• The Transactions of The Korean Institute of Electrical Engineers
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• v.67 no.4
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• pp.491-497
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• 2018

Most of the applications for distribution system operation highly rely on the voltage and current managements from the field devices. Voltage from the remote controlled switch contains unacceptably large measurement error due to the nonlinear characteristics of the bushing potential transformer. This paper proposes a new voltage magnitude estimation method by calculating voltage drop using current measurement, line impedance and loads deployment data. Contract demand power and pole transformer capacity managed by NDIS are used as a key element to improve accuracy of the proposed method. Various case studies using Matlab simulation have been performed to verify feasibility of the propose voltage estimation method.

• The Proceeding of the Korean Institute of Electromagnetic Engineering and Science
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• v.2 no.2
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• pp.3-10
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• 1991

The new structure method of GaAs microwave amplifiers using DC block function and impedance transforming property of DC block/transformer(non-symmetrical two - microstrip coupled line and interdigital three - microstrip coupled line), instead of chip capacitor, is presented. The newly structured microwave amplifier showed wideband characteristics(bandwidth, 3.5 GHz) and flat frequency response. Interdigital three - microstrip coupled line which is used for microwave amplifier can be used to match amplifiers as well as DC blocking.

• Proceedings of the KIEE Conference
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• 1995.11a
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• pp.258-260
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• 1995

This paper deals with the voltage unbalance of DC link voltage in series connected two 6-step inverters with double chopper preregulator. Each output of the 6-step inverter is connected to each transformer. The secondary windings of one of the transformers is zig-zag connected and the other star connected. The secondary terminals of the two transformers are series connected which makes 12-step output voltage waveform. In this case, the characteristics of the two transformers are rather different each other. The difference results in the voltage unbalance of the two 6-step inverter input capacitor voltages which make the DC link voltage. The degree of the voltage unbalance is analysied with the variations of load power, load power factor and % impedance of the transformer.

• Journal of Electrical Engineering and Technology
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• v.10 no.3
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• pp.1154-1161
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• 2015

This paper presents a semi-lumped balun transformer using conventional PCB process and its design theory and geometry for the maximally flat response and wide bandwidth using magnetically coupled LC resonators. The proposed balun is comprised of two pairs of coupled resonators which share one among three LC resonators. It provides an identical magnitude and phase difference of 180° between two balanced ports with DC isolation and an impedance transformation characteristic. Theoretical design and analysis were performed to optimize the inductance and capacitance values of proposed balun device for obtaining the wide bandwidth and maximally flat response in its pass-band. Three balun transformers with a center frequency of 500 MHz were demonstrated for proving the concept of design proposed. They were fabricated by using lumped chip capacitors and planar inductors embedded into a conventional 4-layered PCB substrate. They exhibited a maximum magnitude difference of 0.8 dB and phase difference within 2.4 degrees.

• Proceedings of the KIEE Conference
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• 2000.07c
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• pp.1865-1867
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• 2000

The pulse power system has been widely used to many applications. such as E/P(Electrostatic Precipitator), DeNOx/DeSOx power system, ozon generator. etc. A pulse energy efficiency for load depend on the rising time, peak value, pulse duration, impedance matching. etc. The pulse generator generally required for short pulse duration, high peak value was forced to consider its size and economy. In this study, developing a compact pulse generator that applied for Cascading method to be made of two pulse transformer, we compared cascading voltage with no cascading one by applying the pulse energy to load.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.66 no.1
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• pp.40-47
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• 2017

In this paper, a small signal model for grid-connected inverter with unipolar pulse width modulation method is presented. Small-signal analysis allows to predict the stability and dynamics of the inverter. To regulate output voltage and to achieve power factor correction, inverter has two control loops. Loop gains are useful to identify the stability for multi-loop controlled system. Based on small-signal model, controllers are designed to improve audio susceptibility and output impedance characteristics. Proposed small-signal model and controllers are verified by PSIM simulation and experiments.

• Proceedings of the KIPE Conference
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• 2014.07a
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• pp.323-324
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• 2014

A higher-order power converter topology for an extremely low coupling (less than 0.15) transformer with high efficiency and wide air-gap (23 mm) is presented in this paper. Among the typical resonant converter topologies for contact-less power transferring systems, Series-Series Resonant Converter (SSRC) and Series-Parallel Resonant Converter (SPRC) are widely used in number of power electronic applications. However, when coupling coefficient of a transformer is seriously low (k<0.5), the series-series resonant converter will possibly operate at short circuited condition because of the small magnetizing impedance. To solve this problem, a modified and improved topology of seventh-order resonant converter for contact-less power converter system is proposed and the results are presented.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.58 no.11
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• pp.2089-2094
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• 2009

The fault current has increased due to growth of distributed generations for the large power demand in power distribution system. To solve some problem such as excess of the circuit breaker's cut-off ratings, the superconducting fault current limiter(SFCL) has been progressed. However, the operational characteristics of the relay is changed by SFCL. Therefore, the proper impedance for the SFCL should be selected to keep protective coordination with the SFCL when SFCL is introduced on the neutral line of main transformer in distribution system. In this paper, the proper normal conducting resistance was suggested to solve the problem in case of the protection coordination with SFCL.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.501-502
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• 2007

This paper describes a distance relay that operates in conjunction with a current transformer (CT) compensation algorithm. A distance relay detects a fault based on the ratio of the voltage to the current. If a CT saturates, the calculated impedance becomes larger. This causes maloperation or operating time delay of the distance relay. A compensating algorithm estimates the correct secondary current from the severely distorted currents even when the measurement CTs are used. The correct current is estimated by adding the calculated magnetizing current to the measured secondary current. Test results show that the proposed distance relay can detect a fault without the operating time delay even when the secondary currents are extremely distorted because of use of measurement CTs.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• v.4B no.2
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• pp.54-58
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• 2004

This paper presents the iron core design method of a high temperature superconducting (HTS) transformer considering voltages per turn (V/T). In this research, solenoid type HTS coils were selected for low voltage (LV) winding and double pancake coils for high voltage (HV) winding, just as in conventional large power transformers. V/T is one of the most fundamental elements used in designing transformers, as it decides the core cross sectional area and the number of primary and secondary winding turns. By controlling the V/T, the core dimension and core loss can be changed diversely. The leakage flux is another serious consideration in core design. The magnetic field perpendicular to the HTS wire causes its critical current to fall rapidly as the magnitude of the field increases slowly. Therefore in the design of iron core as well as superconducting windings, contemplation of leakage flux should be preceded. In this paper, the relationship between the V/T and core loss was observed and also, through computational calculations, the leakage magnetic fields perpendicular to the windings were found and their critical current decrement effects were considered in relation to the core design. The ％ impedance was calculated by way of the numerical method. Finally, various models were suggested.