Dong-Il Lee

New formulas for predicting audible noise from overhead HVAC lines using evolutionary computations

Audible noise (AN) produced by corona discharges from high voltage transmission lines is one of the more important considerations in line design. Therefore, line designers must predetermine the AN using prediction formulas. This paper presents the results of applying evolutionary computation techniques using AN data from lines throughout the world to develop new highly accurate formulas for predicting the A-weighted AN during heavy rain and stable rain from overhead AC lines. Calculated ANs using these new formulas and existing formulas are compared with measured data.

Dissolved Gas Analysis of Power Transformer Using Fuzzy Clustering and Radial Basis Function Neural Network

Diagnosis techniques based on the dissolved gas analysis (DGA) have been developed to detect incipient faults in power transformers. Various methods exist based on DGA such as lEC, Roger, Dornenburg, and etc. However, these methods have been applied to different problems with different standards. Furthermore, it is difficult to achieve an accurate diagnosis by DGA without experienced experts. In order to resolve these drawbacks, this paper proposes a novel diagnosis method using fuzzy clustering and a radial basis neural network (RBFNN). In the neural network, fuzzy clustering is effective for selecting the efficient training data and reducing learning process time. After fuzzy clustering, the RBF neural network is developed to analyze and diagnose the state of the transformer. The proposed method measures the possibility and degree of aging as well as the faults occurred in the transformer. To demonstrate the validity of the proposed method, various experiments are performed and their results are presented.

Effective Combination of Soft Magnetic Materials for Magnetic Shielding

This study proposes an effective method in the arrangement of layers of high permeability materials for shielding power frequency magnetic field. The side of a neutral ground reactor was blocked with one or two layers of grain-oriented electrical steel (GO), nonoriented electrical steel (NGO), and permalloy (PC). In a weak magnetic field, PC showed the highest shielding performance, whereas GO was the best in a strong magnetic field. NGO had a lower shielding performance than GO, but was better than PC in a very strong magnetic field. When shielding with two layers directly adjacent to each other, the performance level of GO/PC combination (GO is closer to the field source) was between that of GO/GO and PC/PC combinations. When the two layers were slightly separated, on the other hand, GO/PC was most effective in a wide range of magnetic fields. These results are due to the shunt effect of high permeability materials and change of rank of permeability with magnetic field strength between different magnetic materials. Closely adjacent layers act as one body under the regime of shunt mechanism of magnetic shielding. Once the layers are separated, the GO sheet effectively reduces the strong magnetic field first, and then the PC sheet effectively shields the weakened field.

Electromagnetic interference from a three phase double circuit 765-kV test line

This paper presents the results of long-term electromagnetic interference (EMI) measurements on the bundle of 6 Cardinal conductors tested at Koreas Kochang 765-kV full-scale test line. The instrumentation and the most important features of the facilities are also described. This new 3-phase double circuit test line can be energized at line-to-line voltages up to 850 kV. The analysis of the data shows that the 6-Cardinal conductor bundle meets the radio and television interference guidelines of the Korea Electric Power Corporation (KEPCO).

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.

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.

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.

Failure characteristics of suspension-type porcelain insulators on a 154 kV transmission line

The paper reports on the failure characteristics of porcelain suspension insulators removed from a 154 kV transmission line in Korea. It is found that it is very important to choose the test data describing the homogeneity of porcelain, which is related to the micro-crack propagation in the porcelain body, for leveling the ageing state of the porcelain insulators. Tests such as the Rockwell hardness, is found to be effective in calculating the statistical values on the micro-crack fracture of the porcelain body. The combined thermal and mechanical tests have a close relationship to the dielectric strength of the porcelain body. The use of the Weibull distribution function is shown to be a very reasonable way of calculating the failure probability of aged porcelain insulators

A study on the influence of forest fire on polymer insulators

The forest fire simulation tests were performed with polymer and porcelain insulators at Gochang Power Testing Center. These tests consisted of open flame rising up to 600~820degC as being measured at insulator surface. Mechanical and electrical characteristics such as specific mechanical load, low frequency dry flashover voltage and impulse flashover voltage were analyzed for the polymer insulators before, during and after simulation tests compared with porcelain insulators. At the end of fire simulation tests, there was no detrimental deterioration of any insulators. All insulators passed the criteria of KEPCO specification. This study showed that forest fire simulation had no impact on polymer insulators.

Technique to decrease the electric field intensity on conductor surface using the asymmetrical-sized conductor bundle

Corona discharges form at the surface of a transmission line conductor when the electric-field intensity on the conductor surface exceeds the breakdown strength of air. In order to decrease the electric-field intensity on the conductor surface, a new 6 conductor bundle has been studied. This bundle, asymmetrical-sized conductor bundle, consists of a large subconductor at the bottom two conductor positions in the 6-conductor bundle of each phase of the line. The electric field intensity on these two large subconductors is reduced which in turn reduces the corona noise. It is proven that the newly proposed method is a better solution for decreasing the electric- field intensity than either the conventional bundle or the asymmetric bundle proposed by EPRI(Electric Power Research Institute).