The purpose of a tap changer in a transformer is to regulate the output voltage of the transformer by adjusting the number of turns in the primary or secondary windings. It provides a means to compensate for fluctuations in the input voltage or to meet specific voltage requirements in different situations.

  The tap changer is typically located on the high-voltage winding side of the transformer and can be either an on-load tap changer (OLTC) or an off-load tap changer (OLTC). An OLTC allows for tap changing without interrupting the supply while the transformer is under load, while an OLTC requires the transformer to be de-energized during tap changing.

  The tap changer operates by altering the connection point of the windings to the external circuit. By making the adjustment, the voltage ratio between the primary and secondary windings can be changed, thus regulating the output voltage. This adjustment compensates for variations in the input voltage, ensuring that the desired output voltage is maintained within acceptable limits.

  Tap changers are particularly useful in situations where the input voltage may vary significantly due to fluctuations in the power grid or specific requirements in different regions. For example, in distribution transformers, tap changers are used to control the voltage level supplied to consumers within a specific range by adjusting the taps accordingly.

  In summary, the tap changer in a transformer serves the purpose of regulating the output voltage by adjusting the number of turns in the windings, compensating for fluctuations in input voltage or meeting specific voltage requirements in different situations.