• 전력전자학회:학술대회논문집
• /
• 전력전자학회 2001년도 Proceedings ICPE 01 2001 International Conference on Power Electronics
• /
• pp.523-528
• /
• 2001

This paper deals with two non-conventional HVDC system, that are, the Capacitor Commutated Converter (CCC) in which series capacitors are included between the converter transformer and the valves, and the Controller Series Capacitor Converter (CSCC), based on more conventional topology, in which series capacitors are inserted between the AC filter bus and the AC network. The simulation waveforms show that if these compare to conventional HVDC, these HVDC systems have many advantages in steady-state and transient performance.

• 제어로봇시스템학회:학술대회논문집
• /
• 제어로봇시스템학회 1996년도 한국자동제어학술회의논문집(국내학술편); 포항공과대학교, 포항; 24-26 Oct. 1996
• /
• pp.996-999
• /
• 1996

This paper introduces prototype design of 765kV Substation control system based on fiber optics LAN and distributed network protocol. Two major important facts, immunity of any surge which frequently occurs in Ultra High Voltage Substation and the most suitable communication protocol for substation control system, are considered on the system design conception. To meet the first fact, use of fiber optics cable and isolation transformer are considered, and to satisfy the second fact, DNP3.0(Distributed Network Protocol) which is IEC870-5 compatible is adopted.

• 대한전기학회논문지
• /
• 제37권8호
• /
• pp.534-539
• /
• 1988

The dynamic chatacteristics and stability including steady state characteristic of the currentfed DC-to-DC converter with multiouput, which has a considerable advantage about the multioutut circuit,are analyzed in this paper. It is performed by using the steady state averaging method. As result, we know that the error, which is caused by secondary winding resistance of the transformer, exists between the two outputs in the steady state characteristics. Furthemore, it is verified that the current-fed DC-to-DC converter has also excellent stability in the multioutput application.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 1999년도 추계학술대회 논문집 학회본부 A
• /
• pp.279-281
• /
• 1999

This paper addresses the issues of the parameter error detection and identification in power system. The parameter error identification is carried out as part of the state estimation procedure. The weighted least absolute value(WLAV) estimation method is used for this procedure. The standard formulation of the state estimation problem is modified to include the effects of the parameter errors as well. A two step procedure for the detection and identification of faulted parameters is proposed. Supporting examples are given using IEEE 14 bus system.

• 전기학회논문지
• /
• 제57권6호
• /
• pp.938-943
• /
• 2008

Coupling capacitor voltage transformers(CCVTs) have been used in extra or ultra high voltage systems to obtain the standard low voltage signal for protection and measurement. For fast suppression of the phenomenon of ferroresonance, three winding CCVTs are used instead of two winding CCVTs. A tuning reactor is connected between a capacitor voltage divider and a voltage transformer to reduce the phase angle difference between the primary and secondary voltages in the steady state. Slight distortion of the secondary voltage is generated when no fault occurs. However, when a fault occurs, the secondary voltage of the CCVT has significant errors due to the transient components such as dc offset component and/or high frequency components resulting from the fault. This paper proposes an algorithm for compensating the secondary voltage of a three winding CCVT in the time domain. With the values of the measured secondary voltage of the three winding CCVT, the secondary, tertiary and primary currents and voltages are estimated; then the voltages across the capacitor and the tuning reactor are calculated and then added to the measured voltage. Test results indicate that the algorithm can successfully compensate the distorted secondary voltage of the three winding CCVT irrespective of the fault distance, the fault impedance and the fault inception angle as well as in the steady state.

• Journal of Power Electronics
• /
• 제15권3호
• /
• pp.587-601
• /
• 2015

A high step-up dc-dc converter is proposed for photovoltaic power systems in this paper. The proposed converter consists of an input current doubler, a symmetrical switched-capacitor doubler and an active-clamp circuit. The input current doubler minimizes the input current ripple. The symmetrical switched-capacitor doubler is composed of two symmetrical quasi-resonant switched-capacitor circuits, which share the leakage inductance of the transformer as a resonant inductor. The rectifier diodes (switched-capacitor circuit) are turned off at the zero current switching (ZCS) condition, so that the reverse-recovery problem of the diodes is removed. In addition, the symmetrical structure results in an output voltage ripple reduction because the voltage ripples of the charge/pump capacitors cancel each other out. Meanwhile, the voltage stress of the rectifier diodes is clamped at half of the output voltage. In addition, the active-clamp circuit clamps the voltage surges of the switches and recycles the energy of the transformer leakage inductance. Furthermore, pulse-width modulation plus phase angle shift (PPAS) is employed to control the output voltage. The operation principle of the converter is analyzed and experimental results obtained from a 400W prototype are presented to validate the performance of the proposed converter.

• Transactions on Electrical and Electronic Materials
• /
• 제18권2호
• /
• pp.97-102
• /
• 2017

A current transformer (CT) is a type of sensor that consists of a combination of electric and magnetic circuits, and it measures large ac currents. When a large amount of current flows into the primary winding, the alternating magnetic flux in the iron core induces an electromotive force in the secondary winding. The characteristics of a CT are determined by the iron core design because the iron core is saturated above a certain magnetic flux density. In particular, when a large current, such as a current surge, is input into a CT, the iron core becomes saturated and the induced electromotive force in the secondary winding fluctuates severely. Under these conditions, the CT no longer functions as a sensor. In this study, the characteristics of the secondary winding were investigated using the time-difference finite element method when a current surge was provided as an input. The CT was modeled as a two-dimensional analysis object using constraints, and the saturation characteristics of the iron core were evaluated using the Newton-Rhapson method. The results of the calculation were compared with the experimental data. The results of this study will prove useful in the designs of the iron core and the windings of CTs.

• 전력전자학회논문지
• /
• 제21권4호
• /
• pp.351-355
• /
• 2016

Welding machines are high-capacity systems used in a low-frequency range using IGBT. As their system is similar to a large transformer, most welding machines suffer a great loss because of hard switching and vast leakage inductance. A voltage-balancing circuit is designed to overcome these shortcomings. This circuit can reduce the transformer size by making it into a high frequency and reducing the input voltage by half and by adopting a serial structure that connects two full-bridges in a series to use a MOSFET with a good property at high frequency. In addition, a Schottky diode is used in the primary rectifier to overcome the low efficiency of most welding machines. To use the Schottky diode with a reliably relatively low withstanding voltage, an active snubber is adopted to effectively limit the ringing voltage of the diode cut-off voltage.

• 전기학회논문지P
• /
• 제58권2호
• /
• pp.202-206
• /
• 2009

Evaluation system for calibrating Rogowski coiI(RC) up to primary current of 40,000 A have been established. The system consists of 40,000 A AC high current source, current transformer(CT) comparator, standard CT, RC under test, voltage to current convertor(VCC), buffer and CT burden. An AC high current is applied to the primary windings of both the standard CT and the RC under test, and then the CT comparator measures the ratio error and the phase displacement by comparing the secondary current of the standard CT with output current of VCC. For testing of RC, we have evaluated two RCs under test of primary current ranges of 0 A ${\sim}$ 2,000 A and 0 A ${\sim}$ 40,000 A with the accuracy class of 1 %. The extended uncertainty is 0.02 % ${\sim}$ 0.23 % for ratio error and 0.29 min ${\sim}$ 1.93 min for phase displacement in the primary current ranges of 10 ${\sim}$ 40,000 A.

• 한국초전도ㆍ저온공학회논문지
• /
• 제3권2호
• /
• pp.15-20
• /
• 2001

This paper describes a model flux pump experiment recently performed at the MIT Francis Bitter Magnet Laboratory. The results of the model flux pump will be used in the development of a prototype flux pump that will be couple to a high-temperature superconductor (HTS) insert coil of a high-field NMR (Nuclear Magnetic Resonance) magnet, Such an HTS insert is unlikely to operate in persistent model because of the conductors low index(n) The flux pump can compensate fro field decay in the HTS insert coil and make the insert operate effectively in persistent mode . The flux pump, comprised essentially of a transformer an two switches. all made of superconductor, transfers into the insert coil a fraction of a magnetic energy that is first introduced in the secondary circuit of the transformer by a current supplied to the primary circuit. A model flux pump has been designed. fabricated, and operated to demonstrate that a flux pump can indeed supply a small metered current into a load superconducting magnet. A current increment in the range of microamperes has been measured in the magnet after each pumping action. The superconducting model flux pump is made of Nb$_3$ Sn tape, The pump is placed in a gaseous environment above the liquid helium level to keep its heat dissipation from directly discharged in the liquid: the effluent helium vapor maintains the thermal stability of the flux pump.