• Proceedings of the KIEE Conference
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• 대한전기학회 2004년도 하계학술대회 논문집 A
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• pp.48-50
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• 2004

The energization of high voltage transmission lines and transformers, that is an inevitable process in most countries as the first restorative action for wide-area blackout, may induce overvoltages such as sustained overvoltage, transient overvoltage and harmonic resonant overvoltage. And these may cause damages to power system equipments or failure of surge arresters. The harmonic resonant overvoltage originates in switching operations and nonlinear characteristics of equipments. Actually it is difficult to predict the occurrence of harmonic overvoltage, since they result from nonlinear characteristics of transformers and other equipments. This paper describes the analysis of domestic primary restorative transmission system using PSCAD/EMTDC. The harmonic resonance is verified and the solution to prevent harmonic resonance is proposed in this paper. As a result, the PSCAD/EMTBC simulation showed slightly conflictive results that had been presented by IEEE Power System Restoration Working Group report.

• Journal of Ceramic Processing Research
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• 제13권spc2호
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• pp.428-432
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• 2012

Polyamidimide (PAI)-colloidal silica (CS) nanohybrid films were synthesized by an advanced sol-gel process. The synthesized PAI-CS hybrid films have a uniform and stable chemical bonding and there is no interfacial defects observed by TEM. The thermal degradation ratio of PAI-CS (10 wt%) hybrid films is delayed by 100 ℃ compared with pure PAI sample determined by on set temperature range in TGA. The dielectric constant of PAI-CS (10 wt%) hybrid films decreases with increasing CS content up to about 5 wt% but increases at higher CS content, which is not explained simply by effective medium therories (EMT). The duration time of PAI-CS (10 wt%) hybrid coil is 38 sec, which is very longer than that of pure PAI coil sample. The PAI-CS (10 wt%) hybrid film has a higher breakdown voltage resistance than the pure PAI film at surge environment and exhibits superior heat resistance. The PAI-CS (10 wt%) sample shows the advanced and stable thermal emission properties in transformer module compared with the pure PAI sample. This result illustrates that the advanced thermal conductivity and expansion properties of PAI-CS sample in the case of appropriate sol-gel processes brings the stable thermal emission in transformer system. Therefore, new PAI-CS hybrid samples with such stable thermal emission properties are expected to be used as a high functional coating application in ET, IT and electric power products.

• Journal of the Korea Academia-Industrial cooperation Society
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• 제17권6호
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• pp.400-407
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• 2016

The purpose of this study is to propose a useful method of solving the problem of thermal stability in surge protection devices (SPDs). First of all, the existence of the problem in the developed SPDs was confirmed by experiment. After analyzing the problem, a useful method of solving it is proposed and implemented. An experiment is performed to verify the performance of the implemented device. The results of this study are as follows; it is revealed that the problem of the thermal stability results from the varistor, one of the components in the SPD. A varistor with a built-in thermal fuse is applied to the SPD for the purpose of solving the problem. The experimental results confirmed that the thermal stability was improved by replacing the varistor. As a result of this study, the reliability of radar control units is enhanced and the probability of malfunction is reduced.

• Journal of the Korea Institute of Information and Communication Engineering
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• 제18권10호
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• pp.2503-2508
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• 2014

This study is about the selection and noise test of electronic sensor which is preceded by electric Operating Cell(EOC) development using electronic sensor technology to solve the structural weakness of Mechanism Operated Cell(MOC) in VCB, and has a final target in product development minimizing contact malfunction of the chattering or rebounce states caused by existing MOC. In this test results, when opening and closing VCB, rising velocity of surge voltage in opening time was measured 4.2 times faster than closing time and noise decibel value was measured respectively 120dB and 110dB. When supplying 60kV power frequency overvoltage, we found that sensor output graph in VCB opening and closing times operated stably without distortion. When supplying 150kV $1.2{\times}50{\mu}s$ impulse frequency voltage, we found that voltage graph of output contact in sensor opening and closing sides maintained a normal condition without distortion, and when supplying 2500A current, we found that tested result of electric field noise operated stably without distortion.

• The Journal of the Korea institute of electronic communication sciences
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• 제15권5호
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• pp.857-864
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• 2020

The multi-functional VoIP phone supports the Ethernet protocol in the TIPS(: Tactical IP Switch), which is one of the sub-systems of the tactical information and communication system (TICN). It provides secured voice / video calls in conjunction with VoIP exchanges and supports differential services such as multi-party calls and command functions. In this paper, improving methods have been proposed to reduce power supply defects in the field of multi-functional VoIP phones. The power supply part was improved by applying TVS of the output voltage inlet of the dedicated adapter of the multi-functional VoIP phone, TVS of the PoE module input, adding blocking diodes, and adding DC / DC converters behind the poly-switch. Also, functional and environmental tests were performed to verify the validity of the proposed methods.

• Journal of the Korea Academia-Industrial cooperation Society
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• 제18권11호
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• pp.755-761
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• 2017

In railways powered by AC power, the main circuit breaker (MCB) is used for supplying the electric power to the catenary of the vehicle. Generally, the main circuit breaker is located between the pantograph and the main transformer, and the phase of the power applied to the vehicle changes according to the operation timing of the main circuit breaker. The operation of the main circuit breaker should be actively controlled according to the phase of the power source, since the phase of the power causes unintended transient states in the vehicle's electrical system in the form of an inrush current and surge voltage. However, the MCB has a delay time when it operates which is not constant. Therefore, an intelligent controller is needed to predict the operation delay time and control the opening and closing of the MCB.

• Journal of Advanced Navigation Technology
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• 제19권5호
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• pp.395-402
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• 2015

This paper introduces the design details and test procedures of the lightning induced transient protection device for protecting the damage caused by indirect lightning strike on the computer mounted on the aircraft. Lightning induced surge voltage is bring a malfunction or damage to the aircraft electrical and electronic equipment, that is referred to indirect effects of lightning. In order to protect the electronic equipment on aircraft from the indirect effects of lightning, that is achieved by analyzing the effect on aircraft from lightning and protect design for each devices. In this paper, we introduce an indirect lightning strike level decisions, the protection circuit design method according to the chosen level through the RTCA DO-160G Section 22 category analysis and selection was performed in order to protect the damage caused by indirect lightning strikes in the protected equipment. In addition, we show the indirect lightning effects verification test performed to validate the designed protection circuits.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• 제21권1호
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• pp.118-124
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• 2007

This paper presents the effects of the injected number and amplitude of impulse current on the service life of ZnO varistors for low voltages. To analyze the effects of lightning impulse currents on the performance of ZnO varistors, the measurements of resistive leakage current and power dissipation at the power frequency ac voltage before and after the injections of the $8/20[{\mu}s]$ impulse currents were made. As a consequence, the duration and amplitude of resistive leakage current flowing through ZnO varistor were increased with increasing the number of injections of the $8/20[{\mu}s]$ impulse currents. It is desirable that the service life of ZnO varistors should be evaluated as a function of the number and amplitude of lightning impulse current.

• Journal of Advanced Navigation Technology
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• 제21권5호
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• pp.459-465
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• 2017

In this paper, we introduce the design consideration of the lightning induced transient protection circuit for the indirect lightning strike on the avionics equipment. The lightning induced surge voltage, which is so-called as indirect effects of lightning, may cause a functional failure or physical damage to the electrical and electronic equipment of aircraft. In order to protect the electrical and electronic equipment of aircraft from the indirect effects of lightning, we should analyze the effect of lightning strike on aircraft and consider applying protection design for each avionics device. However, lightning induced transient protection circuits can have unintended consequences because parasitic inductance elements are exist in PCB and TVS diodes. In this paper, we introduce the design method of the protection circuit considering the parasitic inductance of the protection circuit. In addition, we show the result of verification test performed to validate the protection circuits for indirect effects of lightning.

• Journal of the Korean Solar Energy Society
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• 제35권4호
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• pp.67-75
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• 2015

PV module is conventionally connected in series with some solar cell to adjust the output of module. Some bypass diodes in module are installed to prevent module from hot spot and mismatch power loss. However, bypass diode in module exposed outdoor is easily damaged by surge voltage. In this paper, we study the thermal and electrical characteristics change of module with damaged bypass diode to easily find module with damaged bypass diode in photovoltaic system consisting of many modules. Firstly, the temperature change of bypass diode is measured according to forward and reverse bias current flowing through bypass diode. The maximum surface temperature of damaged bypass diode applied reverse bias is higher than that of normal bypass diode despite flowing equal current. Also, the output change of module with and without damaged bypass diode is observed. The output of module with damaged bypass diode is proportionally reduced by the total number of connected solar cells per one bypass diode. Lastly, the distribution temperature of module with damaged bypass diode is confirmed by IR camera. Temperature of all solar cells connected with damaged bypass diode rises and even hot spot of some solar cells is observed. We confirm that damaged bypass diodes in module lead to power drop of module, temperature rise of module and temperature rise of bypass diode. Those results are used to find module with a damaged bypass diode in system.