An autotransformer would be practical in which of the following applications?

An autotransformer is particularly effective in applications where the voltage ratio between the primary and secondary sides is relatively low. This makes it ideal for applications that require voltage adjustments without needing a complete isolation of the circuits.

In the context of high-voltage applications, such as the situation involving a 115 kV to 230 kV system, an autotransformer can efficiently step-up or step-down the voltage by utilizing a single winding that serves as both the primary and secondary winding. This design allows for reduced material requirements, leading to a lighter and more compact transformer, while also enabling improved electrical conductivity and efficiency.

In contrast, for applications like low voltage systems, battery charging, or residential wiring, other types of transformers, such as isolation transformers or standard step-down transformers, would be more appropriate. These alternatives are designed to handle smaller voltages and ensure electrical safety by providing isolation where necessary. Therefore, the scenario involving the 115 kV to 230 kV system exemplifies a practical usage of an autotransformer, leveraging its strengths in high voltage applications.