Frequency-locked and quasiperiodic (QP) oscillations in power systems

It is known that quasiperiodic (QP) oscillations can occur when an unloaded power transformer at the end of a long power line is energised. This occurs when the effect of the core loss of the transformer “becomes negligible” due to the stiff nonlinear characteristic of the core. Usually, such a system is known to exhibit periodic or frequency-locked behaviour. Such a system is an equivalent form of “two nonlinearly coupled oscillators” and the transition from frequency-locked to quasiperiodic behaviour and vice versa depends on the strength of nonlinear coupling between the oscillators. This aspect is examined in this paper