i would like to know how transformer tap changer operate to vary the output voltage. And also why is always connected to the high voltage side of the transformer.
A transformer raises or lowers voltage based on the ratio of the number of coils of wire between the high and low voltage sides. The tap changer adjusts the voltage by changing the point of contact on one of the coils. Bypassing or including coils of wire changes the turns ratio of the transformer which by default will change the output voltage in direct proportion. Assuming you're referring to a tap changer under load Each step will either raise or lower the voltage by 5/8% or 3/4 volt on a 120 volt base. A reactor coil (yet a third smaller coil) is used during each step to temporarily carry the load so the contacts won't be damaged by arcing while switching. In other words, the lights won't blink during a tap change. A control panel constantly monitors the output voltage and automatically raises or lowers the voltage in an attempt to keep the output within its programmed bandwidth. Depending on the design, the tap changer may or may not be on the high voltage side.
Thjey are 2 types on load tap changers Off load tap changers High voltage means low current. Less burning of contacts and sparks!
