Definition: A mechanism usually fitted to the primary winding of a transformer, to alter the turns ratio of the transformer by small discrete amounts over a defined range.
Tap changer – Wikipedia
Electrical test equipment | power station to plug | Megger
How Taps Work | HPS | Hammond Power Solutions
On-load tap-changers –
An Example of Transformer Tap-changer Correct Adjustment
Transformer Tap changer | ECE Tutorials