Sung-Ho Myung

Assessment of Magnetic Field Mitigation and Electrical Environmental Effects for Commercially Operating 154kV Transmission Lines with Passive Loop

Power frequency magnetic field is still a critical problem for new construction of overhead power transmission lines in Korea because most people have been concerned about possibly carcinogenic effects of it. Although reference level of power frequency(60Hz) magnetic field has been set to 200uT in ICNIRP guidelines published in 2010, Korean government has no intention of adjusting 83.3uT specified by law in 2006 to this new reference level in consideration of people’s concerns for the time being. Regardless of the current regulated magnetic field value, electric utility company has been trying to reduce magnetic field in the residential area in the vicinity of overhead power transmission lines to take into account of public concerns on the long-term effect of magnetic fields. In an effort to reduce magnetic field, engineering side has made considerable efforts to develop passive loop based, cost-effective mitigation technique of power frequency magnetic field more than ten years. In order to verify developed power frequency magnetic field mitigation technique based on passive loop, a horizontal type of passive loop was designed and installed for commercially operating 154kV overhead power transmission line for the first time in Korea. The measurement results before and after the installation of passive loop showed that magnetic field could be reduced to about 20%. The electrical environmental effects such as AN, RI and TVI were assessed before and after the installation of passive loop and these values were complied with the requirements specified by electric utility. It has been confirmed from the field test results that passive loop could be commercially and cost-effectively utilized to mitigate power frequency magnetic field.

Development of a New Personal Magnetic Field Exposure Estimation Method for Use in Epidemiological EMF Surveys among Children under 17 Years of Age

A number of scientific researches are currently being conducted on the potential health hazards of power frequency electric and magnetic field (EMF). There exists a non-objective and psychological belief that they are harmful, although no scientific and objective proof of such exists. This possible health risk from ELF magnetic field (MF) exposure, especially for children under 17 years of age, is currently one of Koreas most highly contested social issues. Therefore, to assess the magnetic field exposure levels of those children in their general living environments, the personal MF exposure levels of 436 subjects were measured for about 6 years using government funding. Using the measured database, estimation formulas were developed to predict personal MF exposure levels. These formulas can serve as valuable tools in estimating 24-hour personal MF exposure levels without directly measuring the exposure. Three types of estimation formulas were developed by applying evolutionary computation methods such as genetic algorithm (GA) and genetic programming (GP). After tuning the database, the final three formulas with the smallest estimation error were selected, where the target estimation error was approximately 0.03 μT. The seven parameters of each of these three formulas are gender (G), age (A), house type (H), house size (HS), distance between the subjects residence and a power line (RD), power line voltage class (KV), and the usage conditions of electric appliances (RULE).

Power Frequency Magnetic Field Reduction Method for Residents in the Vicinity of Overhead Transmission Lines Using Passive Loop

A power frequency magnetic field reduction method using passive loop is presented. This method can be used to reduce magnetic fields generated within the restricted area near transmission lines by alternating current overhead transmission lines. A reduction algorithm is described and related equations for magnetic field reduction are explained. The proposed power frequency magnetic field reduction method is applied to a scaled-down transmission line model. The lateral distribution of reduction ratio between magnetic fields before and after passive loop installation is calculated to evaluate magnetic field reduction effects. Calculated results show that the passive loop can be used to cost-effectively reduce power frequency magnetic fields in the vicinity of transmission lines generated by overhead transmission lines, compared with other reduction methods, such as active loop, increase in transmission line height, and power transmission using underground cables.

Occupational and residential personal exposures to magnetic field over 24-hour periods in Korea

The objective of this survey is to characterize personal magnetic field exposure of the general population in Korea. The participants of the survey on magnetic field exposure were selected randomly, by occupation. The participant wore the magnetic field meter for about 25-28 hours and the data were stored in the meter. In this first step survey, the number of participant is 244 and the second step, about 400 subjects is surveyed in the near future. The statistics of the 24-hour exposure data are the major concern of this survey. However the survey provided the opportunity to analyze exposures corresponding to different types of activities. It was analyzed by the separating periods of time corresponding to the following activities: entire 24-hour period, in bed, at work and by occupation. Therefore the database will be established to analyze the status of personal magnetic field exposure and safety.

Evaluation of the resistive current of the metal oxide surge arrester using the differential method

This paper aimed to measure the resistive-leakage-current component of the metal oxide surge arrester with a high degree of reliability, regardless of the quality of the applied voltage. Therefore, in this study, a new detection algorithm was developed to accurately detect the resistive-leakage-current component of the metal oxide surge arrester using the operating voltage of the metal oxide surge arrester. The developed algorithm was found to improve the reliability of the detection of the resistive leakage current, which is the criterion for the diagnosis of the metal oxide surge arrester.

Magnetic Shielding with Thin Magnetic Materials near Power Cables

In this work, wrapping conductors with thin magnetic materials is proposed as a magnetic shielding method. The 0.1 mm thick metal sheets of mu-metal, grain-oriented electrical steel, and non-oriented electrical steel were produced from commercial alloy sheets through cold rolling and followed high temperature annealing. In case of 3-phase electric currents, mu-metal was the best in shielding performance at a B-field magnitude of about 100 , whereas silicon steels were better than mu-metal at a B-magnitude over 500 . In addition, wrapping with silicon steel(inner) together with mu-metal(outer) resulted in a shielding factor less than 0.1 even at 500 . These results are due to changes in hierarchy of magnetic permeabilities of the materials with increasing magnetic field strength. In case of single-phase electric current, B-magnitude outside the magnetic shell was rather increased compared to the unshielded case. This result is explained by vector composition of B-fields near magnetic shielding materials.