The basic principle of a three phase
transformer is shown in the Fig
The three cores are arranged at 120o from each other. Only primary windings are show on the cores for simplicity. The primaries are connected to the three phase supply. The primaries carry the currents IR, IY and IB producing the fluxes ΦR, ΦY and ΦB in the individual cores. The common leg of the cores i.e. centre leg formed carries sum of the all three fluxes.
But at any instant, in a three phase system, ĪR + ĪY + ĪB = 0, hence the sum of the three fluxes is also zero at any instant. Hence the centre leg does not carry any flux. So if centre leg is removed, It hardly makes any difference in the other conditions of the transformer. If is is removed, any two legs provide the return path for the current and hence the flux in the third leg. This is the general principle used in the design of three phase core type transformers
The three cores are arranged at 120o from each other. Only primary windings are show on the cores for simplicity. The primaries are connected to the three phase supply. The primaries carry the currents IR, IY and IB producing the fluxes ΦR, ΦY and ΦB in the individual cores. The common leg of the cores i.e. centre leg formed carries sum of the all three fluxes.
But at any instant, in a three phase system, ĪR + ĪY + ĪB = 0, hence the sum of the three fluxes is also zero at any instant. Hence the centre leg does not carry any flux. So if centre leg is removed, It hardly makes any difference in the other conditions of the transformer. If is is removed, any two legs provide the return path for the current and hence the flux in the third leg. This is the general principle used in the design of three phase core type transformers
