There are two power phases and a ground phase, the two phases provide extra power for industrial purposes . In home only one phase and ground is required. we can have multiple phases to generate the heavy power as required.
The main reason that power utilities prefer three-phase transmission to any other number of phases is as follows:
For a fixed amount of power to be transmitted a fixed distance at a fixed line loss with a fixed voltage between conductors, three-phase is more economical in the use of conductor metal than any other number of phases.
However it should be noted that when a fixed amount of power is transmitted a fixed distance with a fixed loss for the same voltage to neutral, there is no difference between any system of phases regarding the required amount of conductor metal.
The above information was obtained from the book "Alternating-Current Circuits" by Kerchner and Corcoran where proofs are given.
I think it may be useful to add the following explanation:
1. Polyphase systems were originally introduced to solve the problem of severe vibration when single-phase generators were loaded inductively. Balanced polyphase systems make reactive loads draw power from the generator at a uniform rate so that the machine runs smoothly when driven with a uniform torque.
2. All the advantages of polyphase systems are available when three phases are used and generally there is little to be gained by using more than three.
The above information is in the Services Textbook of Electrical Engineering.
