Sebastião da Costa Paolinelli

Determination of the magnetic losses in induction motors based on the generalized Epstein test

The results obtained from the standard method for the characterization of magnetic materials - the Epstein test - lead to significant errors in the estimation of magnetic losses in induction motors. Among the induction motor characteristics not accounted for in the Epstein test method, one can point out: winding distribution, cutting stresses, anisotropy, PWM supply and rotor losses (surface losses and interbar current losses). The generalized Epstein test method - GET - is introduced as an alternative to improve the estimation of magnetic losses in induction motors from tests performed on core material samples similar to the ones used in the standard Epstein test. In this paper, the GET is discussed and applied in the estimation of the magnetic losses in induction motors build from different core materials. Associated methods employed in the determination of the proper excitation harmonics and computation of rotor magnetic losses are also discussed. Experimental results are included to illustrate the proposed method.

Study of the Simultaneous Effects of the Hot Band Grain Size and Cold Rolling Reduction on the Structure and Magnetic Properties of Nonoriented 3% Si Steel

The simultaneous effects of the hot band grain size and cold reduction on the final grain structure, texture and magnetic properties of 3% Si steel were studied by variation of finishing temperature and hot band thickness during hot rolling, followed by cold rolling to final thickness and annealing in H2/N2 atmosphere. The results have shown that there is an optimum combination of hot band thickness and hot band grain size for maximum Eta/Gamma ratio and better magnetic properties (B50 and W1.5/60) after final annealing. For the thicker hot band, it was observed that higher finishing temperature, or larger hot band grain size, was necessary to achieve high Eta/Gamma and better magnetic properties. Too large hot band grain size, however, could result in smaller final grain size due to the intense nucleation on recrystallization in the shear bands and consequently poor core loss values. This behavior was explained based on the hot band grain structure and cold rolling effects on the texture evolution.

A critical analysis of standard methods for characterization of electrical steels: Losses in high speed induction motors

The demand for high speed electrical machines has increased recently, mainly in the electric or hybrid vehicles applications. Speeds as high as 13.000 rpm may be required, demanding new grades of electrical steels with improved magnetic properties. Such magnetic properties are typically characterized using parameters such as B50 and W10/400. However, improvements in these parameters do not necessarily translate into improvements of practical significance. This paper focuses on the performance improvements from newly developed electrical steels for high speed motors. Prototype motors were built for practical validation of the performance of these steels. Practical tests and finite element analysis are used to support the conclusions of this research work.

Excess Loss Localization on the Hysteresis Curve

Two alloys of nonoriented electrical steel, with 2.45 and 3.3%Si, respectively, had their magnetic properties characterized in an Epstein frame. Hysteresis curves for total, quasi-static, and parasitic losses were plotted and overlapped to identify the region where the anomalous loss happens. It was observed that most anomalous loss is from the domain wall movements region and a smaller contribution from nucleation and annihilation regions.

Characterization of electrical steels for high speed induction motor applications: Going beyond the standards

The objective of the present work is to assess the impact of improvements in standard characterization figures of merit of electrical steels, typically found in manufacturers catalogs (B50 and W10/400), in the performance of high speed electrical motors. From the motor manufacturer standpoint, changing to new materials may represent a complicated and costly procedure. Besides, the motor manufacturer has to deal with process variability and building tolerances that may overcome minor improvements in the electric steel. The electrical steel manufacturer has to deal with numerous process variables and long and expensive development times to come up with new products. Hence, even a small improvement in the B50 and W10/400 figures are considered to be great achievements. In order to verify if such improvements really translate into real gains in electrical motors, a series of prototypes were constructed with newly developed electrical steels. The core losses of these prototypes were determined by the loss segregation method. Test results support the conclusion that the standard steel characterization figures of merit do not carry enough information for steel and motor manufacturers to conclude on the performance of an electrical steel grade. A datasheet of the electrical steel is proposed. Such datasheet carries useful information for the electrical motor designer and should also be used in the steel development process as a new product assessment tool.

Simultaneous decarburizing and nitriding: effects on structure and magnetic properties of 3%Si grain-oriented electrical steel

Lab experiments were carried out to check the effect of some process parameters of nitriding, performed simultaneously with decarburization, on magnetic properties of 3%Si Grain-oriented silicon steel produced by a low slab reheating technology. The samples of (GO) 3% Si steel collected as 0.27mm cold-rolled were submitted to a continuous annealing process at two temperatures, 860 and 900°C; three annealing times, 63.6, 95.4, and 119.25s; and three ammonia flows 0.1, 0.2, and 0.4Nm3/h. The nitrogen content obtained after the treatments was much higher than those obtained by the currently used process, and it increased as the ammonia flow rates and soaking times were increased, hindering the primary grain growth that adversely affected the magnetic properties. The increase of annealing temperature improved the decarburization and the magnetic properties. The best magnetic properties were found in the sample with the highest primary grain size and the lowest amount of absorbed nitrogen. The success of this practice, in terms of magnetic properties, was pointed out to be based on a drastic reduction on strip nitrogen increase.

Effect of Sn on the oxide subscale structure formed on a 3% Si steel

Addition of tin in 3% Si steel is a method to improve magnetic properties since tin in steel is known as an element that segregates at grain boundaries, inhibits grain growth and has a dragging effect on grain boundary movement. However, tin is generally known as an element that has a harmful effect on surface coating properties. The oxide subscale formed on the decarburization annealing of a 3% Si steel containing tin was investigated by SEM, EDS, GDS and FTIR. The forsterite film was evaluated by SEM, EDS and GDS. The higher tin content decreased thickness, oxygen and fayalite/silica ratio in the subscale and resulted into a discontinuous forsterite film with poor oxidation resistance. After secondary coating the samples presented a reddish color due to the formation of iron oxide and poor dielectric property.