Answer / shaikh

Frequency is directly proportional to induced voltage of transformer (v=4.44NFphi). if you decrease frequency KVA will decrease and vice versa, because for the same rated voltage flux is also decreased and flux area of t/f decreases.

Answer / k r vishnu narayanan

E/f = 4.44*N*phi(max)

E: induced emf
f: frequency
N: number of turns
phi: max flux in the core

When frequency is reduced keeping E constant(at E(max)), flux(phi(max)) has to increase (from eq:)to saturation and harmonics will come into effect. So, there has to be a maximum allowable voltage at a particular frequency and the current too is limited by the saturation effects implying that both V and I has to be limited at a particular frequency (maximum current is always limited by number of turns). Thus their product(kVA) has to be directly proportional to frequency and the answer to this question is b(decrease).

God bless...

Answer / jinboll

The transformer EMF equation shows that the EMF induced in the secondary or the primary side of a transformer is directly proportional to the product of the flux (Φm) through the transformer core and the frequency. This leads to the flux is proportional to E/f.
For example, the kVA rating of the 500v to 250v 60 Hz transformer will be smaller when used in Europe with a frequency of 50Hz. 500/60 = E/50, E is smaller than 500v on primary side. 250/60 = E/50, E is smaller than 250v on secondary side.

Answer / ashok kumar hudda

hey guys its simple yr
we say that transformers main aim is to maintain constant flux
so if we reduce the frequency for given size of transformer then we have to reduce the voltage to maintain constant flux so due to reduction in voltage KVA also decrease so we can say that KVA is directly proportional to frequency

Answer / 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)

Answer / cameron hunter

The transformer EMF relation shows that the EMF induced in the secondary or the primary side of a transformer is directly proportional to the product of the flux (Φm) and the frequency. This also means that the flux is proportional to EMF over frequency.
As an example, for the 500V to 250V transformer, the kVA rating under 60Hz transformer will be smaller than 50Hz. 500/60 = V/50. V has to be smaller to keep consistency.

Answer / nikhil singh

Transformers are rated in kva and not in KW for taking into
account the core and copper losses which are dependent on
voltage and current respectively without involving power
factor.Now the copper loss is independent of frequency but
the core loss comprising of hysterisis and eddy current
loss is proportional to frequency.So as frequency decreases
core loss decreases and KVA rating decreases.

Answer / guest

remains same since kva rating depends on iron loss and
copper loss which means it depends on voltage and current.

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