• 한국초전도ㆍ저온공학회논문지
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• 제9권3호
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• pp.57-61
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• 2007

The current limiting characteristics of hybrid SFCL with additional power electronic devices was investigated in order to improve operation reliabilities. The hybrid SFCL developed consists of a superconducting trigger (S/T) part, a fast switch (F/S) module and a current limiting (C/L) part. Although hybrid SFCL had shown a excellent current limiting characteristics, this device was rather vulnerable to the residual arc currents which could exist during fast switch operation. This undesirable arc should be extinguished as quickly as possible in order to implement perfect fault current commutation. So, in order to eliminate the residual arcs between fast switch contacts, the power electronic devices (IGBT or GTO) were connected in series between the S/T part and the interrupter of the F/S module. According to the fault tests conducting with an input voltage of $270\;V_{rms}$ and a fault current of $5\;kA_{rms}$, The power electronic devices could perfectly remove the arc generated between the contacts of the interrupter within 4 ms after the fault occurred. From the test analysis, it was confirmed that the hybrid SFCL could enhance the operation reliability by adopting additional power electronic devices.

• 대한전기학회논문지:전력기술부문A
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• 제55권2호
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• pp.62-66
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• 2006

We investigated the characteristics of the hybrid-type superconducting fault current limiter (SFCL) by the number of secondary windings. The SFCL consists of a transformer, which has a primary winding and several secondary windings with serially connected $YB_{a2}Cu_{3}O_{7}$ films. In order to increase the capacity. of the SFCL, the serial connection between each current limiting unit is necessary. Resistive-type SFCL has a difficulty in quenching simultaneously between the units due to slight differences of their critical current densities. The hybrid-type SFCL could achieve the simultaneous quenching through the electrical isolation and the mutual flux linkage among the units. We confirmed that the capacity of the SFCL could be increased effectively through the simultaneous quenching among the units. In addition, the power burden of the system could be reduced by adjusting the number of secondary windings. We will investigate the method to increase the capacity through serial and Parallel connections among current limiting units.

• 한국초전도ㆍ저온공학회논문지
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• 제9권4호
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• pp.32-36
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• 2007

We fabricated and tested a novel hybrid superconducting fault current limiter (SFCL) of three-phase $24kV_{rms}/630A_{rms}$ rating. In order to apply conventional resistive SFCLs into electric power systems, the urgent issues to be settled are as follows, such as initial installation price of SFCL, operation and maintenance cost due to ac loss of superconductor and the life of cryostat, and high voltage and high current problems. The ac loss and high cost of superconductor and cryostat system are main bottlenecks for real application. Furthermore in order to increase voltage and current ratings of SFCL, a lot of superconductor components should be connected in series and parallel which resulted in extreme high cost. In addition, the method to quench all components at the same instant needs very sophisticated skill and careful operation. Due to these problems, the practical applications of SFCL were pending. Therefore, in order to make practical SFCL, the price of SFCL should be lowered and should meet the demand of utilities. We designed novel hybrid SFCL which combines superconductor and conventional electric equipment including vacuum interrupter, power fuse and current limiting reactor. The main purpose of hybrid SFCL is to drastically reduce total usage of superconductor by adopting current commutation method by use of superconductor and high fast switch. Consequently, it was possible to get the satisfactory test results using this method, and further works for field tests are in the process.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 춘계학술대회 논문집 전기기기 및 에너지변환시스템부문
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• pp.393-395
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• 2006

We investigated the operational characteristics of the hybrid-type superconducting fault current limiter (SFCL) according to the serial and parallel connections of secondary circuits. The hybrid-type SFCL consists of a transformer, which has a primary winding and several secondary windings with $YBa_2Cu_3O_7$ films connected in series and parallel. In order to increase the capacity of the SFCL, the serial connection between each current limiting unit is necessary. The hybrid-type SFCL with the serial connection in secondary circuits could show superior characteristics than those of the parallel connections in the current limiting and quench time. The resistances generated in the superconducting units were also lowered at the parallel connections. We confirmed that the parallel connection reduced the power burden of each superconducting unit under the same conditions because of the simultaneous quenching between superconducting units.

• 한국전기전자재료학회논문지
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• 제19권4호
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• pp.391-397
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• 2006

We present investigations of a hybrid type superconducting fault current limiter (SFCL), which consists of transformers and resistive superconducting elements. The secondary windings of the transformer were separated into several electrically isolated circuits and linked inductively with each other by mutual flux, each of which has a superconducting current limiting element of $YBa_2Cu_3O_7$ (YBCO) stripes as a current limiting element. Simple connection in series of the SFCL elements tends to produce ill-timed quenching because of power dissipation unbalance between SFCL elements. Both electrical isolation and mutual flux linkage of the elements provides a solution to power dissipation unbalance, inducing simultaneous quench and current redistribution of the YBCO films. This design enables to increase the voltage rating of SFCL with given YBCO stripes.

• 한국초전도ㆍ저온공학회논문지
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• 제12권3호
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• pp.39-43
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• 2010

In Korea, 22.9kV hybrid SFCL (Superconducting Fault Current Limiter) has been developed and carried out long-term field tests in Gochagn power test center of KEPCO through DAPAS program. The SFCL will be installed at a distribution line of Icheon substation in Korea. For the successful application, we have to design the specifications considering real power system operation. This paper proposes a concept of the operating current based rms value for the protection coordination with protective delays and studies a proper range of the current in Korean distribution power system.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 제38회 하계학술대회
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• pp.102-103
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• 2007

In order to apply resistive superconducting fault current limiters into electric power systems, the urgent issues to be settled are as follows, such as initial installation price of SFCL, operation and maintenance cost due to ac loss of superconductor and the life of cryostat, and high voltage and high current problems. The ac loss and high cost of superconductor and cryostat system are main bottlenecks for real application. Furthermore in order to increase voltage and current ratings of SFCL, a lot of superconductor components should be connected in series and parallel which resulted in extreme high cost. Thus, in order to make practical SFCL, we designed novel hybrid SFCL which combines superconductor and conventional electric equipment including vacuum interrupter, power fuse and current limiting reactor. The main purpose of hybrid SFCL is to drastically reduce total usage of superconductor by adopting current commutation method by use of superconductor and high fast switch. Consequently, it was possible to get the satisfactory test results using this method, and further works for practical applications are in the process.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2009년도 제40회 하계학술대회
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• pp.294_295
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• 2009

Superconducting fault current limiter (SFCL) is an power device of a novel concept. While SFCLs generate no ohmic loss during the operation carrying normal currents, they can limit fault currents very fast making large impedance by their quench characteristics. In 2006, KEPCO has developed a distribution class hybrid type SFCL by a collaborative research project with LS industrial systems. The SFCL has merits in practical and economical points of view. In the SFCL, the superconductor just plays a role of a fault detector and the current limiting is completed by the other current limiting element made of normal metals throu호 the line commutation. As a result, the required amounts of superconductors can be reduced considerably. Consequently, the hybrid SFCL can be fabricated with small size and cost, maintaining perfect current limiting performance. Currently, KEPCO is carrying out a research project at Gochang power test center for the purpose of the verification test of the 22.9 kV/ 630 A class SFCL for the practical application in real grid. Through the project, a long term operational test and fault current test will be done. In this paper, the back ground of development and installation of the SFCL will be explained and the operation plan of the SFCL for the verification test is also introduced.

• 한국초전도ㆍ저온공학회논문지
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• 제13권1호
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• pp.17-21
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• 2011

A hybrid superconducting fault current limiter (SFCL) with fast switch had been previously suggested by our research group. To make a hybrid SFCL, different superconducting wires were wound two pancake coils so that two pancake coils had asymmetric configuration. The impedance of the asymmetric non-inductive coils are zero with applied normal current. However during the fault. currents were distributed unequally into the two pancake coils because each superconducting wires have different electrical characteristics. This unequal distribution of current causes effective magnetic flux which generate repulsive force. Fast switch was thus opened by the force applied to the aluminum plate which consists of SFCL. In this paper, the AC loss characteristics of the asymmetric non-inductive coils with combinations of superconducting wires were studied and calculated by related experiments and finite element method (FEM) simulation. From these results, we suggested the appropriate combination of two superconducting wires to be used for the asymmetric non-inductive coils.

• 전기학회논문지
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• 제64권1호
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• pp.57-63
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• 2015

Fault currents characteristics contain decaying DC offset. First cycle peak value of fault currents is higher than steady-state fault current value. These characteristics can affect the operation of protective device. To reduce the asymmetric fault current, the method using a series connection of two hybrid-type Superconducting Fault Current Limiter(SFCL) components, an auxiliary SFCL and a main SFCL, has been proposed. The auxiliary SFCL limits the first half cycle fault current, while main SFCL limits the steady state fault currents. This paper proposed a decision method of the optimal insertion resistance of auxiliary and main SFCL components. To verify the effectiveness of proposed scheme, the various simulations are performed by using Electromagnetic Transient Program(EMTP).