The switched transformer ensures control of the secondary voltage by modifying the ratio by reconfiguring the transformer tap connections. This transformer is not designed to modify large amounts of energy, its main function is to promote small variations of voltage in series with the system, aiming to adjust reduced deviations in the network. Phases A, B and C are directly connected to the terminals of an autotransformer, called the excitation transformer. leeson
Switching can be done without the need to disconnect the transformer from the mains and in this case the tap-change is usually done by motors controlled by relays that detect any voltage irregularities in the system and send control signals to the motors, which raise or lower the transformation relationship to restore the balance in the network. These devices are called transformers with automatic tap changer.
In a certain overvoltage situation in the system, for example, it is imaginable to change the taps configuration to raise the transform ratio, and consequently reduce the voltage at the secondary terminals of the transformer.
In this way, undervoltage occurs in the system, and the taps can be reconfigured in order to reduce the transformation ratio, increasing the transformer secondary voltages.