Wspólnotowy Serwis Informacyjny Badan i Rozwoju - CORDIS

Influence of geometry and temperature on total energy loss of dielectromagnetics

The influence of geometry on magnetic properties of magnetic cores made of insulated and non-insulated soft magnetic composites was observed. The obtained results indicate that in case of the dielectromagnetics, in the range of tested heights (h=2mm, 4mm, 6mm, 8mm, 10mm) the size of the active cross section of the specimens does not have any influence on the elementary magnetic properties. This means that in case of dielectromagnetics it is possible to design the dielectromagnetic magnetic cores of different shape and sizes without the concern of skin effect and, subsequently, deterioration of magnetic properties (drop of induction, increase of losses), which accompany the increase of height of the magnetic core.

However, one has to take into consideration the fact that some limiting height, the transgression of which makes the dielectromagnetic powder stop condensing homogenously, does exist and that the geometry of the magnetic core might have an influence on the obtained magnetic properties. On the other hand, in the magnetic core made of dielectromagnetics magnetic flux flowing through the whole volume of the core (which is sometimes very large) can cause change of magnetic core temperature, particularly at higher frequencies. This increase of temperature is mainly the result of hysteresis and eddy current loss. It is commonly known that the change of magnetic core's operating temperature changes its magnetic properties. That is why, the next step taken by WP2 when it comes to dielectromagnetics' behaviour in applications was the examination of temperature's effect on dielectromagnetics' total energy. The tests have been carried out with different temperatures of magnetic core 24°C, 40°C, 60°C, 80°C, 100°C at frequencies: 5Hz, 50Hz, 400Hz, 800Hz. The cores were made of pure iron powder and of dielectromagnetic powders: iron powder with a 0.1% addition of dielectric and iron powder with a 0.5% addition of dielectric.

The tests showed that the sample's temperature has an influence on total energy loss generated inside it. The strongest influence was noted for pure iron powder sample in which increase of total energy loss was observed with increase of temperature (ruling out 5Hz where total energy loss decreases along with temperature increase). However, in case of dielectromagnetics, the behaviour of total energy loss with change of temperature is different from the one in case of iron: total energy loss decrease with increase of temperature in the whole range of measuring frequencies. This decrease is nearly independent from the exciting frequency and very similar for both kinds of tested dielectromagnetics. Between 24°C and 100°C it equals about 6-7%. That is why it is advisable to measure the magnetic properties of materials in temperature they really work in. The knowledge of these properties is necessary for the correct calculation of magnetic circuit and has an essential influence on final design and parameters of the electrical machines.

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