The turns ratio of the tapped step-down transformer shown in figure "C" of the illustration is four to one and all taps are equally spaced. If 440-volts were applied between "H1" and "H4", what would appear across "X1" and "X4"? Illustration EL-0082
• Transformer turns ratio: ( V_p / V_s = N_p / N_s ) where V is voltage and N is number of turns. • Tapped windings: All taps are equally spaced, so each section of the winding represents the same number of turns. • Step-down transformer: Primary voltage is higher than secondary voltage; the turns ratio is 4:1 (primary:secondary).
• If the total primary from H1 to H4 has four times as many turns as the total secondary from X1 to X4, what fraction of the primary voltage will appear across the full secondary? • Since 440 V is applied across the entire primary (H1–H4), what voltage corresponds to one-quarter of that, based on the 4:1 turns ratio? • Look at the drawing: are X1 and X4 connected across the whole secondary winding, or only part of it? How does that affect your calculation?
• Confirm that H1 to H4 represents the full primary and X1 to X4 represents the full secondary in figure C. • Use the relationship Vp/Vs = Np/Ns = 4/1 and solve for Vs when Vp = 440 V. • Verify your result is lower than 440 V (because it is a step-down transformer) and matches one of the multiple-choice options.
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