Phasing of transformer windings

    It is well known that the phase of the voltage at the terminals of the choke and the phase of the current through its winding are spaced in time by a quarter of a period (zero voltage coincides with the maximum current and vice versa) - the inductive element "turns the phase". In a transformer, everything is different. Although the operation of a transformer is based on the law of electromagnetic induction, with respect to the phases of the signals, everything is different here.
    Let's try to conduct a simple experiment: load the secondary winding of the transformer with a purely active resistance. We will notice that for our ideal transformer the voltage across the resistive load U1 and hence the current i2 will be in phase with the voltage applied to the primary winding. The equivalent circuit gives us an idea of what happens in this case: we kind of increased our active resistance in n2 times in accordance with the conversion rules (Table 3.4) and turned it on directly to terminals 1-2, to which the primary voltage U is supplied1... On basic electrical diagrams, the "beginnings" and "ends" of the transformer windings are always denoted. It is customary to mark the beginning with a dot, as shown in Fig. 3.15. These points represent the "plus" EMF applied to or arising in the windings. In general, the phasing of the windings is an important matter, which we will have to face more than once "face to face". A two-winding transformer is just one of the possible transformer designs. Quite often there are multi-winding options, which have several secondary windings. A multi-winding transformer can be represented in the equivalent circuit (Fig. 3.16) as a set of parallel-connected loads, recalculated into the primary winding, each through its own transformation ratio.
Semenov B.Yu. "Power electronics from simple to complex"
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Total comments: 1

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    By Oleg Added on October 15, 2020 at 11:22 am

    In Figure 3.15, on its right half, the direction of the current i2 is incorrect.

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