Transformer is electromagnetic static electrical equipment (with no moving parts) which transforms magnetic energy to electrical energy. It consists of a magnetic iron core serving as a magnetic transformer part and transformer cooper winding serving as electrical part. The transformer is high-efficiency equipment, and its losses are very low because there isn’t any mechanical friction inside. Transformers are used in almost all electrical systems from low voltage up to the highest voltage level. It operates only with alternating current (AC), because the direct current (DC) does not create any electromagnetic induction. Depending on the electrical network where the transformer is installed, there are two transformer types, three-phase transformers and single phase transformers. The operation principle of the single-phase transformer is: the AC voltage source injects the AC current through the transformer primary winding.
The AC current generates the alternating electromagnetic field. The magnetic field lines are moving through iron transformer core and comprise the transformer secondary circuit. Thus the voltage is induced in the secondary winding with the same frequency as the voltage of the primary side. The induced voltage value is determine by Faraday’s Law.
f → frequency Hz
N → number of winding turns
Φ → flux density Wb
If the load is connected on the secondary transformer side the current will flow through secondary winding. Basically, the single phase transformers can operate as step up transformer or step down transformers.
The main parts of a transformer are windings, core, and isolation. The windings should have small resistance value and usually they are made of copper (rarely of aluminum). They are wound around the core and must be isolated from it. Also, the windings turns have to be isolated from each other. The transformer core is made from very thin steel laminations which have high permeability. The laminations have to be thin (between 0.25 mm and 0.5 mm) because of decreasing power losses (known as eddy current losses). They have to be isolated from each other, and usually, the insulating varnish is used for that purpose. The transformer insulation can be provided as dry or as liquid-filled type. The dry-type insulation is provided by synthetic resins, air, gas or vacuum. It is used only for small size transformers (below 500 kVA). The liquid insulation type usually means using mineral oils. The oil has a long life cycle, good isolation characteristics, overload capability and also provides transformer cooling. Oil insulation is always used for big transformers.
The single phase transformer contains two windings, one on primary and the other on the secondary side. They are mostly used in the single-phase electrical power system. The three-phase system application means using three single phase units connected in the three-phase system. This is a more expensive solution, and it is used in the high voltage power system.
Applications of Single Phase Transformer
The advantages of three single-phase units are transportation, maintenance, and spare unit availability. The single-phase transformers are widely used in commercial low voltage application as electronic devices. They operate as a step-down voltage transformer and decrease the home voltage value to the value suitable for electronics supplying. On the secondary side, rectifier is usually connected to convert a AC voltage to the DC voltage which is used in electronics application.