Answer Posted / rajendra kumar

If a 500 kva, 400 v, 60 hz t/f is to be operated on 50 hz
frequency then how will its KVA rating change?
expl-
kva rating depends upon V*I.
flux is same for both coil,
V1=4.44.N.f.phi
phi=k.V1/f=k.400/60=6.6
phi2/phi1=v1*f2/V1*f1=50/60=0.833
phi2=phi*0.833
V2 (sencondry side)=4.44 N2.f.phi2(at 50 hz)
=4.44.N2.f1*phi1
i.e no effect on voltage but flus has decreased means current will be decrease by factor 0.833.that is KVA=V*I2=V*I1*0.833 (decreases)

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