• Journal of Mechanical Science and Technology
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• v.18 no.8
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• pp.1368-1374
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• 2004

The remaining life estimation for the aged components in power plants as well as chemical plants are very important because mechanical properties of the components are degraded with in-service exposure time in high temperatures. Since it is difficult to take specimens from the operating components to evaluate mechanical properties of components, nondestructive techniques are needed to evaluate the degradation. In this study, test materials with several different degradation levels were prepared by isothermal aging heat treatment at $630^{\circ}C$. The DC potential drop method and destructive methods such as tensile and fracture toughness were used in order to evaluate the degradation of 1Cr-1Mo-0.25V steels. In this result, we can see that tensile strength and fracture toughness can be calculated from resistivity and it is possible to evaluate material degradation using DC potential drop method, non-destructive method.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.5 no.4
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• pp.668-675
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• 2001

Recently, the performance of the commercial PCS(Personal Communication Service) system has been improved to the uppermost limit and ultimately the next generation mobile communication is to be realized by IMT-2000 (International Mobile Communication-2000) to provide multimedia services. Therefore, the new type receiving system is researched actively and one of the most important part in a receiver is direct conversion method. The direct conversion method is suitable for low power consumption, small size, MMIC, and low price, which is to be adopted to the next generation mobile communication systems. In this case, however, several problems occur due to DC-offset. The DC-offset suppresses amplification of the required signal because of the leakage signal of frequency synthesizer in the system. In this thesis, the removing method of DC-offset was considered. There are four removing techniques of DC-offset, which are AC-coupling, large capacitor, DC-feedback loop, and DC-free coding. Among these, the AC-coupling method is the most simplest method and the DC-feedback loop method has the best performance. Then, the performance of the AC-coupling method and DC-feedback loop method are evaluated by HP's ADS simulation tool. As a result, the AC-coupling method cannot be used to the digital communication systems due to data loss. On the other hand, it was confirmed that the DC-feedback loop method is suitable for the direct conversion receiver.

• Proceedings of the KIPE Conference
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• 2012.11a
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• pp.46-47
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• 2012

In the design of the battery charger it is important to limit the ripple current and voltage according to the manufacturer's recommendation for the reliable service and the extended life of the battery. However, it is often overlooked that these ripple components can cause internal heating of the battery, thereby reducing its service life. Thus the care must be taken in the design of the switching converter for the charge application through the accurate estimation of the output ripple values. In this research analysis on the output ripple of the dc-dc converter is detailed to provide a guideline for the design of the battery charger.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.67 no.1
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• pp.142-147
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• 2018

Private electrical facilities are judged whether it is suitable for the insulation aging condition of their incoming underground cables using DC leakage current test method. In the case where the service point of utility is the secondary side of cut out switch installed in the electric pole, there is a problem that it is difficult to separate the lightning arresters(LA) because of their high position of the pole. Therefore, the field test voltage is applied at value lower than DC 30 kV, which are stated in the inspection guideline. However, this test could reduced the insulation performance of the LA by accelerating the electrical stress of the metal oxide varistor element in the pre-breakdown region. In this study, we analyzed the relationship between the DC test voltage and the leakage current using the non-destructive DC high voltage equipment with leakage current measurement function. The results show that the leakage current increases sharply above the specified test voltage. As a consequence, it could be contributed to improve insulation aging inspection method by selecting the possible test area on the VI characteristic curve of the pre-breakdown area of the LA.

• The Transactions of the Korean Institute of Power Electronics
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• v.26 no.2
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• pp.90-95
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• 2021

In contrast to AC grounding systems, the ground electrode in DC systems continuously maintains positive or negative polarity. Ground electrodes with (+) polarity proceeds by oxidation reaction. Thus, the DC current should flow opposite to the polarity of the leakage current flowing through the (+) ground electrode by using a compensation electrode, and the current flowing through the (+) ground electrode can be 0A. However, according to protecting the (+) ground electrode, the compensation electrode corrodes and gets damaged. Thus, the (+) ground electrode must be protected from corrosion, and the service life of the compensation electrode must be extended. As an alternative, the average value of the current flowing through the compensation electrode should be equal with the value of the leakage current flowing through the (+) ground electrode by using the square waveform. Throughout the experiment, the degree of corrosion on the compensation electrode is analyzed by the frequency of the compensation electrode for a certain time. In the experiment, the frequencies of the square waveform are considered for 0.1, 1, 10, 20, 50, 100 Hz, and 1 kHz. Through experiments and analysis, the optimal frequency for reducing the electrolytic damage of the (+) electrode and compensation electrode in an LVDC grounding environment is determined.

• Journal of Electrical Engineering and Technology
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• v.5 no.2
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• pp.228-238
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• 2010

There is an increasing interest in research to help overcome the energy crisis that has been focused on energy storage applications in various parts of power systems. Energy storage systems are good at enhancing the reliability or improving the efficiency of a power system by creating a time gap between the generation and the consumption of power. As a contribution to the various applications of storage devices, this paper describes a novel algorithm that determines the power and storage capacity of selected energy storage devices in order to improve upon railroad system efficiency. The algorithm is also demonstrated by means of simulation studies for the Korean railroad lines now in service. A part of this novel algorithm includes the DC railroad powerflow algorithm that considers the mobility of railroad vehicles, which is necessary because the electric railroad system has a distinct distribution system where the location and power of vehicles are not fixed values. In order to derive a more accurate powerflow result, this algorithm has been designed to consider the rail voltage as well as the feeder voltage for calculating the vehicle voltage. By applying the resultant control scheme, the charging or discharging within a specific voltage boundary, energy savings and a substation voltage stabilization using storage devices are achieved at the same time.

• Proceedings of the KIPE Conference
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• 2001.10a
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• pp.497-501
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• 2001

Unbundled power quality service is paid much attention under the circumstances of deregulation and diversification of needs of customers for quality and price of electric power. Moreover, distributed generators (DGs) such as photovoltaic generations and wind turbines will be introduced to distribution system more and more, and reverse flow of active power has possibility to cause new problems in the distribution system such as voltage rise of distribution line and protection problem. Flexible, Reliable and Intelligent Electrical eNergy Delivery System, which is called FRIENDS, has been proposed as one of promising distribution system for such requirements, and intensive studies are under way. One of features of the system is introducing Quality Control Center (QCC) into the system for unbundled power quality service and easy installation of DGs. Two types of QCCs for such purposes are proposed, and simulation results are shown in this paper.

• Proceedings of the KIEE Conference
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• 1997.07a
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• pp.279-281
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• 1997

Batteries as an emergency power of stationary standby service are required to provide a reliable source of DC power needed to aid in safe AC power failure. It is important that the properly action in early stage as soon as possible, when the battery's deterioration is detected. This paper describes a practical diagnostic technique to monitor the state-of-health of lead acid batteries in telecommunications power system.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.63 no.4
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• pp.361-367
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• 2014

This paper is related to a new solar power conditioner for a built-in step-up chopper function. In the first step-up chopper proposed solar PV power conditioner for mutually connected in series with the input voltage of the bypass diodes are respectively connected to the positive terminal should install the mutual boosting chopper diode connected in series with the boost chopper switching element between the two power supply and at the same time the first and the second was connected to a second diode and a resonance inductor and a snubber capacitor in series with each other. And the common connection point between the bypass diode and the step-up chopper and the step-up chopper diode common connection point of the switching elements of the input voltage was set to the boost inductor for storing energy. In addition, between the step-up chopper and the step-up chopper diode and a switching element of a joint connection point of the first auxiliary diode and the second common connection point of the auxiliary diode was provided, the resonance capacitor. Between the step-up chopper and the step-up chopper diode and a switching element of a joint connection point and the common connection point of the resonance inductor snubber capacitor and connecting the third secondary diode, between two power supply lines is characterized by configuring the DC link capacitor bus lines in parallel. Therefore, it is possible to suppress the switching loss through, DC link bus lines, as well as there could seek miniaturization and weight reduction of the power conditioner itself by using a common capacitor of the non-polar non-polar electrolytic capacitor having a capacitor, the service life of the circuit can be extended and it is possible to greatly reduce the loss can be greatly improve the reliability of the product and the operation of the product itself.

• Proceedings of the KSR Conference
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• 2003.10c
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• pp.493-499
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• 2003

Railroad, a superior mode of public transportation provides safe, efficient, speedy, comfortable and economical service, has fundamentally different characteristics from airplanes, ships and cars. Among the unique characteristics of a railroad is the fact that it operates on fixed track with multiple car trains. The subway system was first selected as the best solution to difficult automobile traffic conditions and environmental problems. Seoul subway no.1line (Jongno line) was opened for service on August 15, 1974. Seoul city has completed and now operates eight subway lines (286.7km) since 1974. At present the subways operate in Busan, Daegu and Incheon city, and are under construction in Gwangju and Daejeon city. The power source for subway trains has been electricity since 1896, and power supply systems are the third rail type and/or the catenary system. The typical catenary system is the rigid bar type. R-bar and T-bar are used in the rigid bar type of catenary system, and the two types of R-bar and T-bar are uesd in Korea also. R-bar is used only for AC 25kV power supply and T-bar for DC 1,500V. From 30 years of subway experience I would like to suggest the most economic catenary system to ensure of safety, reliability and expediency for the railway lines to be constructed and the forthcoming replacement due to the life cycle after studying and analysing the characteristics, advantages and disadvantages of R-bar and T-bar.