 14.8 /spl mu/T at 0.5 m. Electric fields were measured at 1 m height on the same area and on two other lines. The highest electric field was 4.6 kV/m. The highest magnetic fields were caused by the crossing of a busbar and an outgoing feeder with the highest load, and by a 20 kV cable from the transformer to a 20 kV switchgear. The highest electric fields were caused by conductors passing below bus bars.

Magnetic fields from electric power systems in living environment

The aim of this study was to investigate the levels of extremely low frequency magnetic fields levels from previous studies to evaluate the magnetic fields from power systems in living environment Four different power system environments were studied: transmission and distribution lines, substations, distribution substations and indoor mounting in the buildings. Results were gathered together to find out the essential sources of magnetic fields in living environment. The magnetic fields from 400 kV and 110 kV transmission lines, substations and indoor distribution substations exceeded the immunity level, 3.8 μT, for electric appliances.

Calculation Of Induced Currents In A HumanBody Represented By A Spheroidal Model

There has been much discussion about possible health risks from exposure to power system electric and magnetic fields. The induced current densities in a human body located in these extremely low frequency fields can be determined by calculation. The basic restriction of the ICNIRP (International Commission on Non-Ionizing Radiation Protection) guidelines for 50 Hz fields is 10 mA/nf (to workers). The aim of this study is to examine the induced current densities due to power system fields in the working environment by using the spheroidal calculation model. The study includes 27 workers exposed to electric and magnetic fields from power systems in different work environments. The fields in the workplaces were measured for calculation. The internal field and current density induced in a human body by the electric and magnetic fields was calculated using the spheroidal model, which is suitable for evaluating the current density in the whole body. Tissue conductivity of 0.2 S/m was used in this calculation. The highest measured values in different workplaces were 0.14 kV/m ... 11.2 kV/m for electric fields and 0.57 uT ... 16.2 uT for magnetic fields. The calculated internal fields caused by the electric fields were 0.097 mV/m ... 7.79 mV/m. The induced internal currents were 0.019 mA/nf ... 1.56 rnA/m^ by electric fields and 0.0050 mA/nf ... 0.14 mA/nf by magnetic fields. When the current densities were roughly summed the values were 0.024 mA/nf ... 1.70 mA/nf. The internal current densities are clearly below the ICNIRP guidelines, 10 mA/m\ For the general public the exposure limits are lower because of safety margins. The calculated values are far from these values as well. The calculated internal currents caused by electric fields are about ten times higher than the currents caused by magnetic fields.

Measurement of Exposure to Magnetic Fields from Electrical Appliances

The reason for magnetic field measurements from electrical appliances is to find out what is the exposure caused by them. Another reason for the increasing amount of measurements is the EMC (electromagnetic compatibility) standard, which sets the magnetic field immunity level for appliances 1.

Long-Term Measurement of Magnetic Fields in Exposure Assessment

The number of magnetic field measurements has increased in recent years. One reason for this trend is public concern about the possible health risks of magnetic fields from electrical appliances and wiring. Another important reason is the technical EN-standard for electromagnetic compatibility (EMC) of appliances1. The aim of this study was to investigate the extremely low frequency magnetic fields in work and living environments and test different methods for measurement.

Attenuation of extremely low frequency magnetic fields from appliances

The main reason for magnetic field measurements is to find out what causes disturbances in electrical appliances. Another reason for the increasing amount of measurements is the EMC (electromagnetic compatibility) standard, which sets the magnetic field immunity level for appliances [1]. Besides these technical points of view, possible health effects caused by the power frequency magnetic fields have also been discussed in recent years, and there are already guidelines for exposure to these fields [2, 3].