• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.18 no.10
• /
• pp.960-964
• /
• 2005

In this paper, we dealt with a partial discharge(PD) measurement method that has been accepted as an effective and non-destructive technique to estimate insulation performance of low-voltage electric and electronic devices. The PD measurement system Is composed of a coupling network, a low noise amplifier, and associated electronics. h shielded box Is adopted to make a better measurement environment against around noise. A low cut-off frequency of the coupling network estimated by a sinusoidal wave input was 125 kHz (-3 dB). Calibration tests on laboratory set-up have shown that the PD measurement system has a stable sensitivity of 10 mV/pC. In an application test oil a low-voltage three phase Induction motor (5 HP), we could detect 0.53 pC level of partial discharge at the applied voltage of AC 650 $V_{peak}$.

• Journal of Power Electronics
• /
• v.13 no.5
• /
• pp.877-883
• /
• 2013

This paper discussed a transformer-less shunt static synchronous compensator (STATCOM) with consideration of the following aspects: fast compensation of the reactive power, harmonic cancelation and reducing the unbalancing of the 3-phase source side currents. The STATCOM control algorithm is based on the theory of instantaneous reactive power (P-Q theory). A self charging technique is proposed to regulate the dc capacitor voltage at a desired level with the use of a PI controller. In order to regulate the DC link voltage, an off-line Genetic Algorithm (GA) is used to tune the coefficients of the PI controller. This algorithm arranged these coefficients while considering the importance of three factors in the DC link voltage response: overshoot, settling time and rising time. For this investigation, the entire system including the STATCOM, network, harmonics and unbalancing load are simulated in MATLAB/SIMULINK. After that, a 35KVA STATCOM laboratory setup test including two parallel converter modules is designed and the control algorithm is executed on a TMS320F2812 controller platform.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.18 no.5
• /
• pp.431-438
• /
• 2005

In this paper, we propose the built-in current testing circuit for improving reliability As the integrated CMOS circuits in a chip are increased, the testability on design and fabrication should be considered to reduce the cost of testing and to guarantee the reliability In addition, the high degree of integration makes more failures which are different from conventional static failures and introduced by the short between transistor nodes and the bridging fault. The proposed built-in current testing method is useful for detecting not only these failures but also low current level failures and faster than conventional method. In normal mode, the detecting circuit is turned off to eliminate the degradation of CUT(Circuits Under Testing). The differential input stage in detecting circuit prevents the degradation of CUT in test mode. It is expected that this circuit improves the quality of semiconductor products, the reliability and the testability.

• Journal of Information Technology Applications and Management
• /
• v.13 no.2
• /
• pp.127-143
• /
• 2006

As the number of Internet users increases, online shopping malls are gradually flourishing and sales are continuously growing. However, since consumers are not able to check what they purchase when buying products on the Internet, they are bound to have higher risk perception than buying directly from off-line stores. Especially, sporting goods require a special attention because a preliminary test is important. Therefore, the risk perception is much higher when people purchase sporting goods online. This study first identifies the multi-dimensionality of risk perception. Then, it investigates whether online purchasing experience of sporting goods makes differences in the level of risk perception. In addition, it examines whether the risk perception by those who had an experience in purchasing sporting goods online affects the customer satisfaction. This study has identified five dimensions in the concept of risk perception, such as financial risk, performance risk, security risk, delivery risk, and psychological/physical risk. A statistical analysis shows that people without an experience in purchasing sporting goods online have perceived significantly higher performance risk, security risk, and psychological/physical risk than those with online purchasing experiences. Finally, this study has found that delivery risk, financial risk, and psychological/physical risk have significant negative influences on the customer satisfaction.

• Journal of the Architectural Institute of Korea Structure & Construction
• /
• v.34 no.6
• /
• pp.55-61
• /
• 2018

This study aims to analyze the performance of Heated-nonslip using renewable energy to prevent nonslip freezing during winter. For this purpose, power generation system and congratulatory devices using solar energy are designed, and it is designed to provide regular electricity to heat up nonslip through Electrical storage system(ESS). In this study, It is intended to analyze the level of electrical energy suitable for nonslip using 24V or 48V, and to measure the temperature changes and temperature distribution according to the location of the test object. As a result of the experiment, nonslip's frame temperature was measured at $-7.5{\sim}-5^{\circ}C$ on average, and $-1{\sim}-2^{\circ}C$ on the heating cable during the supply of 24V and this could not be the solution for defrosting freezing nonslip in the winter. As a result of heating nonslip by supplying 48V with an electrical power of 8W, the temperature of the nonslip was shown to be between $5^{\circ}C$ and $11^{\circ}C$ to $13^{\circ}C$. Even if the power supply was switched on and off every minute, the temperature did not drop below $4^{\circ}C$ and the frozen ice melted on the nonslip without freezing.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.27 no.3
• /
• pp.175-179
• /
• 2022

Magnetic arc extinguishing technology is effective as an extinguishing device for low-voltage direct current (DC) circuit breakers with a resistive load of ≤4 kW. The separation distance between the magnet and the electrical contact must be shortened to increase the magnetic arc extinguishing force. However, if the magnet is installed too close to the electrical contact points, the magnet is exposed to high temperatures due to the arc current generated when the load current is cut off and the magnetism is lost. To solve this problem, the effective magnetic flux density at the electrical contact can be maintained high by placing the arc extinguishing magnet in a tandem structure with the electrical contact point between them, and the proper separation distance between the contact points and the magnet can be maintained. In addition, an electric arc extinguishing technology that emits arc energy using a series circuit of diode and resistor is used to suppress the continuous arc voltage generated by the inductive load. For the proposed circuit breaker, the breaking characteristics are analyzed through the breaking test for the DC load of the 760 V level, the load power of 4 kW, and the time constant of 5 ms, and an appropriate arc extinguishing design guideline is proposed.

• ALGAE
• /
• v.37 no.1
• /
• pp.63-74
• /
• 2022

Perennial stipitate kelps are globally distributed and individual species can inhabit broad latitudinal ranges, expressing notably longevous persistence. Despite the foundational role kelps provide to their communities, little is known about the variability in persistence of the stipitate kelps at local spatial scales. We studied the population persistence of Eisenia arborea, a heat- and wave force-tolerant perennial stipitate kelp with a distributional range extending from British Columbia to south of the range limit of all other northeast Pacific kelps, in Baja California Sur, Mexico. Persistence characteristics for E. arborea among sites were compared and used to test the hypothesis that stand persistence varied at local spatial scales around Isla Natividad, a Pacific island off the Baja California peninsula with documented spatiotemporal environmental heterogeneity. Collected individuals around the island were "aged" using the previously validated age estimation technique of counting annual cortical dark rings. After detecting no significant differences among sites in the covariation between estimated ages for collected individuals and stipe length, we utilized in-situ population-level stipe length measurements to more rapidly predict age structures within six stands around the island. Predicted age structures, and associated stand densities, revealed persistence characteristics and density varied at local scales and a strong positive relationship existed between stand density and stand mean and maximum ages. We speculate that stands responded differently to deterministic influences (e.g., the 2014-2016 marine heatwave and / or competition with Macrocystis) resulting in heterogenous local persistence of this foundation species.

• Membrane and Water Treatment
• /
• v.13 no.2
• /
• pp.105-110
• /
• 2022

Al₂O₃ positively charged nanofiltration composite membrane was successfully prepared with aluminate coupling agent (ACA) as modifier, sodium bisulfite (NaHSO₃) and potassium persulfate (K₂S₂O₈) as initiator and methacryloyloxyethyl trimethylammonium chloride (DMC) as crosslinking monomer. The surface of the membrane before grafting and after polymerization were characterized by SEM and FT-IR. Three factor and three-level orthogonal experiments were designed to explore the optimal conditions for membrane preparation, and the optimal group was successfully prepared. The filtration experiments of different salt solutions were carried out, and the retention molecular weight was determined by polyethylene glycol (PEG). The results showed that the polymerization temperature had the greatest effect on the rejection rate, followed by the reaction time, and the concentration of DMC had the least effect on the rejection rate. The rejection rates of CaCl₂, MgSO₄, NaCl and Na₂SO₄ in the optimal group were 83.8%, 81.3%, 28.1% and 23.6% (average value), respectively. The molecule weight cut-off of 90% (MWCO) of the optimal group was about 460, which belongs to nanofiltration membrane.

• International conference on construction engineering and project management
• /
• 2013.01a
• /
• pp.475-478
• /
• 2013

To carry out a one-off construction project successfully, effective and accurate early cost estimation is crucial, especially during the conceptual stage where very limited minimum information of construction project is given. As the level of accuracy of the early cost estimation has huge impacts on precise budgeting and cost management of a project, in other words, reducing the risk of a project, cost must be managed with special awareness. In an effort to improve the estimate accuracy of cost during the conceptual stage, this research introduces a Parameter Impact (PI) which can quantify weights of parameters and rank them; and PI development derived from the principle of impulse in physics is explicated. For a case study, 76 public apartment building cases in Korea are analyzed. To examine the validity of the proposed PI, a validation in terms of CBR applicability test and estimate accuracy comparisons using 10-nearest neighbor cases are carried out. The validation results support that the suggested PI can be applied in quantifying the weights of the parameters and CBR method for early cost estimation.

• Journal of Preventive Medicine and Public Health
• /
• v.28 no.3 s.51
• /
• pp.706-714
• /
• 1995

This is to analyze and compare the distribution of the liver function test and its abnormal rates of the preemployment screening for office workers in asymptomatic young age groups between female and male. Liver function test(SGPT and SGOT) of 8,184 young adults(2,633 in female and 5,551 in male ) were examined during the period from Jan.1, 1994 to Dec.31, 1994. The results were as follows; 1. Mean level of SGPT was $9.1{\pm}7.6(IU/L)$ in female, $21.0{\pm}27.9(IU/L)$ in male, and that of SGOT was $15.1{\pm}6.0(IU/L)$ in female, $20.5{\pm}26.5(IU/L)$ in male. There were significant differences(p<0.01) between female and male in both SGPT and 5G07 And also there was significant increasing trend(p<0.05) by age groups in male for SGPT, decreasing trend(p<0.01) in female for SGOT, 2. In the abnormal rates of liver function test by the level of cut-off value, there were significant differences up to twice between the lowest and the highest cut-off value in both female(0.4% vs 0.7%) and male(6.5% vs 32.4%) 3. Abnormal rate of SGPT was 0.4% in female and 6.3% in male, and that of SGOT was 0.2% in female and 1.2% in male with significant differences between female and male in both tests.