High-permeability Grain-oriented Electrical Steel Research Articles

Coupled statistical and dynamic loss prediction of high-permeability grain-oriented electrical steel

Power transformer design requires to model the loss and hysteresis behavior of the laminated steel core, constructed out of high-permeability grain-oriented electrical steel. This work predicts the magnetic loss and hysteresis behavior in the rolling direction of three transformer grade steels, for magnetic flux densities up to and including 1.9 T, and frequencies up to and including 300 Hz. Material characterization parameters for the excess loss, obtained by statistical loss separation for sinusoidal concentric hysteresis loops, are applied in a hysteresis model and govern the dynamic field behavior. The modeled loss is compared and verified with measurement data obtained by an Epstein frame for each steel gauge.

A measurement method of minor hysteresis loss of electrical steel sheet by means of a single sheet tester

This paper investigates measurement methods of iron losses of asymmetric minor hysteresis loops of electrical steel sheets by means of a single sheet tester. As inverter-driven electric machines have been increased, consideration of harmonic iron losses is indispensable to design highly-efficient electric machines. In general, measurement of iron losses of asymmetric minor hysteresis loops has been carried out by using a fluxmeter to detect a dc component in addition to ac components measured by means of a B-coil because the asymmetric minor loops are dc-biased. However, the fluxmeter has a drift problem which results in inaccurate evaluation of harmonic iron losses. Therefore, the distorted waveform method which adopts only ac measurement is conceived. Furthermore, the dc-biased method is improved by estimating the dc components from a normal magnetization curve, which is obtained by connecting tips of symmetric hysteresis loops. In order to demonstrate their effectiveness, the iron losses of asymmetric minor hysteresis loops of non- and high permeability grain-oriented electrical steel sheets are measured up to the high flux density region.

The Relationship Between Inhibitors and Secondary Recrystallization Characteristics of High Permeability Grain-Oriented Electrical Steel

In order to understand the secondary recrystallization characteristics of high-permeability grain-oriented electrical steel, we studied microstructure, Goss orientation, onset secondary recrystallization temperature and Σ3, Σ5 and Σ9 grain boundaries during high temperature annealing. In particular, we examined the effect of different amounts of AlN inhibitors on the secondary recrystallization behavior. First, with the increase of AlN amount, the onset secondary recrystallization temperature and magnetic properties increase. Second, when the inhibitory ability is weak, the fraction of grains that have Goss±5, Goss±10, and Goss±15 keep constant before secondary recrystallization; with the increase of AlN amount, the fraction of grains that have Goss±15 keep almost constant, but the Goss±5 and Goss±10 grains increase obviously with the increase of temperature. Third, the frequency of Σ3, Σ5, Σ9 grain boundaries around Goss grains and general grains keeps almost constant with the increase of temperature before secondary recrystallization when having enough AlN inhibitors; however, when the content of AlN is very low, the frequency of Σ3, Σ5 and Σ9 grain boundaries around Goss grains will decrease to the level of that around general grains, which eventually leads to unsuccessful secondary recrystallization.

Effect of Ball Scribing on Magnetic Barkhausen Noise of Grain-oriented Electrical Steel

Effect of ball scribing on magnetic Barkhausen noise (MBN) of conventional grain-oriented (CGO) and high-permeability grain-oriented (HGO) electrical steel was investigated. The results showed that after ball scribing, root mean square of MBN (MBNrms) of CGO electrical steel increased 9.8% with 4 mm scribing spacing at 1.2 T, and that of HGO electrical steel apparently decreased 17.3% with 16 mm scribing spacing at 1.2 T. Through the formation and development of free magnetic poles and secondary magnetic domains due to compressive stress, primary magnetic domain space of grain-oriented electrical steel becomes smaller, which reflects as a variation of MBN in the macroscopic magnetic properties. Through correlation formula derivation of MBNrms and equilibrium distance between domain walls, effect of domain refinement on grain-oriented electrical steel was also interpreted, and optimum equilibrium distance between domain walls was determined.

Rotational Power Losses and Vector Loci Under Controlled High Flux Density and Magnetic Field in Electrical Steel Sheets

This paper presents the rotational power loss P, curves measured for nonoriented, conventional grain-oriented and high-permeability grain-oriented electrical steel under controlled loci of flux density B, or magnetic field H. The P is measured at 10, 50, and 250 Hz with the radius of circular loci of B being controlled from 0.5 to 2.0 T and the radius of circular loci of H from 50 to 20 kA/m. The well-known phenomenon of decreasing P at higher magnetization is confirmed in the results. The maximum P under controlled circular H can be up to 2.5 times higher than under controlled circular B and up to six times higher than the value of alternating loss for anisotropic electrical steels. In thicker laminations at higher frequencies, the peaks in P curves vanish due to increased contribution of eddy currents

Domain refinement of high-permeability grain-oriented electrical steel using low-friction ball units

A new method has been developed for domain refinement, and hence loss reduction of high-permeability grain-oriented electrical steel, utilising large low-friction ball unit assemblies to create lines of stress across the steel, which simulate the effect of artificial grain boundaries. Application of appropriate loads to ball units of diameter up to 39.7 mm has been shown to reduce the power loss of the steel by up to 9.6%, when using a stress line spacing of 7.5–10 mm. This is achieved without damaging the surface insulation layer. The method is relatively inexpensive to set up on a commercial scale and is amenable to high-speed operation. A patent application is currently being progressed.