Answer / sumit

in absence of 3 phase supply no rotating magneic field will
produce . . .. . .

Answer / kj

A 3 phase supply is the lowest number of phases where a
rotating field is produced. No extra starting controls are
needed (e.g. capacitor start or start windings)
Two phase systems have been used and can produce a rotating
field but it has to use a setup with separate neutrals for
each of the 2 phase. It therefore requires 4 wires to each
motor instead of 3 and it is also not as efficient.
Three phases also has the advantage of the currents in the
nuetral not being the sum of the 3 phase currents. In that
way only a single neutral can be used as the return for any
single phase load on all the 3 phases.

Answer / t lakshmi narayana

Why because two phase supply cannot work.Let us consider 2
phase a,b.If a=0 then b=180 electrical degrees apart. Both
are out of phase i.e net torque is equal to zero.
Electrical degree = 360/phases.
In 2 phase it is 180
In 3 phase it is 120 which gives a torque.

Answer / wareagle

Because it does not exist.

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