The construction of any generator there is a displacement of three coils de-fazed in space, on a circle with 120 geometrical degrees. There will be at a certain rotational speed of the rotor against the static coils on the stator, an electric current called alternative, or AC. Unlike continuous current, the c.c. is changing its polarity many times a second. This changing in polarity is called the frequency of AC. This is measured in Hertz.Because is common parameter only for the alternative current. The continuous current doesn’t have “phases”. It only have a stable polarity: the “-” and “+” wires. On the AC, the + and – are combined all together in one wire called “phase”.
We know about the phases, we should know that in three phases generator, the current will be provided by all three cables (each one for one phase) in which the phases will be delayed in shifting the +on – or viceversa with 120 degrees or in time with the speed of the rotor per second divided by three.
There are electric engines which uses all three phases and here are a bunch of possibilities on tiding all three coils of the engine.
In our homes and other civil buildings there is a energy supply with one phase and “zero” wire. All the appliances which uses the AC electric energy, uses only one phase.
Regarding the three phased electric engines, they can use all those three phase, with or without the zero wire. That’s simply because the delaytment in shifting between phases the “+” polarity from one wire meets the “-” of another so the current will flow, and than another “+” wire will provide the current with the previous”-”.
The connections between the three coils in an engine is made in “star” or “triangle”(or delta) displacement.
This means that in “star” connection, the three phases meet in the middle and there is or may be not the “zero” wire connected also.
On the other hand the “triangle”–delta– connection is formed by coupling the ends of a coil with the next one forming a closed loop, or in this case a triangle. The three phases will be provided on the connections of two consecutive coil ends.
These arrangements are made because one of them is more powerful and it request a lot of energy before the starting of the rotation of the rotor, and might burn up the wires.That’s why this kind of generator comes out equipped with both of the arrangements , being started on one, and than on full speed shifted on the other.
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