How three phase give 440v?

Three-phase is transmitted at many different voltages but a 440 v 3-ph supply has 440 v between the phase wires by convention and is used in supplying power to groups of houses or small businesses.

The voltage between any of the phases and neutral is 440/sqrt(3) which equals 254 v.

A typical 440 v 3-ph transformer might be able to supply 700 amps, which gives 180 kVA, enough for about 90 houses.