Hysteresis Loss Explained

Hysteresis loss is an energy loss that occurs in ferromagnetic materials when they are subjected to a cycle of magnetization and demagnetization. This loss happens because the magnetic domains within the material resist changes in their alignment. Work must be done to rotate these domains, and this work is dissipated as heat. The amount of hysteresis loss is directly related to the area enclosed by the material's hysteresis loop.

The power loss due to hysteresis can be represented by Steinmetz's equation, which, in a simplified form relating to the loop area, suggests the loss is proportional to the area of the hysteresis loop:

$$ P_h \propto A $$

where $P_h$ represents the hysteresis loss (often per unit volume or mass) and $A$ is the area of the B-H hysteresis loop.

Analyzing Options to Reduce Hysteresis Loss

Hysteresis Loss: Material Choice

The question asks how to reduce hysteresis loss. Let's analyze the given options:

• Using material of narrow hysteresis loop: Hysteresis loss is directly proportional to the area of the hysteresis loop ($A$). Materials like soft iron or silicon steel have very narrow hysteresis loops compared to hard magnetic materials. A narrow loop indicates that less energy is required to magnetize and demagnetize the material during each cycle. Therefore, selecting materials with a narrow hysteresis loop is an effective way to minimize hysteresis loss. This aligns with the principle shown in Steinmetz's equation.

Lamination vs. Hysteresis Loss

• Laminating the magnetic circuit: Laminating the core involves using thin sheets of the magnetic material insulated from each other. This technique is primarily used to reduce eddy current loss, which is another type of energy loss in magnetic cores. Eddy currents are induced circulating currents within the core material due to the changing magnetic flux. Laminations increase the electrical resistance path for these currents, thereby reducing them and the associated power loss. While crucial for overall efficiency, lamination does not directly reduce hysteresis loss itself.

M.M.F. and Hysteresis Loss

• Increasing m.m.f. of the circuit: The magnetomotive force (m.m.f.) is the driving force that creates magnetic flux in a magnetic circuit. While increasing m.m.f. increases the magnetic flux density (B) in the core, it does not inherently reduce the width (area) of the hysteresis loop. In fact, operating at higher flux densities, especially if the material approaches saturation, might even increase hysteresis loss if the material characteristics lead to a wider loop in that region.

Conclusion on Hysteresis Loss Reduction

Based on the analysis, the most direct and effective method to reduce hysteresis loss is by choosing magnetic materials that exhibit a narrow hysteresis loop.