How can the value of a secondary voltage be changed on a transformer?

The value of a secondary voltage on a transformer can be changed by adjusting the no-load tap changer while the transformer is energized. This method allows for the fine-tuning of the output voltage without having to disconnect the transformer or disrupt the power supply. Tap changers are designed to alter the turns ratio of the transformer, which directly affects the voltage levels across the primary and secondary sides.

Utilizing a no-load tap changer enables operators to adjust the voltage based on load requirements or changes in the power system, ensuring efficient operation. This adjustment is particularly useful in maintaining voltage levels within specified limits and compensating for variations in load.

Options involving replacing the transformer entirely or turning off the transformer would not provide a practical or efficient means to adjust secondary voltage. While increasing the primary voltage could potentially influence secondary voltage, it would result in an overall increase in both primary and secondary voltages, rather than a controlled and specific adjustment. Thus, using a no-load tap changer while the transformer is energized is the most effective and immediate method for changing secondary voltage.