Cutting and punching of the electrical steel can cause edge burrs which lead to interlaminar short circuits between the laminations. In this paper, based on an equivalent electric circuit of the eddy current path, an analytical method has been developed to estimate the eddy current power loss of the magnetic cores, caused by the interlaminar faults, in a wide range of flux density and magnetizing frequency. Important factors, such as skin effect, nonuniform flux density distribution, complex relative permeability, and the nonlinear relation of B (H), which are often neglected in the literature, are highlighted. Fundamental concepts of the interlaminar fault and its consequences, the effect of interlaminar faults on the configuration of magnetic cores, and finite-element method verification are presented in this Part I paper. Modeling of eddy current, together with experimental results of eddy current measurements of packs of shorted laminations, are reported in Part II.

The increase in losses due to burrs occurring on cut edges of electrical steel laminations in transformer cores is difficult to quantify. Artificial burrs were applied to a 350 kVA, three-phase, five packet, transformer core. Total core loss, flux density distribution and local loss near the burrs were measured. Burrs applied to a portion of a packet of laminations in one limb caused the flux distribution to become more nonuniform than normal throughout the whole core. Local losses increased significantly outside the burr region. The loss increased to over 1000 W/kg in the severely burred region at 1.8 T, 50 Hz. Measured flux distribution data was used in simplified eddy current calculations to predict the total and localized losses. The predicted and measured localised losses in the burred regions followed similar trends but did not agree well in magnitude probably due to the errors caused by the simplifications and assumptions which were necessary in the eddy current analysis.

A system has been developed for measuring localized power loss of electrical steel laminations based on the initial rate of rise of temperature method. Hardware and software components were designed and developed individually to make an accurate measuring system. Three experiments were carried out to calibrate the system and quantify its accuracy over a wide measurement range. The application of the measuring system was demonstrated in two cases of measuring localized power losses near bolt holes in laminations and near artificial lamination edge burrs in a 300 kVA, 3 phase transformer core. The experimental results show that the developed system can measure localized power loss over a wide range with uncertainty of measurement less than ± 2%, but precautions are necessary when interpreting measurements in regions where the magnitude of the loss varies significantly over distances of less than a few centimeters.

Interlaminar faults between laminations of the magnetic cores increase core losses and could cause major damage to electrical machines. A system has been developed to detect an interlaminar fault between the laminations of the magnetic cores by means of the flux injection probe (FIP). Experimental work was carried out to calibrate the measuring system and qualify its accuracy over a wide measurement range. Application of a prototype FIP to quality assessment of transformer laminations was investigated in two stages: 1) inspection of stack of laminations with known interlaminar faults applied by artificial shorts and 2) inspection of stack of laminations with unknown quality. The experimental results show that the developed system is capable of detecting an interlaminar fault between as few as two laminations.

Hysteresis phenomenon is a distinctive approach to describe natural behaviour of the magnetic materials and magnetic cores. This paper proposes a phenomenological approach for core quality assessment and condition monitoring of magnetic cores with grain-oriented electrical steels. The developed technique is based on the hysteresis phenomenon and interpreting the most distinctive parameters of the measured dynamic hysteresis loops. In this study, artificial short circuits were introduced between the laminations of stacks of two, three and four Epstein size strips of Fe-3 wt % Si grain oriented steel. The results showed that, condition monitoring of the magnetic cores can be effectively performed by measuring and analysing the hysteresis loops.

This study investigates the influence of a wide range of magnetising frequencies and peak flux densities on the magnetic properties of the electrical steels. In the relevant studies some important factors and operational properties, for example, skin effect, non‐uniform flux density distribution, complex relative permeability and magnetisation characteristic of the material, which are often neglected in the literature, are highlighted. Analytical modelling and experimental works were performed for 3% grain oriented silicon steel. In order to show the impact of peak flux density on the magnetic properties, two peak flux densities 1.3 T as a high permeability point and 1.7 T as a low permeability point were considered. The results highlighted that magnetising frequency and peak flux density are two determinant factors with significant effect on the magnetic properties of electrical steels.