What liquid is the tap changer switch immersed in?

The tap changer switch is immersed in oil due to its excellent electrical insulating properties and its ability to dissipate heat effectively. Tap changers are used in transformers to adjust the output voltage by changing the number of turns in the winding that the electrical current flows through. As they operate, they generate heat due to the electrical load they handle; therefore, the insulation oil helps to cool the tap changer while also preventing electrical breakdown by forming a barrier against moisture and air, which could lead to corrosion and other damage.

Oil also has desirable characteristics such as a high dielectric strength, which is crucial in maintaining safe operation under high voltages. Hence, the choice of oil for this application is essential for both performance and longevity of the equipment. Other options provided, while they may have cooling or insulating properties, do not match the specific requirements needed for the function of a tap changer in a power transformer context.