What is the difference between 3-phase and 1-phase?

Answer 1

Up to 10 Ampere standard applications are designed with phase power supply.

For conducting current larger than 10 A, especially for driving motors in industrial applications, all the applications are normally designed for three phase power supplies.

AnswerA three-phase system is more economical, in terms of the volume of copper required (around 75%), than a corresponding single-phase line supplying the same load. Three-phase systems deliver energy continuously, rather than in pulses. Three-phase motors are self-starting and more compact than a single-phase motor of similar capacity. Despite this, 'most' homes don't require three-phase supplies and are provided with a single-phase service (having said that, in some countries, such as Cyprus, three-phase residential supplies are common).

Answer 2

Naturally, we are dealing with ac circuits here. A single phase supply will have only two conductors - a supply and a return.

A three phase supply has three wires, and on each wire the phase of the signal differs by 120O from the other two. This also means that the voltage difference between phases is much greater than that between any one phase and ground.

For example, in our 230V ac system, single phase, the voltage difference between any two of the other wires in a three phase system, the voltage is 440V ac.

This of great aid when starting large motors under load. For the brief starting period, the applied voltage may be 440v, and this will energise the motor more strongly. Of course, the motor is generating almost twice the power (440/230) as under normal conditions, and it will only stand this overload for a brief period.

After this brief starting period, the motor's coils will be then switched so that it operates as a 230V motor. [The Star Delta system, named after the wiring diagram.]

The power is generated at the power station as a three phase supply, for this means the generator is running more smoothly than it would if it were only a single phase machine. The load comes on six times per rotation, rather than two times. That's why you'll see the HV overhead wires are in groups of three.

And the power distribution company will usually connect each house of a group of three to the different phases, thus roughly balancing the load on each phase.