If the three-phase stator coils are arranged symmetrically in space, i.e. with a 120°displacement as shown
in Fig. 2.7(a), and the sum of the phase voltages is zero(ua(t) + ub(t) + uc(t) = 0, neglecting the case of
zero sequences), the three-phase stator voltages can be expressed by an equivalent space voltage vector ~uss
,
i.e. with two-phase quadrature quantities as