The stacking factor (also lamination factor or space factor
[Barry W. Kennedy, ''Energy Efficient Transformers'', p. 140, McGraw Hill Professional, 1998 .]) is a measure used in electrical
transformer
A transformer is a passive component that transfers electrical energy from one electrical circuit to another circuit, or multiple circuits. A varying current in any coil of the transformer produces a varying magnetic flux in the transformer' ...
design and some other
electrical machine
In electrical engineering, electric machine is a general term for machines using electromagnetic forces, such as electric motors, electric generators, and others. They are electromechanical energy converters: an electric motor converts electricity ...
s. It is the ratio of the effective cross-sectional area of the
transformer core to the physical cross-sectional area of the transformer core. The two are different because of the way cores are constructed.
Transformer cores are usually made up of thin metal sheets stacked in layers. The layers are
laminated
Lamination is the technique/process of manufacturing a Raw material, material in multiple layers, so that the composite material achieves improved strength of materials, strength, stability, sound insulation, visual appearance, appearance, or ...
with varnish or other
insulating material. The purpose is to reduce
eddy current
Eddy currents (also called Foucault's currents) are loops of electrical current induced within conductors by a changing magnetic field in the conductor according to Faraday's law of induction or by the relative motion of a conductor in a mag ...
s in the core, while keeping a high
magnetic flux
In physics, specifically electromagnetism, the magnetic flux through a surface is the surface integral of the normal component of the magnetic field B over that surface. It is usually denoted or . The SI unit of magnetic flux is the weber ( ...
. Since the insulator is non-
ferro-magnetic, little, if any, magnetic flux is contained within it. It is mainly in the metal sheets. The insulation takes up a finite space, so the effective area the flux occupies is less than the physical area of the core.
The stacking factor is used when calculating the
magnetic flux density
A magnetic field is a vector field that describes the magnetic influence on moving electric charges, electric currents, and magnetic materials. A moving charge in a magnetic field experiences a force perpendicular to its own velocity and to ...
within the core. Because the flux is confined within a smaller area in a laminated core, the flux density is higher than it would be in a
homogeneous
Homogeneity and heterogeneity are concepts often used in the sciences and statistics relating to the uniformity of a substance or organism. A material or image that is homogeneous is uniform in composition or character (i.e. color, shape, siz ...
core.
Laminated cores always have a stacking factor less than unity; a stacking factor of unity implies no laminate at all. Stacking factors are typically 0.95 or higher for transformer cores and machine
stator
The stator is the stationary part of a rotary system, found in electric generators, electric motors, sirens, mud motors or biological rotors. Energy flows through a stator to or from the rotating component of the system. In an electric mot ...
s. However, cores made from
amorphous metal
An amorphous metal (also known as metallic glass, glassy metal, or shiny metal) is a solid metallic material, usually an alloy, with disordered atomic-scale structure. Most metals are crystalline in their solid state, which means they have a high ...
have a stacking factor of around 0.8, compared to 0.96 for
silicon steel
Electrical steel (E-steel, lamination steel, silicon electrical steel, silicon steel, relay steel, transformer steel) is an iron alloy tailored to produce specific magnetic properties: small hysteresis area resulting in low power loss per cycle ...
.
[
A related concept in transformer design is window space factor. This is defined as the ratio of the area occupied by the copper windings to the area of the space they pass through (the "window"). The higher the operational voltage of the transformer, the smaller this ratio needs to be in order to provide more space for insulation.][M. V. Deshpande, ''Design and Testing of Electrical Machines'', p. 119, PHI Learning,, 2010 ]
References
{{Electric transformers
Electric transformers