The working principle of a three-phase column transformer is based on the principle of electromagnetic induction. When an AC voltage is applied to the secondary winding, an AC current flows into the winding, generating excitation and alternating magnetic flux in the iron core. This alternating magnetic flux not only passes through the secondary winding, but also through the primary winding, causing induced electromotive force in both windings. If the secondary winding is connected to the load of the external circuit, AC current will flow out and output electrical energy. A three-phase transformer can be seen as a combination of three single-phase transformers of the same capacity, with each core column wound around two coils of the same phase - a high voltage coil and a low voltage coil, and outputting three-phase power. Connect the high voltage winding of the transformer in a Y connection (the phase voltage can be equal to 57.7% of the line voltage), and determine the connection between the medium voltage winding and the low voltage winding based on the relationship between the voltage phasor of the medium voltage transmission system and the voltage phasor of the low voltage transmission system.
The design of three-phase transformers also takes into account the symmetry of the three-phase main magnetic flux. When a symmetrical three-phase voltage is applied to the primary winding, the three-phase main magnetic flux remains symmetrical, and the magnetic flux passing through the middle common iron core column is the sum of the phase quantities of the three-phase main magnetic flux. This design ensures that the neutral current of the Y-shaped connection circuit is zero when the load is symmetrical, thereby ensuring the stable operation of the transformer.
