How does a large power transformer maintain output voltage as load changes?

A large power transformer maintains output voltage as load changes primarily through the use of a tap-changer. This device allows for adjustments to be made to the transformer’s turns ratio while it is in operation, thereby enabling the output voltage to be regulated effectively as the load varies. When the load increases or decreases, a tap-changer can redistribute the voltage levels, ensuring that the output remains stable despite fluctuations in demand. This capability is critical for maintaining consistent voltage levels in power systems, which helps protect equipment and maintain system reliability.

In contrast to this, increasing the transformer size does not inherently control output voltage with load changes; instead, it refers to the physical dimensions of the transformer, which do not impact voltage regulation directly. Controlling the input voltage is also not a primary function of the transformer itself; rather, it is typically managed by the power supply system. Additionally, reducing the load current does not maintain voltage—it merely decreases the demand, which could lead to lower voltage if the system is not designed to provide consistent voltage regardless of load variations. Thus, using a tap-changer is the most effective and relevant method for maintaining output voltage in response to load changes.