The tap-changer of a power transformer is used to regulate the output voltage of the transformer. Because the voltage in the power system is not the same everywhere in the power grid, to make the transformer output the rated voltage no matter where it is installed in the power grid, the high-voltage winding of the transformer is provided with multiple taps, and the taps are connected to the tap changer and connected to the grid by switching.
The main role is to transmit electrical energy, therefore, the rated capacity is its main parameter. The rated capacity is a customary value that expresses the power, it is a characterization of the amount of power transmitted, expressed in kVA or MVA when the rated voltage is applied to the transformer, according to which the rated current does not exceed the temperature rise limit under the specified conditions.
