Explain why the three phase voltage is not 660V
Because of 120 degrees difference among every 2 phases. In the three-phase system, there is a 120-degree phase angle between phases and that is why at any moment two phases will be on a positive cycle and one phase will be on the negative side At a time One-half cycle is in a negative half cycle with respect to time .thats way output voltage is 415 and not 660.
The 415 volt means voltage between two phases and 220 volt means voltage between any phase and neutral. The 3 phase voltages can’t meet at the same time on a sine waveform… that’s why you can never have 660v