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Single phase power has a sine wave voltage that crosses zero before reversing its polarity. In the region near the zero-crossing there is not much power. At zero there is none at all. So single phase loads often need some trickery to deliver output in this area. Often it is just the inertia of the motor or appliance. Three phase power is always delivering power on one of its phases, and is thus preferred for generators, motors, machines and appliances that use lots of power. If the application is large power, or small power with weight restrictions (like automobiles!) Three Phase is preferred. DC (Direct Current) is the next step up for smooth high-power devices but requires rectification, regulation and smoothing to be useful.

Another problem with DC is that, for efficient long distance transmission, it cannot be simply converted to much higher voltages than the voltage at which it was generated at the power station. Similarly DC cannot be transformed down to safer, much lower mains voltages for use by consumers.

AC (Alternating Current) is used for high power generation and distribution because it can easily be transformed, using Transformers, to achieve very efficient power transmission over very long distances and can then be transformed down to low voltages for distribution to consumers. Two phase, and higher multi-phases are also used but very rarely.

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Related Questions

Single phase and three phase circuit?

Yes, there is a difference between single phase and three phase circuits.


Is there a difference between three phase and single phase electrical supplies?

Yes, there a difference between three phase and single phase electrical supply services.


What is the phase difference between the current through the resistor and inductor in an AC circuit?

The phase difference between the current through the resistor and inductor in an AC circuit is 90 degrees.


What is the difference between single phase circuit and tree phase circuit?

A single-phase circuit has one live conductor and one neutral conductor, typically used for residential applications. A three-phase circuit has three live conductors and one neutral conductor, used for higher power industrial applications due to its ability to provide a more balanced power distribution.


Why phase difference exists between voltage and current in ac circuit?

because of the reactances in the circuit


What difference between using 4poles circuit breaker and using 3 single pole breakers?

3 pole would be for 3 phase, 4 pole would be 3 phase & neutral


Difference between two phase and three phase welding machine?

Three phase uses a safety circuit away from the machine, two phases uses you as the safety circuit


What is the difference between a one phase and a three phase motor. And if a three phase motor is given a single phase supply will it run or not?

The difference between a single phase and a three phase motor is the amount of power conductors that feed the device. As to the other part of the question a three phase motor will not start or run on single phase. The phase angles on three phase are 120 degrees apart on a single phase system they are 180 degrees apart.


In a 240 volt single phase circuit A phase is 4000 watts B phase is 7000 watts what is the neutral load?

Question is incorrect. in a 240 Volt single phase circuit, how can you have A phase and B phase?


Compare the phase relationship between the voltage and current in a purely resistive circuit and an RL circuit?

In a pure resistive circuit the voltage and current are in phase. In an inductive circuit they are fro zero to 180 degrees out of phase. If they are in phase the Power Factor is 1 and 180 degrees the PF is zero. The exact amount of the phase difference depends on the specific circuit.


Why is there a difference between a domestic and industrial electricity supply?

actually there is no difference between them. However in some counteries, single phase is used for domestic and three phase is used for industrial.


What is an acceptable difference in resistance between phases on a 3 phase motor?

The currents between legs of a three phase circuit should be within about 10% of each other.