Which of the following is NOT a typical sign of a failing transformer?

Consistent temperature readings are not indicative of a failing transformer. In a well-functioning transformer, temperature should be relatively stable under normal operating conditions. If a transformer is operating effectively, it should maintain a steady temperature that reflects its design specifications.

On the other hand, unstable voltage levels, excessive humming noise, and the odor of burnt material all signal potential issues with a transformer. Unstable voltage levels may indicate internal faults or insulation breakdown, excessive humming noise could be a result of mechanical vibrations or electrical imbalances, and a burnt odor typically suggests overheating or insulation failure. Therefore, while the other signs point toward problems, consistent temperature readings suggest normal operation, making it the correct choice.