Subelement C: Components— Topic 21: Transformers
Question 3-21C5
Element 3 (GROL)A power transformer has a single primary winding and three secondary windings producing 5.0 volts, 12.6 volts, and 150 volts. Assuming similar wire sizes, which of the three secondary windings will have the highest measured DC resistance?
Explanation
A transformer's output voltage is directly proportional to the number of turns in its secondary winding relative to the primary. To produce 150 volts, that secondary winding must have a significantly greater number of turns compared to the windings producing 5.0 volts or 12.6 volts.
Assuming similar wire sizes (gauge), the DC resistance of a winding is primarily determined by the total length of the wire used. Since the 150-volt winding requires the most turns, it will use the longest length of wire. A longer wire, with the same cross-sectional area, will naturally have a higher measured DC resistance. Therefore, the 150-volt winding will exhibit the highest DC resistance.
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