• The Transactions of the Korean Institute of Electrical Engineers A
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• v.52 no.12
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• pp.722-730
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• 2003

Current differential relay is commonly used to protect power transformer. However, current differential relay will be tripod by judging like internal fault during inrush occurring in transformer. To resolve such problem, this paper proposes a new protective relaying algorithm using Neuro-Fuzzy Inference. A variety of transformer transition states are simulated by BCTRAN and HYSDT of EMTP. Primary phase voltage and differential current are obtained from simulation. The target data which are used in Neuro-Fuzzy algorithm are obtained from transformed primary voltage and current. Then, these are trained by Neuro-Fuzzy algorithm. The trained Neuro-Fuzzy algorithm correctly distinguishes whether internal fault occurs or not, within 1/2 cycle after fault. Accordingly, it is evaluated that the proposed algorithm has good relaying characteristics.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.57 no.2
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• pp.198-201
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• 2008

We investigated the operating characteristics of the flux-lock type superconducting fault current limiter(SFCL) with the parallel connection between the primary and secondary windings which are connected with two superconducting units in series. The parallel connection for current level increase of the flux-lock type SFCL is necessary to apply the SFCL into the power system. The resistance generated in superconducting units was dependent upon the winding direction of the primary and the secondary coils, which can reduce the power burden. The resistance of the superconducting elements in the subtractive polarity winding is higher than that of the additive polarity winding. The fault current limiting effect of the subtractive polarity winding is better than that of the additive polarity winding. From this results, we confirmed that the power capacity of the flux-lock type SFCL could be increased by the parallel connection of the superconducting units.

• Journal of the Korean Institute of Intelligent Systems
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• v.17 no.3
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• pp.374-379
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• 2007

This paper focuses on the improvement of fault detection algorithm in FRTU(feeder remote terminal unit) on the feeder of distribution power system. FRTU is applied to fault detection schemes for phase fault and ground fault. Especially, cold load pickup and inrush restraint functions distinguish the fault current from the normal load current. FRTU shows FI(Fault Indicator) when the fault current is over pickup value or inrush current. STFT(Short Time Fourier Transform) analysis provides the frequency and time Information. FCM(Fuzzy C-Mean clustering) algorithm extracts characteristics of harmonics. The neural network system as a fault detector was trained to distinguish the inruih current from the fault status by a gradient descent method. In this paper, fault detection is improved by using FCM and neural network. The result data were measured in actual 22.9kV distribution power system.

• Transactions on Electrical and Electronic Materials
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• v.6 no.4
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• pp.159-163
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• 2005

We analyzed the fault current limiting characteristics of a flux-lock type $high-T_c$ super­conducting fault current limiter (HTSC-FCL) using series resonance between capacitor for series resonance and magnetic field coil which was installed in coil 3. The capacitor for the series resonance in the flux-lock type HTSC-FCL was inserted in series with the magnetic field coil to apply enough magnetic field into HTSC element, which resulted in higher resistance of HTSC element. However, the impedance of the flux lock type HTSC-FCL has started to decrease since the current of coil 3 exceeded one of coil 2 after a fault accident. The decrease in the impedance of the FCL causes the line current to increase and, if continues, the capacitor for the series resonance to be destructed. To avoid this operation, the flux-lock type HTSC-FCL requires an additional device such as fault current interrupter or control circuit for magnetic field. From the experimental results, we investigated the parameter range where the operation as mentioned above for the designed flux-lock type HTSC-FCL using series resonance occurred.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.64 no.12
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• pp.1659-1665
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• 2015

In general, AT(Auto-transformer) is used to improve voltage sag and inductive interference in power lines and communication lines in AC electrical railway feeding system. Especially, Korean AT feeding system has different composition compared to other countries like Japan or France, so that it has some special characteristics. However, relays imported from other countries have been used in Korea, and settings of these relays should be modified and reflect distinct characteristics of Korean AT feeding system. Therefore, study about fault analysis based on modeled AT feeding system is important. In this paper, we modeled a single track AT feeding system by using PSCAD and analyzed fault current flow in case of trolley-rail short circuit fault. Finally, we presented current magnitude of each branch expressed by boosting current of AT.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.16 no.3
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• pp.74-83
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• 2002

The maximun short circuit current of modern power system is becoming so large that circuit breaker is not expected to be able to shut down the current in the future In order cut over-currents, a system composed of a superconducting fault current limiter(SFCL) and traditional breaker seems to provide a promising solution for furture power operation. In present paper, three line-to-ground fault is assumed to happen at the center of 345kV transmission lines in a large capacity electric power system. The superconducting fault current limiter was represented using a commutation type, which consists of a non-inductive superconducting coil and current limiting element (resistor or reactor). from the viewpoint of current limiting performance, the prevention of the voltage drop at the load bus and comparision characteristics for two type SFCL. Desired design specification and operation parameters of SECL were also given qualitatively by the performance.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.58 no.1
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• pp.85-89
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• 2009

We investigated the quench characteristics in accordance with increase of turns number of trigger coil and shunt resistance of matrix-type superconducting fault current limiter (SFCL) with $2{\times}3$ array. The matrix-type SFCL consists of the trigger part to apply magnetic field and the current-limiting part to limit fault current. The fault current limiting characteristics according to the increase of magnetic field and applied voltage were nearly same. This is because the application of magnetic field hasn't an affect on total impedance of the SFCL. When turns number of a reactor increased, the voltage difference between two superconducting units in the current-limiting part according was decreased. The resistance difference generated in two superconducting units was also decreased. Therefore, we confirmed that the differences of the critical behaviors between superconducting units were reduced by application of magnetic field. By this results, we could decide the optimum turns number of reactor to apply magnetic field.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.55 no.6
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• pp.255-258
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• 2006

We investigated the operating characteristics of the hybrid-type superconducting fault current limiter (SFCL) according to the inductance of secondary windings. The hybrid type SFCL consists of a transformer that has a primary winding and a secondary winding with serially connected $YBa_2Cu_3O_7$ (YBCO) films. The resistive-type SFCL has difficulty when it comes to raising the capacity of the SFCL due to slight differences of critical current densities between units and structure of the SFCL. The hybrid-type SFCL with closed-loop is able to achieve capacity increase through the electrical isolation and reduction of the inductance of the secondary winding with a superconducting element of the same critical current. On the other hand, the current limiting characteristics were nearly identical in the hybrid-type SFCL with open-loop compared to closed-loop, but quench time was longer than the hybrid-type SFCL with closed-loop. We confirmed that the capacity of the SFCL was increased effectively by the reduced inductance of the secondary winding. In addition, the power burden of the system also could be lowered by reducing the inductance of secondary winding.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.57 no.3
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• pp.343-348
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• 2008

We investigated the quench characteristics accordance with increase of turns and applied voltage of matrix-type superconducting fault current limiter (SFCL) with $1{\times}3$ matrixes. The matrix-type SFCL consists of the trigger part to apply magnetic field and the current-limiting part to limit fault current. The fault current limiting characteristics according to the increase of magnetic field and applied voltage were nearly same. This is because the application of magnetic field has not an affect on total impedance of SFCL. When number of turns of reactor increased, the voltage difference between two superconducting units in the current-limiting part according was decreased. The resistance difference generated in two superconducting units also was decreased. Therefore, we confirmed that the differences of critical behaviors between superconducting units by application of magnetic field were decreased. By this results, we could be decided the optimum number of turns of reactor to apply magnetic field.

• Progress in Superconductivity and Cryogenics
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• v.14 no.3
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• pp.13-17
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• 2012

KEPCO Research Institute has been researching a Superconducting Fault Current Limiter (SFCL) which is considered one of solutions of fault current problems with Korea Institute of Machinery & Materials (KIMM) and Hanyang University since 2011. In this paper, we fabricated a current limiting module and conducted electrical short circuit tests for checking the validity of the transmission level SFCL design. Based on the short circuit characteristics of the second generation High Temperature Superconductor (HTS), we analyzed the short circuit characteristics of 3 parallel connected superconducting wires. The structure of the HTS wire is as follows: the stainless steel stabilizer of $100{\mu}m$ is laminated on the superconductor layer and under the substrate, both of which are electrically jointed with solder. We fabricated the current limiting module which has 40 series and 6 parallel connections and studied the short circuit characteristics of the module under various voltage levels.