To prevent magnetic flux leakage to the maximal extent, increase the coupling coefficient of high-power inductive power transfer (IPT) system, and reduce the electromagnetic radiation in water medium, a novel underwater loosely coupled transformer (LCT) based on the semiclosed magnetic core structure is proposed in this paper. Power loss of the devised LCT is investigated comparatively in three media including air, freshwater, and seawater. It is shown that winding loss and core loss in the three media are basically identical. However, additional eddy current (AEC) loss in various water media is different for the sake of the difference in conductivity. In particular, AEC loss is extremely low in freshwater and relatively significant in seawater. Furthermore, when the operating frequency exceeds a certain value, AEC loss will be greater than core loss and winding loss, and become the major factor in restricting transmission efficiency of LCT in seawater. Finally, theoretical analysis and simulation are demonstrated by the underwater experiment on an IPT prototype system, which can transfer 10 kW at 91% maximal transmission efficiency and over a 25 mm air gap.

Design and Loss Analysis of Loosely Coupled Transformer for an Underwater High-Power Inductive Power Transfer System

Accurate prediction of temperature-dependent ac winding loss effects is crucial in the design of electrical machinery. Average ac winding loss as a function of operating frequency is commonly characterized by the ratio of the equivalent ac and dc resistances (Rac/Rdc). However, as the ac and dc components of the winding loss scale differently with temperature, a single value of Rac/Rdc derived for one temperature can be inadequate when used in thermal modeling. In this paper, methods of deriving the Rac/Rdc ratio, together with scaling techniques of the ac winding loss accounting for thermal effects, are discussed. As an alternative to computationally intensive 3-D finite-element analysis, an experimental approach based on tests on full-scale stator assemblies is proposed. A previously proposed scaling technique of the ac winding loss is discussed and developed further. The proposed techniques of deriving the ac winding loss accounting for temperature variation are illustrated using both theoretical analysis and experimental data.

Derivation and Scaling of AC Copper Loss in Thermal Modeling of Electrical Machines

This paper presents a methodology for analysing ac winding loss effects which can be significant when considering high-power density, high-efficiency and high-speed machine designs. A combination of finite element analysis (FEA) and experimental measurement has been employed to evaluate the components that contribute to the overall winding power loss. A number of conductor profiles and conductor arrangements have been investigated to give a more general insight into the ac winding phenomena. An experimental approach based on a partially wound stator is employed to allow different winding and conductor arrangements to be evaluated in a timely and accurate manner, as compared with numerical analysis or hardware tests on the complete machine assembly. The outcomes identify the temperature variation of ac winding loss, which can reduce with increasing temperature, and proposes an effective modelling and test method through which the effects can be quantified and experimentally verified.

Experimental and analytical determination of proximity losses in a high-speed PM machine

http://www.lbrce.ac.in/autonomous/2010-11%20-%20CSE.pdf

Academic regulations course structure and detailed syllabus

The accurate prediction of the ac copper loss together with its thermal behaviour is crucial in the design of electrical machines, transformers and inductors. The commonly used figure of merit, when describing the ac copper loss, is a ratio of the equivalent ac and dc resistance (R ac /R dc ). This ratio defines the average ac copper loss as a function of frequency. However, as the ac and dc components of the copper loss scale differently with temperature a single value of R ac /R dc derived for one temperature might be inadequate when used in thermal modelling. In this paper, the authors discuss limitations and applicability of the existing scaling techniques. The emphasis is placed on the method proposed earlier by the authors. The proposed scaling approach is illustrated on example test coils. Both theoretical and experimental data is provided and discussed.

Scaling of AC copper loss in thermal modeling of electrical machines

A practical method for calculating eddy current losses in transformer windings is reported. The method improves the classical loss presentation by introducing a loss coefficient, called eddy current factor kc. In this paper, eddy current losses in round conductors are discussed. A graphical approximation of kc as a function of wire diameter, frequency, layer number, copper packing factors in the direction parallel and perpendicular to the layer is provided. The graphs are obtained by analytical expressions compared with FEM simulations. To unify the approach for different cases, a reference diameter, apparent and equivalent frequency are defined. A few short examples for applying the method in transformer design are given. The method is applicable for a variety of transformers with different frequencies, wire diameters and conductor fittings. The proposed method is verified by designing several transformers. As an example, a 2.5 kW transformer is fully described. The experiments show good matching with the calculations.

/pdf/practical-wide-frequency-approach-for-calculating-eddy-1etp23cg6l.pdf

Stefan Barudov

Papers

Practical Wide Frequency Approach for Calculating Eddy Current Losses in Transformer Windings