Three-phase current

Three-phase currentThree-phase alternating current is widely used in modern industry. It has many advantages over single-phase current. In fact, the three-phase system is a variant of a multi-phase system. The latter consists of a number of electric circuits. The sinusoidal electromotive forces in the circuits have the same frequency but different phases.Another essential condition is that these electromotive forces must be produced by the same source.To create a three-phase system using the simplest schematics we need three AC generators. Their rotors should be interconnected. The stator coils of the generators should be placed at an angle of 120 degrees to each other.In this way the electromotive force produced by the second generator will not have the time to change relative to that of the first generator. In other words, it will be 120 degrees late. Similarly the electromotive force of the third generator will be 120 degrees late relative to that of the second generator.Today all stator coils are usually mounted within the same frame. However, they are still placed at an angle of 120 degrees to each other.The advantages of the three-phase system over the single-phase system are as follows:- economical production and transfer of electricity in comparison to single-phase systems;- it is quite easy to produce circular rotating magnetic field necessary for a three phase induction motor;- it is possible to have two operating voltages in one station, that is the phase and the line voltages;6 wires are necessary to turn on a three-phase generator. In order to cut the number of wires the coils of the generator and the collector must be interconnected. Thus a three-phase system is formed.There are 2 types of connections: star- and delta-connection.The phases of the source usually have a star-connection, the phases of the consumer can either have a star- or a delta-connection. Both the methods help decrease the number of wires used.