Construction of a Transformer

Three Main Parts of a Transformer

High-voltage winding (many turns of small gauge wire, thicker insulation)

The high-voltage winding is made up of many turns of relatively thin, insulated wire wound around the core. This winding is thinner than the low-voltage winding because it is designed to handle lower currents. The insulation on this winding must be able to withstand the stress of the higher voltage applied across it.

Low-voltage winding (fewer turns of larger gauge wire, thinner insulation)

The low-voltage winding has fewer turns of thicker, insulated wire around the core. This thicker winding is designed to handle higher currents. However, the insulation on this winding does not have to withstand the same high stress as the high-voltage winding.

Core (laminated sheet steel)

The purpose of the core is to concentrate the flux lines so that as much of the flux as possible links with both the primary and secondary coils. Ideally, the material used in the core should have high permeability, low retentivity, and high electrical resistance:

• This core is a conductor and having magnetic lines of flux constantly cutting through it will result in an induced voltage. One way we can reduce this effect is with laminations. We take the solid iron core and chop it into thin slices and layer them with a thin plastic barrier between them, which does not hinder the flow of the flux lines, but does prevent electrical currents from circulating.

• It is varnished to insulate laminations against eddy currents and to prevent oxidization.

• The higher the permeability, the greater the number of flux lines created for a given level of current in the windings.

• The lower the retentivity, the less energy is lost in the form of heat due to hysteresis losses. As the magnetic field expands and contracts, it causes the magnetic domains to constantly be realigned, resulting in friction. Hysteresis loss is caused by molecular friction in ferromagnetic materials that results in heat, a form of wasted energy, which forces the material to take its energy from the circuit. 

• The higher the resistance, the less energy is lost in the form of heat due to circulating (eddy) currents in the core. We often use ferromagnetic cores to reduce the magnetic reluctance of a coil. 

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