T. Ishigohka

Single-line-to-ground fault test of a 3-phase superconducting fault current limiting reactor

The current limiting behavior of a 3-phase superconducting fault current limiting reactor (SCFCLR) in a model power system at a single-line-to-ground (SLTG) fault is experimentally confirmed. A small arc gap is attached on one phase of the model transmission line. A single-line-to-ground fault is activated. The behavior of the grounding current and the arc is observed. It is shown that: (1) the fault current is limited to a very small value by the large zero-phase-sequence reactance of the SCFCLR, and the self-extinction of the fault arc is observed; (2) the power flow is not disturbed by a SLTG fault at all, and no power system disturbances are observed; and (3) the windings do not quench for a SLTG fault. A supplementary experiment for a two-phase short circuit fault was also carried out. >

Fundamental Characteristics of Superconducting Fault Current Limiter Using LC Resonance Circuit

A new type of fault current limiter (FCL) utilizing series LC resonance circuit composed of a superconducting coil and a capacitor is proposed. The superconducting coil is wound by Bi-2223/Ag HTS tape conductor. The new FCL can suppress the rapid increase of a fault current by its energy storing capacity. Both theoretical analysis and experiments are carried out. The experimental result shows the current limiting ability of this FCL. The obtained experimental result agrees well with the theoretical one

Quench detection of superconducting magnets using ultrasonic wave

An ultrasonic quench-detection method for superconducting magnets is presented. This nondestructive method monitors the change of the acoustic transfer function of a superconducting magnet induced by a local temperature rise or an epoxy crack. Experiments were carried out on a small epoxy-impregnated magnet. The experimental results show that a local temperature rise of about 2-3 K can be detected by this method. It is concluded that the technique can provide early quench warning by monitoring continuously the change of the acoustic transfer function of the magnet. >

Preliminary study on AC superconducting machines

Issues involved in developing AC superconducting machines are reviewed with respect to the development of a superconducting coil and the overcurrent protection system of a superconducting transformer. A 4-kVA superconducting coil using 100-A-class 50/60-Hz superconductors was made and tested. As an extension of the 4 kVA coil, a model superconducting transformer was made and examined. The transformer has a novel quench-protection system with an auxiliary coil on the low-voltage side only. The behavior of the overcurrent protection system is described and experimentally confirmed. >

Test of Resonance-Type Superconducting Fault Current Limiter

A resonance-type superconducting fault current limiter (FCL) using Bi-2223 superconducting coils was developed and tested in order to demonstrate its actual operation. Over-current tests of the FCL were carried out for 50 Hz steady-state current of up to 120 A with relevant combinations of a superconducting reactor, an arrester, a capacitance and a copper reactor. The test results showed that the currents during faults were controlled within low levels. It was also demonstrated that the FCL could promptly recover to the steady state after the faults were cleared

AE measurement of the LHD helical coils

The authors have measured AE signals from the helical coils of the LHD (Large Helical Device) system at NIFS (National Institute of Fusion Science, Gifu, Japan) in order to monitor the state of the superconducting coils. Four AE sensors are attached on the surface of the vessel containing the helical coils, and preamplifiers are installed close to the sensors in the area with a leakage magnetic field of about 0.02 T. The measuring system is remotely controlled by PCs via a LAN system. The AE signals are recorded and analyzed. Their relation with the balance voltage signal of the coil has been investigated. The obtained experimental result shows that (1) the AE signals have been successfully recorded despite the leakage magnetic field on preamplifier, (2) the AE signal shows a good correlation with the balance voltages, (3) the AE signal is observed only when the excitation current is changing, (4) the pattern of the observed AE signal is stable for each excitation pattern.

A feasibility study on a world-wide-scale superconducting power transmission system

The author has conceptually designed two types of superconducting DC power cable (SCDCPC) using high temperature superconductors. One is cooled by liquid hydrogen, and the other is cooled by liquid nitrogen. The former has a capacity of 50 GW, and the latter has a capacity of 20 GW, So as to reduce losses as low as possible, the DC system has been selected. The rated voltage for both systems is /spl plusmn/250 kV. Because of the merit of DC operation, these cables generate neither conductor loss nor dielectric loss induced by AC operation, and so have extremely high efficiency. In the case of 10,000 km transmission, Including the refrigeration power, the total loss is lower than 1%. A concept of a world-wide superconducting power transmission system using SCDCPCs is presented.<<ETX>>

A feasibility study on a superconducting power transformer

The feasibility of a UHV superconducting transformer(SCT) in an electric power system is studied. A 1100/550kV, 1750MVA SCT is conceptually designed, which has windings of ultra-fine filament superconducting wire and an amorphous alloy core. The total loss of the SCT is calculated to be about 300kW at room temperature assuming that the refrigerator efficiency is 1/500. In this calculation, the heat leak loss, stray loss, etc. are included. This value of the total loss is about 20 - 25% of that of conventional transformers.

Equivalent circuit and leakage reactances of superconducting 3-phase fault current limiter

The authors have been studying a novel type of superconducting fault current limiting reactor (SCFCLR). The SCFCLR is a reactor which has three superconducting windings with the same numbers of turns wound on a single iron core. An equivalent circuit is proposed for the SCFCLR. Using this equivalent circuit, the leakage reactances of the SCFCLR were calculated, and they agree well with the experimental data. Ground fault tests in a model power system were carried out. When the SCFCLR was inserted in the model transmission line, a ground fault was not observed.<<ETX>>

Fundamental test of new DC superconducting fault current limiter

A novel superconducting DC fault current limiter (SCDCFCL) for suppressing a short-circuit current in a DC transmission line is presented. The SCDCFCL is composed of two superconducting windings wound on a single iron core. A small experimental SCDCFCL was fabricated, and the fundamental operation was confirmed. The experimental results are presented. Considerations for a future full-size design are also presented.