what if we energize 50 Hz h.v side of the transformer with 40Hz, is the transformation ratio don't matter? Suppose 400/200, single phase transformer which is designed to operate at 50Hz. If you provide it 40Hz the output will remain unaffected by frequency?
Electronic – Transformer Ratio
electric-machineelectrically-conductivetransformer
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Best Answer
If you supply a transformer with less than the rated frequency, you have to supply it with proportionately less than the rated voltage, otherwise it's likely to saturate. The maximum voltage/frequency ratio (or voltage.period product) you can feed to the transformer is limited by the area of the core.
In this case, your 400/200 50Hz transformer becomes a 320/160 transformer at 40Hz. It will still have the same transformation ratio. It will still handle the same current, so its VA will have dropped to 80% of the 50Hz value.
If the original transformer has been designed conservatively, well clear of saturation, then it will tolerate a slightly higher voltage/frequency ratio. Monitor the magnetising current, that is the current taken by the primary with no load on the secondary, at the correct rated voltage/frequency ratio. Decide a maximum value for this current that you are prepared to tolerate (the limit is mostly \$I^2R\$ heating in copper windings). Now increase the primary voltage slowly, while monitoring the magnetising current. When it's reached your limit, stop increasing the voltage further.
The reason behind this behaviour is the way iron behaves in a magnetic field. As it approaches saturation, its permeability crashes from typically 2000 to something nearer 1. It's the high permeability of the iron that keeps the magnetising current managable. Once it has stopped working as designed, the current rises.