Answer / iamdon

A 50-Hz designed transformer can be used at 60-Hz system
but a 60-Hz designed transformer cannot be utilized at 50-
Hz system.

Because in later case, the transformer windings(primary and
econdary)will draw approximately 20 % greater current than
the rated one.More current flowing will produce more
winding heating loss.The temperature of winding rises
(Beacuse cooling system was designed for rated current
which was lower as compared to present higher value of
current at low frequency operation)and it get burnt.

Author:arbelectbit@yahoo.com

Answer / brajeshjhaa

For a transformer the voltage is proportional to the product of flux and frequency.
case-I
Voltage = constant
Frequency = increased from 50 to 60Hz i.e. change by 120%
For Transformer:
Voltage = flux * frequency * K; k is a constant
so when frequency increases by 120% flux decreases to 83.3% Now;
Hysteresis loss = flux^2 * frequency^2 * T; T is constant
At 50 Hz
Hy. Loss@50 = flux^2 * Frequency^2 * T
At 60 Hz
Hy. Loss@60 = (.833flux)^2 * (1.2Frequency)^2 * T
On evaluation:
Hysteresis loss@50Hz = Hysteresis loss@50Hz

Eddy Current Loss

Eddy C. L. = flux^1.6 * f * C; C is a constant
Eddy@50 HZ = flux^1.6 * f * C
Eddy@60 Hz = (.833flux)^1.6 * 1.2F * C
On evaluation;
Eddy@60Hz = 0.895 * Eddy@50HZ

So it is seen that a 50HZ transformer when operated at at 60Hz has same hysteresis loss eddy current decreases. As the core loss decreases the transformer can be safely operated.

But if a 60Hz transformer is operated at 50Hz, then just the reverse of above the core loss i.e. eddy current loss will increase and hence the core loss will go high; hence not advisable to operate.

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