1. General principles and different couplings

1.1 First approach

Consider an electrical system consisting of three independent loads Z ₁ , Z ₂ and Z ₃ supplied by three voltage sources e ₁ (t), e ₂ (t) and e ₃ (t) (figure 1 ).

Every single-phase circuit has an "out" conductor and a "return" conductor, essential for completing the circuit.

Such a system has interesting properties in the particular case where :