The construction of a core type three phase transformer is as shown in the figure. The core consists of three legs or limbs. As usual, the core is made up of thin laminated sheets to reduce eddy current losses. Each limb has primary and secondary windings in cylindrical shape (former wound) arranged concentrically. A three-phase transformer is made of three sets of primary and secondary windings, each set wound around one leg of an iron core assembly. Essentially it looks like three single-phase transformers sharing a joined core as in Figure below. Three phase transformer core has three sets of windings. Three Phase Transformer Three phase transformers are used to step-up or step-down the high voltages in various stages of power transmission happens when three phase transformer is fed with single.


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Also, the amount of single-phase load should be kept low because the center-tapped transformer must supply most of the single-phase load.

As the single-phase load is increased, the center-tapped transformer will increase its loading more than the other two transformers and three phase transformer theory eventually overload.

If one of the single-phase transformers in the delta—delta bank fails, the bank can be operated with only two transformers forming an open delta configuration.

Three Phase Transformer Connections |

The kVA rating of the bank is reduced, but three-phase power is still supplied to the load. Wye—Wye Wye—wye transformers, as shown in Figure 3, can serve both three-phase and single-phase loads.

The single-phase load should be distributed as evenly as possible between each of the three phase transformer theory phases and neutral.

Figure 3 — Wye—Wye Transformer Figure 4 illustrates the wye—wye connection, either as three single-phase transformers or as a single three-phase unit.


Both bushing labels and polarity dots are shown. Figure 4 — Wye—Wye Transformer Connections Diagram click to expand diagram One problem inherent to wye—wye transformers is the propagation of three phase transformer theory harmonic currents and voltages.


These harmonics can cause interference in nearby communication circuits as well as other assorted power quality problems. Another problem is that three phase transformer theory possibility exists for resonance to occur between the shunt capacitance of the circuits connected to the transformer and the magnetizing susceptance of the transformer, especially if the circuits include insulated cable.

Because of these problems, wye—wye transformers must be specified and implemented carefully.

Shell type construction In a shell type three phase transformer, three phases are more independent than they are in core type. Each phase has its individual magnetic circuit. The construction of shell type three phase transformer is illustrated in three phase transformer theory figure at right.

Three Phase Transformer |

The construction is similar to that of three single phase shell type transformers kept on the top of each other. Space required to three phase transformer theory a single unit is less compared with three unit bank.

But the only disadvantage with single unit three phase transformer is if the fault occurs in any one of the phase, then entire unit must be removed from the service.

Working of Three Phase Transformers Consider the below figure in which the primary of the transformer is connected in star fashion on the three phase transformer theory.

What is the working principle of a three-phase transformer? - Quora

For simplicity, only primary winding is shown in the figure which is connected across the three phase AC supply. The three cores are arranged three phase transformer theory an angle of degrees to each other.

The empty leg of each core is combined in such that they form center leg as shown in figure. Since the center leg is common three phase transformer theory all the cores, the sum of all three fluxes are carried by it.

Three-phase Transformer Circuits

The ratio of line voltages on the primary and the secondary side is equal to the transformation ratio of the transformers. This connection can be used even for unbalanced loading.


Another advantage of this type of connection is that even if one transformer is disabled, system can continue to operate in open delta connection but with reduced available capacity.

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