where we use 1 phase & 3 phase supply ?what is major
advantage using 3 phase over than single phase ?

Answer Posted / b. salazar

Three phase requires less current than single phase. The more power, the more likely you will need to use three phase. The reason is the physics of the source of electricity. Basically, a single phase circuit experiences 0V for a very tiny amount of time in each half cycle. Building up from 0V takes energy and thus requires more current. Three phase phases individually experience a 0V period, but the other phases do not hit 0V at the same time. This means that there is no build up of power in every half cycle. This need for increased current is negligible for very small machines. The larges sing phase machine in the NEC is 10 HP which requires 50A at 230V, but 10 HP at 230V three phase only requires 28A.

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