Hysteresis

Definition - What does Hysteresis mean?

Hysteresis is an action which leads to the loss or wastage of heat energy in electrical equipment, generally in electrical transformers. Whenever a magnetic force is applied to a magnetic material, the molecules of this magnetic material tend to align in one direction, generally, in the direction of the magnetic force, but when such force is reversed, i.e., applied in the opposite direction of the aligned molecules, there is certain internal friction which opposes the magnetism reversal thereby creating a magnetic hysteresis. In order to overcome this internal friction, a part of magnetizing force is used which creates the heat energy. Since this heat energy generated is just wasted to oppose the internal friction, it is termed as hysteresis loss.

Petropedia explains Hysteresis

Hysteresis and the loss of energy associated with hysteresis usually occurs in magnetic materials or in those materials that work based on the principles of magnetism, for example, electrical parts in electrical machines and equipment such as transformers. Hysteresis provides a relationship between the strength of Magnetic Field “H” and the Magnetic Flux Density “B”.

As per the magnetic hysteresis loop curve below, the curve represents that magnetic force tends to align the atoms in the direction of magnetic field strength (H) and the net effect of this alignment results in the increase of the magnetic flux density (B). With the gradual increase, the flux density increases till the saturation point after which the alignment of the atoms of a magnetic material tends to move in the reverse direction of the magnetic field, thus, decrease in magnetic field is administered. When “H” becomes zero, “B” still remains positive. This state is called remanence (or residual induction). The situation that depicts “Coercive Force” is the point where “B” becomes zero when “H” is negative. Further increase in “H” in the negative direction, causes the flux density to again reach at the saturated point where it is reversed and again aligns the magnetic atoms to reverse their direction. This process makes a complete loop which is called hysteresis and the energy lost in reversing the magnetization of material is called the Hysteresis Loss which is directly proportional to the area of this hysteresis loop.

In order to avoid the hysteresis loss in transformers that make use of magnetic field, the cores of transformers are made with such type of materials that create narrow hysteresis loop and less wastage of energy.

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