What is a tap changer in a transformer

Explain the tap changing process in a transformer

Transformer with a variable number of turns of the secondary winding. The secondary winding has multiple taps and some of them typically are excludable in order to regulate the secondary side voltage. Usually, the excludible taps are placed in the middle of the winding to balance the electromechanical force due to the current flowing. They can be divided into an on-load tap changer (able to modify the selected tap during operation) and an offload tap changer (need to stop the machine to change the tap). The most common use of the first case is to keep the secondary side voltage constant in case of fluctuations of the primary side voltage, while the most common use for the second case is to optimize the power flow of the network by regulating the secondary side voltage a priori, in order to minimize losses. It’s a mechanism used to increase or decrease the number of windings in the primary side of the power transformer to maintain rated voltage at secondary side

A tap changing device is a sort of switch which provides a connection between two or more tapings of the specific secondary winding of a transformer to the load. There are two types 1-Off load tap changer 2-On load tap changer.