Transformer with two power supplies, "EX10-V1/2".

Determine the currents and voltages of a transformer circuit. Knowing that in a DC voltage circuit the orientation of the arrow of a current reveals its direction of flow, whereas in AC voltage it is the phase angle of a current that reveals its direction of flow, we therefore check whether the current in the primary winding and that in the secondary winding are in phase opposition, their phase shift must be (+ or - 180°), and also the voltage at the terminals of the primary winding and that of the secondary winding are in phase. During one voltage half-wave (n), the primary winding must act as a receiver and the secondary winding as a generator supplying the load. The voltage and current arrows on the primary winding oppose each other, while those on the secondary winding point in the same direction. This is what we need to check via the phases.
If a transformer is supplied by a single voltage source or a single current source, the coil supplied by the source is considered to be the primary of the transformer and the coil not supplied by the source is considered to be the secondary of the transformer. In this application exercise, the transformer is supplied by two current sources, located on either side of the transformer, so we don't know which of the two coils is the primary. However, we can assume that it is supplied by a single current source nIs1(t), while the source Is2(t) and R2 are seen as a load. This poses no problem, because the term primary or secondary is just a name, and does not affect the flow of currents or voltages. The currents and voltages remain proportional to the transformer's transformation ratio ‘n’.