Question

A neighborhood transformer on the top of a utility pole transforms 12.0 kV 60.0 Hz alternating voltage down to 120.0 V to be used inside a house. If the secondary coil of the transformer has 134.0 turns, then how many turns does the primary coil have

Answer 1

Answer:

The primary coil has 13,400 turns

Explanation:

Voltage Transformers

A transformer is an electrical apparatus that converts an alternating electrical voltage to another. Step-down transformers lower the voltage from higher levels (kilovolts) to consumer levels (120/240 Volts).

The ratio between both voltages can be computed as

$\displaystyle r=\frac{V_1}{V_2}$

Where V1 is the primary voltage and V2 is the secondary voltage. This ratio depends on the turns ratio of the coils wounded in a common magnetic core.

$\displaystyle r=\frac{N_1}{N_2}$

Being N1 the number of turns of the coils of the primary side and N2 the number of turns in the secondary coil. Both relations give us

$\displaystyle \frac{N_1}{N_2}=\frac{V_1}{V_2}$

Solving for N1

$\displaystyle N_1=\frac{V_1}{V_2}\cdot N_2$

We have:

$V_1=12,000\ V\\V_2=120\ V\\N_2=134$

Calculate N1

$\displaystyle N_1=\frac{12,000}{120}\cdot 134=13,400$

The primary coil has 13,400 turns