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

Question

A step-up transformer is designed to have an output voltage of 2200 V (rms) when the primary is connected across a 110 V (rms) source.

(a) If the primary winding has 78 turns, how many turns are required on the secondary?
_______ turns
(b) If a load resistor across the secondary draws a current of 1.10 A, what is the current in the primary, assuming ideal conditions?
________ A
(c) If the transformer actually has an efficiency of 98.0%, what is the current in the primary when the secondary current is 1.20 A?
________ A

Explanation / Answer

a)
use:
Ns/Np = Vs/Vp
Ns/78 = 2200/110
Ns = 1560 turns
Answer: 1560 turns

b)
use:
Ip/Is = Vs/Vp
Ip/1.1 = 2200/110
Ip = 22 A
Answer: 22 A

c)
If effeciency was 98 %, Vs = 1.2 A
Let Is for 100 % effeciency be I
98% of I =1.2
0.98*I =1.2
I = 1.2245 A

Ip/Is = Vs/Vp
Ip/1.2245 = 2200/110
Ip = 24.5 A
Answer: 24.5 A

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