Transformer formulas

Autotransformers are used when galvanic isolation from the supply network (i.e. between the input and output windings) can be dispensed with. In this case, the input and output windings are electrically connected. A distinction is made here between feed-through power and design power, whereby the design power is always lower than the feed-through power. The lower the difference between the input and output voltage, the lower the power rating.

The corresponding standard for autotransformers is EN 61558-2-13.

Calculation formula:
Power rating = rated power * (1-(undervoltage/overvoltage))