Abstract: In this paper, some unkown physical processes in power systems are dissclosed by using the methods of Runge-Kutta and Galerkin. Such as the connection between the low-frequency resonances and the abnormity of magnetic hysteresis loop, the polarization of subharmonic bifurcations, the frequency region where the subharmonic resonances together with harmonic resonances exist and so on.

Key words: low-frequency resonance, odd subharmonic bifurcation, abnormity of magnetic hysteresis loop, polarization of subharmonic fifurcation