Flux-lock Type Superconducting Fault Current Limiter Research Articles

자속구속형 고온초전도 사고전류 제한기의 사고제거 후 회복특성

To apply the superconducting fault current limiter(SFCL) into a power system, the analysis for its recovery characteristics as well as the consideration for its cooperation with other protecting machine such as a circuit breaker is required. The recovery characteristics of the flux-lock type SFCL like its current limiting characteristics are dependent on the winding direction of two coils. In this paper, the experiments of the current limiting and the recovery characteristics of the flux-lock type SFCL with YBCO thin film were performed. From the analysis on the experimental results due to the winding direction of two coils, the limited fault current in case of the additive polarity winding was observed to be lower than that for the case of the subtractive polarity winding. In addition, the recovery time was found to be faster in case of the additive polarity winding compared to the subtractive polarity winding.

Recovery characteristics of flux-lock type superconducting fault current limiter

The flux-lock type superconducting fault current limiter (SFCL) has attractive characteristics that the current limiting level can be adjusted by a winding direction and the inductance ratio between two coils. We changed the winding direction and the number of coils to compare the resistive type SFCL with the flux-lock type SFCL. The initial limiting current (Iini) and quench characteristic were dependent on the winding direction and the inductance ratio of two coils. As a winding number was increased from 21 to 42, Iini and quench characteristic were proportionally increased. In additive polarity winding, Iini was 10.2A and the quench time (Tq) was 0.53ms, which was faster than that of a subtractive polarity winding.The consumed energy and recovery characteristics in a superconducting element showed the same tendency. Recovery characteristics in the flux-lock type SFCL were dependent on the consumed energy of a superconducting element. The recovery time was related to a heat energy and it was represented as the consuming time of the heat energy. As the heat energy was shown in H=0.24I2Rt, the recovery time was shortened in the following order: a subtractive polarity winding, a resistive type and an additive polarity winding. It was known that the recovery time was proportional to a consumed energy of a superconducting element.

Operational Characteristics of Flux-Lock Type SFCL With Series Connection of Two Coils

In this paper, we investigated the operational characteristics of the flux-lock type superconducting fault current limiter (SFCL) with series connection of two coils, which was suggested by us previously. This SFCL has the similar fault current limiting characteristics to the flux-lock type SFCL with parallel connection of two coils. The current limiting operation of the SFCL is performed by the generation of the magnetic flux between two coils when a fault happens and the fault current limiting characteristics of the SFCL are dependent on the inductance ratio and the winding direction of two coils. To confirm it, the operational characteristics of this SFCL were analysed based on its electrical equivalent circuit and the fault current limiting characteristics of this SFCL were investigated through the fault current limiting experiments. Through the analysis, it was shown that the limited fault current and the resistance of high-TC superconducting (HTSC) element could be adjusted by two coils' inductance ratio and the winding direction of two coils.

Operating Performance of the Flux-Lock and the Transformer Type Superconducting Fault Current Limiter Using the YBCO Thin Films

The operating characteristics of the flux-lock and the transformer type superconducting fault current limiters (SFCLs) have been tested and compared each other. The SFCLs are composed of the primary and secondary coils and the YBCO thin film as a current limiting unit. The turn ratios between the primary and secondary windings were 63:21 and 63:42, respectively. The winding direction between the primary and secondary windings was subtractive. When a fault occurred under the same conditions, the line current was limited more effectively in the transformer type SFCL. That is, the current value of the flux-lock type SFCL was approximately 2 times as high as that of the transformer type SFCL at the turn ratio of 63:42. However, the flux flowing into the iron core of the flux-lock type was less saturated than in the transformer type due to its flux distribution. The resistance generated in the YBCO thin film was higher in the flux-lock type where its voltage was also higher because of the winding direction between the primary and secondary windings. The initial limiting current of the flux-lock type was 2 times as high as that of the transformer type at the turn ratio of 63:42. The power consumed in the YBCO thin film of the transformer type was also remarkably low because the resistance, the current, and the voltage of the YBCO thin film are all lower. Consequently, we found that the transformer type had advantages for the current limiting effect and power burden of the YBCO thin film.

Quench characteristics of HTSC elements in integrated three-phase flux-lock type SFCL according to ground-fault types

The quench characteristics of high-TC superconducting (HTSC) elements in the integrated three-phase flux-lock type superconducting fault current limiter (SFCL), which consisted of HTSC elements and a three-phase flux-lock reactor wound on one iron core with the same turn’s ratio between coil 1 and coil 2 in each single phase, were investigated. In a normal condition, the magnetic flux generated in the iron core is zero because the magnetic flux generated between two coils of each single phase is canceled out. However, unlike other three-phase SFCL with three isolated iron cores, the integrated three-phase flux-lock type SFCL showed the different fault current limiting characteristics for the three-phase faults such as the single line-to-ground fault, the double line-to-ground fault, the line-to-line fault and the triple line-to-ground fault. In addition, the power burden of HTSC elements comprising the integrated three-phase flux-lock type SFCL can be decreased.In this paper, we investigated the quench characteristics of HTSC elements in the integrated three-phase flux-lock type SFCL according to three-phase ground fault types. Through the experiments for the fault current limiting characteristics of this type SFCL according to three-phase ground fault types, the quench characteristics of HTSC elements were analyzed and compared with those of three-phase resistive type SFCL.

히스테리시스 특성을 고려한 자속구속형 고온초전도 사고전류 제한기의 사고전류 제한특성 분석

자속구속형 초전도 사고전류 제한기는 평상시 자기적인 결합에 의해 철심의 히스테리시스 손실이 발생하지 않는 특징이 있다. 그러나 사고시에는 사고전류증가로 인해 고온초전도 소자의 저항발생과 함께 철심의 포화가 발생할 경우 제한기의 사고전류제한 특성을 저하시키는 현상이 발생하게 된다. 따라서 본 논문에서는 이를 분석하고 억제하기 위한 설계방안을 도출하기 위해 자속구속형 고온초전도 사고전류 제한기의 구성요소인 자속구속 리액터의 히스테리시스 특성을 고려한 사고전류 제한특성을 분석하였다. 이를 위해 제한기의 등가회로와 사고전류 제한실험으로부터 히스테리시스 곡선을 도출하였다. 1,2차권선의 인덕턴스 비에 따른 히스테리시스 곡선으로부터 인덕턴스비가 증가함에 따라 제한되는 사고전류크기는 증가한 반면 사고시 자속구속형 사고전류제한기의 구성요소인 철심의 포화가 억제됨을 확인할 수 있었다.

자속구속형 초전도 전류제한기의 철심조건에 따른 특성

초전도전류제한기(SFCL)는 전력계통내 적용시 계통보호를 보다 향상시킬 수 있는 방안으로써 수초이내에 신속하게 사고전류를 제한한다. 이러한 SFCL 중 자속구속형 전류제한기의 설계구조는 자속구속리액터인 하나의 철심에 1차측과 2차측 코일이 병렬로 결선되어 있다. 또한 전류제한소자인 YBCO박막과 2차측 코일을 직렬로 결선하여 설치장소의 조건에 따라 인덕턴스와 2차측 코일의 극성방향으로 과도전류 크기를 조절할 수 있다. 이러한 동작특성은 철심을 자속매개체로 적용되기 때문에 철심조건에 따른 성능평가실험은 필수적이다. 가극결선에서 전원전압을 200[Vrms] 인가시 피크전류는 폐루프가 30.71[A], 개루프가 32.01[A]까지 상승됨에 따라 초기과도 응답특성은 폐루프가 유리하였다. 하지만, 소자에 발생되는 전압이 폐루프가 220.14[V], 개루프가 142.73[V]까지 상승함에 따라, 폐루프 철심구조시 전류제한소자의 부담이 가중됨을 알 수 있었다. 결과적으로 자속구속형 SFCL의 전력계통내 적용시 각각의 철심구조에 따른 다양한 운전특성을 적절히 설계시 장점을 극대화 할 수 있을 것이다.

Quench characteristics of HTSC elements in series-connected flux-lock type SFCLs through magnetic flux-linkage

We investigated simultaneous quench characteristics of high-TC superconducting (HTSC) elements in the flux-lock type superconducting fault current limiters (SFCLs) connected in series through the magnetic flux-linkage. To apply the flux-lock type SFCL into power system, its current and voltage ratings are required to increase, which can be achieved by increasing the number of HTSC elements connected in series and in parallel. However, the slight difference in critical currents among HTSC elements, especially connected in series, causes uneven quenches. The suggested structure in this paper, which each flux-lock type SFCL unit was wound in series on the same iron core, can induce the simultaneous quench among HTSC elements by the magnetic flux-linkage generated in each flux-lock type SFCL unit. Through analysis for the fault current limiting experiments using HTSC elements based on YBCO thin films, the mutual flux linkage among the flux-lock type SFCL units was confirmed to be effective for the balanced power burden of HTSC elements in series-connected flux-lock type SFCLs.

Quench Characteristics of Current Limiting Elements in a Flux-Lock Type Superconducting Fault Current Limiter

We investigated the quench characteristics of a flux-lock type superconducting fault current limiter (SFCL) according to the number of the serial connection between the superconducting elements at the subtractive polarity winding of a transformer. The flux-lock type SFCL consists of two coils. The primary coil is wound in parallel to the secondary coil through an iron core, and the secondary coil is connected to the superconducting elements in series. The operation of the flux-lock type SFCL can be divided into the subtractive and the additive polarity windings according to the winding directions between the primary and secondary coils. In this paper, the analyses of voltage, current, and resistance in serial connection between superconducting elements were performed to increase the applied voltage of flux-lock type SFCL. The power burden was reduced through the simultaneous quenching between the superconducting elements. This enabled the flux-lock type SFCL to be easy to increase the capacity of power system

Current Limiting Characteristics of Integrated Three-Phase Flux-Lock Type SFCL

The short circuit analysis of the integrated three phase flux-lock type superconducting fault current limiter (SFCL), which consisted of three-phase flux-lock reactor wound on an iron core with the same turn's ratio between coil 1 and coil 2 for each single phase, was performed. In a normal time, the flux generated in the iron core is zero because the flux generated between two coils of each single-phase is canceled out. In a fault time, the integrated three-phase flux-lock type SFCL showed the different fault current limiting characteristics from other three-phase SFCLs with the separated three iron cores. Through the computer simulation for the three-phase circuit with its equivalent circuit, the current limiting characteristics of the integrated three-phase flux-lock type SFCL were analyzed

Current Limiting Characteristics of Flux-lock Type SFCL according to Inductance Variation

We investigated the current limiting characteristics of flux-lock type superconducting fault current limiter(SFCL) according to inductance variation of coil 2. The flux-lock type SFCL consists of two coils. The primary coil is wound in parallel to the secondary coil through an iron core, and the secondary coil is connected to the superconducting element in series. The operation of the flux-lock type SFCL can be divided into the subtractive and the additive polarity winding operations according to the winding directions between the coil 1 and coil 2. The current limiting characteristics in two winding directions were dependent of on the ratio of the number of turns of coil I and coil 2. The fault current increased when the number of turns of coil 2 increased in the subtractive polarity winding. On the contrary, the fault current decreased under the same conditions in case of the additive polarity winding.

Fault Current Limiting Characteristics of Flux-lock Type SFCL with Several Secondary Windings

We investigated fault current limiting characteristics of the flux-lock type superconducting fault current limiter (SFCL), which consisted of a primary winding and several secondary windings connected in series between <TEX>$high-T_C$</TEX> superconducting (HTSC) thin films. Each YBCO thin film has a 2 mm wide and 42 cm long meander line with 14 stripes of different length. The power imbalance due to the slight difference of Ie between YBCO current limiting elements causes the significant power burden on YBCO element with lower <TEX>$I_C$</TEX>. We confirmed from our experiments that the mutual coupling between the primary winding and secondary windings of the flux-lock type SFCL reduced the power imbalance between YBCO current limiting elements compared with the resistive type SFCL connected in series.

사고각에 따른 자속구속형 전류제한기의 전류제한특성

We Investigated the current limiting characteristics of the flux-lock type superconducting fault current limiter(SFCL) by fault angles. The flux-lock type SFCL consists of the primary and the secondary copper coils wound in parallel through the iron core and YBCO thin film. In this paper, the current limiting characteristics of the flux-lock type SFCL by fault angles in case of the subtractive and the additive polarity windings were compared and analyzed. The flux-lock type SFCL limited fault current more quickly as the fault angles increased. On the other hand, the initial power burden of the superconducting element during the fault increased as the fault angles increased. In addition, we found that the resistance of the flux-lock type SFCL in case of the subtractive polarity winding was more increased than that of the additive polarity winding. The peak current of the fault current in case of the subtractive polarity winding was larger than that of the additive polarity winding.

자속구속형 고온초전도 전류제한기의 동작전류와 각 코일의 전류분류 분석

A flux-lock type superconducting fault current limiter(SFCL) consists of two coils, which are wound in parallel each other through an iron core, and a high-<TEX>$T_c$</TEX> Superconducting(HTSC) thin film connected in series with coil 2. If the current of the HTSC thin film exceeds its critical current by the fault accident, the resistance of the HTSC thin film generated, and thereby the fault current can be limited by the impedance of the fluk-lock type SFCL. In this paper, we investigated the dependence of both the fault current limiting characteristics and the current distribution between two coils on the operational current of the flux-lock type SFCL through the equivalent circuit analyses and short circuit tests. From the comparison of both the results, the experimental results well agreed with the analyses for equivalent circuit.

Analysis of Operational Characteristics of Flux-Lock Type SFCL Combined With Power Compensator

The flux-lock type superconducting fault current limiter (SFCL) combined with a power compensator was proposed in this paper. This SFCL consists of a flux-lock reactor and a power compensator. The former, which has coil 1 and coil 2 wound in parallel through high-T/sub C/ superconducting (HTSC) element, can perform the fault current limiting operation during a fault period. The latter is composed of a current-controlled inverter and an AC/DC converter between coil 3 and grid, which can be operated as the power compensator for nonlinear load during a normal operation. The specification for a test model was determined and its operational characteristics were analyzed through computer simulation using PSIM program. It was confirmed that the suggested flux-lock type SFCL, combined with the power compensator, could protect the system from over-current by a short circuit accident and compensate the reactive power due to a nonlinear load during a normal operation as well.

Impedance Variation of a Flux-Lock Type SFCL Dependent on Winding Direction Between Coil 1 and Coil 2

The flux-lock type superconducting fault current limiter (SFCL) uses the magnetic coupling between two coils connected in parallel with each other. This SFCL has the merit that both the resistance of high-T/sub C/ superconducting (HTSC) element and the limiting current capacity can be simultaneously increased through the application of magnetic field into HTSC element. However, unlike other types SFCLs, the different fault current limiting characteristics can appear according to the winding direction between the two coils. In this paper, the relation of the impedance of the flux-lock type SFCL with the resistance of HTSC element was derived from its equivalent circuit using the current and the voltage relationship between the two coils. The limiting impedances of the flux-lock type SFCL due to the winding direction through the discrete fourier transform (DFT) analysis for the voltage and the current data obtained from the fault current limiting experiments were extracted and analyzed from the point of view of the limited line current and the resistance of HTSC element.

자속구속형과 저항형 초전도 전류제한기의 특성비교

we compared the operating characteristics between flux-lock type and resistive type superconducting fault current limiters(SFCLs). Flux-lock type SFCL consists of two coils, which are wound in parallel each other through an iron core, and a high-Tc superconducting(HTSC) element is connected with coil 2 in series. The the flux-lock type SFCL can be divided into the subtractive polarity winding and the additive polarity winding operations according to the winding directions between the coil 1 and coil 2. It was confirmed from experiments that flux-lock type SFCL could improve both the quench characteristics and the transport capacity compared to the resistive type SFCL, which means, the independent operation of HTSC element.

Fault current limiting characteristics due to winding direction between coil 1 and coil 2 in a flux-lock type SFCL

The flux-lock type high- T c superconducting fault current limiter (SFCL) has different fault current limiting characteristics according to the winding direction between coil 1 and coil 2. In this paper, the fault current limiting characteristics and the resistance of high- T c superconducting (HTSC) element in the flux-lock type SFCL without the 3rd winding due to the winding direction were analyzed based on the equivalent circuit with the magnetization branch. In addition, we investigated the fault current limiting characteristics of it along the number of turns of coil 2 with the fixed number of turns of coil 1 through the fault current limiting experiments. In case that coil 1 was wound to the same winding direction as coil 2, or, subtractive polarity winding, the more the number of turns in coil 2 for the fixed turns of coil 1, the higher the resistance of HTSC element and the limited line current. On the other hand, the additive polarity winding case, which coil 1 was wound to the reverse winding direction of coil 2, showed the opposite operational characteristics to the case of the subtractive polarity winding. The experimental results for each winding direction were well coincided with the analyzed ones from the equivalent circuit.

Current limiting characteristics of flux-lock type high-T/sub c/ superconducting fault current limiter with control circuit for magnetic field

A flux-lock type superconducting fault current limiter (SFCL) can change the amplitude of the magnetic field by adjusting either the inserting resistance or the phase adjusting capacitor. However, the magnetic field coil cannot generate enough magnetic field for some time after a fault happens due to resonance between the phase adjusting capacitor and the magnetic field coil. It is also required for the magnetic field generated to be controlled for the application to high-T/sub C/ superconducting (HTSC) elements which have different critical characteristics. This paper proposes a flux-lock type SFCL with a control circuit for the magnetic field, which is composed of solid state switches connected with the magnetic field coil. A current limiting experiment of this model was carried out. We showed that the amplitude of the fault current as well as the magnetic field could be controlled by the sinusoidal pulse width modulation (SPWM) operation, one of the switching techniques for controlling the magnetic field.