• Proceedings of the KIEE Conference
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• 2006.07a
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• pp.266-267
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• 2006

A coupling capacitor voltage transformer (CCVT) is used in extra high voltage and ultra high voltage transmission systems to obtain the standard low voltage signal for protection and measurement. To obtain the high accuracy at the power system frequency, a tuning reactor is connected between a capacitor and a voltage transformer (VT). Thus, no distortion of the secondary voltage is generated when no fault occurs. However, when a fault occurs, the secondary voltage of the CCVT has some errors due to the transient components resulting from the fault. This paper proposes an algorithm for compensating the secondary voltage of the CCVT in the time domain. With the values of the secondary voltage of the CCVT, the secondary and the primary currents are obtained; then the voltage across the capacitor and the tuning reactoris calculated and then added to the measured secondary voltage. The proposed algorithm includes the effect of the non-linear characteristic of the VT and the influence of the ferro-resonance suppression circuit. Test results indicate that the algorithm can successfully compensate the distorted secondary voltage of the CCVT irrespective of the fault distance, the fault inception angle and the fault impedance.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2010.06a
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• pp.334-334
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• 2010

In order to fabricate the multilayer piezoelectric transformer by tape casting method, we investigated the effect of $TiO_2$ and PZT powder additions on the Ag/Pd electrode. Meanwhile, effects of $TiO_2$ and PZT powder additives on the microstructure and electrical properties of Ag/Pd electrode were investigated in detail. In addition, the multilayer piezoelectric transformers were fabricated and the characteristics with various load resistance were measured at resonance frequency. The voltage step-up ratio was continuously change with increasing input voltage and load resistance, and then output voltage and powers were increased with increasing input voltage at matching impedance. The temperature rise of multilayer piezoelectric transformers were increased with increasing input voltage and load resistance. Meanwhile, multilayer piezoelectric transformers sintered at $1100^{\circ}C$ show the favorable characteristics with a power of 15 W at $100\;{\Omega}$.

• Progress in Superconductivity
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• v.5 no.2
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• pp.128-131
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• 2004

The resistive superconducting fault current limiters (SFCLs) are very attractive devices for the electric power network. But they have some serious problems when the YBCO thin films were used for the current limiting materials due to the in homogeneities caused by manufacturing process. When the YBCO films have some inhomogeneities, simultaneous quenches are difficult to achieve when the fault current limiting units are connected in series for increasing operating voltage ratings. Magnetic field application is one of the prospective way of inducing simultaneous quenches far the series-connected resistive FCL components. Magnetic field was typically generated by the fault current thorough a coil, which is connected to components of the fault current limiter in series, leaving the problem, which provides significant inductance to the power line and suppresses critical current density of the superconducting components. In this article we investigated the possible application of the protective current transformer (p-CT), which is available current source to the magnetic coil. This system inductively coupled to the circuit, therefore, remarkably reducing impedance to the circuit. The current by the protective current transformer was directly fed to the coil, generating magnetic field large enough to reduce critical current density of the components. This successfully induced simultaneous quenches of the series-connected resistive FCL components.

• The Journal of The Korea Institute of Intelligent Transport Systems
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• v.10 no.5
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• pp.79-86
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• 2011

In this paper, a S-band coaxial waveguide-based spatial combiner is proposed. The proposed combiner consists of coaxial waveguide, impedance transformer, and finline-to-microstrip transformer. The coaxial waveguide is used as the host of the combining circuits for higher output power and better uniformity by equally distributing the input power to each element. The finline-to-microstrip transformer is designed by using antipodal antenna, and obtained low reflection coefficient by applying the small reflection theorem. The measurement results show the coaxial waveguide combiner has a maximum combining efficiency of 95%.

• The Proceedings of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.11 no.6
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• pp.90-95
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• 1997

In designing a resonant circuit of the inverter which puts induction heating with high frequency to the load, an inductance L of the circuit, the coupling coefficient of a transformer transfering the output power to load, and the coupling coefficient of load circuit heating with coil affect to the output power of a resonant circuit, the circuit Q and the frequency. Those characteristics of the circuit are analyzed through Thevenan's equivalent circuit of the coupling coefficient type which is derived from the T-type equivalent circuit of a transformer. On this equivalent circuit, the impedance of a transformer referred to its primary side is not only proportional the square of turn ratio, nZ, but also the square of coupling coefficient, K2 This paper proposed a more accurate fundamental method to design a resonant circuit of the inverter by using the Thevenan's equivalent circuit.

• Progress in Superconductivity and Cryogenics
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• v.8 no.1
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• pp.49-53
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• 2006

This paper specifies the new power supply paradigm converting 154kV voltage level into 22.9kV class with equivalent capacity using superconducting rower facilities and analyze the fault current characteristics with and without HTS-FCL (High Temperature Superconducting-Fault Current Limiter). Superconducting new power system is the power system to which applies the 22.9kV HTS cable in parallel to HTS transformer and HTS-FCL with low-voltage and mass-capacity characteristics replacing 154kV conventional cable and transformer. The fault current of superconducting new power system will increase greatly because of the mass capacity and low impedance of HTS transformer and cable. This means that the HTS-FCL is necessary to reduce the fault current below the breaking current of circuit breaker. This paper analyze the fault current and suggests the parallel HTS-FCL scheme complementing the inherent problem of HTS-FCL, that is recovery after quenching is impossible within shorter than a few seconds.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.26 no.8
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• pp.1188-1195
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• 2022

The 6-port phase correlator consists of one in-phase power divider and three 3-dB 90-degree phase difference power dividers, and is mainly used in a demodulation circuit that determines the phase of an input signal. This paper proposes the wideband 6-port phase correlator that consists of an in-phase power divider using a wideband 2:1 impedance transformer with three 37.5-Ω coaxial cables, and a 3-dB 90-degree phase difference power divide using Wireline. The proposed wideband phase correlator fabricated at a center frequency of 1000MHz has the value of the input reflection coefficient(S₁₁ and S₂₂) -14dB or less in the frequency range of 640~1270MHz. Also, the signal transmission characteristic(S_i1), from the in-phase power divider input port to four output ports, has the amplitude of -6.5±0.6dB and the phase error of within ±3.4°, and the signal transmission characteristic(S_i2), from the 90 degree phase difference power divider input port to four output ports, has the amplitude of -6.1±0.6dB and the phase error of within ±6.2°.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.31A no.1
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• pp.26-32
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• 1994

In this paper, using the newly developed GaAs Schottky beam-lead diode made by Marconi company, we have developed and evaluated the waveguide type single-ended mixer at Q-band. The various components of the mixer were separately designed and optimized using the Super-Compact software. These studies included the design of the step waveguide impedance transformer and the RF-choke filter, and the optimization of a high and low impedance for the RF-choke filter. Moreover, this RF-choke filter pattern included a section to reject the second harmonic frequency of the RF signal. Finally, this Q-band mixer with 1.4GHz/400MHz IF frequency exhibits an average conversion loss of 5.3 dB over 33-50GHz bandwidth.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.21 no.6
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• pp.1587-1595
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• 1996

We obtained the predicted and measured results for the reflection coefficient and radiation pattern of Ka-band (20- GHz) corrugated horn, which is usually used for feeder of reflector antenna for satellite communication, using suface impedance condition. In order to predict the reture losses of corrugated horn, we analyzed propagation constant of hybrid mode in the corrugated waveguide and then obtained the total reflection coefficient using the circuti theory of multi-step transformer. We also got the radiation pattern of corrugated horn with small flare angle, considering the phase deviation and integrate transverse field on aperture. A test model of corrugated horn antenna for Ka-band designed using theory and program displayed performance and the results agree with the theoretical prediction.

• Proceedings of the KIEE Conference
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• 2001.04a
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• pp.449-451
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• 2001

This study presents a study on modified algorithm to operating train simulation of AT feeding systems. In this study equivalent impedance is constructed by $Z_c,\;Z_r,\;Z_f,\;Z_{cr},\;Z_{rf},\;Z_{fc}$. The train current flows through the all auto-transformer corresponding to track impedance. To calculate train voltage from analyzing the railway systems, the algorithm is based on the K. C. L, K. V. L, superposition and circuit separation method. Multi-train's voltages are determined by calculating the catenary voltage at each train's position and adding up these train's voltage drop. Case studies use a field operational data, show that the proposed method is easily applied.