high-Tc Superconducting Fault Current Limiter Research Articles

Development of the World's First HTS Power Substation

With the increasing depletion of fossil fuels and growing environmental pressure, the mankind has got known the need to vigorously develop the renewable energy and the energy-saving technology. The high Tc superconducting (HTS) power technology will be very helpful to enhance the stability, reliability, and efficiency and transmission capacity of the power grid which would be dominated by the renewable energy. In this paper, we will report the installation and operation of a 10 kV HTS power substation which includes a 75 m/1.5 kA HTS power cable, a 10 kV/1.5 kA HTS fault current limiter, a 1 MJ/0.5 MVA high Tc SMES and a 630 kVA/10 kV/0.4 kV HTS power transformer.

Dielectric Characteristics of EPR for 66 kV-Class Power Leads of High-Tc Superconducting Fault Current Limiter

A 66 kV-class power lead insulation system has been developed for high-Tc superconducting fault current limiters (SCFCL). The power leads are insulated with ethylene-propylene rubber without organic filler, and have excellent crack resistance. This system was evaluated by an insulation model and was shown to have strong enough electrical insulation properties for 66 kV-class equipment. To minimize insulation layer thickness, the dielectric characteristics of this EPR were investigated in detail. The specimens were made 0.3-10 mm thick: near the thickness of an actual power lead insulation layer. The breakdown stress was measured at room temperature and at liquid nitrogen temperature. The V-t characteristic was also measured. Based on the study, the power lead insulation model was constructed and its electrical insulation properties were evaluated

Design and Test Results of 66 kV High-Tc Superconducting Fault Current Limiter Magnet

This paper describes the design of a 66 kV high-Tc superconducting fault current limiter (FCL) magnet and the test results obtained. The magnet mainly consists of a vacuum vessel, a nitrogen bath, a pair of current leads, cryocoolers, and six sets of coils wound with Bi2223 tape. The rated current is 750 A. The insulation voltage of the magnet is of the 66 kV class. In the final year of the project, all six sets of the coils are set connected in the cryostat and evaluation tests have been implemented. In the cooling test, sub-cooled nitrogen of 65 K was obtained, with homogenous temperature distribution in the cryogen. The rated current of 750 A was successfully obtained for both direct and alternating current tests. In addition, the magnet passed the simultaneous current and voltage application test. The dielectric test results showed that the magnet satisfied the insulation for 66 kV apparatus in the Japanese Electrotechnical Committee Standard. Finally, the magnet was combined with a rectifier bridge circuit to form an FCL. In a fault current limiting test with a short-circuit generator, the FCL successfully limited short circuit current up to 20 kV applied voltage. The obtained result was in good agreement with the design and the Electro-Magnetic Transients Program (EMTP) analysis

Visualization Study on Boiling of Nitrogen During Quench for Fault Current Limiter Applications

For the development of a 13.2 kV/630 A bifilar winding type high-Tc superconducting fault current limiter (SFCL), a visualization study has been conducted to clarify boiling characteristics during the quench of the high-Tc SFCL. A series of experiments was carried out using a stainless steel strip on a G10 plate as a heating element to simulate the quench state of the high-Tc SFCL. A pulse of DC power input was applied to the strip in saturated and subcooled liquid nitrogen. The magnitude of the heat generation was varied from 10 W/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> to 170 W/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and the period of the heat impulse was fixed at approximately 100 ms. Bubble behavior was observed by a high-speed camera through view ports of a cryostat. The boiling phenomena, the temperature rising of the strip and the recovery time were compared for different power densities and liquid nitrogen operating conditions. The bubble suppression was clearly observed with respect to the degree of subcooling

System Technology and Test of CURL 10, a 10 kV, 10 MVA Resistive High-Tc Superconducting Fault Current Limiter

A full scale three-phase resistive high-Tc superconducting fault current limiter (SCFCL) designed for 10 kV, 10 MVA, has been developed, manufactured, and tested within a publicly funded German project called CURL 10. The device is based on 90 bifilar coils of MCP BSCCO-2212 bulk material. The operating temperature of 66 K is achieved by cooling of liquid nitrogen using two Stirling cryocoolers. Until today, this is the largest HTS fault current limiter world wide. We report on the design features, the composition, and the operation parameters of the SCFCL system. From April 2004 on CURL 10 is installed and tested within the network of the utility RWE at Netphen near the city of Siegen, Germany. The results of the laboratory test and the field test of CURL 10 are given.

66 kV/1 kA High-&amp;lt;tex&amp;gt;$rm T_rm c$&amp;lt;/tex&amp;gt;Superconducting Fault Current Limiter Magnet

One of the items included in the Super-conductive AC Equipment (Super-ACE) project, being performed from 2000 to 2004, is development of a 66 kV/1 kA class high-Tc superconducting (HTS) fault current limiter (FCL) magnet. This research focuses on fundamental technical items essential for a 66 kV class fault current limiter, that is, high current-capacity, high voltage-insulation, and sub-cooled nitrogen cooling. This paper describes the design of the magnet and the test results obtained. The magnet mainly consists of a vacuum vessel, a nitrogen bath, a pair of current leads, cryocoolers, and six sets of coils wound with Bi2223 tape. The rated current of the magnet is 750 Ap. The insulation voltage of the magnet is of the 66 kV class. In the final year of the project, all six sets of the coils are set connected in the cryostat and evaluation tests have been implemented. In the cooling test, sub-cooled nitrogen of 65 K was obtained, with homogenous temperature distribution in the cryogen. The rated current of 750 Ap was successfully obtained for both direct and alternating current tests. In addition, the magnet passed the simultaneous current and voltage application test. Finally, the dielectric test results showed that the magnet satisfied the insulation for 66 kV apparatus in the Japanese Electrotechnical Committee Standard (JEC) standard.

Reduction of fault current peak in an inductive high-Tc superconducting fault current limiter

This paper dealt with current-limiting performances of an inductive high-Tc superconducting fault current limiter with an auxiliary coil. The fault current limiter mainly consists of the primary copper coil, secondary high-Tc superconducting rings, and auxiliary high-Tc superconducting coils, which are magnetically coupled through three-legged core. The superconducting fault current limiter as a series element in the power system is inserted to limit the fault current. The device presents fast variable-impedance features in the event of a fault condition. The fault current peak can become relatively large for certain ranges of the flux and the fault instant due to the core saturation. The auxiliary coil proposed in this paper was proven to increase the impedance of the SFCL up to more than 31% while preventing the core saturation.

The improved hysteresis characteristics of flux-lock type SFCL using third winding

In this paper, we showed that the third winding of the flux-lock type high- T c superconducting fault current limiter (HTSC-FCL) could be operated as the damping coil to suppress the saturation of the iron core during a fault period. This third winding of the HTSC-FCL was installed to apply the magnetic field into HTSC element simultaneously after a fault happened. To confirm it, the hysteresis characteristics of an iron core of the flux-lock type HTSC-FCL were investigated from the equivalent circuit of a saturable transformer including the nonlinear magnetizing characteristic. Due to the magnetic coupled structure of the flux-lock reactor together with the third winding, the iron core of the flux-lock type HTSC-FCL could be restrained from saturation during a fault period. Through the analysis for the fault current limiting characteristics and the hysteresis ones obtained from the experimental results, the fault current limiting level as well as the saturation of the iron core of the flux-lock type HTSC-FCL with the third winding could be more improved than that of the flux-lock type HTSC-FCL without the third winding.

Operational Characteristics of a Flux-Lock-Type High-Tc Superconducting Fault Current Limiter With a Tap Changer

The authors investigate the operational characteristics of a flux-lock-type high-T/sub c/ superconducting (HTSC) fault current limiter (SFCL) with a tap changer which could adjust the number of turns of the third winding. In the case of conventional flux-lock-type SFCL, the phase adjusting capacitor is connected in series with magnetic field coil to adjust the magnetic field applied to the HTSC element in phase with the current flowing through the HTSC element during a fault time. However, the current flowing at the third winding, which is connected with magnetic field coil, affects the fault current limiting characteristics. To analyze the influence of current flowing at the third winding on the fault current limiting characteristics, the fault current limiting characteristics of the flux-lock type SFCL, whose inductance of coil 3 could be adjustable through a tap changer, are investigated through the experiments and the computer-aided simulations. The relation of line currents flowing into the flux-lock-type SFCL during a fault time and numbers of turns of a tap changer is drawn.

The fault current limiting characteristics of a flux-lock type high- Tc superconducting fault current limiter using series resonance

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. This paper investigated the parameter range where the operation as mentioned above for the designed flux-lock type HTSC-FCL using series resonance occurred from the experimental results. In the design of the flux-lock type HTSC-FCL, the some methods to avoid the continuous increase of the line current were suggested and confirmed by the experiments that the suggested methods were available to prevent the continuous increase of the line current after a fault happened.

유도형 고온초전도 한류기용 Prototype 직류 리액터의 설계와 제작

In this paper, dc reactor lot the inductive high-Tc superconducting fault current limiter (SFCL) was optimally designed by finite element method(FEM). The Prototype high-Tc do reactor was manufactured and compared to the results of design. This dc reactor consists of 4∼stacked double pancake coils which are wounded with Bi-2223 wire coated with SUS315L. Kapton tape is used for the insulation of turn to turn and layer to layer. Each pancake is connected in series by soldering Finally, optimal design and manufacture method lot the dc reactor is suggested in this paper. Through the comparison of result of optimal design and experimental result of prototype high-Tc superconducting dc reactor, reliance on the design of the high-Tc dc reactor tot the 1.2 kV/80 A SFCL is proved.

Dynamic simulation and tests of a three-phase high Tc superconducting fault current limiter

Dynamic simulation was performed on a three-phase high Tc superconducting fault current limiter (HTSFCL). A prototype HTSFCL of this type was made and tested. It employs one high Tc superconducting coil, which is connected with the secondary windings of three single-phase transformers. The operating characteristics of the HTSFCL have been investigated. The results are also presented.

A variation of impedance of a high-Tc superconducting fault current limiter with an open core

The high-Tc superconducting fault current limiter (SFCL) is studied worldwide to be classified into a resistive type and an inductive type such as a magnetic shielding type and a DC reactor type. The high-Tc SFCL with an open core belongs to the magnetic shielding type SFCL. Unlike conventional magnetic shielding type SFCLs, it uses the open core to reduce the mechanical vibrations and installed space. The high-Tc SFCL with an open core was designed and manufactured by stacking three BSCCO-2212 tubes and it was tested in the maximum source voltage of 400 Vrms and the results such as the reduction of fault current and impedance of the SFCL are described in this paper. The results show that the fault current in the source voltage of 400 Vrms was reduced to be about 123 A peak and it is about 3.9 times as the normal state current. Also, the impedance of the high-Tc SFCL was about 9 /spl Omega/ to be about 9 times the normal state impedance. The impedance of the SFCL appears just after the fault, and the size of it is dependent on the source voltage. From the impedance, the inductance of the SFCL was calculated.

Design and characteristic analysis of a rod type high-Tc superconducting fault current limiter through electromagnetic analysis

The existence of large air gaps, between a high-Tc superconducting (HTS) tube and an iron core, or between a primary winding and a HTS tube, possibly causes some undesirable voltage drops under the condition of normal operation. It makes the power system unstable. For this reason, the optimization of air gaps is essential in designing a high-Tc superconducting fault current limiter (SFCL). In this paper, the optimal values of air gaps are determined through electromagnetic analysis, and the comparison between computational and experimental results is provided.

Design and test results of 6.6 kV high-Tc superconducting fault current limiter

A 6.6 kV single-phase fault current limiter (FCL) using a high-Tc superconducting coil as a limiting coil was developed. The development is a preliminary step to investigate the feasibility of the FCL application for high-voltage transmission lines. The FCL is of the rectifier type and is mainly comprised of a limiting coil, a sub-cooled nitrogen cryostat with a cryocooler, and a rectifier bridge. The limiting coil, wound as a solenoid by Ag/Mn sheathed Bi-2223 tapes, has an inductance of 30 mH. It is immersed in a liquid nitrogen bath in the cryostat. A Gifford-McMahon cryocooler cools the cryogen below 77.3 K. A pressure regulator keeps the cryogen at an atmospheric pressure. The coil has a critical current of 70 A at 64 K and endures a 50 Hz overvoltage of 22 kV against the ground. In a fault current limiting test with a short-circuit generator, a short-circuit current of 12.5 kA was limited to 1.2 kA.

Improvement on current limiting performance of current limiting devices with damping coils

An improved model of the current limiting devices such as the high-Tc superconducting fault current limiter (SFCL) and the reactor have been developed. The high-Tc SFCL mainly consists of the primary copper coil, the secondary high-Tc superconducting rings, and the damping coils, which are magnetically coupled through a three-legged magnetic core. Because a portion of the magnetic flux above the saturation point generated by the fault current is cancelled by the damping coil, thereby the magnetic core is prevented from getting into the saturated state. The limiting current level and the saturation of the core could be controlled by the air-gap length of the central leg with the damping coil. A new design of the SFCL is found to increase the effective impedance by about 60 to 70%, compared to the SFCL design without the damping coils.

Novel design and operational characteristics of inductive high-Tc superconducting fault current limiter

A novel prototype of an inductive superconducting fault current limiter with an iron core and an air gap was fabricated and tested. If its impedance is not high enough to limit the fault current, then destructive damage occurs in the power system. The authors attained magnetic saturation under the higher current by introducing an air gap in the three-legged magnetic core. The fault current was successfully limited to two times as much as the nominal current without high fault current within 1/4 cycles at a 60 Hz source having an effective voltage of 70 V.

The analysis of the fault currents according to core saturation and fault angles in an inductive high-Tc superconducting fault current limiter

In this paper, we investigate the fault currents in an inductive high-Tc superconducting fault current limiter (SFCL). The currents can cause serious damage to the reliability and stability of the power system. To analyze the transient fault characteristics of the SFCL, we fabricated an inductive high-Tc SFCL and tested it under different fault conditions. To simulate a fault condition, a fault angle controller was connected to a load. As the firing angle of the triac in the fault angle controller was controlled, various angles of the fault instant can be selected. An important parameter for the design and the fabrication of the SFCL is the reduction of the fault currents. If abnormally high currents due to low impedance of SFCL do not occur in the network with SFCL, the currents flowing under fault conditions can be limited to a desired value within one cycle. The fault current reduction depends on saturation, normal zone propagation velocity, turns ratio, and the fault angle (the instant of the fault occurrence within a cycle).

Detergents used in oil fields

In the present study, a novel solenoid type bifilar coil is proposed for high-Tc superconducting fault current limiter (SFCL) which is composed of two windings in a bobbin and their winding directions are opposite with each other to have non-inductive characteristics. The two windings are connected in parallel at the current terminals for large current capacity. Besides, the current terminals are at the ends of the coil so that the electrical insulation design may be easier than that of other non-inductive coils. The novel solenoid type bifilar coil for SFCL is fabricated with BSCCO 2223 and tested in LN2 bath at 77 K to investigate the current and voltage sharing as well as the current limiting effects. According to the test results, the current is limited effectively at first peak after the fault and the current sharing performance in each winding is verified under the normal and fault conditions. In order to compare with other bifilar coils, the AC losses are measured.