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
The reason three phase voltage is not 660V has some thing to do with phase to phase voltages as can observed from voltages of about 400V in many systems and it has to do with line line and line to neutral voltages measurements. In a balanced three-phase system, the voltage difference between any two phases, the line voltage, is also linked to the voltage between a phase and the neutral, the phase voltage.
Where
Ex: In the most normal 3 phase 4 wire AC supply system having line to neutral voltage of 230V, the line to line voltage becomes about 400V. For example, if a line-to-line voltage was requested at 660V, the line to neutral voltage was approximately 381V, which are very uncommon voltage values in most electrical systems. This relationship between the voltages is the reason why we do not have 660V as a common three phase voltage class.