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# AC Circuits

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A. A small, mains, step-down transformer is used to power a 12 V apparatus. The transformer's rating label is attached.

(i)Describe the constructional features of the transformer's core and explain why one winding is made of wire of a greater diameter than the other.

(ii)The rating `T130' on the transformer's label refers to a temperature. Explain the meaning of this rating.

(iii)If the primary and secondary winding resistances are 125 &#8486; and 0.7 &#8486; respectively, calculate the transformer's copper losses at full load.

b. A large power transformer has a turns ratio N1/N2 of 1:5. When the primary voltage is 400 V and it is connected to a resistive load its secondary current is 100 A.

(i)Calculate the required value of source resistance of the supply to give maximum power transfer.

(ii)If the total losses in the transformer amount to 4 kW for the conditions in (i) above, calculate the transformer's efficiency.