Itsuya Muta

DC reactor effect on bridge type superconducting fault current limiter during load increasing

In high power applications, the fault current limiter has been discussed for many years because of some limitations of conventional circuit breakers. Many types of fault current limiter have already been introduced in papers. In this work, a simple bridge-type fault current limiter has been designed and constructed. The performances of the limiter have been tested successfully. In the bridge-type current limiter, a DC reactor appears in the line when the connected load is increasing. This causes a voltage drop across the load terminal during load changing. The DC reactor effect of the current limiter has been studied. Some experimental results regarding the reactor effect of the limiter have been considered and compared with the results obtained from computer simulation.

Theoretical analysis of a YBCO squirrel-cage type induction motor based on an equivalent circuit

A HTS induction motor, with a HTS squirrel-cage rotor, is analysed using an electrical equivalent circuit. The squirrel-cage winding in the rotor consists of rotor bars and end rings, and both are considered to be made of YBCO film conductors. A wide range of electric field versus current density in YBCO film is formulated based on the Weibull function, and analysed as a non-linear resistance in the equivalent circuit. It is shown that starting and accelerating torques of the HTS induction motor are improved drastically compared to those of a conventional induction motor. Furthermore, large synchronous torque can also be realized by trapping the magnetic flux in the rotor circuit because of the persistent current mode.

An upwind Galerkin finite element analysis of linear induction motors

An upwind Galerkin finite-element method (GFEM) for electromagnetic problems in moving media is proposed. In the conventional GFEM, when the cell Peclet number becomes greater than the critical value of 2, many undesirable flux loops due to oscillatory solutions appear in the flux plots. It is shown that the upwind GFEM can stabilize such oscillations successfully. Although the extra-fine subdivision of elements makes it possible to suppress such oscillations without upwinding, the 13 mm length of a mesh in the present model must be subdivided into 2.43 mu m in order that the Peclet number in the back iron shall not exceed the critical value of 2 or there will be a need for enormous computation time and memories. For this reason, the present GFEM is the most promising numerical method for convective diffusion equation solvers with larger cell Peclet number. >

Load test on superconducting transformer and fault current limiting devices for electric power system

A superconducting fault current limiting transformer has been investigated to find out its feasibility. In general, the following two types of superconducting fault-current limiters could be expected: noninductive two-port and four-port devices based on superconductive-to-normal state transition. The authors have investigated the transient phenomena in the transformer and then designed a 10 kVA superconducting fault current limiting transformer. First of all, in order to understand performances during quenching in the main coils of the transformer at power system faults, no-load and short-circuit tests in the auxiliary coils were performed. With the same test for the main coils and four windings, exciting conductance, susceptance and leakage impedance were estimated. Under a constant resistive load, actual load tests and sudden short-circuit tests were carried out. Test results are presented. >

Recovery time of superconducting non-inductive reactor type fault current limiter

A superconducting fault current limiting device for electric power systems has been investigated to determine its feasibility. A noninductive reactor type fault current limiter has been constructed using a metal superconductor. Two bifilar wound solenoids were connected in antiparallel or antiseries. On each connection, a fault current limiting test was performed by suddenly short-circuiting a resistive load. The recovery (normal-to-superconductive state transition) time after the current limiting mode has been studied using a small-scale model of a fault current limiter for an LV power distribution line. The results reveal that the current limiter could be operated under a repetitive fault current accident which was removed within a few cycles of the limiting mode. The recovery time is a function of the dissipated energy under current limiting mode. Test results are presented.

Design of bi-2223/Ag coil based on genetic algorithm and finite element method

We designed Bi-2223/Ag coils based on genetic algorithm and finite element method. The winding geometry as well as the operating current of the coil was optimized for the minimization of its loss, on condition that its operating temperature, stored energy and total length of the conductor were constant. The loss was calculated with the use of the analytical expressions that could quantitatively describe the current transport characteristics in high T/sub c/ superconductor including their magnetic anisotropy and temperature dependence. Some optimized results were shown and discussed in this paper.

Analysis of shielding layers in HTS cable taking account of spiral structure

Analysis code for shielding layers of HTS cable, which was taken account of spiral structure of Bi-2223/Ag tape conductors, was developed based on finite element method. The 66 kV class HTS cable, which was fabricated and successfully tested in cooperation of Tokyo Electric Power Co. (TEPCO) and Sumitomo Electric Industries, Ltd. (SEI), was subjected in this study. Electric field vs. current density property was expressed based on percolation depinning model (Yamafuji-Kiss model). Multifilamentary structure of the tapes and spiral structure of the conductors were directly modeled in order to analyze precisely. Systematic analysis results were presented and discussed.

The effect of excitation methods on electrical characteristics of fully superconducting generator model

The authors have fabricated a 20 kW fully superconducting AC generator in which both the armature and field coils are made of superconductors. Two different types of excitation system were selected and tested: a brushless excitation method consisting of a magnetic flux pump and a conventional excitation method equipped with a collector ring and brushes. The paper describes the experimental machine model and the comparison of test results between the two different types of excitation methods. >

Electrical characteristics of fully superconducting synchronous generator in persistent excitation mode

A brushless-excited superconducting generator with a superconducting dynamo, i.e., a magnetic flux pump, has been fabricated. Concurrently, a fully superconducting generator in which both armature and field coils are made of superconductors has been investigated. The authors describe the experimental machine model and the test results on electrical characteristics. >

A 30 kVA superconducting generator development and basic tests

A 30 kVA superconducting generator has been designed, developed and successfully tested by the Korea Electrotechnology Research Institute (KERI). The design is based on a 2-dimensional electromagnetic field analysis of cylindrical coordinates. The field winding of rotor has been wound with superconducting wire of NbTi alloy and tested after assembly with other rotor components. The stator has air-gap type armature windings, which produce higher terminal voltage, and a more sinusoidal voltage waveform than conventional iron cored machines. Steady-state open and short-circuit tests and lamp load tests have also been conducted. The results of these tests are given in this paper and compared with design quantities. Moreover, the cooling scheme and characteristics of the test system are included.