M. Iwahara

Development of passive fault current limiter in parallel biasing mode

So far literature reports on the magnetic fault current limiter (FCL) are based on the series biasing mode in which the flux due to line current flows through the permanent magnet. As a result there is a high possibility of demagnetization of the permanent magnet. A passive fault current limiter is a combination of passive elements such as permanent magnet and saturable core. The permanent magnet is used to bias the core. In order to avoid severe demagnetization of the permanent magnet, we have investigated the performance of passive fault current limiters based on permanent magnet and saturable core in parallel biasing mode. The functional characteristics have been analyzed by Tableau approach and the simulation results are presented, The experimental results for a small scale prototype model are also presented for verification.

Permanent magnet bearings for horizontal- and vertical-shaft machines: A comparative study

Two types of magnetic bearing systems employing permanent magnets to be used for vertical-shaft and horizontal-shaft machines, respectively, have been designed and fabricated in our laboratory. In this article we report a comparative evaluation of (i) the permanent magnet configuration and its effect on radial disturbance attenuation, (ii) magnetic losses and their effect on energy storage, and (iii) the off-state position of the rotor magnet in two types of bearing systems. Experimental results are presented.

Investigation of the performances of a permanent magnet biased fault current limiting reactor with a steel core

There is an increasing need in power system applications for fault current limiter, to limit the fault current in semiconductor devices and switchgear. These fault current limiters must be reliable, compact and inexpensive. This paper reports the result of an investigation of the characteristics of a fault current limiter (FCL) consisting of a steel core and permanent magnet. Design criteria are presented. The FCL characteristics are simulated using a Tableau approach and the simulation results have been compared with experimental results.

A COMPARISON BETWEEN A TWO-MATERIAL AND THREE-MATERIAL MAGNETIC CURRENT LIMITER

This paper investigates the inductance versus current characteristics of a two-material and a three-material magnetic current limiter. The two-material device consists of a NdFeB permanent magnet, a high saturation flux density magnetic material, and a high saturation flux density magnetic pole piece placed on both sides of the magnet. The three-material device consists of a NdFeB permanent magnet, a high saturation flux density magnetic material, and a low saturation flux density material. Finite-element results for the three-material device agree with the results obtained using design equations. In contrast, the results obtained for the two-material device show that the transition current is overestimated and that the ratio of the maximum safe current and transition current, as well as the unsaturated inductance is underestimated. Extending the magnet beyond the adjoining surfaces improves the sharpness of the transition characteristics when the ratio of the core length to the core width is large.

A numerical method for analyzing a passive fault current limiter considering hysteresis

Fast transient analysis of a passive fault current limiter (FCL) using permanent magnets can be done by direct numerical solution of a single non-linear differential equation. The non-linear B-H excursion that is caused by hysteresis is incorporated in the computation using a transient hysteresis model. Rational fractions are used to represent the parent hysteresis loop curves. Since the method uses preconstructed expressions as applicable to FCL schemes only, computation time required is less.

Flux distribution of passive fault current limiter based on saturable core and permanent magnet

From the point of view concerned with the development of the information, oriented functions in social activities, recently power consumption has rapidly increased. On the other hand, ability of power supply has not been increased to follow this increasing consumption, because it is difficult to construct new power generation plants. Therefore, reserve capacity of power supply is going to be decreased and power down has become a serious problem. To prevent the serious power down and to maintain a stable power supply, we had already proposed a passive fault current limiter using a permanent magnet with high coercive force, high remanent magnetic flux density and a ferrite core with high permeability, low saturated flux density compared to that of a permanent magnet. In this paper, the flux distribution of the limiter is investigated using the three dimensional finite element method.

Design and performance analysis by means of Tableau approach of passive fault-current limiter using steel core

In this paper we report the design and performance analysis by means of Tableau approach of passive fault-current limiter (FCL) using steel core. Since the steel core has a very high value of saturation flux density, configuration of FCL with steel core is little complicated. To make it possible we have proposed in this paper two stacked sections having different cross-sectional area of the steel core. Some design criterion have been discussed and for a sample system the performance of FCL has been simulated by means of the Tableau approach including the eddy current in the permanent magnet (PM). The simulated results show the possibility of using a steel core in the practical implementation of FCL.