Analysis of High Frequency Planar Sandwich Transformers for Switching Converters

This paper presents the results of investigations on a planar sandwich air-gapped transformer with two different winding configurations. Experimental results of the coil self inductances, voltage ratio versus frequency, and the numerical results for the magnetic flux and eddy-current distributions are presented. It is shown that the voltage ratio and turns ratio are not equivalent and that the voltage ratio is frequency dependent

Experimental Results for a Two-Material Passive di/dt Limiter

The purpose of this paper is to experimentally verify the current limiting characteristics of a two material magnetic device consisting of a ferrite and permanent magnet material. A resonant pulsed excitation source and a 60 Hz ac source are used to test the characteristics of the device. The experiments confirm that there is a saturated and unsaturated inductance operating region and a current limiting and loss of current limiting kneepoint

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. © 1998 American Institute of Physics

Defect Images by Planar ECT Probe of Meander-Mesh Coils

This paper presents results pertaining to image data obtained from a planar meander-mesh coupled coil type ECT probe. The image data makes it possible to detect not only the existence of a defect but also to extract detailed information regarding the nature of the defect, such as its position, shape, length, and direction. In order to recognize a defect distinctly, we have fabricated the high sensitive planar coil which can be used to image a 2-D representation of the ECT signal. The relationships between the image pattern and defect shape are discussed

A Novel Compact Magnetic Current Limiter for Three Phase Applications

The fabrication and development of a novel compact three phase magnetic current limiter consisting of permanent magnets (PM) and saturable cores is described in this paper. Simulation results using the tableau approach are presented for varying operating conditions. Experimental results are in good agreement with the simulation results. The proposed current limiter has potential in moderately low voltage applications

Eddy Current Testing Probe Composed of Planar Coils

This paper presents a new eddy-current probe composed of a micro-planar mesh coil and meander coil. The probe can be used to detect the existence and the size of cracks in metallic structures. Experimental results for the sensed output voltage of this device are presented. The output signal is shown to have a discrete nature. Also, the results show that the signal strength is weak and that an offset voltage exists. Improved probe characteristics are obtained by connecting two mesh coils in series, stacking the coils on top of each other and orienting the two coils 180° apart

Development of Passive Fault Current Limiter in Parallel Biasing Mode

So far the reported literature on the magnetic fault current limltcr(FCL) arc based on series biasing mode in which the flux due to Hue current flows through the permanent magnet, As a result there ta a high possibility of demagnetization of the permanent mngnet. A passive Cault current limiter lu a combination or passive elements such a.s permanent magnet and saturablc core. Permanent mngnet Is used to bias (he core, In order to avoid severe demagnetization of permanent magnet, in this paper we have Investigated the performances of passive fault current limiter based on permanent magnet nnd saliirablc core In parallel biasing mode, the functional characteristics have been analyzed by Tableau approach and the simulation results arc presented. The experimental results for a small scale prototype model are also presented for verification

Design Improvements to a Three-Material Passive Magnetic Current Limiter

This paper shows that flux nonuniformity in a passive magnetic fault current limiter softens the transition characteristics from the saturated to the unsaturated state. Soft transition characteristics lead to higher core losses and a derating in the maximum nominal operating current. Flux uniformity is improved by using a combination of extended magnets and an anisotropic saturable core. The use of distributed permanent magnets or an extended magnet leads to larger differential inductance ratios