• Proceedings of the KIPE Conference
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• 1998.10a
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• pp.452-457
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• 1998

This paper deal with problems of leakage current, shaft voltage, bearing current, and EMI, in valiable-speed AC drives. The originating mechanism is illustrated with a high-frequency equivalent circuit. Reduction methods are classified in to six categories based on the equivalent circuit. Some experimental results show that a common-mode transformer (CMT) and a common-noise canceler (ACC) can solve the problems, which have been proposed the authors.

• The Transactions of the Korean Institute of Electrical Engineers
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• v.37 no.2
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• pp.73-79
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• 1988

A fault current in Simultaneous faults is calulated, which satisfies the reliability for expansion of power scale. New algorithm for analyzing fault current is developed, which calculates exactly thevnin equivalent impedance from fault point by cecomposing increment bus admittance matrix ( Ybus), and fault current is calculated by applying multiport theory. The signeficant results are as follows ` 1) When system fault changes system configulation, equivalent impedance can be calculated simply with this new algorithm. 2) Mutual coupling of transmission line can be calculated efficiently. 3) Simultaneous fault current is analyzed by applying multiport theory, which can be applicable to large scale systems.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.11
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• pp.67-78
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• 2005

In this paper, impedance characteristics of overhead medium-voltage (MV) power line for power line communication (PLC) is analyzed. For analysis, a two-port equivalent network model of MV power lines is derived. By applying the equivalent model and basic transmission line theory, input impedance at the signal induction part is calculated. And also calculated input impedance of power line itself that the medium voltage coupler and coaxial cable effect are removed. For verification, impedance of power lines is measured at a test field for an MV PLC. The results show that impedance of MV power line itself is between $200\;{\Omega}\;and\;300\;{\Omega}$ and converges to a half of their characteristic impedance with increasing frequency. And also measured data is very similar to calculated data.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.12 no.6
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• pp.2739-2746
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• 2011

This paper proposes the method for more effectively calculating X/R which is the ratio of equivalent reactance(X) and resistance(R) of the bulk power system and analyses the characteristic of X/R values by applying the proposed method to the real bulk power systems. X/R is used to determine the rating of the relay in the bulk power systems and its value has been accepted to be big enough to ignore the equivalent resistance of the bulk power systems. However, X/R is calculated as a big number when only the upper transformer and transmission line are considered. The correct approach to calculating X/R needs to consider all the parameters including generators, transformers, lines and loads. This paper calculates X/R of the bulk power systems using dynamic models which have been used to analyse the power system stability. The effectiveness of the proposed method is verified by applying it to the test system and X/R values of the real bulk power systems are analyzed. In addition, the dependence of X/R on the closeness of its calculating locations to the generator is verified by using the marginal loss factor which has been used in the electricity market.

• Journal of Electrical Engineering and Technology
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• v.12 no.2
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• pp.840-845
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• 2017

In this paper, in order to investigate the lifetime of oil-paper insulation, specimens were artificially aged with thermal and electrical multiple stresses. Accelerated ageing factors and equivalent operating years for each aging temperatures were derived from results of tensile strengths for the aged paper specimens. Also, the evaluation for the multi-stress aged specimens were carried out through the measurement of impulse breakdown voltage at high temperature of $85^{\circ}C$. The lifetimes of the oil-paper insulations were calculated with the value of 66.7 for 1.0 mm thickness specimens and 69.7 for 1.25 mm thickness specimens throughout the analysis of impulse BD voltages using equivalent operating years, which means that dielectric strengths would not be severely decreased until the mechanical lifetime limit. Therefore, for the lifetime evaluation of the oil-paper insulation, thermal aging would be considered as a dominant factor whereas electrical degradation would be less effective.

• Proceedings of the KIEE Conference
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• 1991.07a
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• pp.417-421
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• 1991

In electromagnetic transient analysis, complex transmission system should be modelled in detail. But in large system, this full representation of power transmission system has a big burden in many sides such as computation time, modelling efforts, etc. It is very required, therefore, in electromagnetic transients studies to represent parts of a complete system in a reduced or an equivalent form. This paper develops the method from which system equivalents may be derived. The suggested method is of an essentially transient form, and allows travelling wave interaction between the equivalent and explicit transmission network to be modelled.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.58 no.2
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• pp.207-213
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• 2009

Electrolytic capacitors have been widely used in power electronics system because of the features of large capacitance, small size, high-voltage, and low-cost. Electrolytic capacitors, which is most of the time affected by aging effect, plays a very important role for the power electronics system quality and reliability. Therefore it is important to estimate the parameter of an electrolytic capacitor to predict the failure. This paper proposed a novel fault diagnosis method of an electrolytic capacitor used for voltage smoothing in boost DC converter. The equivalent series resistance(ESR) of electrolytic capacitor estimated from FFT result of filtered waveform of capacitor voltage/current. Main advantage of the proposed method include circuit simplicity and easy implementation. Simulation and experimental results are shown to verify the performance of the proposed method.

• Proceedings of the KIPE Conference
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• 2000.07a
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• pp.1-5
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• 2000

This paper deals with the modeling and analysis of the high voltage flyback transformer (HVFBT) often utilized in small-sized high voltage DC power supplies. The parasitic capacitance of th HVFBT with the large turns of the secondary winding causes the undesirable parasitic resonance in the transient state which produces the high current stress and limits the switching frequency of the converter. In order to analyze this phenomenon the equivalent circuit model including the parasitic capacitance is derived and the frequency characteristics are provided. The parasitic resonance in the switching states is also investigated based on this equivalent circuit model. The derived model and analysis is finally validated through the SPICE simulation and experiments.

• Journal of Electrical Engineering and Technology
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• v.11 no.1
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• pp.257-264
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• 2016

In this paper, new electric railway feeding system which has active transformer is modeled for evaluating the steady state analysis using PSCAD/EMTDC. Equivalent models including power supply, feeder, train and transformers are proposed for simplifying the model of the feeding system in high speed electric railway. In case study, simulation results applied to proposed model are compared with the conventional and new systems through the catenary voltage, three-phase voltage of PCC (Point of Common Coupling) and the efficiency of regenerative braking energy.

• Journal of Korean Ophthalmic Optics Society
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• v.5 no.1
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• pp.155-157
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• 2000

A variable process of blur circle is calculated for a artificial hyperopia. The calculation is used to the value of Gullstrand's theoretical eye and a method of geometrical optics. The theoretical eye simplified a entrance pupil and the retina. Ophthalmic lens and eye changed a equivalent lens. Refractive power of a equivalent lens is converted to focal length within theoretical eye, and this is calculated about relation of a blur circle on the retina and ophthalmic lens.