Mun-No Ju

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.

Calculation of Ion-Flow Field of HVdc Transmission Lines in the Presence of Wind Using Finite Element-Finite Difference Combined Method With Domain Decomposition

A combined method adopting the domain decomposition is proposed for analyzing the ion-flow field of high-voltage direct current transmission lines, including the effect of the transverse wind. The upstream finite-element method is used with a dense triangle mesh in the vicinity of bundle conductors to guarantee the accuracy. The upstream finite-difference method is proposed and the larger uniform quadrilateral grid is applied to simulate the ion-flow field in the rest of the region with a satisfactory precision. The calculation process of the Poisson equation is iterated with the Dirichlet-Neumann algorithm to coordinate the solution between adjacent subdomains. The proposed approach improves the efficiency and remains stable with high wind speed. Finally, the influence of wind on the ion-flow field is analyzed and calculations are in good agreement with experimental data and results in the previous literature.

High-Efficient Evaluation of the Lightning Electromagnetic Radiation Over a Horizontally Multilayered Conducting Ground With a New Complex Integration Path

An efficient approach to evaluate the radiated electromagnetic field of a lightning channel over a horizontally stratified conducting ground is proposed in this paper. The electromagnetic field component produced by a lightning channel, expressed in the form of generalized Sommerfeld integral (GSI) with a complicated integrand, is calculated along a newly proposed path in the complex plane. Due to the change of the integration path, the integrand in the GSI turns out to decay dramatically fast and without any oscillation at all. As explained in this paper, the larger horizontal distance will become the benefit to achieve a quicker convergence, which is just opposite to the case that the integration path is along the real axis. The validity of the proposed methodology is justified by the extensive comparison with the results in other publications. As a matter of fact, the methodology in this paper can be generalized to evaluate stratified conducting ground with any number of layers.

Efficient evaluation of the earth return mutual impedance of overhead conductors over a horizontally multilayered soil

Purpose – The per-unit-length earth return mutual impedance of the overhead conductors plays an important role for analyzing electromagnetic transients or couplings of multi-conductor systems. It is impossible to have a closed-form expression to evaluate this kind of impedance. The purpose of this paper is to propose an efficient numerical approach to evaluate the earth return mutual impedance of the overhead conductors above horizontally multi-layered soils. Design/methodology/approach – The expression of the earth return mutual impedance, which contains a complex highly oscillatory semi-infinite integral, is divided into two parts intentionally, i.e. the definite and the tail integral, respectively. The definite integral is calculated using the proposed moment functions after fitting the integrand into the piecewise cubic spline functions, and the tail integral is replaced by exponential integrals with newly developed asymptotic integrands. Findings – The numerical examples show the proposed approach ha...

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).

Design of the DC ±500kV full scale transmission test line in Gochang

A HVDC test line that functions as a prototype variation was constructed in Korea, after considering the main functions and characteristics of diverse ±500kV DC transmission test line towers and the results of the analysis of the lines insulation, environment, fitting, transmission equipment, economic feasibility, and operational efficiency. The variable prototype test line has advantages in line-related researches, including in the fitting design, insulation coordination design, line construction technology and transmission equipment development, and does not require high-cost towers, unlike overseas test lines. The maximum applied voltage of the newly constructed DC test line was ±600 kV, and a measurement system was established around the line to evaluate the interference factors. Tests on various environmental characteristics will be performed to derive the optimal pole arrangement coordinates for the Korean environment, while changing the pole arrangement and height of the line using a large hoist installed at special arms in tower No. 2 and 3.

Semianalytical Approach to the Inverse Fourier Transform and Its Application in Evaluating Lightning Horizontal Electric Field

A semianalytical inverse Fourier transform, which can evaluate the time response at arbitrary time, is proposed. The basic idea is fitting the response in frequency domain by a sum of piecewise cubic spline functions with an adaptive sampling strategy, and the response in time domain is evaluated with the help of the moment functions to avoid calculating the highly oscillatory integral. A recursive algorithm is derived, which can efficiently calculate the moment functions with different ranks. As an application of the proposed approach, the underground horizontal electric field of a lightning channel is evaluated in the time domain. In comparison with the results in the published literature, the numerical examples show that the proposed approach can save the computational time at least 50 times compared to the one using a conventional inverse Fourier transform technique. The proposed approach, in fact, can be generalized to apply to other scenarios when the inverse Fourier transform is involved.

Efficient Evaluation of Earth Return Impedances of Arbitrary Conductor Arrangements With a Horizontally Multilayered Soil

The evaluation of the earth return mutual impedance of arbitrary conductor arrangements with a horizontally multilayered nonmagnetic soil is of great significance when the electromagnetic compatibility is concerned. To evaluate the earth return impedance accurately and efficiently, a semianalytical approach is proposed in this paper. With the proposed approach, the expression of the earth return impedance, which includes a complex highly oscillatory integrand, is divided into two parts, i.e., the definite and the tail integral. The definite integral is evaluated by using the moment technique and the tail integral is evaluated by using the exponential integrals with an asymptotic integrand. The numerical examples show that the proposed algorithm can evaluate the earth return impedance with various parameters and arbitrary conductor arrangements accurately and efficiently and the required computational time of the proposed approach is almost independent of the geometric and electric parameters.

Ground Admittance of an Underground Insulated Conductor and its Characteristic in Lightning Induced Disturbance Problems

The evaluation of the ground admittance of an underground insulated conductor with a homogeneous nonmagnetic earth is of great significance when the electromagnetic compatibility is concerned. To evaluate the ground admittance efficiently, researchers proposed that the ground impedance of the conductor should be evaluated first and the ground admittance is related to the ground impedance through the wave number in the soil. There are several approximated analytical expressions for the evaluation of the ground impedance with a homogeneous earth and this fact makes the ground admittance easy to obtain. The characteristic of the approximated ground admittance evaluation approach is examined in this paper. Numerical examples illustrate that at frequencies with which the burial depth is much larger than the skin depth in the soil, the ground admittance and the ground impedance of the buried cable are well-related through the wave number in the soil. However, at other frequencies, the approximated approach fails to evaluate the ground admittance accurately. This paper also reveals that the discrepancy of the ground admittance will lead to a noticeable difference in the lightning induced voltage on buried cables.

A Hermite interpolation model for reconstructing the frequency spectrum of the lightning horizontal electric field

Purpose – The purpose of this paper is to propose a fast algorithm to calculate the lightning horizontal electric field over a lossy ground. Design/methodology/approach – The lightning horizontal electric field in frequency domain is approximated by a number of piecewise cubic polynomial functions by using the proposed adaptive Hermite strategy. To utilize the Hermite strategy, the frequency domain spectrum and its derivative with respect to frequency are required. The integral kernel of the derivative appears singular along the real axis. To overcome this singularity and accelerate the calculation, a new integration path is proposed. With the help of the Hermite interpolation model and the new path, the lightning horizontal electric field in time domain can be obtained rapidly. Findings – The singularity problem has been overcome with the new integration path and the adaptive Hermite strategy proposed in this paper is at least 50 times faster than the one using the equally spaced sampling approach. Origi...