Transformer Current

[erickench]

Here's a question for all you engineers out there. Let us suppose you have a transformer with the secondary short circuited i.e. full load. Instead of applying a small voltage as you would in a short circuit test we apply the rated voltage instead. What would be the primary current? I would of thought of just applying the basic formula of rated Voltage-Amperes divided by rated Voltage equals Current flow of the primary. But I could be wrong. It's pretty clear that the secondary current would be very high but what about the primary? Would the turns ratio apply in this situation too?

[vishnu21]

hi..

the primary current will depend upon secondory curent but i think it will not be according to the transformatiopn ratio.I think it need to be calculated using prim power=sec. power consumed..it will give approximate value..

[erickench]

Yes I would have thought that the KVA rating of the transformer is sort of a maximum. If the secondary is shorted the voltage would be almost zero but the current would be very high. If it were possible to determine the exact voltage even at milllivolts or microvolts and then multiply it by the short circuit curent which would be on the order of thousands of amps then you would come up with the rated KVA value. But the primary voltage would not be zero because it is isolated. I would've thought that the primary current would be rated current which in this case is the maximum. I wish there was some technical material that specifically addresses the subject of short circuited secondaries with rated voltage applied to the primary.

[shivamshiva]

By short circuiting the secondary and start increasing the primary voltage then up to saturation of transformer core secondary current increases with primary current but after the core saturates even though we increase primary current by increasing primary voltage the secondary current will not increases.

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