The turns ratio of a 3-phase transformer is 115 to 1; with a 13.8 kV primary, what is the approximate secondary voltage?

• A. 12 V
• B. 1,200 V
• C. 120 V
• D. 13.8 V

Answer: (C)

The voltage scales with the turns ratio. If the transformer has a primary-to-secondary ratio of 115:1, the secondary voltage is the primary voltage divided by 115.

Convert 13.8 kV to volts: 13,800 V. Then 13,800 ÷ 115 = 120 V.

So the approximate secondary voltage is 120 volts. In a three-phase setup, this same ratio applies to the line voltages, so the result is consistent with common distribution step-downs.