Core coils
If a magnetic material is placed in the magnetic field of a coil, the magnetic flux density (B) changes. Under the influence of the magnetic field, the "magnetic dipoles" present in the material orient themselves in the direction of the field and increase the magnetic flux density and thus also the inductance of the coil. The increase in inductance depends on both the core material used and the core design.
In so-called core coils, a body made of a material with magnetic properties, the core, is located in the magnetic field of the coil. The core amplifies the magnetic field and thus increases the inductance of the coil. Depending on the core design, the inductance can be increased many times over (factors of 3 to >100) compared to the air core coil. The core coil has a lower ohmic resistance or a smaller design compared to the air-core coil, as fewer turns or thinner wire have to be applied to the winding for the same inductance. One disadvantage of the core coil is its limited current carrying capacity. It is not about the electrical load capacity of the copper winding, whose load capacity is given by the cross-section of the copper wire, but about saturation phenomena in the core material. in contrast to the air core coil, where the magnetic field becomes stronger the greater the current in the coil (linear relationship), there is a point in core coils at which the magnetic field no longer increases to the same extent despite the increase in current. This behavior is called saturation. Disengagement into the saturation range is associated with non-linear behavior of the coil and causes distortions that occur in the higher power range. The saturation limits can be investigated by measuring the distortion factor when the current through the coil is increased. If the distortion factor rises sharply, the saturation range has been reached. An air-core coil does not exhibit such distortions due to its design. The saturation behavior of a core coil is determined by the core material, core design and cross-section.
