Answer Posted / d.ramesh classes

Technical explanation

When the windings of a 3-phase motor are connected in STAR:
the voltage applied to each winding is reduced to only (1 /.'/'3) [1 divided by root three] of the voltage applied to the winding when it is connected directly across two incoming power service lines in DELTA.

the current per winding is reduced to only (1 /.'/'3) [1 divided by root three] of the normal running current taken when it is connected in DELTA.

so, because of the Power Law V [in volts] x I [in amps] = P [in watts],

the total output power when the motor is connected in STAR is:

PS = [VL x (1/.'/'3)] x [ID x (1/.'/'3)] = PD x (1/3) [one third of the power in DELTA]

where:
VL is the line-to-line voltage of the incoming 3-phase power service
ID is the line current drawn in DELTA
PS is the total power the motor can produce when running in STAR
PD is the total power it can produce when running in DELTA.

by D.RAMESH CLASSES

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