Resistive-type Fault Current Limiter Research Articles

Transport characteristics of meander and bispiral types resistive fault current limiters

The resistive type fault current limiter based on YBCO thin film with high critical current density was proposed and developed because of its fast recovery characteristics. We have been developing a magnetic field measurement system with hall sensor to study the critical current density distribution or magnetic properties of high- T c superconductors such as thin film, tape conductor and coated conductors. In this study, the transport current distribution in straight line and U-corner region of meander type resistive fault current limiter using YBCO thin film was investigated experimentally. The both axial and radial self-magnetic field components according to the direct (DC) and alternating (AC) transport currents were measured by two-axis hall probe to estimate the current distribution. And also, the self-magnetic field at the corner of bispiral type fault current limiter was measured by two-axis hall probe with a high spatial resolution to compare with the meander type fault current limiter.

Verification of metal layer design for large-capacity superconducting fault current limiting elements using YBCO thin film

A superconducting fault current limiter (FCL) is one of the most attractive solutions to an increase of short-circuit current in electric power networks. The authors have studied resistive type FCLs using YBCO thin film superconductor with the patterning of superconducting and metal layers to increase the capacity of their current and voltage. A new design concept of fault current limiting element has been proposed, which has a meander-shaped gold layer on a wide I-shaped YBCO thin film. Experimental study and comparison between experimental and numerical analysis results verify the validity of the new FCL design concept.

Influence of Fault Current Limiter on Allowable Interconnecting Time Period of Customer Power System with Synchronous Generator

Distributed generators will be disconnected from a grid with a short-circuit fault to protect the generator and load in the customer system. In order to keep an isolated operation of the generator after the disconnection of customer system from the utility system, the customer system must adjust the power balance between supply and demand. This paper has investigated an influence of a fault current limiter on a probability of isolated operation after the disconnection of customer system with a synchronous generator from a medium voltage feeder. An allowable interconnecting time period, which is a critical time period from the fault occurrence to the isolated operation, has been simulated. It was assumed that the fault current limiter was installed in an interconnecting line between customer system with the synchronous generator and power distribution system. It was found that a resistive type fault current limiter does not improve the allowable interconnecting time period since the consumption power of fault current limiter causes the generator to decelerate. However, it was shown that the allowable interconnecting time period increases owing to the application of inductive type fault current limiter. This is because the active power of load is nearly equal to the generator output.

Attenuation of Electromagnetic Pulse Using High Temperature Superconductor

A high-speed thin-film resistive type fault current limiter (FCL) manufactured from YBCO thin film has been developed. It is designed to protect the front-end of the communication systems from damage due to electromagnetic pulses caused by thunder strikes or unexpected radiations. A 50 Omega coplanar waveguide (CPW), fabricated on an YBCO thin film coated on an MgO or LaAlO3 substrate up to 3 inch diameter, is used as the FCL. The resistivity of the YBCO central stripe will raise many orders of magnitude in a very short time automatically if the current pulse exceeds the critical current (Ic ) of the superconductor film. We design a meandering pattern to increase the effective length of the CPW, and also the normal state resistance. This FCL design is shown to have a switching time less than 10 ns, and the capability of tackling electromagnetic pulses with very large magnitude. The samples were cooled below 89 K in vacuum by a closed-cycle refrigerator, and tested with pulse-modulated 2 GHz electromagnetic signals of power up to 50 dBm. Our results show an 18 dB power attenuation while the input power exceeds 34~44 dBm at various temperatures slightly below Tc.

The stability behavior of ReBCO coated conductors laminated with copper or stainless steel

We have experimentally studied the dependence of quench and recovery characteristics of ReBCO coated conductors stabilized with copper or stainless steel on the amplitude of over pulse current and its duration time. Stability tests of the samples were performed in a liquid nitrogen bath cooling condition by applying a short period over pulse currents for 100 ms with amplitude up to six times of its critical current. The copper stabilized samples were also studied for the fixed amplitude of over pulse current with varying its duration time. We analyzed the quench and recovery behavior of three test samples using the current voltage characteristics. The analyses showed that copper and stainless steel were good stabilizers for the coated conductor to be used for applications like motors and resistive type fault current limiters, respectively.

Optimized Current Path Pattern of YBCO Films for Resistive Superconducting Fault Current Limiters

High critical current density, high n value and fast recovery characteristics of YBCO thin films are attractive characteristics for developing resistive type fault current limiters (FCLs). In order to get desirable resistance during quench state, it is important to design optimum current path etched on the surface of YBCO films, Therefore it is needed to determine the optimum current path patterns of YBCO thin films in order to prevent the distortion caused by both localized heat caused by excessive fault currents and breakdown occurred from intensification of electric field during quench period. In this study, to clarify the optimum current path design of YBCO films, electromagnetic analysis of various current paths including meander pattern, spiral pattern, and bi-spiral pattern were considered and to verify the analysis results, experimental tests including quench test, and insulation tests were performed. From the analytical and the experimental results, it was concluded that bi-spiral pattern of YBCO thin film was rather effective for quench and insulation than the other patterns. Finally, this bi-spiral current path pattern was adopted for YBCO thin film design for developing 6.6 kV/200 A 3 phase resistive fault current limiters, and it was possible to get satisfactory results.

Effect of Fault Current Limiter on Shaft Torsional Torque

We investigated the influence of a resistive type (R-type) and inductive type (L-type) fault current limiter (FCL) on the behaviour of the shaft torsional torque of a synchronous generator installed in a consumer system connected to a utility distribution system. In the case that the generator has relatively low natural oscillation frequency f 0 under about 40 Hz, the L-type FCL suppresses the maximum value of the shaft torsional torque τ sm to lower level than the R-type FCL. The R-type FCL with low limiting resistance may instead increase τ sm under the condition of low f 0 . On the other hand, for higher f 0 , R-type FCL limits τ sm at any limiting resistance as well as L-type FCL. The limiting effect of R-type FCL on τ sm is larger than that of L-type FCL.

Numerical Study on Fundamental Properties of a Resistive Type Fault Current Limiter With QMG Bulk Superconductor Reinforced by Metal Bypass

This paper describes the numerical results of electrical, thermal and mechanical properties in a model current limiting device with QMG bulk superconductor reinforced by various kinds of metal bypass. The electric circuit analysis for simulation of current sharing is coupled at each time step with the finite difference method to calculate the temperature distribution inside the device. The obtained results are compared with experimental data carried out previously, and they have a good agreement with each other. The profile of internal stress in the limiting devices is also estimated by means of a commercial code of finite element analysis, and it is concluded that the magnitude of mechanical stress applied to the superconductor is less than an allowable level for each model device.

Influence of Output Power Out of Synchronous Generator Installed in Customer System on Current Limiting Effect due to Fault Current Limiter

In this paper, it was assumed that a synchronous generator in a customer system was connected to a distribution system via the fault current limiter (FCL). We theoretically investigated the influence of the output power of the generator on the limiting effect of the fault current when the three-phase short-circuit fault occurs. It was shown that the fault current out of the customer system, limited by the FCL, rises with the output power of generator. It was found that the larger the output power is, the higher the fault current at the fault point is when the limiting resistance is less than 15Ω in the case of the resistive type FCL. On the other hand, the fault current at the fault point decreases with an increase in the output power for the limiting resistance more than 15Ω. By contrast, it was found that the suppressing effect on the fault current at the fault point due to the inductive type FCL hardly depends on the output power.

Transport properties of kA class QMG current limiting elements

In order to estimate the feasibility of a resistive type fault current limiter made of QMG, transport properties of QMG current limiting elements which can transport about 1 kA continuously in a superconducting state were studied. QMG is a rare earth based bulk superconductor that has high J c properties and relatively high electrical resistivity in a normal state. Because of these properties, QMG is a promising bulk material for superconducting fault current limiter applications. A bar-shaped sample in which the cross-section and the effective length were 2.2×0.8 mm 2 and 30 mm, respectively, was prepared. Bypass resistance of 7 mΩ was connected in parallel with the sample. A field assist mechanism that can apply a magnetic field of about 0.9 T to the sample was installed. A half cycle of AC current up to about 3 kA was applied to the samples at 77 K. In the case when applied current ( I) was less than 1000 A in a self-field, flux flow voltage was less than 0.5 mV. The n-value was about 6. In the applied field of 0.9 T, a rapid increase of voltage (quench) was observed around I=1820 A. The quench phenomena reproduced without degradation in the case of I>1820 A. From these results, it was found that QMG fault current elements can endure the thermal shock of the quench by the optimization of bypass resistance and the applied field.

Quench development and ultimate normal zone propagation "velocity" in superconductors under fast current change

Normal zone evolution or quench development is a major feature for resistive type fault current limiters design. We studied quench development under fast current rise in several samples of multifilament superconducting wires with a highly resistive matrix. At very fast current rise rates simultaneous quench of the entire sample takes place. It may be described by a characteristic time of a quench. We found that at the highest current rise rate this time is the same for samples with different lengths and cooling conditions made from the same wire. Apparent normal zone determined by this time is an ultimate velocity for a given length of a superconducting wire of certain type. We present experimental data about quench development under fast current rise and provide the theoretical estimations of quench parameters.

KA class resistive fault current limiting device development using QMG HTC bulk superconductor

kA class HTC bulk superconducting elements of devices for a resistive type fault current limiter for 6 kV distribution networks have been developed and tested. The YBCO devices made with the quench melt growth (QMG) method has 20000 30000 A/cm/sup 2/ critical current densities at 77 K and 1 T determined by the 1 /spl mu/V/cm criterion for the current flow parallel to the a-b plane. The QMG device has 5 /spl mu//spl Omega/-m normal state resistivity and an n-value of approximately 6 for the same direction of current flow. An element of the device with a 1.5/spl times/1.5 mm/sup 2/ cross-section with silver electrodes formed by sputtering could successfully carry exceeding 2200 A/sub peak/ AC transport current in self field at 77 K.

S-N transitions of QMG current limiting elements with metal coat

To estimate the feasibility of resistive type FCL (fault current limiter) consisting of QMG (melt processed YBa/sub 2/Cu/sub 3/O/sub 7-x//Y/sub 2/BaCuO/sub 5/ composite bulk superconductor), S-N transitions of various metal-coated samples made from large bulk QMG were studied at 77.3 K and 87.3 K (boiling point of argon) using single rectangular pulse current. It was found that the metal coating dramatically improves the endurance of element against the current flow after S-N transition and that optimization of the endurance and resistance should be required to realize QMG-FCL.