What type of transformer has a 1:12 fixed voltage transformation ratio?

A transformer with a 1:12 fixed voltage transformation ratio is categorized as a step-up transformer. This type of transformer increases the voltage from the primary coil to the secondary coil. In this case, for every 1 volt on the primary side, there would be 12 volts on the secondary side, which is indicative of a step-up function.

Step-up transformers are used in applications where a higher voltage is required for efficient power transmission and distribution, as it allows for the reduction of current, which minimizes losses due to resistance in the conductors. This characteristic is particularly important in electrical systems where long-distance transmission of power is needed.

The other options refer to different transformer functionalities. A step-down transformer would reduce voltage instead of increasing it, while an isolation transformer primarily serves to separate different sections of a system while maintaining the same voltage level. An auto-transformer, while it can provide step-up or step-down functionality, does so by using a single winding with taps rather than separate primary and secondary coils, and it usually has a lower voltage transformation ratio.

In summary, the correct identification of a transformer with a 1:12 voltage transformation ratio as a step-up transformer is based on its primary function of increasing voltage.