Understanding Transformers
A transformer transfers electrical power between two circuits at different voltages, using the ratio of its winding turns to step voltage up or down.
Step-up and step-down
A step-down transformer reduces voltage from primary to secondary, while a step-up transformer increases it. Which one a transformer is depends on whether the primary or secondary winding has more turns.
Turns ratio
The turns ratio is the ratio of primary to secondary voltage (or equivalently, primary to secondary winding turns). A 4:1 ratio means the primary voltage is four times the secondary voltage.
kVA rating
A transformer's kVA rating describes how much apparent power it can deliver. It's used to find the maximum current available at either the primary or secondary voltage.
Primary and secondary current
Current is inversely related to voltage across a transformer: the side with lower voltage carries proportionally higher current, for the same kVA rating.