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Information about frequency dependence of complex permeability of silicon steel is a vital input parameter in calculations of transformer winding inductance used for modeling high-frequency behavior (100 Hz-1 MHz). We present two ways of determining small signal complex permeability spectra in frequency domain and compare and discuss the results. The first method is based on an optimization procedure, in which inductance of a winding is measured and calculated by analytical formulas and finite-element modeling. The second method makes use of a single sheet tester. We show that the magnitude of effective permeability of the silicon steel laminations remains significant up to about 100 kHz. We also report on the effect of magnetic viscosity on complex permeability. Index Terms--Complex permeability, magnetic viscosity, power transformers, silicon steel, single sheet tester.

The flow electrification process occurring at the oil-pressboard interface in high power transformers seems to cause electrical discharge incidents and may cause failures. The goal of this experimental study is to measure and to compare the streaming current obtained from unused pressboard, pressboard artificially degraded by electrical discharges, and pressboard obtained from a damaged power transformer. The influence of additive 1,2,3 Benzotriazole (BTA) in oil is also analyzed. The results show that flow electrification is greatly increased by the degraded pressboards compared with the new one. On the other hand, adding of BTA significantly reduces flow electrification.

This paper presents an effective shielding technique and a simple structure for printed-circuit-board (PCB) transformers. Performance of PCB transformers using the proposed shielding technique is evaluated using thin ferrite plates and copper sheets. Without affecting the transformer energy efficiency, the shielding method under investigation can achieve 28 dB shielding effectiveness (SE), which is much higher than the SE (about 4 dB) obtained by shielding the transformer windings with only two ferrite plates. The proposed PCB transformer structure is very simple and has high energy efficiency (>90%) for Megahertz operation. Index Terms--EMC, printed-circuit-board transformers, shielding techniques.

This experimental study separates the hysteresis, eddy current, and electromechanical motion losses of a soft magnetic material for electric power energy conversion applications. Mechanical responses of the magnetic material to sine and square wave voltage excitation are compared. Commercially-available, METGLAS 2605S3-A tape cores were evaluated up to 300 C for sine wave and square wave voltage excitation frequencies 1-100 kHz. Data presented illustrates the effects of maximum flux density, frequency, waveshape, and temperature on the specific core loss and size and shape of the B-H loops. Relative losses play a major role in material selection for electronic and electric power applications including power converters, transformers, controllers, and filter elements. Dynamic measurements of the magnetostrictive response of these specific toroidal test cores were made using a sensitive, capacitive probe and a unique application of frequency modulation. The dynamic behavior of the toroidal test cores and the related unusual B-H loop characteristics were compared to results obtained by an electromechanical model.

Superconducting shields have been incorporated as key components in the design of fault current-limiting and special-purpose transformers. Specifically, three prototypes were built to investigate the electromagnetic behavior of high-temperature and low-temperature superconducting shields in shielded-core transformers for current limitation, voltage limitation, arc welding and furnace power supply applications.

Using high performance soluble imide polymer as a binder, it was possible to accomplish a substantial mechanical strength in iron particle cores molded under uniaxial compacting pressure which was much lower than that was commonly applied by others in the past. The directional ordering of oblate spheroidal iron particles occurred despite the low compacting pressure resulting in strong anisotropy in the magnetic properties and mechanical strength in the fabricated cores. The low molding pressure, however, resulted in a low density of core which, in turn, caused the low permeability.

This paper describes the performance of a high-voltage power supply incorporating a ceramic transformer. Since the transformer is constructed using a ceramic bar containing no magnetic material, the power supply can operate under a magnetic field of 1.5 Tesla with no degradation of performance. Feedback is used to stabilize high-voltage output such that a supply voltage of 3 V provides from 1500 to 2500 V at a load of more than 10 M[Omega] with efficiency higher than 50%; and with a supply voltage of 2 V, 3000 V is supplied at a load of 20 M[Omega] In fact, a supply voltage of 5 V is sufficient to provide 4000 V at the same load. A network of high-voltage power supplies is also described. Most functions of the power supply are thereby monitored and controlled through the network.