http://doi.org/10.5207/JIEIE.2024.38.1.001

Jai-Won Chung ; Sangsu Park ; Seok-Oh Bang ; Seong-Sik Yoo ; Hyun-Seok Choi ; Jin-Sung Rho

Few studies have looked at the prediction method for preferred dimming level of lighting user using usage environment data(usage time, weather, etc.) and machine learning methods. In this paper, we propose the random forest model for prediction of preferred dimming level of lighting user using usage environment data. Temperature, relative humidity, precipitation, wind speed, hour, AM/PM status, day of the week, weekday/ weekend status, and dimming setting were measured at one hour interval through the experiment, and the relation of each variable were investigated through the PhiK correlation coefficient. About 70% of the total data (n = 171) was used as the training set data (n = 119) for construction of the random forest model. The model using the 3-fold cross validation method were constructed using the training set data. About 30% of the total data was used as the test set data (n = 52) for evaluation of the model. The accuracy of random forest model using two values(hour, temperature) were 78.9%.

http://doi.org/10.5207/JIEIE.2024.38.1.008

Jae-Jun Ko ; Sung-Won Kim ; You-Jung Lee

The digital smart lighting devices industry is experiencing a rapid progression in digital transformation, evolving into smart lighting that not only offers diverse content but also delivers customized information to consumers through varied communication channels. In the advertising lighting market, the approach goes beyond traditional methods of placing ads on electronic signs outside buildings. It extends past advertising and information, spanning traditional and digital media, outdoor advertising, and mobile advertising in the realm of out-of-home advertising. This concept expands by integrating with other media through the use of digital smart lighting devices like broadcasting. Transportation advertising using digital smart lighting devices is a growing trend, and external advertising on buses is being developed as an alternative product. However, due to related regulations, companies' product development and market launch are delayed. This study examines the domestic laws related to installation of digital smart lighting devices products on bus vehicles. We intend to study the regulatory status and conformity assessment standards to ensure safety.

http://doi.org/10.5207/JIEIE.2024.38.1.015

Minchan Bae ; Yong Wook Lee

In this paper, we demonstrated the separate measurement of refractive index(RI) and temperature using a combination of the multi-mode interference(MMI) of no-core fiber(NCF) and the grating resonance of double-clad fiber(DCF). An NCF segment concatenated with a long-period fiber grating (LPFG) inscribed on DCF was utilized as the sensor head. We selected two resonance dips in the transmitted spectrum generated by the MMI and the grating resonance as sensor indicators DMMI and DLPFG. First, we observed how the two sensor indicators responded to external RI variations by increasing the concentration of the sucrose solution injected around the sensor head from 0% to 50%(1.3330 ∼ 1.4201RIU) with increments of 10%. While one sensor indicator DMMI formed by the MMI showed a total wavelength shift of ∼6.6nm with an adjusted R2 value of 0.99821, another sensor indicator DLPFG formed by the grating resonance of the LPFG written on DCF showed a total wavelength shift of ∼0.28nm with an adjusted R2 value of 0.43149. This result indicates that DMMI is 23 times more sensitive to RI than DLPFG and that DMMI can be employed to measure RI almost independently of ambient temperature changes. On the other hand, to investigate the temperature response of the sensor indicators, the sensor head was placed inside the glass container filled with distilled water, and the temperature of the incubated distilled water(0% sucrose solution) was increased using a hot plate. With the increase of the applied temperature from 30 to 55℃, DLPFG showed a total wavelength shift of ∼1.86nm with an adjusted R2 value of 0.9991. In contrast, for the same temperature change, DMMI exhibited a total wavelength shift of ∼0.18nm with an adjusted R2 value of 0.92857. This implies that DLPFG is sufficient to be used for temperature measurement nearly independent of external RI variations. As a result, the two sensor indicators DMMI and DLPFG of the proposed sensor head can be utilized for the separate measurement of RI and temperature changes, respectively.

http://doi.org/10.5207/JIEIE.2024.38.1.020

Jin Lee

The purpose of this study is to compare the muscle fatigue estimation performance of three complexity measures, LZ(Lempel-Ziv), PLZ(Permutation LZ) and DLZ(Dispersion LZ) with the conventional frequency measure (MDF:median frequency) based on robustness and sensitivity. Surface EMG(electrmyogram) signals(a total of 198 signals) were recorded in biceps brachii muscle with isometric 20%, 50% and 80%MVC(maximal voluntary contraction)s from eleven subjects and then, in this study for the first time, DLZ measure was applied to estimate muscle fatigue from these signals. Four measures were calculated from the 198 SEMG signals and the resulting fatigue estimation performance was evaluated in the point of robustness and sensitivity. Results show that DLZ measure with adopting four symbolic sequence(k=4) is appropriate for muscle fatigue estimation and the conventional MDF measure is more robust (over mean 12%) and sensitive(over mean 88%) than three LZ complexity measures(LZ, PLZ, DLZ) for estimating muscle fatigue from surface EMG signal.

http://doi.org/10.5207/JIEIE.2024.38.1.028

Woocheol Shin ; Junyoung Park ; Hyoungku Kang

This study investigates the insulation breakdown characteristics of superconducting magnets under high vacuum conditions, focusing on the effects of localized vacuum degradation and the material properties of the stabilizer layer used in superconducting wires. To understand the influence of vacuum pressure variations and electrode material on insulation strength, experiments were conducted using spherical electrodes composed of five different materials. These experiments demonstrated how changes in vacuum pressure affect insulation breakdown characteristics, following the pattern of Paschen’s curve. A notable decrease in breakdown voltage was observed in mid-vacuum regions, while an increase was seen in high vacuum conditions, underscoring the significant impact of vacuum pressure on insulation breakdown mechanisms. The results also highlighted the role of electrode material’s work function in high vacuum conditions, where materials with higher work functions exhibited higher breakdown voltages. This was particularly evident in the comparison of alloys like Brass, which, despite having a high work function, showed lower breakdown voltages due to surface impurities promoting discharge. In contrast, high-strength metals like Stainless Steel demonstrated higher breakdown voltages, attributed to their chemical stability and resistance to oxidation and corrosion.

http://doi.org/10.5207/JIEIE.2024.38.1.035

Hoon Jung ; Joon-Ho Ahn

Recently, Industrial complexes have been undergoing rapid changes not only in the global economy, but also in the energy sector, such as in response to climate change and the Fourth Industrial Revolution. It is extremely difficult to supply 100% of the energy consumption of industrial parks with new renewable energy, and currently solar power generation, small wind power, hydrophobic power, etc. are mainly used. In this paper, we conducted an economic analysis based on Net Present Value (NPV) and found that, with the exception of solar power generation, the return on construction costs is in the red due to high unit prices and installation and operation costs. As a result of predicting the average price of carbon credits over the next 20 years, By combining the electricity bill revenue of about 5.6 billion won and the carbon emissions credit revenue of about 20 billion won due to the expansion of distributed energy sources, it is expected to generate a profit of about 25.6 billion won compared to the investment in distributed energy resources of 18.88 billion won. It is judged that renewable energies such as small wind power and hydrophobic power should be considered depending on the location of the industrial park and the surrounding environment.

http://doi.org/10.5207/JIEIE.2024.38.1.040

Byeong-Hyeon An ; Jae-Deok Park ; Jun-Soo Che ; Tae-Hun Kim ; Tae-Sik Park

Many studies have been conducted around the world to reduce carbon emissions. In the power sector, a policy is being implemented to reduce the proportion of coal power generation and convert to new and renewable energy. However, unlike synchronous generators, renewable power sources vary in power generation depending on environmental changes such as weather. And the increase in distributed generator means that the number of inverter-based power generator in the grid increases and the proportion of synchronous generators decreases. Therefore, the inertia and reserve power of the system are reduced, which poses a threat to system frequency stability. Generally, when analyzing frequency response, the lowest frequency (Frequency Nadir) and Rate of Change of Frequency (RoCoF) are used as representative indicators. To improve frequency stability, many studies have focused on grid-forming converters using inverters and virtual inertial control of wind power. In this paper, we propose a variable frequency transformer (VFT) method to improve the frequency stability of the power grid. VFT allows frequency variations and bidirectional power transmission by controlling the rotation direction and speed of the rotor and has rotational inertia. Using this feature, the grid frequency stability can be improved with VFT. The performance of the proposed scheme was verified through Matlab Simulink simulation.

http://doi.org/10.5207/JIEIE.2024.38.1.049

Sang-Yeop Kim ; Eun-Hyeok Choi

On January 1, 2021, it was enacted and revised to facilitate the application of the relevant industry in order to meet international standards and improve and supplement the requirements by conducting code changes and technical reviews during the grace period for application of the Korea Electrical Equipment Regulations. Based on this background, 'KEC', the standard for installing electrical equipment in Korea, was developed so that the grounds for many foreign regulations could be identified based on IEC standards similar to those of the domestic electrical environment and applied to domestic sites. The ground resistance and ground resistance were measured and the simulation results were derived and interpreted by applying the KEC grounding method revised through the on-site project. So, we checked how the KEC grounding method was applied in the field and learned the technical characteristics and construction method.

http://doi.org/10.5207/JIEIE.2024.38.1.055

Junyoung Park ; Woocheol Shin ; Hyoungku Kang

This study investigates the impact of surface roughness on the surface discharge characteristics of solid insulators under high vacuum conditions, essential for the insulation design of superconducting magnets operated in such environments. Experiments were conducted to analyze the surface discharge properties in relation to the surface roughness of Polyether ether ketone (PEEK), a material commonly used as a solid insulator in superconducting applications, both in atmospheric and high vacuum conditions. Furthermore, additional experiments were carried out on other widely used solid insulators in superconducting applications, namely Monomer Casting (MC) Nylon, Glass Fiber Reinforced Polymer (GFRP), and Teflon, to assess their surface discharge characteristics under high vacuum. The results indicated that the surface discharge behavior of these solid insulators is significantly influenced by their surface roughness under high vacuum conditions. It was observed that an increase in surface roughness led to a decrease in surface discharge values, whereas a decrease in roughness resulted in higher discharge values. This trend is attributed to the variation in the amount of residual charge on the insulator’s surface, which is affected by the surface texture. Consequently, for enhanced electrical stability of superconducting magnets in high vacuum, it is crucial to optimize the surface roughness of solid insulators to minimize residual charges and prevent insulation breakdown due to collision ionization.

http://doi.org/10.5207/JIEIE.2024.38.1.061

Ung-Hui Yun ; Seong-Hun Kim ; Jin-Gyu Kim

Dielectric barrier discharge(DBD) is categorized into volumetric dielectric barrier discharge (VDBD) and surface dielectric barrier discharge(SDBD). In the field of particle charging, VDBD devices have a complex structure compared to SDBD devices, and the plasma’s generation direction hinders the flow of particles. In addition, the research on the waveform of the applied voltage is limited to relatively regular non-sinusoidal waves such as square waves and triangular waves. Therefore, in this study, the energy and power consumption characteristics of SDBD under four low-frequency applied voltage waveforms were studied. The results of the study show that Type 4 has a higher energy and power consumption than other types of applied voltage waveforms, 4.75W and 6.10W, respectively, according to the calculation method using the Lissajous curve and voltage × current, and this can be visually verified through discharge photograph.

http://doi.org/10.5207/JIEIE.2024.38.1.067

Jae-Deok Park ; Tae-Hun Kim ; Byeong-Hyeon An ; Jun-Soo Che ; Tae-Sik Park

The global response to the climate crisis has led to the implementation of various policies worldwide, with a domestic focus on increasing the share of renewable energy sources such as wind and solar power. However, the rapid expansion of renewable energy sources may induce power supply instability due to their intermittent nature. In this paper, we propose the application of Variable Frequency Transformers (VFT) to address the instability in power supply systems. VFTs are bidirectional power devices capable of connecting asynchronous power systems. To determine optimal installation locations for VFTs, the power system is partitioned based on voltage sensitivity. VFTs are then strategically placed between the partitioned power system regions, and an analysis of the safety of power supply across transmission lines, considering the intermittent generation patterns of renewable energy, is conducted to identify the most suitable installation points. The proposed approach is validated using the IEEE 39 bus system, and simulations in MATLAB demonstrate the enhanced power supply stability and the impact of VFT application.

http://doi.org/10.5207/JIEIE.2024.38.1.074

Yongchul Kim ; Youngwoo Noh

As automotive steering technology advances and becomes electrified, high-level safety designs such as fault-tolerant or fault-operation are required to maintain the primary function even when a failure occurs. For this purpose, a dual-winding electric motor was introduced in the steering system, making it possible to maintain the driver’s steering assistance function even in the event of breakdown cases. Dual-winding motors can take into account various winding arrangements depending on the pole-slot combination of machines, and accordingly, when driven with only one 3-phase winding, non-uniformity of the magnetic flux linkage to the phase windings may occur and eventually lead to different magnitudes of mutual inductance. This paper presents a mathematical model of dual-winding motors and studies how the imbalance of mutual inductance for each winding arrangement affects the characteristics of the electric machine. As a result, it was derived through the calculation results of the mathematical model that the electrical secondary torque ripple appears significantly in the winding method where the mutual inductance imbalance is significant, and the validity of the calculation results of the mathematical model was proven by comparing it with the finite element analysis results.