SERIES FERRORESONANCE IN POWER-SYSTEMS

Nonlinear oscillations in power systems involving the excitation of nonlinear inductance with a linear capacitance in series have been termed ferroresonant oscillations, Such oscillations are unpredictable and their occurrence is of serious concern predominantly because of possible damage to equipment such as transformers. The probability of system disruption due to the occurrence of ferroresonant has increased with improvements in the characteristics of transformer steel and the use of higher and higher voltages for transmission of bulk power. Conditions that lead to the occurrence of ferroresonant oscillation, given a system, therefore, need to be known. It will be shown that for any disturbance the autonomous form of the nonlinear differential equation representing the system with two-degrees of freedom decays to a point attractor; that is, it is always stable. The non-autonomous form of the system's equation, however, exhibits the possibility of occurrence of a cyclic fold bifurcation which causes ferroresonant oscillations with two stable states to co-exist. Each stable state can, however, be either harmonic, periodic, subharmonic or aperiodic. Aperiodic oscillations occur when satisfactory conditions for the occurrence of subharmonic cascade exist.