Electricity is distributed from electrical substations to neighborhoods at 1.3×1

Question

Electricity is distributed from electrical substations to neighborhoods at 1.3×104 V . This is a 60Hz oscillating (AC) voltage. Neighborhood transformers, seen on utility poles, step this voltage down to the 120V that is delivered to your house. No energy is lost in an ideal transformer, so the output power Pout from the secondary coil equals the input power Pin to the primary coil. Suppose a neighborhood transformer delivers 300 A at 120 V. What is the current in the 1.3×104 V line from the substation?

Explanation / Answer

since no energy lost in transformer so effieciency is 100%

hence

input power = ouput power

Pi = Po

let v1 be the voltage across primary coil

i1 be current through primary coil

V2 be the voltage across secondary coil

i2 be the current through secondary coil

v1 i1 = v2 i2

1.3*104 V * i1 = 120V (300A)

i1 = (120V)(300A) / (1.3*104 V) = 2.769 A

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