4th Year Lineman Apprentice Practice Exam 2026 - Free Apprentice Practice Questions and Study Guide

To calculate the high side coil current for a 13800V 3-phase transformer, it's important to understand the relationship between power (in kilovolt-amperes, in this case), voltage, and current in a three-phase system.

The formula to find the current on the high side (primary) of a transformer is derived from the apparent power formula, which states that for a 3-phase system, the power (in kVA) is equal to the square root of 3 multiplied by the line voltage (in volts) and multiplied by the line current (in amperes). In mathematical terms, this can be expressed as:

\[

\text{Power (kVA)} = \sqrt{3} \times \text{Voltage (V)} \times \text{Current (A)} / 1000

\]

To isolate the current, you rearrange the formula as follows:

\[

\text{Current (A)} = \text{Power (kVA)} \times 1000 / (\sqrt{3} \times \text{Voltage (V)})

\]

In the case mentioned:

1. The transformer is rated at 10 kVA.

2. The voltage on the high side (primary