What is whirling currents?

Let's consider the metal core in the coil with alternating current (fig. 1, a). At noted in fig. 1, and the direction of current the magnetic flux in the serdechniyoka is directed along the axis of the serdechniyok up.

Высокочастотное магнитное поле

High-frequency magnetic field.

Mozhyono mentally to separate the metal core into the number of the layers closed on themselves which axis matches the axis of the serdechniyok. Each such layer predstavyolyat itself the closed round in which the variable flow inyoduktirutsya the EMF and current, napravyolenny in the planes, perpendikuyolyarny to the axis of the magnetic flux.

Considering set of tayoky closed circuits, it is possible to imagine the whirling currents which are becoming isolated around the axis of the magnetic flux in the body of the serdechniyok.

Рис. 1 Вихревые токи

Fig. 1 Whirling currents.

The direction of vortex toyok is defined by the Lenz rule. At increase in the magnetic flux whirling currents are directed clockwise if to look at the core from above.

Whirling currents according to Lenz Joule law soproyovozhdatsya by heat production in the core. This phenomenon is used in practice for heating of metals (melting of steel, heating under tempering and other purposes).

In cores of electrical machines, transformers and elektriyochesky devices there are whirling currents too. But here they are nezhelayotelna because increase the general losses of energy in devices and cause additional their heating.

For the purpose of reduction of losses of energy cores of devices of pereyomenny current gather from sheet electrotechnical steel (thickness of 0,35 mm) which sheets are isolated from each other by spetsialyyony varnish.

Reduction of whirling currents is in such a way reached thanks to the fact that contours on which in the continuous core whirling currents become isolated are cut on the part, isolated from each other (fig. 1, b). Besides, weakening of whirling currents is reached by increase in unit electrical resistance of material of cores. For this purpose silicon additive up to 4% is entered into electrotechnical steel.

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