Three-phase three-core column is to put three windings of three phases on three core columns respectively, and the three core columns are also connected by upper and lower iron yokes to form a closed magnetic circuit. The arrangement of windings is the same as that of single-phase transformer. Compared with the three-phase iron core, the three-phase five-core column has two more branch iron core columns on the left and right sides of the iron core column, which becomes a bypass. The windings of each voltage level are respectively sleeved on the middle three core columns according to the phase, while the side yoke has no windings, thus forming a three-phase five-core column transformer.
Because the magnetic flux of each phase of the three-phase five-column iron core can be closed by the side yoke, the three-phase magnetic circuits can be regarded as independent of each other, unlike the common three-phase three-column transformer in which the magnetic circuits of each phase are interrelated. Therefore, when there is asymmetric load, the zero-sequence magnetic flux generated by the zero-sequence current of each phase can be closed by the side yoke, so its zero-sequence excitation impedance is equal to that of symmetrical operation (positive sequence).
Three-phase and three-column transformers with medium and small capacity are adopted. Large-capacity three-phase transformer is often limited by transportation height, and three-phase five-column transformer is often used.
Iron-shell single-phase transformer has a central core column and two branch core columns (also called side yokes), and the width of the central core column is the sum of the widths of the two branch core columns. All the windings are placed on the central core column, and the two branch core columns surround the outer side of the windings like "shells", so it is called shell transformer. Sometimes it is also called single-phase three-column transformer.
Post time: May-24-2023