Hysteresis losses

Hysteresis losses are energy losses that occur in ferromagnetic materials such as iron when they are exposed to a periodically changing magnetic field. They belong to the so-called iron losses and occur in particular in components that are operated with electrical energy. The losses are caused by the fact that the magnetization of a material does not follow the external magnetic field directly and without loss. This effect is known as hysteresis. The energy lost in the process is converted into heat.

Physical background

The origin of hysteresis losses lies in the physics of ferromagnetic materials. These consist of magnetic domains, i.e. the smallest areas in which the magnetic moments are aligned in the same direction. If an external magnetic field is generated – for example by a current flowing in a coil – these domains react to the field.

When a magnetization cycle is completed, the magnetic flux density (B) describes a closed curve, the hysteresis loop, as a function of the magnetic field strength (H). This represents a basic function for describing the magnetic behavior. The area of this loop corresponds to the energy that is lost per cycle.

Losses

The hysteresis losses are caused by several microscopic processes in the material. The movement of the domain walls is particularly important. These have to overcome internal resistance caused by material defects or stresses.

In addition, the magnetic moments within the domains are rotated. This process also requires energy. As these processes are not completely reversible, energy is lost.

These losses occur together with other types of losses, such as eddy current losses, and are therefore often considered as part of the total iron losses. Other additional losses can also occur as a result of complex interactions in the material.

Influencing factors

The amount of hysteresis loss depends on various factors. One key factor is the material used. Special soft magnetic materials such as transformer steel have lower losses than hard magnetic materials.

The frequency of the current also has a major influence. The faster the magnetic field changes, the more frequently the loss mechanism occurs. The maximum magnetization also plays a role.

Temperature, mechanical stresses and the quality of the material also influence the losses. These factors are often investigated as part of technical analyses and measurements in electrical engineering in order to precisely determine the behavior of the materials.

Significance in practice

Hysteresis losses are relevant in many technical applications, particularly in transformers, electric motors and generators. In all of these devices, the current flow is used to generate magnetic fields, which inevitably results in losses.

This causes the systems to heat up and reduce their efficiency. In industrial applications, even small losses can have a major impact as they add up over long operating times. Specially manufactured metal sheets are often used to reduce overall losses.

Understanding this physical effect is therefore crucial for the development of efficient electrical machines.

Reduction of hysteresis losses

Special materials are used to minimize losses, in particular soft magnetic alloys such as silicon steel. These materials are characterized by a narrow hysteresis loop and thus reduce energy losses.

The processing of the material also plays a role. Internal stresses can be reduced through heat treatment. In addition, the design of the components is optimized to minimize overall losses.

In practice, these measures are often combined in order to minimize iron losses, eddy current losses and additional losses.

Summary

Hysteresis losses are a central component of iron losses in ferromagnetic materials. They are caused by physical processes during remagnetization and lead to the conversion of energy into heat. The effect occurs wherever magnetic fields are generated. However, these losses can be significantly reduced through targeted material selection, optimized component function and precise measurement – especially in the field of electrical engineering.