If rated DC voltage is applied instead of ac to the primary of a transformer

A. Secondary of the transformer will burn 
B. Primary of the transformer will burn 
C. Secondary Voltage will be excessively high 
D. There will be no Secondary voltage 

Answer: B. Primary of the transformer will Burn 

Explanation:
The resistance of the transformer winding is very less.

When we apply DC voltage to the transformer, the reactance of its winding will be zero since reactance is frequency-dependent and the frequency of a DC supply is zero.

Flux produced by the flow of direct current will be constant.

When a DC voltage is applied to the primary winding of a transformer, due to low resistance, the winding acts as a short circuit across the terminals of the DC source that lead to the flow of heavy current through the winding resulting in overheating of the winding.

Eventually, the source or the winding will be damaged. 

The effect of current on winding depends on the applied DC voltage, rating of the transformer, winding resistance and how powerful the DC source is. “Nothing will happen if 5Vdc is applied to a 50KVA transformer!”.


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