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Poster has been reminded to post all schoolwork type questions in the Homework Help forums and use the Template

This particular question is for an assignment. However, I believe that I have the final (correct) answer, but want to check the understanding.

I am required to calculate the resistance of the secondary winding of a transformer. The transformer is a 415:11000 V step-up, rated at 200kVA but with a unity power factor, so I can conveniently treat this as 200kW.

The question asks for the resistance value of the secondary winding, when the output across the transformer has 2% voltage regulation. This means that the voltage across the terminals will be 10780 V.

As I have the power rating, I can divide by the voltage to determine the current. Then, when I have the current I can divide the voltage by the current to get the resistance.

The question is, do I determine the secondary winding resistance using the 11000 or 10780 voltage? Obviously these will both give a different answer for the resistance, but if the question was specific about the rating (kVA), then I would assume that it needs to be constant. Examples:

200,000 W / 11,000 V = 18.1818 A, then 11,000 V / 18.1818 A = 605 Ohms.

200,000 W / 10,780 V = 18.5528 A, then 10,780 V / 18.5528 A = 581.04 Ohms.

Both equate to 200 kW, but are different answers for the resistance. The question also requires me to factor in a reflected resistance and leakage reactance (from the primary side), but those two figure need to be the total of the secondary winding so that I can calculate (by removing the reflected component) the secondary winding resistance only.

Thanks for any assistance.

I am required to calculate the resistance of the secondary winding of a transformer. The transformer is a 415:11000 V step-up, rated at 200kVA but with a unity power factor, so I can conveniently treat this as 200kW.

The question asks for the resistance value of the secondary winding, when the output across the transformer has 2% voltage regulation. This means that the voltage across the terminals will be 10780 V.

As I have the power rating, I can divide by the voltage to determine the current. Then, when I have the current I can divide the voltage by the current to get the resistance.

The question is, do I determine the secondary winding resistance using the 11000 or 10780 voltage? Obviously these will both give a different answer for the resistance, but if the question was specific about the rating (kVA), then I would assume that it needs to be constant. Examples:

200,000 W / 11,000 V = 18.1818 A, then 11,000 V / 18.1818 A = 605 Ohms.

200,000 W / 10,780 V = 18.5528 A, then 10,780 V / 18.5528 A = 581.04 Ohms.

Both equate to 200 kW, but are different answers for the resistance. The question also requires me to factor in a reflected resistance and leakage reactance (from the primary side), but those two figure need to be the total of the secondary winding so that I can calculate (by removing the reflected component) the secondary winding resistance only.

Thanks for any assistance.