Ferroresonance Oscillations in Substations

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The motivation for this book was the increase in the appearance of ferroresonance oscillation in substations. The price pressure on the operating authorities and as well on component manufacturers i.e. for instrument transformer, power transformer and grading capacitors for high-performance circuit breakers has led to gradually increasing demands on power system and components. In the IEC Dictionary the following definition can be found for ferroresonance: "a resonance of the capacitance of an apparatus with the inductance of saturable magnetic circuit of an adjacent apparatus". Ferroresonance refers to non-linear oscillations that can occur in power systems where inductive components with a ferromagnetic core, together with capacitances and an AC voltage source comprise a system capable of oscillation. In contrast to a linear resonant circuit, a circuit with non-linear inductance exhibits no well-defined resonance frequency. A sinusoidal source voltage of a fixed frequency can excite different frequencies (harmonic and subharmonic frequencies). In addition, the amplitude of the excited oscillations is not limited only by the power loss in the resonant circuit. For each oscillation mode, a resultant oscillation amplitude can be found. This book provides an overview of the undesired phenomenon of ferroresonance oscillations in high and medium voltage networks in connection with the inductive voltage transformers (VT). Ferroresonance oscillations can cause considerable damage to the VT and neighboured equipment. Because of the various forms of manifestation, cases of ferroresonance are not always recognized as such. The book is addressed to designers and operators of high voltage power installations and manufacturers of inductive voltage transformers.