A step-up transformer is designed to have an output of 2200 V (rms) when the pri

Question

A step-up transformer is designed to have an output of 2200 V (rms) when the primary is connected across a 120-V (rms) source.

(a) If there are 80 turns on the primary winding, how many turns required on the secondary?

(b) If a load resistor across the secondary draws a current of 1.50 A, what is the current in the primary, assuming no power is lost to heat?

(c) If the transformer actually has an efficiency of 95.0%, what is the current in the primary when the secondary current is 1.20 A?

Hint: We define the efficiency of any transformer to be the percentage of the input power that is delivered to a load attached to the secondary:

efficieny = e = 100 ( P2/P1) in which P2is the power that the secondary delivers to the load and P1is the power delivered to the primary (by the AC power line, e.g.).

Explanation / Answer

Vs = 2200 V

Vp = 120 V

Part A ) : Np = 80 turn

              Ns = Np.Vs/Vp = 80.2200/120

             Ns = 1466.67 turn 1467 turn

Part B) : Ip = Vs.Is/Vp = 2200.1.50/120

             Ip = 2.75 A

Part C) : Vp.Ip.0.95 = Vs.Is

                  Ip = Vs.Is/(Vp.0.95) = 2200.1.20 /(120.0.95)

                  Ip = 23.16 A

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