What would happen if a power transformer designed for operation on 50 Hz (frequency) were connected to a 5 Hz (frequency) source of the same voltage?

Dear Arif, 

To fully understand what will happen to the transformer, let us have a look at the design and workings of Power Transformer. The magnetic permeability of ferromagnetic materials is given by:

                                                                            B = u H

To understand the magnetic permeability of a perticular ferromagnetic material, we need to look at the plot of flux produced in the core againt the magnetomotive force producing it. This type of curve / plot is called saturation curve or magnetization curve and is non-linear in nature. If we look at this curve, we will notice that at first small increase in 'H' causes a huge increase in 'B'. Finally, there comes a point on the curve, where any increase in 'H' causes almost no change in 'B'. This region on the curve is called saturation region and in this region, the output at the secondary of the transformer will equate to the primary of the transformer. 

Now when we apply a voltage source with same magnitude but lower frequency e.g5Hz to a Power transformer that is designed to work at50Hz, the reactance X (xL =2*pi*f*L) offered by the primary windings working at5Hz source will be lower resulting in an increase in magnetizing current. The increase in magetizing current will result in abnormal saturation of the transformer core and will also cause over heating and can lead to breakdown of winding insulation due to over heating.

Hope this helps.

Kind Regards

Hammad Khan  

The transformer will get too hot due to high current losses and and total output efficiency decrease too badly

Transformer Inductance reactance is directly proportional to the Frequency.With low frequency supply,  primary winding of the transfer will have very low rectance which will increase the current flowing in the winding and will ultimately damage the transformer/burn the winding.

In short

after that you should buy or design new one :P

normally current inversely proportional to frequency so if frequency is reduced automatically current (I) will get increased so primary will have insufficient reactance and too much primary current will flow thatsy considerable copper loss will occur. as a result of this transformer starts to smoke. 

 over heating and winding insulation will breakdown later

I cant add much to the brilliant engineers above nice effort ; but all I can say is that power transformers are narrowly optimized for thier specified applications and can only opreate with the designed frequency with a certain exception that the energizing voltage does not exceed83% of the transformer nominal voltage

powe transforme is made to operate in one particular frequency,usually50 HZ.If the frequency is too low,primary will have insufficient reactance and too much pimary current will flow,producing a considrable copper losses

Lower frequency results in increase magnetising current which in turn heat up the windings and cause damage.

This leads to increase the "eddy" and "hystersis" losses which both are frequency dependent and thus transformer will get extra heating and noise  which can damage it .

you can increase the frequency without harming the transformer... rather the size may be reduced by increasing the frequency... but if you decrease the frequency the core gets saturated...and  gets heated up... damaging the insulations... PS... you cant decrease the frequency on a working transmission/distribution system...