If the number of turns in the secondary winding is twice that in the primary winding, what type of transformer is it?

In a transformer, the relationship between the number of turns in the primary and secondary windings directly influences the voltage transformation. When the number of turns in the secondary winding is greater than that in the primary winding, the transformer increases the voltage from the primary to the secondary side. This is referred to as a step-up transformer.

In this scenario, since the secondary winding has twice as many turns as the primary winding, it will produce a higher output voltage compared to the input voltage. This principle is based on the transformer formula, which states that the voltage ratio is equal to the turns ratio. Therefore, with more turns in the secondary, the transformer steps up the voltage.

The other transformer types mentioned serve different functions. A step-down transformer decreases the voltage by having fewer turns in the secondary than the primary. An isolation transformer is designed primarily to isolate different circuits and does not necessarily change voltage levels. A three-phase transformer refers specifically to a transformer used for three-phase power systems and is not defined solely by the winding turns. Thus, identifying this transformer as a step-up transformer is accurate based on the relationship between turns and the resulting voltage change.