During an excitation current test on a power transformer, why might two of the currents be higher than the third reading?

The two currents being higher than the third reading during an excitation current test on a power transformer can be considered a normal reading due to the nature of how transformers operate. Transformers are designed to have different exciting currents for each phase, particularly in three-phase systems.

In a balanced three-phase transformer, variations can occur due to phase angle differences, impedance, or minor imbalances in the windings and load conditions. It is common to see some disparity in the currents due to these factors, which does not necessarily indicate a malfunction or a need for correction. As such, understanding that fluctuations can occur due to the standard operating conditions of a transformer helps clarify why higher readings in two phases compared to the third can be acceptable and expected.

In contrast, options implicating faults or errors suggest issues that imply the need for further investigation, which may not be warranted in this scenario when the readings are within typical operating parameters. Therefore, acknowledging these variances as part of normal operational characteristics of power transformers is crucial in interpreting excitation current test results correctly.