Hysteresis loss is a core loss (core losses are also called as iron losses) in electrical machines. Hysteresis loss occurs in electrical machines both in generators and motors and also electrical transformers.
Hysteresis loss occurs due the reversal of magnetic field in
the core of the armature during rotation. As the core alternatively passes under the north and south poles of the magnetic field, for every 360 electrical degrees rotation (i.e. under one pair of poles) the core undergoes one cycle of magnetic reversal. Similarly in a transformer when an alternating current is applied at the primary winding of the transformer, it sets up alternating magnetic field. This alternating magnetic field undergoes periodic reversal depending on the frequency of the applied current.
the core of the armature during rotation. As the core alternatively passes under the north and south poles of the magnetic field, for every 360 electrical degrees rotation (i.e. under one pair of poles) the core undergoes one cycle of magnetic reversal. Similarly in a transformer when an alternating current is applied at the primary winding of the transformer, it sets up alternating magnetic field. This alternating magnetic field undergoes periodic reversal depending on the frequency of the applied current.
The hysteresis loss greatly depends on the material of the core and can be reduced by using high grade core material. It also depends of the volume and maximum flux density of the core. In transformers, cold rolled grain oriented (CRGO) silicon steel is widely used for minimized core loss, recently amorphous metal transformers are gaining popularity for their very low losses. The given below is the expression for determining the hysteresis core loss, which was given by Steinmetz formula.
Where,
Kh = hysteresis coefficient, depends on the quality of the core material.
Bm = maximum flux density.
x = Steinmetz’s constant varies between 1.5 to 2.6 depending on the magnetic property of core material. For normal flux densities it is taken as 1.6.
V=volume of the core material.
f= frequency of magnetic reversal. In transformers, it is the supply frequency usually 60 Hz (in USA) or 50 Hz. In machines, it is PN/120, where, P is the number of poles and N is speed of rotation in rpm.
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